team-validator.ts

/**
 * Team Validator
 * Pokemon Showdown - http://pokemonshowdown.com/
 *
 * Handles team validation, and specifically learnset checking.
 *
 * @license MIT
 */

import { Dex, toID } from './dex';
import type { MoveSource } from './dex-species';
import { Utils } from '../lib/utils';
import { Tags } from '../data/tags';
import { Teams } from './teams';
import { PRNG } from './prng';
import { type RuleTable } from './dex-formats';

/**
 * Describes a possible way to get a pokemon. Is not exhaustive!
 * sourcesBefore covers all sources that do not have exclusive
 * moves (like catching wild pokemon).
 *
 * First character is a generation number, 1-8.
 * Second character is a source ID, one of:
 *
 * - E = egg, 3rd char+ is the father in gen 2-5, empty in gen 6-7
 *   because egg moves aren't restricted to fathers anymore
 * - S = event, 3rd char+ is the index in .eventData
 * - D = Dream World, only 5D is valid
 * - V = Virtual Console or Let's Go transfer, only 7V/8V is valid
 *
 * Designed to match MoveSource where possible.
 */
export type PokemonSource = string;

/**
 * Represents a set of possible ways to get a Pokémon with a given
 * set.
 *
 * `new PokemonSources()` creates an empty set;
 * `new PokemonSources(dex.gen)` allows all Pokemon.
 *
 * The set mainly stored as an Array `sources`, but for sets that
 * could be sourced from anywhere (for instance, TM moves), we
 * instead just set `sourcesBefore` to a number meaning "any
 * source at or before this gen is possible."
 *
 * In other words, this variable represents the set of all
 * sources in `sources`, union all sources at or before
 * gen `sourcesBefore`.
 */
export class PokemonSources {
	/**
	 * A set of specific possible PokemonSources; implemented as
	 * an Array rather than a Set for perf reasons.
	 */
	sources: PokemonSource[];
	/**
	 * if nonzero: the set also contains all possible sources from
	 * this gen and earlier.
	 */
	sourcesBefore: number;
	/**
	 * the set requires sources from this gen or later
	 * this should be unchanged from the format's minimum past gen
	 * (3 in modern games, 6 if pentagon is required, etc)
	 */
	sourcesAfter: number;
	isHidden: boolean | null;
	/**
	 * `limitedEggMoves` is a list of moves that can only be obtained from an
	 * egg with another father in gen 2-5. If there are multiple such moves,
	 * potential fathers need to be checked to see if they can actually
	 * learn the move combination in question.
	 *
	 * `null` = the current move is definitely not a limited egg move
	 *
	 * `undefined` = the current move may or may not be a limited egg move
	 */
	limitedEggMoves?: ID[] | null;
	/**
	 * Moves that should be in limitedEggMoves that would otherwise be skipped
	 * because they can be learned universally in a past generation
	 */
	possiblyLimitedEggMoves?: ID[] | null;
	/**
	 * Moves that should be in limitedEggMoves that would otherwise be skipped
	 * because they can be learned via Gen 1-2 tradeback
	 */
	tradebackLimitedEggMoves?: ID[] | null;
	/**
	 * Tracks level up egg moves for female-only Pokemon
	 */
	levelUpEggMoves?: ID[] | null;
	/**
	 * Moves that can be learned via Pomeg glitch and does not require a
	 * particular parent to learn
	 */
	pomegEggMoves?: ID[] | null;
	/**
	 * Event egg source that may be used with the Pomeg glitch
	 *
	 * `null` = definitely not an event egg that can be used with the Pomeg glitch
	 */
	pomegEventEgg?: string | null;
	/**
	 * For event-only Pokemon that do not have a minimum source gen identified by its moves
	 */
	eventOnlyMinSourceGen?: number;
	/**
	 * A list of movepools, identified by gen and species, which moves can be pulled from.
	 * Used to deal with compatibility issues for prevo/evo-exclusive moves
	 */
	learnsetDomain?: string[] | null;
	/**
	 * Some Pokemon evolve by having a move in their learnset (like Piloswine
	 * with Ancient Power). These can only carry three other moves from their
	 * prevo, because the fourth move must be the evo move. This restriction
	 * doesn't apply to gen 6+ eggs, which can get around the restriction with
	 * the relearner.
	 */
	moveEvoCarryCount: number;

	babyOnly?: string;
	sketchMove?: string;
	dreamWorldMoveCount: number;
	hm?: string;
	isFromPokemonGo?: boolean;
	pokemonGoSource?: string;
	restrictiveMoves?: string[];
	/** Obscure learn methods */
	restrictedMove?: ID;

	constructor(sourcesBefore = 0, sourcesAfter = 0) {
		this.sources = [];
		this.sourcesBefore = sourcesBefore;
		this.sourcesAfter = sourcesAfter;
		this.isHidden = null;
		this.limitedEggMoves = undefined;
		this.moveEvoCarryCount = 0;
		this.dreamWorldMoveCount = 0;
	}
	size() {
		if (this.sourcesBefore) return Infinity;
		return this.sources.length;
	}
	add(source: PokemonSource, limitedEggMove?: ID | null) {
		if (this.sources[this.sources.length - 1] !== source) this.sources.push(source);
		if (limitedEggMove) {
			if (source.substr(0, 3) === '1ET') {
				this.tradebackLimitedEggMoves = [limitedEggMove];
			}
		}
		if (limitedEggMove && this.limitedEggMoves !== null) {
			this.limitedEggMoves = [limitedEggMove];
		} else if (limitedEggMove === null) {
			this.limitedEggMoves = null;
		}
	}
	addGen(sourceGen: number) {
		this.sourcesBefore = Math.max(this.sourcesBefore, sourceGen);
		this.limitedEggMoves = null;
	}
	minSourceGen() {
		if (this.eventOnlyMinSourceGen) return this.eventOnlyMinSourceGen;
		if (this.sourcesBefore) return this.sourcesAfter || 1;
		let min = 10;
		for (const source of this.sources) {
			const sourceGen = parseInt(source.charAt(0));
			if (sourceGen < min) min = sourceGen;
		}
		if (min === 10) return 0;
		return min;
	}
	maxSourceGen() {
		let max = this.sourcesBefore;
		for (const source of this.sources) {
			const sourceGen = parseInt(source.charAt(0));
			if (sourceGen > max) max = sourceGen;
		}
		return max;
	}
	intersectWith(other: PokemonSources) {
		if (this.pomegEventEgg && other.pomegEggMoves) {
			const newSources = [];
			for (const source of other.sources) {
				newSources.push(source.substr(0, 2) === '3E' ? this.pomegEventEgg : source);
			}
			other.sources = newSources;
		} else if (other.pomegEventEgg && this.pomegEventEgg !== null) {
			const newSources = [];
			for (const source of this.sources) {
				newSources.push(source.substr(0, 2) === '3E' ? other.pomegEventEgg : source);
			}
			this.sources = newSources;
			this.pomegEventEgg = other.pomegEventEgg;
		} else if (!other.pomegEggMoves && !other.sourcesBefore) {
			this.pomegEventEgg = null;
		}
		if (other.sourcesBefore || this.sourcesBefore) {
			// having sourcesBefore is the equivalent of having everything before that gen
			// in sources, so we fill the other array in preparation for intersection
			if (other.sourcesBefore > this.sourcesBefore) {
				for (const source of this.sources) {
					const sourceGen = parseInt(source.charAt(0));
					if (sourceGen <= other.sourcesBefore) {
						other.sources.push(source);
					}
				}
			} else if (this.sourcesBefore > other.sourcesBefore) {
				for (const source of other.sources) {
					const sourceGen = parseInt(source.charAt(0));
					if (sourceGen <= this.sourcesBefore) {
						this.sources.push(source);
					}
				}
			}
			this.sourcesBefore = Math.min(other.sourcesBefore, this.sourcesBefore);
		}
		if (this.sources.length) {
			if (other.sources.length) {
				const sourcesSet = new Set(other.sources);
				const intersectSources = this.sources.filter(source => sourcesSet.has(source));
				this.sources = intersectSources;
			} else {
				this.sources = [];
			}
		}

		if (other.restrictedMove && other.restrictedMove !== this.restrictedMove) {
			if (this.restrictedMove) {
				// incompatible
				this.sources = [];
				this.sourcesBefore = 0;
			} else {
				this.restrictedMove = other.restrictedMove;
			}
		}
		if (other.limitedEggMoves) {
			if (!this.limitedEggMoves) {
				this.limitedEggMoves = other.limitedEggMoves;
			} else {
				this.limitedEggMoves.push(...other.limitedEggMoves);
			}
		}
		if (other.possiblyLimitedEggMoves) {
			if (!this.possiblyLimitedEggMoves) {
				this.possiblyLimitedEggMoves = other.possiblyLimitedEggMoves;
			} else {
				this.possiblyLimitedEggMoves.push(...other.possiblyLimitedEggMoves);
			}
		}
		if (other.tradebackLimitedEggMoves) {
			if (!this.tradebackLimitedEggMoves) {
				this.tradebackLimitedEggMoves = other.tradebackLimitedEggMoves;
			} else {
				this.tradebackLimitedEggMoves.push(...other.tradebackLimitedEggMoves);
			}
		}
		if (other.levelUpEggMoves) {
			if (!this.levelUpEggMoves) {
				this.levelUpEggMoves = other.levelUpEggMoves;
			} else {
				this.levelUpEggMoves.push(...other.levelUpEggMoves);
			}
		}
		if (other.pomegEggMoves) {
			if (!this.pomegEggMoves) {
				this.pomegEggMoves = other.pomegEggMoves;
			} else {
				this.pomegEggMoves.push(...other.pomegEggMoves);
			}
		}
		if (other.learnsetDomain) {
			if (!this.learnsetDomain) {
				this.learnsetDomain = other.learnsetDomain;
			} else {
				this.learnsetDomain.filter(source => other.learnsetDomain?.includes(source));
			}
		}
		if (this.possiblyLimitedEggMoves && !this.sourcesBefore) {
			const eggSources = this.sources.filter(source => source.charAt(1) === 'E');
			let minEggGen = parseInt(eggSources[0]);
			for (const source of eggSources) {
				minEggGen = Math.min(minEggGen, parseInt(source.charAt(0)));
			}
			if (minEggGen) {
				for (const eggMoveAndGen of this.possiblyLimitedEggMoves) {
					if (!this.limitedEggMoves) this.limitedEggMoves = [];
					if (parseInt(eggMoveAndGen.charAt(0)) < minEggGen) {
						const eggMove = toID(eggMoveAndGen.substr(1));
						if (!this.limitedEggMoves.includes(eggMove)) this.limitedEggMoves.push(eggMove);
					}
				}
			}
		}
		let eggTradebackLegal = false;
		for (const source of this.sources) {
			if (source.substr(0, 3) === '1ET') {
				eggTradebackLegal = true;
				break;
			}
		}
		if (!eggTradebackLegal && this.tradebackLimitedEggMoves) {
			for (const eggMove of this.tradebackLimitedEggMoves) {
				if (!this.limitedEggMoves) this.limitedEggMoves = [];
				if (!this.limitedEggMoves.includes(eggMove)) this.limitedEggMoves.push(eggMove);
			}
		}
		this.moveEvoCarryCount += other.moveEvoCarryCount;
		this.dreamWorldMoveCount += other.dreamWorldMoveCount;
		if (other.sourcesAfter > this.sourcesAfter) this.sourcesAfter = other.sourcesAfter;
		if (other.isHidden) this.isHidden = true;
	}
}

export class TeamValidator {
	readonly format: Format;
	readonly dex: ModdedDex;
	readonly gen: number;
	readonly ruleTable: RuleTable;
	readonly minSourceGen: number;

	readonly toID: (str: any) => ID;
	constructor(format: string | Format, dex = Dex) {
		this.format = dex.formats.get(format);
		if (this.format.effectType !== 'Format') {
			throw new Error(`format '${format}' should be a 'Format', but was a '${this.format.effectType}'`);
		}
		this.dex = dex.forFormat(this.format);
		this.gen = this.dex.gen;
		this.ruleTable = this.dex.formats.getRuleTable(this.format);

		this.minSourceGen = this.ruleTable.minSourceGen;

		this.toID = toID;
	}

	validateTeam(
		team: PokemonSet[] | null,
		options: {
			removeNicknames?: boolean,
			skipSets?: { [name: string]: { [key: string]: boolean } },
		} = {}
	): string[] | null {
		if (team && this.format.validateTeam) {
			return this.format.validateTeam.call(this, team, options) || null;
		}
		return this.baseValidateTeam(team, options);
	}

	baseValidateTeam(
		team: PokemonSet[] | null,
		options: {
			removeNicknames?: boolean,
			skipSets?: { [name: string]: { [key: string]: boolean } },
		} = {}
	): string[] | null {
		const format = this.format;
		const dex = this.dex;

		let problems: string[] = [];
		const ruleTable = this.ruleTable;
		if (format.team) {
			if (team) {
				return [
					`This format doesn't let you use your own team.`,
					`If you're not using a custom client, please report this as a bug. If you are, remember to use \`/utm null\` before starting a game in this format.`,
				];
			}
			const testTeamSeed = PRNG.generateSeed();
			try {
				const testTeamGenerator = Teams.getGenerator(format, testTeamSeed);
				testTeamGenerator.getTeam(options); // Throws error if generation fails
			} catch (e) {
				return [
					`${format.name}'s team generator (${format.team}) failed using these rules and seed (${testTeamSeed}):-`,
					`${e}`,
				];
			}
			return null;
		}
		if (!team) {
			return [
				`This format requires you to use your own team.`,
				`If you're not using a custom client, please report this as a bug.`,
			];
		}
		if (!Array.isArray(team)) {
			throw new Error(`Invalid team data`);
		}

		if (team.length < ruleTable.minTeamSize) {
			problems.push(`You must bring at least ${ruleTable.minTeamSize} Pok\u00E9mon (your team has ${team.length}).`);
		}
		if (team.length > ruleTable.maxTeamSize) {
			return [`You may only bring up to ${ruleTable.maxTeamSize} Pok\u00E9mon (your team has ${team.length}).`];
		}

		// A limit is imposed here to prevent too much engine strain or
		// too much layout deformation - to be exact, this is the limit
		// allowed in Custom Game.
		if (team.length > 24) {
			problems.push(`Your team has more than than 24 Pok\u00E9mon, which the simulator can't handle.`);
			return problems;
		}

		const teamHas: { [k: string]: number } = {};
		let lgpeStarterCount = 0;
		let deoxysType;
		for (const set of team) {
			if (!set) return [`You sent invalid team data. If you're not using a custom client, please report this as a bug.`];

			let setProblems: string[] | null = null;
			if (options.skipSets?.[set.name]) {
				for (const i in options.skipSets[set.name]) {
					teamHas[i] = (teamHas[i] || 0) + 1;
				}
			} else {
				setProblems = (format.validateSet || this.validateSet).call(this, set, teamHas);
			}

			if (set.species === 'Pikachu-Starter' || set.species === 'Eevee-Starter') {
				lgpeStarterCount++;
				if (lgpeStarterCount === 2 && ruleTable.isBanned('nonexistent')) {
					problems.push(`You can only have one of Pikachu-Starter or Eevee-Starter on a team.`);
				}
			}
			if (dex.gen === 3 && set.species.startsWith('Deoxys')) {
				if (!deoxysType) {
					deoxysType = set.species;
				} else if (deoxysType !== set.species && ruleTable.isBanned('nonexistent')) {
					return [
						`You cannot have more than one type of Deoxys forme.`,
						`(Each game in Gen 3 supports only one forme of Deoxys.)`,
					];
				}
			}
			if (setProblems) {
				problems = problems.concat(setProblems);
			}
			if (options.removeNicknames) {
				const useCrossSpeciesNicknames = format.name.includes('Cross Evolution') || ruleTable.has('franticfusionsmod');
				const species = dex.species.get(set.species);
				let crossSpecies: Species;
				if (useCrossSpeciesNicknames && (crossSpecies = dex.species.get(set.name)).exists) {
					set.name = crossSpecies.name;
				} else {
					set.name = species.baseSpecies;
					if (species.baseSpecies === 'Unown') set.species = 'Unown';
				}
			}
		}

		for (const [rule, source, limit, bans] of ruleTable.complexTeamBans) {
			let count = 0;
			for (const ban of bans) {
				if (teamHas[ban] > 0) {
					count += limit ? teamHas[ban] : 1;
				}
			}
			if (limit && count > limit) {
				const clause = source ? ` by ${source}` : ``;
				problems.push(`You are limited to ${limit} of ${rule}${clause}.`);
			} else if (!limit && count >= bans.length) {
				const clause = source ? ` by ${source}` : ``;
				problems.push(`Your team has the combination of ${rule}, which is banned${clause}.`);
			}
		}

		for (const rule of ruleTable.keys()) {
			if ('!+-*'.includes(rule.charAt(0))) continue;
			const subformat = dex.formats.get(rule);
			if (subformat.onValidateTeam && ruleTable.has(subformat.id)) {
				problems = problems.concat(subformat.onValidateTeam.call(this, team, format, teamHas) || []);
			}
		}
		if (format.onValidateTeam) {
			problems = problems.concat(format.onValidateTeam.call(this, team, format, teamHas) || []);
		}

		if (!problems.length) return null;
		return problems;
	}

	getEventOnlyData(species: Species, noRecurse?: boolean): { species: Species, eventData: EventInfo[] } | null {
		const dex = this.dex;
		const learnset = dex.species.getLearnsetData(species.id);
		if (!learnset?.eventOnly) {
			if (noRecurse) return null;
			return this.getEventOnlyData(dex.species.get(species.prevo), true);
		}

		if (!learnset.eventData && species.forme) {
			return this.getEventOnlyData(dex.species.get(species.baseSpecies), true);
		}
		if (!learnset.eventData) {
			throw new Error(`Event-only species ${species.name} has no eventData table`);
		}

		return { species, eventData: learnset.eventData };
	}

	getValidationSpecies(set: PokemonSet): { outOfBattleSpecies: Species, tierSpecies: Species } {
		const dex = this.dex;
		const ruleTable = this.ruleTable;
		const species = dex.species.get(set.species);
		const item = dex.items.get(set.item);
		const ability = dex.abilities.get(set.ability);

		let outOfBattleSpecies = species;
		let tierSpecies = species;
		if (ability.id === 'battlebond' && toID(species.baseSpecies) === 'greninja' &&
			this.format.mod !== 'gen9legendsou') {
			outOfBattleSpecies = dex.species.get('greninjabond');
			if (ruleTable.has('obtainableformes')) {
				tierSpecies = outOfBattleSpecies;
			}
		}
		if (ability.id === 'owntempo' && toID(species.baseSpecies) === 'rockruff') {
			outOfBattleSpecies = dex.species.get('rockruffdusk');
			if (ruleTable.has('obtainableformes')) {
				tierSpecies = outOfBattleSpecies;
			}
		}

		if (ruleTable.has('obtainableformes')) {
			const canMegaEvo = dex.gen <= 7 || ruleTable.has('+pokemontag:past');
			if (item.megaStone?.[species.name]) {
				tierSpecies = dex.species.get(item.megaStone[species.name]);
			} else if (item.id === 'redorb' && species.id === 'groudon') {
				tierSpecies = dex.species.get('Groudon-Primal');
			} else if (item.id === 'blueorb' && species.id === 'kyogre') {
				tierSpecies = dex.species.get('Kyogre-Primal');
			} else if (
				canMegaEvo && species.id === 'rayquaza' && set.moves.map(toID).includes('dragonascent' as ID) &&
				!ruleTable.has('megarayquazaclause')
			) {
				tierSpecies = dex.species.get('Rayquaza-Mega');
			} else if (item.id === 'rustedsword' && species.id === 'zacian') {
				tierSpecies = dex.species.get('Zacian-Crowned');
			} else if (item.id === 'rustedshield' && species.id === 'zamazenta') {
				tierSpecies = dex.species.get('Zamazenta-Crowned');
			}
		}

		return { outOfBattleSpecies, tierSpecies };
	}

	validateSet(set: PokemonSet, teamHas: AnyObject): string[] | null {
		const format = this.format;
		const dex = this.dex;
		const ruleTable = this.ruleTable;

		let problems: string[] = [];
		if (!set) {
			return [`This is not a Pokemon.`];
		}

		let species = dex.species.get(set.species);
		set.species = species.name;
		// Backwards compatibility with old Gmax format
		if (set.species.toLowerCase().endsWith('-gmax') && this.format.id !== 'gen8megamax') {
			set.species = set.species.slice(0, -5);
			species = dex.species.get(set.species);
			if (set.name?.endsWith('-Gmax')) set.name = species.baseSpecies;
			set.gigantamax = true;
		}
		if (set.name && set.name.length > 18) {
			if (set.name === set.species) {
				set.name = species.baseSpecies;
			} else {
				problems.push(`Nickname "${set.name}" too long (should be 18 characters or fewer)`);
			}
		}
		set.name = dex.getName(set.name);
		let item = dex.items.get(Utils.getString(set.item));
		set.item = item.name;
		let ability = dex.abilities.get(Utils.getString(set.ability));
		set.ability = ability.name;
		let nature = dex.natures.get(Utils.getString(set.nature));
		set.nature = nature.name;
		if (!Array.isArray(set.moves)) set.moves = [];

		set.name = set.name || species.baseSpecies;
		let name = set.species;
		if (set.species !== set.name && species.baseSpecies !== set.name) {
			name = `${set.name} (${set.species})`;
		}

		if (!set.level) set.level = ruleTable.defaultLevel;

		let adjustLevel = ruleTable.adjustLevel;
		if (ruleTable.adjustLevelDown && set.level >= ruleTable.adjustLevelDown) {
			adjustLevel = ruleTable.adjustLevelDown;
		}
		if (set.level === adjustLevel || (set.level === 100 && ruleTable.maxLevel < 100)) {
			// Note that we're temporarily setting level 50 pokemon in VGC to level 100
			// This allows e.g. level 50 Hydreigon even though it doesn't evolve until level 64.
			// Leveling up can't make an obtainable pokemon unobtainable, so this is safe.
			// Just remember to set the level back to adjustLevel at the end of validation.
			set.level = ruleTable.maxLevel;
		}
		if (set.level < ruleTable.minLevel) {
			problems.push(`${name} (level ${set.level}) is below the minimum level of ${ruleTable.minLevel}${ruleTable.blame('minlevel')}`);
		}
		if (set.level > ruleTable.maxLevel) {
			problems.push(`${name} (level ${set.level}) is above the maximum level of ${ruleTable.maxLevel}${ruleTable.blame('maxlevel')}`);
		}

		const setHas: { [k: string]: true } = {};

		if (!set.evs) set.evs = TeamValidator.fillStats(null, ruleTable.evLimit === null ? 252 : 0);
		if (!set.ivs) set.ivs = TeamValidator.fillStats(null, 31);

		if (ruleTable.has('obtainableformes')) {
			problems.push(...this.validateForme(set));
			species = dex.species.get(set.species);
		}
		const setSources = this.allSources(species);

		for (const [rule] of ruleTable) {
			if ('!+-*'.includes(rule.charAt(0))) continue;
			const subformat = dex.formats.get(rule);
			if (subformat.onChangeSet && ruleTable.has(subformat.id)) {
				problems = problems.concat(subformat.onChangeSet.call(this, set, format, setHas, teamHas) || []);
			}
		}
		if (format.onChangeSet) {
			problems = problems.concat(format.onChangeSet.call(this, set, format, setHas, teamHas) || []);
		}

		// onChangeSet can modify set.species, set.item, set.ability
		species = dex.species.get(set.species);
		item = dex.items.get(set.item);
		ability = dex.abilities.get(set.ability);

		if (!['M', 'F'].includes(set.gender)) set.gender = '';
		if (this.gen <= 5 || ruleTable.has('obtainablemisc')) {
			set.gender = species.gender || set.gender;
		}

		const { outOfBattleSpecies, tierSpecies } = this.getValidationSpecies(set);
		if (ability.id === 'battlebond' && toID(species.baseSpecies) === 'greninja') {
			if (ruleTable.has('obtainablemisc')) {
				if (set.gender && set.gender !== 'M') {
					problems.push(`Battle Bond Greninja must be male.`);
				}
				set.gender = 'M';
			}
		}
		if (species.id === 'melmetal' && set.gigantamax && this.dex.species.getLearnsetData(species.id).eventData) {
			// Gigantamax Melmetal cannot be obtained through the Max Soup
			setSources.sourcesBefore = 0;
			setSources.sources = ['8S0 melmetal'];
		}
		if (!species.exists) {
			return [`The Pokemon "${set.species}" does not exist.`];
		}

		if (item.id && !item.exists) {
			return [`"${set.item}" is an invalid item.`];
		}
		if (ability.id && !ability.exists) {
			if (dex.gen < 3) {
				// gen 1-2 don't have abilities, just silently remove
				ability = dex.abilities.get('');
				set.ability = '';
			} else {
				return [`"${set.ability}" is an invalid ability.`];
			}
		}
		if (nature.id && !nature.exists) {
			if (dex.gen < 3) {
				// gen 1-2 don't have natures, just remove them
				nature = dex.natures.get('');
				set.nature = '';
			} else {
				problems.push(`"${set.nature}" is an invalid nature.`);
			}
		}
		if (set.happiness !== undefined && isNaN(set.happiness)) {
			problems.push(`${name} has an invalid happiness value.`);
		}
		if (set.hpType) {
			const type = dex.types.get(set.hpType);
			if (!type.exists || ['normal', 'fairy', 'stellar'].includes(type.id)) {
				problems.push(`${name}'s Hidden Power type (${set.hpType}) is invalid.`);
			} else {
				set.hpType = type.name;
			}
		}
		if ((this.gen === 9 && !ruleTable.has('terastalclause')) || ruleTable.has('bonustypemod')) {
			const type = dex.types.get(set.teraType || species.requiredTeraType || species.types[0]);
			if (!type.exists || type.isNonstandard) {
				problems.push(`${name}'s Terastal type (${set.teraType}) is invalid.`);
			} else if (species.requiredTeraType && species.requiredTeraType !== type.name && ruleTable.has('obtainablemisc')) {
				problems.push(`${species.name}'s Terastal type needs to be ${species.requiredTeraType}.`);
			}
			set.teraType = type.name;
		} else {
			delete set.teraType;
		}

		let problem = this.checkSpecies(set, species, tierSpecies, setHas);
		if (problem) problems.push(problem);

		problem = this.checkItem(set, item, setHas);
		if (problem) problems.push(problem);
		if (ruleTable.has('obtainablemisc')) {
			if (dex.gen === 4 && item.id === 'griseousorb' && species.num !== 487) {
				problems.push(`${set.name} cannot hold the Griseous Orb.`, `(In Gen 4, only Giratina could hold the Griseous Orb).`);
			}
			if (dex.gen <= 1 || dex.currentMod === 'gen7letsgo') {
				if (item.id) {
					// no items allowed
					set.item = '';
				}
			}
		}

		if (!set.ability) set.ability = 'No Ability';
		if (ruleTable.has('obtainableabilities')) {
			if (dex.gen <= 2 || dex.currentMod === 'gen7letsgo') {
				set.ability = 'No Ability';
			} else {
				if (!ability.name || ability.name === 'No Ability') {
					problems.push(`${name} needs to have an ability.`);
				} else if (!Object.values(species.abilities).includes(ability.name)) {
					if (tierSpecies.abilities[0] === ability.name) {
						set.ability = species.abilities[0];
					} else {
						problems.push(`${name} can't have ${set.ability}.`);
					}
				}
				if (ability.name === species.abilities['H']) {
					setSources.isHidden = true;

					let unreleasedHidden = species.unreleasedHidden;
					if (unreleasedHidden === 'Past' && this.minSourceGen < dex.gen) unreleasedHidden = false;

					if (unreleasedHidden && ruleTable.has('-unreleased')) {
						problems.push(`${name}'s Hidden Ability is unreleased.`);
					} else if (dex.gen === 7 && ['entei', 'suicune', 'raikou'].includes(species.id) && this.minSourceGen > 1) {
						problems.push(`${name}'s Hidden Ability is only available from Virtual Console, which is not allowed in this format.`);
					} else if (dex.gen === 6 && ability.name === 'Symbiosis' &&
						(set.species.endsWith('Orange') || set.species.endsWith('White'))) {
						problems.push(`${name}'s Hidden Ability is unreleased for the Orange and White forms.`);
					} else if (dex.gen === 5 && set.level < 10 && (species.maleOnlyHidden || species.gender === 'N')) {
						problems.push(`${name} must be at least level 10 to have a Hidden Ability.`);
					}
					if (species.maleOnlyHidden) {
						if (set.gender && set.gender !== 'M') {
							problems.push(`${name} must be male to have a Hidden Ability.`);
						}
						set.gender = 'M';
						setSources.sources = ['5D'];
					}
				} else {
					setSources.isHidden = false;
				}
			}
		}

		ability = dex.abilities.get(set.ability);
		problem = this.checkAbility(set, ability, setHas);
		if (problem) problems.push(problem);

		if (!set.nature || dex.gen <= 2) {
			set.nature = '';
		}
		nature = dex.natures.get(set.nature);
		problem = this.checkNature(set, nature, setHas);
		if (problem) problems.push(problem);

		if (set.shiny && dex.gen === 1) {
			set.shiny = false;
		}

		if (set.moves && Array.isArray(set.moves)) {
			set.moves = set.moves.filter(val => val);
		}
		if (!set.moves?.length) {
			problems.push(`${name} has no moves (it must have at least one to be usable).`);
			set.moves = [];
		}
		if (set.moves.length > ruleTable.maxMoveCount) {
			problems.push(`${name} has ${set.moves.length} moves, which is more than the limit of ${ruleTable.maxMoveCount}.`);
			return problems;
		}

		const pokemonGoProblems = this.validatePokemonGo(outOfBattleSpecies, set, setSources);
		if (ruleTable.isBanned('nonexistent')) {
			problems.push(...this.validateStats(set, species, setSources, pokemonGoProblems));
		}

		const moveLegalityWhitelist: { [k: string]: true | undefined } = {};
		for (const moveName of set.moves) {
			if (!moveName) continue;
			const move = dex.moves.get(Utils.getString(moveName));
			if (!move.exists) return [`"${move.name}" is an invalid move.`];

			problem = this.checkMove(set, move, setHas);
			if (problem) {
				let allowedByOM;
				if (problem.includes('hacking or glitches') &&
					ruleTable.has('omunobtainablemoves')) {
					problem = `${name}'s ${problem}`;
					allowedByOM = !this.omCheckCanLearn(move, outOfBattleSpecies, setSources, set, problem);
				}
				if (!allowedByOM) {
					problems.push(problem);
				} else {
					moveLegalityWhitelist[move.id] = true;
				}
			}
		}

		const learnsetSpecies = dex.species.getLearnsetData(outOfBattleSpecies.id);
		let isFromRBYEncounter = false;
		if (this.gen === 1 && ruleTable.has('obtainablemisc') && !this.ruleTable.has('allowtradeback')) {
			let lowestEncounterLevel;
			for (const encounter of learnsetSpecies.encounters || []) {
				if (encounter.generation !== 1) continue;
				if (!encounter.level) continue;
				if (lowestEncounterLevel && encounter.level > lowestEncounterLevel) continue;

				lowestEncounterLevel = encounter.level;
			}

			if (lowestEncounterLevel) {
				if (set.level < lowestEncounterLevel) {
					problems.push(`${name} is not obtainable at levels below ${lowestEncounterLevel} in Gen 1.`);
				}
				isFromRBYEncounter = true;
			}
		}
		let isUnderleveled;
		let requiredLevel;
		if (!isFromRBYEncounter && ruleTable.has('obtainablemisc')) {
			// FIXME: Event pokemon given at a level under what it normally can be attained at gives a false positive
			let evoSpecies = species;
			while (evoSpecies.prevo) {
				if (set.level < (evoSpecies.evoLevel || 0)) {
					isUnderleveled = evoSpecies.name;
					requiredLevel = evoSpecies.evoLevel;
					break;
				}
				evoSpecies = dex.species.get(evoSpecies.prevo);
			}
		}

		let moveProblems;
		if (ruleTable.has('obtainablemoves')) {
			moveProblems = this.validateMoves(outOfBattleSpecies, set.moves, setSources, set, name, moveLegalityWhitelist);
			problems.push(...moveProblems);
		}

		let eventOnlyData;

		if ((!setSources.sourcesBefore && setSources.sources.length) || isUnderleveled) {
			let checkGoLegality = false;
			let skippedEggSource = true;
			const legalSources = [];
			if (isUnderleveled && !setSources.sources.length) {
				let evoSpecies = species;
				while (evoSpecies.prevo) {
					const eventData = dex.species.getLearnsetData(evoSpecies.id).eventData;
					if (eventData) {
						for (let eventIndex = 0; eventIndex < eventData.length; eventIndex++) {
							const eventLevel = eventData[eventIndex].level;
							if (eventLevel && set.level >= eventLevel) {
								setSources.sources.push(`${eventData[eventIndex].generation}S${eventIndex} ${evoSpecies.id}`);
							}
						}
					}
					if (evoSpecies.name === isUnderleveled) break;
					evoSpecies = dex.species.get(evoSpecies.prevo);
				}
			} else {
				checkGoLegality = true;
			}
			for (const source of setSources.sources) {
				if (isUnderleveled) {
					if (source.charAt(1) === 'S') {
						const eventSpecies = dex.species.get(source.substr(3)).baseSpecies;
						const underleveledSpecies = dex.species.get(isUnderleveled).baseSpecies;
						// Can only be an FE species or in a three-stage line, the prevo
						if (eventSpecies !== species.baseSpecies && eventSpecies !== underleveledSpecies) continue;
					} else if (source !== '8V') {
						continue;
					}
				}
				if (['2E', '3E'].includes(source.substr(0, 2)) && set.level < 5) continue;
				skippedEggSource = false;
				if (this.validateSource(set, source, setSources, outOfBattleSpecies)) continue;
				legalSources.push(source);
			}
			if (checkGoLegality && !legalSources.includes('8V')) setSources.isFromPokemonGo = false;
			if (setSources.isFromPokemonGo !== false && pokemonGoProblems && !pokemonGoProblems.length) {
				if (!legalSources.length) setSources.isFromPokemonGo = true;
				if (!legalSources.includes('8V')) legalSources.push('8V');
			}
			if (legalSources.length) {
				setSources.sources = legalSources;
			} else if (isUnderleveled) {
				problems.push(`${name} must be at least level ${requiredLevel} to be evolved.`);
				const firstEventSource = setSources.sources.find(source => source.charAt(1) === 'S');
				if (firstEventSource) {
					const eventProblems = this.validateSource(
						set, firstEventSource, setSources, outOfBattleSpecies, ` to be underleveled`
					);
					if (eventProblems) problems.push(...eventProblems);
				}
				if (pokemonGoProblems?.length) {
					problems.push(`It failed to validate as a Pokemon from Pokemon GO because:`);
					for (const pokemonGoProblem of pokemonGoProblems) {
						problems.push(pokemonGoProblem);
					}
				}
			} else {
				let nonEggSource = null;
				for (const source of setSources.sources) {
					if (source.charAt(1) !== 'E') {
						nonEggSource = source;
						break;
					}
				}
				if (!nonEggSource) {
					// all egg moves
					if (skippedEggSource) {
						problems.push(`${name} is from a Gen 2 or 3 egg, which cannot be obtained at levels below 5.`);
					} else {
						problems.push(`${name} can't get its egg move combination (${setSources.limitedEggMoves!.join(', ')}) from any possible father.`);
						problems.push(`(Is this incorrect? If so, post the chainbreeding instructions in Bug Reports)`);
					}
				} else {
					if (species.id === 'mew' && pokemonGoProblems && !pokemonGoProblems.length) {
						// Whitelist Pokemon GO Mew, which cannot be sent to Let's Go
						setSources.isFromPokemonGo = true;
					} else {
						if (setSources.sources.length > 1) {
							problems.push(`${name} has an event-exclusive move that it doesn't qualify for (only one of several ways to get the move will be listed):`);
						}
						const eventProblems = this.validateSource(
							set, nonEggSource, setSources, outOfBattleSpecies, ` because it has a move only available`
						);
						if (eventProblems) problems.push(...eventProblems);
						if (species.id === 'mew' && pokemonGoProblems?.length) {
							problems.push(`Additionally, it failed to validate as a Pokemon from Pokemon GO because:`);
							for (const pokemonGoProblem of pokemonGoProblems) {
								problems.push(pokemonGoProblem);
							}
						}
					}
				}
			}
		} else if (ruleTable.has('obtainablemisc') && (eventOnlyData = this.getEventOnlyData(outOfBattleSpecies))) {
			const eventSpecies = eventOnlyData.species;
			let eventData = eventOnlyData.eventData;
			if (ruleTable.has('fullarceusclause') && eventSpecies.baseSpecies === 'Arceus') {
				// Hall of Origin Arceus
				eventData = [...eventData, { generation: 4, level: 80, moves: ['refresh', 'futuresight', 'recover', 'hyperbeam'] }];
			}
			let legal = false;
			for (const event of eventData) {
				if (this.validateEvent(set, setSources, event, eventSpecies)) continue;
				setSources.eventOnlyMinSourceGen = event.generation;
				legal = true;
				break;
			}
			if (!legal && species.gen <= 2 && dex.gen >= 7 && !this.validateSource(set, '7V', setSources, species)) {
				legal = true;
			}
			if (!legal) {
				if (!pokemonGoProblems || (pokemonGoProblems?.length)) {
					if (eventData.length === 1) {
						problems.push(`${species.name} is only obtainable from an event - it needs to match its event:`);
					} else {
						problems.push(`${species.name} is only obtainable from events - it needs to match one of its events:`);
					}
					for (const [i, event] of eventData.entries()) {
						if (event.generation <= dex.gen && (event.generation >= this.minSourceGen || dex.gen > 8)) {
							const eventInfo = event;
							const eventNum = i + 1;
							const eventName = eventData.length > 1 ? ` #${eventNum}` : ``;
							const eventProblems = this.validateEvent(
								set, setSources, eventInfo, eventSpecies, ` to be`, `from its event${eventName}`
							);
							if (eventProblems) problems.push(...eventProblems);
						}
					}
					if (pokemonGoProblems?.length) {
						problems.push(`Additionally, it failed to validate as a Pokemon from Pokemon GO because:`);
						for (const pokemonGoProblem of pokemonGoProblems) {
							problems.push(pokemonGoProblem);
						}
					}
				} else {
					setSources.isFromPokemonGo = true;
				}
			}
		}

		// Hardcoded forced validation for Pokemon GO
		const pokemonGoOnlySpecies = ['meltan', 'melmetal', 'gimmighoulroaming'];
		if (ruleTable.has('obtainablemisc') && (pokemonGoOnlySpecies.includes(species.id))) {
			setSources.isFromPokemonGo = true;
			if (pokemonGoProblems?.length) {
				problems.push(`${name} is only obtainable from Pokemon GO, and failed to validate because:`);
				for (const pokemonGoProblem of pokemonGoProblems) {
					problems.push(pokemonGoProblem);
				}
			}
		}

		// Attempt move validation again after verifying Pokemon GO origin
		if (ruleTable.has('obtainablemoves') && setSources.isFromPokemonGo) {
			setSources.restrictiveMoves = [];
			setSources.sources = ['8V'];
			setSources.sourcesBefore = 0;
			if (moveProblems && !moveProblems.length) {
				problems.push(...this.validateMoves(outOfBattleSpecies, set.moves, setSources, set, name,
					moveLegalityWhitelist));
			}
		}

		if (ruleTable.has('obtainablemoves')) {
			if (species.id === 'keldeo' && set.moves.includes('secretsword') && this.minSourceGen > 5 && dex.gen <= 7) {
				problems.push(`${name} has Secret Sword, which is only compatible with Keldeo-Ordinary obtained from Gen 5.`);
			}
			const requiresGen3Source = setSources.maxSourceGen() <= 3;
			if (requiresGen3Source && dex.abilities.get(set.ability).gen === 4 && !species.prevo && dex.gen <= 5) {
				// Ability Capsule allows this in Gen 6+
				problems.push(`${name} has a Gen 4 ability and isn't evolved - it can't use moves from Gen 3.`);
			}
			const canUseAbilityPatch = dex.gen >= 8 && format.mod !== 'gen8dlc1';
			if (setSources.isHidden && !canUseAbilityPatch && setSources.maxSourceGen() < 5) {
				problems.push(`${name} has a Hidden Ability - it can't use moves from before Gen 5.`);
			}
			if (
				species.maleOnlyHidden && setSources.isHidden && setSources.sourcesBefore < 5 &&
				setSources.sources.every(source => source.charAt(1) === 'E')
			) {
				problems.push(`${name} has an unbreedable Hidden Ability - it can't use egg moves.`);
			}
		}

		if (teamHas) {
			for (const i in setHas) {
				if (i in teamHas) {
					teamHas[i]++;
				} else {
					teamHas[i] = 1;
				}
			}
		}
		for (const [rule, source, limit, bans] of ruleTable.complexBans) {
			let count = 0;
			for (const ban of bans) {
				if (setHas[ban]) count++;
			}
			if (limit && count > limit) {
				const clause = source ? ` by ${source}` : ``;
				problems.push(`${name} is limited to ${limit} of ${rule}${clause}.`);
			} else if (!limit && count >= bans.length) {
				const clause = source ? ` by ${source}` : ``;
				if (source === 'Obtainable Moves') {
					problems.push(`${name} has the combination of ${rule}, which is impossible to obtain legitimately.`);
				} else {
					problems.push(`${name} has the combination of ${rule}, which is banned${clause}.`);
				}
			}
		}

		for (const [rule] of ruleTable) {
			if ('!+-*'.includes(rule.charAt(0))) continue;
			const subformat = dex.formats.get(rule);
			if (subformat.onValidateSet && ruleTable.has(subformat.id)) {
				problems = problems.concat(subformat.onValidateSet.call(this, set, format, setHas, teamHas) || []);
			}
		}
		if (format.onValidateSet) {
			problems = problems.concat(format.onValidateSet.call(this, set, format, setHas, teamHas) || []);
		}

		const nameSpecies = dex.species.get(set.name);
		if (nameSpecies.exists && nameSpecies.name.toLowerCase() === set.name.toLowerCase()) {
			// nickname is the name of a species
			if (nameSpecies.baseSpecies === species.baseSpecies) {
				set.name = species.baseSpecies;
			} else if (nameSpecies.name !== species.name &&
				nameSpecies.name !== species.baseSpecies && ruleTable.has('nicknameclause')) {
				// nickname species doesn't match actual species
				// Nickname Clause
				problems.push(`${name} must not be nicknamed a different Pokémon species than what it actually is.`);
			}
		}

		if (!problems.length) {
			if (this.gen > 5 && !ruleTable.has('obtainablemisc')) {
				set.gender ||= 'N';
			}
			if (adjustLevel) set.level = adjustLevel;
			return null;
		}

		return problems;
	}

	validateStats(set: PokemonSet, species: Species, setSources: PokemonSources, pokemonGoProblems: string[] | null) {
		const ruleTable = this.ruleTable;
		const dex = this.dex;

		const allowAVs = !ruleTable.has('lgpenormalrules');
		const evLimit = ruleTable.evLimit;
		const canBottleCap = dex.gen >= 7 && (set.level >= (dex.gen < 9 ? 100 : 50) || !ruleTable.has('obtainablemisc'));

		if (!set.evs) set.evs = TeamValidator.fillStats(null, evLimit === null ? 252 : 0);
		if (!set.ivs) set.ivs = TeamValidator.fillStats(null, 31);

		const problems = [];
		const name = set.name || set.species;

		const maxedIVs = Object.values(set.ivs).every(stat => stat === 31);
		for (const moveName of set.moves) {
			const move = dex.moves.get(moveName);
			if (move.id === 'hiddenpower' && move.type !== 'Normal') {
				if (!set.hpType) {
					set.hpType = move.type;
				} else if (set.hpType !== move.type && ruleTable.has('obtainablemisc')) {
					problems.push(`${name}'s Hidden Power type ${set.hpType} is incompatible with Hidden Power ${move.type}`);
				}
			}
		}
		if (set.hpType && maxedIVs && ruleTable.has('obtainablemisc')) {
			if (dex.gen <= 2) {
				const HPdvs = dex.types.get(set.hpType).HPdvs;
				set.ivs = { hp: 30, atk: 30, def: 30, spa: 30, spd: 30, spe: 30 };
				let statName: StatID;
				for (statName in HPdvs) {
					set.ivs[statName] = HPdvs[statName]! * 2;
				}
				set.ivs.hp = -1;
			} else if (!canBottleCap) {
				set.ivs = TeamValidator.fillStats(dex.types.get(set.hpType).HPivs, 31);
			}
		}
		if (!set.hpType && set.moves.some(m => dex.moves.get(m).id === 'hiddenpower')) {
			set.hpType = dex.getHiddenPower(set.ivs).type;
		}

		const cantBreedNorEvolve = (species.eggGroups[0] === 'Undiscovered' && !species.prevo && !species.nfe);
		const isLegendary = (cantBreedNorEvolve && !species.tags.includes('Paradox') && ![
			'Pikachu', 'Unown', 'Dracozolt', 'Arctozolt', 'Dracovish', 'Arctovish', 'Gouging Fire', 'Raging Bolt', 'Iron Boulder', 'Iron Crown', 'Terapagos',
		].includes(species.baseSpecies)) || [
			'Manaphy', 'Cosmog', 'Cosmoem', 'Solgaleo', 'Lunala',
		].includes(species.baseSpecies);
		const diancieException = species.name === 'Diancie' && !set.shiny;
		const has3PerfectIVs = setSources.minSourceGen() >= 6 && isLegendary && !diancieException;

		if (set.hpType === 'Fighting' && ruleTable.has('obtainablemisc')) {
			if (has3PerfectIVs) {
				// Legendary Pokemon must have at least 3 perfect IVs in gen 6+
				problems.push(`${name} must not have Hidden Power Fighting because it starts with 3 perfect IVs because it's a Gen 6+ legendary.`);
			}
		}

		if (has3PerfectIVs && ruleTable.has('obtainablemisc')) {
			let perfectIVs = 0;
			for (const stat in set.ivs) {
				if (set.ivs[stat as 'hp'] >= 31) perfectIVs++;
			}
			if (perfectIVs < 3) {
				if (!pokemonGoProblems || pokemonGoProblems?.length) {
					const reason = (this.minSourceGen === 6 ? ` and this format requires Gen ${dex.gen} Pokémon` : ` in Gen 6 or later`);
					problems.push(`${name} must have at least three perfect IVs because it's a legendary${reason}.`);
					if (pokemonGoProblems?.length) {
						problems.push(`Additionally, it failed to validate as a Pokemon from Pokemon GO because:`);
						for (const pokemonGoProblem of pokemonGoProblems) {
							problems.push(pokemonGoProblem);
						}
					}
				} else {
					setSources.isFromPokemonGo = true;
				}
			}
		}

		if (set.hpType && !canBottleCap) {
			const ivHpType = dex.getHiddenPower(set.ivs).type;
			if (set.hpType !== ivHpType) {
				problems.push(`${name} has Hidden Power ${set.hpType}, but its IVs are for Hidden Power ${ivHpType}.`);
			}
		} else if (set.hpType) {
			if (!this.possibleBottleCapHpType(set.hpType, set.ivs)) {
				problems.push(`${name} has Hidden Power ${set.hpType}, but its IVs don't allow this even with (Bottle Cap) Hyper Training.`);
			}
		}

		if (dex.gen <= 2) {
			// validate DVs
			const ivs = set.ivs;
			const atkDV = Math.floor(ivs.atk / 2);
			const defDV = Math.floor(ivs.def / 2);
			const speDV = Math.floor(ivs.spe / 2);
			const spcDV = Math.floor(ivs.spa / 2);
			const expectedHpDV = (atkDV % 2) * 8 + (defDV % 2) * 4 + (speDV % 2) * 2 + (spcDV % 2);
			if (ivs.hp === -1) ivs.hp = expectedHpDV * 2;
			const hpDV = Math.floor(ivs.hp / 2);
			if (expectedHpDV !== hpDV) {
				problems.push(`${name} has an HP DV of ${hpDV}, but its Atk, Def, Spe, and Spc DVs give it an HP DV of ${expectedHpDV}.`);
			}
			if (ivs.spa !== ivs.spd) {
				if (dex.gen === 2) {
					problems.push(`${name} has different SpA and SpD DVs, which is not possible in Gen 2.`);
				} else {
					ivs.spd = ivs.spa;
				}
			}
			if (dex.gen > 1 && !species.gender) {
				// Gen 2 gender is calculated from the Atk DV.
				// High Atk DV <-> M. The meaning of "high" depends on the gender ratio.
				const genderThreshold = species.genderRatio.F * 16;

				const expectedGender = (atkDV >= genderThreshold ? 'M' : 'F');
				if (set.gender && set.gender !== expectedGender) {
					problems.push(`${name} is ${set.gender}, but it has an Atk DV of ${atkDV}, which makes its gender ${expectedGender}.`);
				} else {
					set.gender = expectedGender;
				}
			}
			if (
				set.species === 'Marowak' && toID(set.item) === 'thickclub' &&
				set.moves.map(toID).includes('swordsdance' as ID) && set.level === 100
			) {
				// Marowak hack
				set.ivs.atk = Math.floor(set.ivs.atk / 2) * 2;
				while (set.evs.atk > 0 && 2 * 80 + set.ivs.atk + Math.floor(set.evs.atk / 4) + 5 > 255) {
					set.evs.atk -= 4;
				}
			}
			if (dex.gen > 1) {
				const expectedShiny = !!(defDV === 10 && speDV === 10 && spcDV === 10 && atkDV % 4 >= 2);
				if (expectedShiny && !set.shiny) {
					problems.push(`${name} is not shiny, which does not match its DVs.`);
				} else if (!expectedShiny && set.shiny) {
					problems.push(`${name} is shiny, which does not match its DVs (its DVs must all be 10, except Atk which must be 2, 3, 6, 7, 10, 11, 14, or 15).`);
				}
			}
			set.nature = 'Serious';
		}

		for (const stat in set.evs) {
			if (set.evs[stat as 'hp'] < 0) {
				problems.push(`${name} has less than 0 ${allowAVs ? 'Awakening Values' : 'EVs'} in ${Dex.stats.names[stat as 'hp']}.`);
			}
		}

		if (dex.currentMod === 'gen7letsgo') { // AVs
			for (const stat in set.evs) {
				if (set.evs[stat as 'hp'] > 0 && !allowAVs) {
					problems.push(`${name} has Awakening Values but this format doesn't allow them.`);
					break;
				} else if (set.evs[stat as 'hp'] > 200) {
					problems.push(`${name} has more than 200 Awakening Values in ${Dex.stats.names[stat as 'hp']}.`);
				}
			}
		} else { // EVs
			for (const stat in set.evs) {
				if (set.evs[stat as StatID] > 255) {
					problems.push(`${name} has more than 255 EVs in ${Dex.stats.names[stat as 'hp']}.`);
				}
			}
			if (dex.gen <= 2) {
				if (set.evs.spa !== set.evs.spd) {
					if (dex.gen === 2) {
						problems.push(`${name} has different SpA and SpD EVs, which is not possible in Gen 2.`);
					} else {
						set.evs.spd = set.evs.spa;
					}
				}
			}
		}

		let totalEV = 0;
		for (const stat in set.evs) totalEV += set.evs[stat as 'hp'];
		if (!this.format.debug) {
			if (set.level > 1 && evLimit !== 0 && totalEV === 0) {
				problems.push(`${name} has exactly 0 EVs - did you forget to EV it? (If this was intentional, add exactly 1 to one of your EVs, which won't change its stats but will tell us that it wasn't a mistake).`);
			} else if (![508, 510].includes(evLimit!) && [508, 510].includes(totalEV)) {
				problems.push(`${name} has exactly ${totalEV} EVs, but this format does not restrict you to 510 EVs (If this was intentional, add exactly 1 to one of your EVs, which won't change its stats but will tell us that it wasn't a mistake).`);
			}
			// Check for level import errors from user in VGC -> DOU, etc.
			// Note that in VGC etc (Adjust Level Down = 50), `set.level` will be 100 here for validation purposes
			if (set.level === 50 && ruleTable.maxLevel !== 50 && !ruleTable.maxTotalLevel && evLimit !== 0 && totalEV % 4 === 0) {
				problems.push(`${name} is level 50, but this format allows level ${ruleTable.maxLevel} Pokémon. (If this was intentional, add exactly 1 to one of your EVs, which won't change its stats but will tell us that it wasn't a mistake).`);
			}
		}

		if (evLimit !== null && totalEV > evLimit) {
			if (!evLimit) {
				problems.push(`${name} has EVs, which is not allowed by this format.`);
			} else {
				problems.push(`${name} has ${totalEV} total EVs, which is more than this format's limit of ${evLimit}.`);
			}
		}

		return problems;
	}

	/**
	 * Not exhaustive, just checks Atk and Spe, which are the only competitively
	 * relevant IVs outside of extremely obscure situations.
	 */
	possibleBottleCapHpType(type: string, ivs: StatsTable) {
		if (!type) return true;
		if (['Dark', 'Dragon', 'Grass', 'Ghost', 'Poison'].includes(type)) {
			// Spe must be odd
			if (ivs.spe % 2 === 0) return false;
		}
		if (['Psychic', 'Fire', 'Rock', 'Fighting'].includes(type)) {
			// Spe must be even
			if (ivs.spe !== 31 && ivs.spe % 2 === 1) return false;
		}
		if (type === 'Dark') {
			// Atk must be odd
			if (ivs.atk % 2 === 0) return false;
		}
		if (['Ice', 'Water'].includes(type)) {
			// Spe or Atk must be odd
			if (ivs.spe % 2 === 0 && ivs.atk % 2 === 0) return false;
		}
		return true;
	}

	validateSource(
		set: PokemonSet, source: PokemonSource, setSources: PokemonSources, species: Species, because: string
	): string[] | undefined;
	validateSource(
		set: PokemonSet, source: PokemonSource, setSources: PokemonSources, species: Species
	): true | undefined;
	/**
	 * Returns array of error messages if invalid, undefined if valid
	 *
	 * If `because` is not passed, instead returns true if invalid.
	 */
	validateSource(
		set: PokemonSet, source: PokemonSource, setSources: PokemonSources, species: Species, because?: string
	) {
		let eventData: EventInfo | undefined;
		let eventSpecies = species;
		if (source.charAt(1) === 'S') {
			const splitSource = source.substr(source.charAt(2) === 'T' ? 3 : 2).split(' ');
			const dex = (this.dex.gen === 1 ? this.dex.mod('gen2') : this.dex);
			eventSpecies = dex.species.get(splitSource[1]);
			const eventLsetData = this.dex.species.getLearnsetData(eventSpecies.id);
			eventData = eventLsetData.eventData?.[parseInt(splitSource[0])];
			if (!eventData) {
				throw new Error(`${eventSpecies.name} from ${species.name} doesn't have data for event ${source}`);
			}
		} else if (source === '7V') {
			const isMew = species.id === 'mew';
			const isCelebi = species.id === 'celebi';
			const g7speciesName = (species.gen > 2 && species.prevo) ? species.prevo : species.id;
			const isHidden = !!this.dex.mod('gen7').species.get(g7speciesName).abilities['H'];
			eventData = {
				generation: 2,
				level: isMew ? 5 : isCelebi ? 30 : 3, // Level 1/2 Pokémon can't be obtained by transfer from RBY/GSC
				perfectIVs: isMew || isCelebi ? 5 : 3,
				isHidden,
				shiny: isMew ? undefined : 1,
				pokeball: 'pokeball',
				from: 'Gen 1-2 Virtual Console transfer',
			};
		} else if (source === '8V') {
			const isMew = species.id === 'mew';
			eventData = {
				generation: 8,
				perfectIVs: isMew ? 3 : undefined,
				shiny: isMew ? undefined : 1,
				from: 'Gen 7 Let\'s Go! HOME transfer',
			};
		} else if (source.charAt(1) === 'D') {
			eventData = {
				generation: 5,
				level: 10,
				from: 'Gen 5 Dream World',
				isHidden: !!this.dex.mod('gen5').species.get(species.id).abilities['H'],
			};
		} else if (source.charAt(1) === 'E') {
			if (this.findEggMoveFathers(source, species, setSources)) {
				return undefined;
			}
			if (because) throw new Error(`Wrong place to get an egg incompatibility message`);
			return true;
		} else {
			throw new Error(`Unidentified source ${source} passed to validateSource`);
		}

		// complicated fancy return signature
		return this.validateEvent(set, setSources, eventData, eventSpecies, because as any) as any;
	}

	findEggMoveFathers(source: PokemonSource, species: Species, setSources: PokemonSources,
		getAll?: false, pokemonBlacklist?: ID[], noRecurse?: true): boolean;
	findEggMoveFathers(source: PokemonSource, species: Species, setSources: PokemonSources, getAll?: true): ID[] | null;
	findEggMoveFathers(source: PokemonSource, species: Species, setSources: PokemonSources,
		getAll?: boolean, pokemonBlacklist?: ID[], noRecurse?: boolean) {
		if (!pokemonBlacklist) pokemonBlacklist = [];
		if (!pokemonBlacklist.includes(species.id)) pokemonBlacklist.push(species.id);
		// tradebacks have an eggGen of 2 even though the source is 1ET
		const eggGen = Math.max(parseInt(source.charAt(0)), 2);
		const fathers: ID[] = [];
		// Gen 6+ don't have egg move incompatibilities
		// (except for certain cases with baby Pokemon not handled here)
		if (!getAll && eggGen >= 6 && !setSources.levelUpEggMoves && !species.mother) return true;

		let eggMoves = setSources.limitedEggMoves;
		if (eggGen === 3) eggMoves = eggMoves?.filter(eggMove => !setSources.pomegEggMoves?.includes(eggMove));
		// must have 2 or more egg moves to have egg move incompatibilities
		if (!eggMoves) {
			// happens often in gen 1-6 LC if your only egg moves are level-up moves,
			// which aren't limited and so aren't in `limitedEggMoves`
			return getAll ? ['*'] : true;
		}
		if (!getAll && eggMoves.length <= 1 && !setSources.levelUpEggMoves) return true;
		if (setSources.levelUpEggMoves && eggGen >= 6) eggMoves = setSources.levelUpEggMoves;

		// gen 1 eggs come from gen 2 breeding
		const dex = this.dex.gen === 1 ? this.dex.mod('gen2') : this.dex;
		// In Gen 5 and earlier, egg moves can only be inherited from the father
		// we'll test each possible father separately
		let eggGroups = species.eggGroups;
		if (species.id === 'nidoqueen' || species.id === 'nidorina') {
			eggGroups = dex.species.get('nidoranf').eggGroups;
		} else if (species.id === 'shedinja') {
			// Shedinja and Nincada are different Egg groups; Shedinja itself is genderless
			eggGroups = dex.species.get('nincada').eggGroups;
		} else if (dex !== this.dex) {
			// Gen 1 tradeback; grab the egg groups from Gen 2
			eggGroups = dex.species.get(species.id).eggGroups;
		}
		if (eggGroups[0] === 'Undiscovered') eggGroups = dex.species.get(species.evos[0]).eggGroups;
		if (eggGroups[0] === 'Undiscovered' || !eggGroups.length) {
			throw new Error(`${species.name} has no egg groups for source ${source}`);
		}
		// no chainbreeding necessary if the father can be Smeargle
		if (!getAll && eggGroups.includes('Field') && !this.dex.species.get('Smeargle').isNonstandard) return true;

		// try to find a father to inherit the egg move combination from
		for (const father of dex.species.all()) {
			// can't inherit from CAP pokemon
			if (father.isNonstandard) continue;
			// can't breed mons from future gens
			if (father.gen > eggGen) continue;
			// father must be male
			if (father.gender === 'N' || father.gender === 'F') continue;
			// can't inherit from dex entries with no learnsets
			if (!dex.species.getLearnsetData(father.id).learnset) continue;
			// something is clearly wrong if its only possible father is itself
			// (exceptions: ExtremeSpeed Dragonite, Self-destruct Snorlax)
			if (pokemonBlacklist.includes(father.id) && !['dragonite', 'snorlax'].includes(father.id)) continue;
			// don't check NFE Pokémon - their evolutions will know all their moves and more
			// exception: Combee/Salandit, because their evos can't be fathers
			if (father.evos.length) {
				const evolvedFather = dex.species.get(father.evos[0]);
				if (evolvedFather.gen <= eggGen && evolvedFather.gender !== 'F') continue;
			}

			// must be able to breed with father
			if (!father.eggGroups.some(eggGroup => eggGroups.includes(eggGroup))) continue;

			// father must be able to learn the move
			if (!this.fatherCanLearn(species, father, eggMoves, eggGen, pokemonBlacklist, noRecurse)) continue;

			// father found!
			if (!getAll) return true;
			fathers.push(father.id);
		}
		if (!getAll) return false;
		return (!fathers.length && eggGen < 6) ? null : fathers;
	}

	/**
	 * We could, if we wanted, do a complete move validation of the father's
	 * moveset to see if it's valid. This would recurse and be NP-Hard so
	 * instead we won't. We'll instead use a simplified algorithm: The father
	 * is allowed to have multiple egg moves and a maximum of one move from
	 * any other restrictive source; recursion is done only if there are less
	 * egg moves to validate or if the father has an egg group it doesn't
	 * share with the egg Pokemon. Recursion is also limited to two iterations
	 * of calling findEggMoveFathers.
	 */
	fatherCanLearn(baseSpecies: Species, species: Species, moves: ID[], eggGen: number, pokemonBlacklist: ID[],
		noRecurse: boolean | undefined) {
		if (!this.dex.species.getLearnsetData(species.id).learnset) return false;

		if (species.id === 'smeargle') return true;
		const canBreedWithSmeargle = species.eggGroups.includes('Field') &&
			!this.dex.species.get('Smeargle').isNonstandard;

		const allEggSources = new PokemonSources();
		allEggSources.sourcesBefore = eggGen;
		for (const move of moves) {
			const eggSources = new PokemonSources();
			for (const { learnset, species: curSpecies } of this.dex.species.getFullLearnset(species.id)) {
				const eggPokemon = curSpecies.prevo ? curSpecies.id : '';
				if (learnset[move]) {
					for (const moveSource of learnset[move]) {
						if (eggGen > 8 && parseInt(moveSource.charAt(0)) <= 8) continue;
						if (parseInt(moveSource.charAt(0)) > eggGen) continue;
						const canLearnFromSmeargle = moveSource.charAt(1) === 'E' && canBreedWithSmeargle;
						if (!'ESDV'.includes(moveSource.charAt(1)) || canLearnFromSmeargle) {
							eggSources.addGen(parseInt(moveSource.charAt(0)));
							break;
						} else {
							if (moveSource.charAt(1) === 'E') {
								eggSources.add(moveSource + eggPokemon, move);
								if (eggGen === 2 && this.dex.moves.getByID(move).gen === 1) eggSources.add('1ET' + eggPokemon, move);
							} else {
								eggSources.add(moveSource + eggPokemon);
							}
						}
					}
				}
				if (eggSources.sourcesBefore === eggGen) break;
			}

			if (eggSources.sourcesBefore === eggGen) continue;
			if (!eggSources.sourcesBefore && !eggSources.sources.length) return false;
			const onlyEggSources = eggSources.sources.filter(source => source.charAt(1) === 'E');
			if (eggGen >= 3 && onlyEggSources.length && eggSources.limitedEggMoves === null && eggSources.sourcesBefore) {
				eggSources.possiblyLimitedEggMoves = [toID(`${eggSources.sourcesBefore}${move}`)];
			}
			allEggSources.intersectWith(eggSources);
			if (!allEggSources.size()) return false;
		}
		pokemonBlacklist.push(species.id);
		if (allEggSources.limitedEggMoves && allEggSources.limitedEggMoves.length > 1) {
			if (noRecurse) return false;
			let canChainbreed = false;
			for (const fatherEggGroup of species.eggGroups) {
				if (!baseSpecies.eggGroups.includes(fatherEggGroup)) {
					canChainbreed = true;
					break;
				}
			}
			if (!canChainbreed && allEggSources.limitedEggMoves.length === moves.length) return false;
			const setSources = new PokemonSources();
			setSources.limitedEggMoves = allEggSources.limitedEggMoves;
			return this.findEggMoveFathers(allEggSources.sources[0], species, setSources, false, pokemonBlacklist, true);
		}
		return true;
	}

	motherCanLearn(species: ID, move: ID) {
		if (!species) return false;
		const fullLearnset = this.dex.species.getFullLearnset(species);
		for (const { learnset } of fullLearnset) {
			if (learnset[move]) return true;
		}
		return false;
	}

	validateForme(set: PokemonSet) {
		const dex = this.dex;
		const name = set.name || set.species;

		const problems = [];
		const item = dex.items.get(set.item);
		const species = dex.species.get(set.species);

		if (species.name === 'Necrozma-Ultra') {
			const whichMoves = (set.moves.map(toID).includes('sunsteelstrike' as ID) ? 1 : 0) +
				(set.moves.map(toID).includes('moongeistbeam' as ID) ? 2 : 0);
			if (item.name !== 'Ultranecrozium Z') {
				// Necrozma-Ultra transforms from one of two formes, and neither one is the base forme
				problems.push(`Necrozma-Ultra must start the battle holding Ultranecrozium Z.`);
			} else if (whichMoves === 1) {
				set.species = 'Necrozma-Dusk-Mane';
				set.ability = 'Prism Armor';
			} else if (whichMoves === 2) {
				set.species = 'Necrozma-Dawn-Wings';
				set.ability = 'Prism Armor';
			} else {
				problems.push(`Necrozma-Ultra must start the battle as Necrozma-Dusk-Mane or Necrozma-Dawn-Wings holding Ultranecrozium Z. Please specify which Necrozma it should start as.`);
			}
		} else if (species.baseSpecies === 'Zygarde') {
			if (species.name === 'Zygarde-Complete' || species.name === 'Zygarde-Mega') {
				problems.push(`${species.name} must start the battle as Zygarde or Zygarde-10% with Power Construct. Please specify which Zygarde it should start as.`);
			}
			if (item.id === 'zygardite' && set.ability !== 'Power Construct') {
				problems.push(`Zygarde holding Zygardite can only Mega Evolve with the Power Construct ability.`);
			}
		} else if (species.baseSpecies === 'Terapagos') {
			set.species = 'Terapagos';
			set.ability = 'Tera Shift';
		} else if (species.battleOnly) {
			if (species.requiredAbility && set.ability !== species.requiredAbility) {
				// Darmanitan-Zen
				problems.push(`${species.name} transforms in-battle with ${species.requiredAbility}, please fix its ability.`);
			}
			if (species.requiredItems) {
				if (!species.requiredItems.includes(item.name)) {
					// Mega or Primal
					problems.push(`${species.name} transforms in-battle with ${species.requiredItem}, please fix its item.`);
				}
			}
			if (species.requiredMove && !set.moves.map(toID).includes(toID(species.requiredMove))) {
				// Meloetta-Pirouette, Rayquaza-Mega
				problems.push(`${species.name} transforms in-battle with ${species.requiredMove}, please fix its moves.`);
			}
			if (typeof species.battleOnly !== 'string') {
				// Ultra Necrozma and Complete Zygarde are already checked above
				throw new Error(`${species.name} should have a string battleOnly`);
			}
			// Set to out-of-battle forme
			set.species = species.battleOnly;
		} else {
			if (species.requiredAbility) {
				// Impossible!
				throw new Error(`Species ${species.name} has a required ability despite not being a battle-only forme; it should just be in its abilities table.`);
			}
			if (species.requiredItems && !species.requiredItems.includes(item.name)) {
				if (dex.gen >= 8 && (species.baseSpecies === 'Arceus' || species.baseSpecies === 'Silvally')) {
					problems.push(
						`${name} needs to hold ${species.requiredItems.join(' or ')}.`,
						`(It will revert to its Normal forme if you remove the item or give it a different item.)`
					);
				} else {
					// Memory/Drive/Griseous Orb/Plate/Z-Crystal - Forme mismatch
					const baseSpecies = this.dex.species.get(species.changesFrom);
					problems.push(
						`${name} needs to hold ${species.requiredItems.join(' or ')} to be in its ${species.forme} forme.`,
						`(It will revert to its ${baseSpecies.baseForme || 'base'} forme if you remove the item or give it a different item.)`
					);
				}
			}
			if (species.requiredMove && !set.moves.map(toID).includes(toID(species.requiredMove))) {
				const baseSpecies = this.dex.species.get(species.changesFrom);
				problems.push(
					`${name} needs to know the move ${species.requiredMove} to be in its ${species.forme} forme.`,
					`(It will revert to its ${baseSpecies.baseForme} forme if it forgets the move.)`
				);
			}

			// Mismatches between the set forme (if not base) and the item signature forme will have been rejected already.
			// It only remains to assign the right forme to a set with the base species (Arceus/Genesect/Giratina/Silvally).
			if (item.forcedForme && species.name === dex.species.get(item.forcedForme).baseSpecies) {
				set.species = item.forcedForme;
			}
		}

		if (species.name === 'Pikachu-Cosplay') {
			const cosplay: { [k: string]: string } = {
				meteormash: 'Pikachu-Rock-Star', iciclecrash: 'Pikachu-Belle', drainingkiss: 'Pikachu-Pop-Star',
				electricterrain: 'Pikachu-PhD', flyingpress: 'Pikachu-Libre',
			};
			for (const moveid of set.moves) {
				if (moveid in cosplay) {
					set.species = cosplay[moveid];
					break;
				}
			}
		}

		if (species.name === 'Keldeo' && set.moves.map(toID).includes('secretsword' as ID) && dex.gen >= 8) {
			set.species = 'Keldeo-Resolute';
		}

		const crowned: { [k: string]: string } = {
			'Zacian-Crowned': 'behemothblade', 'Zamazenta-Crowned': 'behemothbash',
		};
		if (species.name in crowned) {
			const behemothMove = set.moves.map(toID).indexOf(crowned[species.name] as ID);
			if (behemothMove >= 0) {
				set.moves[behemothMove] = 'ironhead';
			}
		}
		if (species.baseSpecies === "Hoopa" && dex.gen >= 9) {
			const moves = set.moves.map(toID);
			const hyperspaceHole = moves.indexOf('hyperspacehole' as ID);
			const hyperspaceFury = moves.indexOf('hyperspacefury' as ID);
			if (species.name === "Hoopa" && hyperspaceFury >= 0) {
				problems.push(`In Generation 9, Hoopa cannot run Hyperspace Fury because it gets replaced with Hyperspace Hole upon changing forme.`);
			} else if (species.name === "Hoopa-Unbound" && hyperspaceHole >= 0) {
				problems.push(`In Generation 9, Hoopa-Unbound cannot run Hyperspace Hole because it gets replaced with Hyperspace Fury upon changing forme.`);
			}
		}

		if (species.baseSpecies === "Greninja" && toID(set.ability) === 'battlebond') {
			set.species = "Greninja-Bond";
		}
		if (species.baseSpecies === "Rockruff" && toID(set.ability) === 'owntempo') {
			set.species = "Rockruff-Dusk";
		}

		if (species.baseSpecies === "Unown" && dex.gen === 2) {
			let resultBinary = '';
			for (const iv of ['atk', 'def', 'spe', 'spa'] as const) {
				resultBinary += set.ivs[iv].toString(2).padStart(5, '0').slice(1, 3);
			}
			const resultDecimal = Math.floor(parseInt(resultBinary, 2) / 10);
			const expectedLetter = String.fromCharCode(resultDecimal + 65);
			const unownLetter = species.forme || "A";
			if (unownLetter !== expectedLetter) {
				problems.push(`Unown has forme ${unownLetter}, but its DVs give it the forme ${expectedLetter}.`);
			}
		}
		return problems;
	}

	checkSpecies(set: PokemonSet, species: Species, tierSpecies: Species, setHas: { [k: string]: true }) {
		const dex = this.dex;
		const ruleTable = this.ruleTable;

		// https://www.smogon.com/forums/posts/8659168
		if (
			(tierSpecies.id === 'zamazentacrowned' && species.id === 'zamazenta') ||
			(tierSpecies.id === 'zaciancrowned' && species.id === 'zacian')
		) {
			species = tierSpecies;
		}

		setHas['pokemon:' + species.id] = true;
		setHas['basepokemon:' + toID(species.baseSpecies)] = true;

		let isMega = false;
		if (tierSpecies !== species) {
			setHas['pokemon:' + tierSpecies.id] = true;
			if (tierSpecies.isMega || tierSpecies.isPrimal) {
				setHas['pokemontag:mega'] = true;
				isMega = true;
			}
		}

		let isGmax = false;
		if (tierSpecies.canGigantamax && set.gigantamax) {
			setHas['pokemon:' + tierSpecies.id + 'gmax'] = true;
			isGmax = true;
		}
		if (tierSpecies.baseSpecies === 'Greninja' && toID(set.ability) === 'battlebond') {
			setHas['pokemon:greninjabond'] = true;
		}
		if (tierSpecies.baseSpecies === 'Rockruff' && toID(set.ability) === 'owntempo') {
			setHas['pokemon:rockruffdusk'] = true;
		}

		const tier = tierSpecies.tier === '(PU)' ? 'ZU' : tierSpecies.tier === '(NU)' ? 'PU' : tierSpecies.tier;
		const tierTag = 'pokemontag:' + toID(tier);
		setHas[tierTag] = true;

		const doublesTier = tierSpecies.doublesTier === '(DUU)' ? 'DNU' : tierSpecies.doublesTier;
		const doublesTierTag = 'pokemontag:' + toID(doublesTier);
		setHas[doublesTierTag] = true;

		const ndTier = tierSpecies.natDexTier === '(PU)' ? 'ZU' :
			tierSpecies.natDexTier === '(NU)' ? 'PU' : tierSpecies.natDexTier;
		const ndTierTag = 'pokemontag:nd' + toID(ndTier);
		setHas[ndTierTag] = true;

		// Only pokemon that can gigantamax should have the Gmax flag
		if (!tierSpecies.canGigantamax && set.gigantamax) {
			return `${tierSpecies.name} cannot Gigantamax but is flagged as being able to.`;
		}

		let banReason = ruleTable.check('pokemon:' + species.id);
		if (banReason) {
			return `${species.name} is ${banReason}.`;
		}
		if (banReason === '') return null;

		if (tierSpecies !== species) {
			banReason = ruleTable.check('pokemon:' + tierSpecies.id);
			if (banReason) {
				return `${tierSpecies.name} is ${banReason}.`;
			}
			if (banReason === '') return null;
		}

		if (isMega) {
			banReason = ruleTable.check('pokemontag:mega', setHas);
			if (banReason) {
				return `Mega evolutions are ${banReason}.`;
			}
		}

		if (isGmax) {
			banReason = ruleTable.check('pokemon:' + tierSpecies.id + 'gmax');
			if (banReason) {
				return `Gigantamaxing ${species.name} is ${banReason}.`;
			}
		}

		banReason = ruleTable.check('basepokemon:' + toID(species.baseSpecies));
		if (banReason) {
			return `${species.name} is ${banReason}.`;
		}
		if (banReason === '') {
			// don't allow nonstandard speciess when whitelisting standard base species
			// i.e. unbanning Pichu doesn't mean allowing Pichu-Spiky-Eared outside of Gen 4
			const baseSpecies = dex.species.get(species.baseSpecies);
			if (baseSpecies.isNonstandard === species.isNonstandard) {
				return null;
			}
		}

		// We can't return here because the `-nonexistent` rule is a bit
		// complicated in terms of what trumps it. We don't want e.g.
		// +Mythical to unban Shaymin in Gen 1, for instance.
		let nonexistentCheck = Tags.nonexistent.genericFilter!(tierSpecies) && ruleTable.check('nonexistent');

		const EXISTENCE_TAG = ['past', 'future', 'lgpe', 'unobtainable', 'cap', 'custom', 'nonexistent'];

		for (const ruleid of ruleTable.tagRules) {
			if (ruleid.startsWith('*')) continue;
			const tagid = ruleid.slice(12) as ID;
			const tag = Tags[tagid];
			if ((tag.speciesFilter || tag.genericFilter)!(tierSpecies)) {
				const existenceTag = EXISTENCE_TAG.includes(tagid);
				if (ruleid.startsWith('+')) {
					// we want rules like +CAP to trump -Nonexistent, but most tags shouldn't
					if (!existenceTag && nonexistentCheck) continue;
					return null;
				}
				if (existenceTag) {
					// for a nicer error message
					nonexistentCheck = 'banned';
					break;
				}
				return `${species.name} is tagged ${tag.name}, which is ${ruleTable.check(ruleid.slice(1)) || "banned"}.`;
			}
		}

		if (nonexistentCheck) {
			if (tierSpecies.isNonstandard === 'Past' || tierSpecies.isNonstandard === 'Future') {
				return `${tierSpecies.name} does not exist in Gen ${dex.gen}.`;
			}
			if (tierSpecies.isNonstandard === 'LGPE') {
				return `${tierSpecies.name} does not exist in this game, only in Let's Go Pikachu/Eevee.`;
			}
			if (tierSpecies.isNonstandard === 'CAP') {
				return `${tierSpecies.name} is a CAP and does not exist in this game.`;
			}
			if (tierSpecies.isNonstandard === 'Unobtainable') {
				return `${tierSpecies.name} is not possible to obtain in this game.`;
			}
			if (tierSpecies.isNonstandard === 'Gigantamax') {
				return `${tierSpecies.name} is a placeholder for a Gigantamax sprite, not a real Pokémon. (This message is likely to be a validator bug.)`;
			}
			return `${tierSpecies.name} does not exist in this game.`;
		}
		if (nonexistentCheck === '') return null;

		// Special casing for Pokemon that can Gmax, but their Gmax factor cannot be legally obtained
		if (tierSpecies.gmaxUnreleased && set.gigantamax) {
			banReason = ruleTable.check('pokemontag:unobtainable');
			if (banReason) {
				return `${tierSpecies.name} is flagged as gigantamax, but it cannot gigantamax without hacking or glitches.`;
			}
			if (banReason === '') return null;
		}

		banReason = ruleTable.check('pokemontag:allpokemon');
		if (banReason) {
			return `${species.name} is not in the list of allowed pokemon.`;
		}

		return null;
	}

	checkItem(set: PokemonSet, item: Item, setHas: { [k: string]: true }) {
		const dex = this.dex;
		const ruleTable = this.ruleTable;

		setHas['item:' + item.id] = true;

		let banReason = ruleTable.check('item:' + (item.id || 'noitem'));
		if (banReason) {
			if (!item.id) {
				return `${set.name} not holding an item is ${banReason}.`;
			}
			return `${set.name}'s item ${item.name} is ${banReason}.`;
		}
		if (banReason === '') return null;

		if (!item.id) return null;

		banReason = ruleTable.check('pokemontag:allitems');
		if (banReason) {
			return `${set.name}'s item ${item.name} is not in the list of allowed items.`;
		}

		// obtainability
		if (item.isNonstandard) {
			banReason = ruleTable.check('pokemontag:' + toID(item.isNonstandard));
			if (banReason) {
				if (item.isNonstandard === 'Unobtainable') {
					return `${item.name} is not obtainable without hacking or glitches.`;
				}
				return `${set.name}'s item ${item.name} is tagged ${item.isNonstandard}, which is ${banReason}.`;
			}
			if (banReason === '') return null;
		}

		if (item.isNonstandard && item.isNonstandard !== 'Unobtainable') {
			banReason = ruleTable.check('nonexistent', setHas);
			if (banReason) {
				if (['Past', 'Future'].includes(item.isNonstandard)) {
					return `${set.name}'s item ${item.name} does not exist in Gen ${dex.gen}.`;
				}
				return `${set.name}'s item ${item.name} does not exist in this game.`;
			}
			if (banReason === '') return null;
		}

		return null;
	}

	checkMove(set: PokemonSet, move: Move, setHas: { [k: string]: true }) {
		const dex = this.dex;
		const ruleTable = this.ruleTable;

		setHas['move:' + move.id] = true;

		let banReason = ruleTable.check('move:' + move.id);
		if (banReason) {
			return `${set.name}'s move ${move.name} is ${banReason}.`;
		}
		if (banReason === '') return null;

		banReason = ruleTable.check('pokemontag:allmoves');
		if (banReason) {
			return `${set.name}'s move ${move.name} is not in the list of allowed moves.`;
		}

		// obtainability
		if (move.isNonstandard) {
			banReason = ruleTable.check('pokemontag:' + toID(move.isNonstandard));
			if (banReason) {
				if (move.isNonstandard === 'Unobtainable') {
					return `${move.name} is not obtainable without hacking or glitches${dex.gen >= 9 && move.gen < dex.gen ? ` in Gen ${dex.gen}` : ``}.`;
				}
				if (move.isNonstandard === 'Gigantamax') {
					return `${move.name} is not usable without Gigantamaxing its user, ${move.isMax}.`;
				}
				return `${set.name}'s move ${move.name} is tagged ${move.isNonstandard}, which is ${banReason}.`;
			}
			if (banReason === '') return null;
		}

		if (move.isNonstandard && move.isNonstandard !== 'Unobtainable') {
			banReason = ruleTable.check('nonexistent', setHas);
			if (banReason) {
				if (['Past', 'Future'].includes(move.isNonstandard)) {
					return `${set.name}'s move ${move.name} does not exist in Gen ${dex.gen}.`;
				}
				return `${set.name}'s move ${move.name} does not exist in this game.`;
			}
			if (banReason === '') return null;
		}

		return null;
	}

	checkAbility(set: PokemonSet, ability: Ability, setHas: { [k: string]: true }) {
		const dex = this.dex;
		const ruleTable = this.ruleTable;

		setHas['ability:' + ability.id] = true;

		if (this.format.id.startsWith('gen9pokebilities')) {
			const species = dex.species.get(set.species);
			const unSeenAbilities = Object.keys(species.abilities)
				.filter(key => key !== 'S' && (key !== 'H' || !species.unreleasedHidden))
				.map(key => species.abilities[key as "0" | "1" | "H" | "S"]);

			if (ability.id !== this.toID(species.abilities['S'])) {
				for (const abilityName of unSeenAbilities) {
					setHas['ability:' + toID(abilityName)] = true;
				}
			}
		}

		let banReason = ruleTable.check('ability:' + ability.id);
		if (banReason) {
			return `${set.name}'s ability ${ability.name} is ${banReason}.`;
		}
		if (banReason === '') return null;

		banReason = ruleTable.check('pokemontag:allabilities');
		if (banReason) {
			return `${set.name}'s ability ${ability.name} is not in the list of allowed abilities.`;
		}

		// obtainability
		if (ability.isNonstandard) {
			banReason = ruleTable.check('pokemontag:' + toID(ability.isNonstandard));
			if (banReason) {
				return `${set.name}'s ability ${ability.name} is tagged ${ability.isNonstandard}, which is ${banReason}.`;
			}
			if (banReason === '') return null;

			banReason = ruleTable.check('nonexistent', setHas);
			if (banReason) {
				if (['Past', 'Future'].includes(ability.isNonstandard)) {
					return `${set.name}'s ability ${ability.name} does not exist in Gen ${dex.gen}.`;
				}
				return `${set.name}'s ability ${ability.name} does not exist in this game.`;
			}
			if (banReason === '') return null;
		}

		return null;
	}

	checkNature(set: PokemonSet, nature: Nature, setHas: { [k: string]: true }) {
		const dex = this.dex;
		const ruleTable = this.ruleTable;

		setHas['nature:' + nature.id] = true;

		let banReason = ruleTable.check('nature:' + nature.id);
		if (banReason) {
			return `${set.name}'s nature ${nature.name} is ${banReason}.`;
		}
		if (banReason === '') return null;

		banReason = ruleTable.check('allnatures');
		if (banReason) {
			return `${set.name}'s nature ${nature.name} is not in the list of allowed natures.`;
		}

		// obtainability
		if (nature.isNonstandard) {
			banReason = ruleTable.check('pokemontag:' + toID(nature.isNonstandard));
			if (banReason) {
				return `${set.name}'s nature ${nature.name} is tagged ${nature.isNonstandard}, which is ${banReason}.`;
			}
			if (banReason === '') return null;

			banReason = ruleTable.check('nonexistent', setHas);
			if (banReason) {
				if (['Past', 'Future'].includes(nature.isNonstandard)) {
					return `${set.name}'s nature ${nature.name} does not exist in Gen ${dex.gen}.`;
				}
				return `${set.name}'s nature ${nature.name} does not exist in this game.`;
			}
			if (banReason === '') return null;
		}
		return null;
	}

	validateEvent(
		set: PokemonSet, setSources: PokemonSources, eventData: EventInfo, eventSpecies: Species
	): true | undefined;
	validateEvent(
		set: PokemonSet, setSources: PokemonSources, eventData: EventInfo, eventSpecies: Species,
		because: string, from?: string
	): string[] | undefined;
	/**
	 * Returns array of error messages if invalid, undefined if valid
	 *
	 * If `because` is not passed, instead returns true if invalid.
	 */
	validateEvent(
		set: PokemonSet, setSources: PokemonSources, eventData: EventInfo, eventSpecies: Species,
		because = ``, from = `from an event`
	) {
		const dex = this.dex;
		let name = set.species;
		const species = dex.species.get(set.species);
		const maxSourceGen = this.ruleTable.has('allowtradeback') ? Utils.clampIntRange(dex.gen + 1, 1, 8) : dex.gen;
		if (!eventSpecies) eventSpecies = species;
		if (set.name && set.species !== set.name && species.baseSpecies !== set.name) name = `${set.name} (${set.species})`;

		const fastReturn = !because;
		if (eventData.from) from = `from ${eventData.from}`;
		const etc = `${because} ${from}`;

		const problems = [];

		if (dex.gen < 8 && this.minSourceGen > eventData.generation) {
			if (fastReturn) return true;
			problems.push(`This format requires Pokemon from gen ${this.minSourceGen} or later and ${name} is from gen ${eventData.generation}${etc}.`);
		}
		if (maxSourceGen < eventData.generation) {
			if (fastReturn) return true;
			problems.push(`This format is in gen ${dex.gen} and ${name} is from gen ${eventData.generation}${etc}.`);
		}

		if (eventData.japan && dex.currentMod !== 'gen1jpn') {
			if (fastReturn) return true;
			problems.push(`${name} has moves from Japan-only events, but this format simulates International Yellow/Crystal which can't trade with Japanese games.`);
		}

		if (eventData.level && (set.level || 0) < eventData.level) {
			if (fastReturn) return true;
			problems.push(`${name} must be at least level ${eventData.level}${etc}.`);
		}
		if ((dex.gen === 3 || dex.gen === 4) && eventData.level === 100 && set.evs) {
			let statName: StatID;
			for (statName in set.evs) {
				const ev = set.evs[statName];
				if (ev > 100) {
					problems.push(
						`${name} can't have more than 100 EVs in any stat, because it is only obtainable from level 100 events. Level 100 Pokemon can only gain EVs from vitamins (Carbos etc), which are capped at 100 EVs.`,
					);
				}
				if (!(
					ev % 10 === 0 ||
					(ev % 10 === 8 && ev % 4 === 0)
				)) {
					problems.push(
						`${name} can only have EVs that are multiples of 10, because it is only obtainable from level 100 events. Level 100 Pokemon can only gain EVs from vitamins (Carbos etc), which boost in multiples of 10.`,
					);
				}
			}
		}
		if ((eventData.shiny === true && !set.shiny) || (!eventData.shiny && set.shiny)) {
			if (fastReturn) return true;
			const shinyReq = eventData.shiny ? ` be shiny` : ` not be shiny`;
			problems.push(`${name} must${shinyReq}${etc}.`);
		}
		if (eventData.gender) {
			if (set.gender && eventData.gender !== set.gender) {
				if (fastReturn) return true;
				problems.push(`${name}'s gender must be ${eventData.gender}${etc}.`);
			}
		}
		const canMint = dex.gen > 7;
		if (eventData.nature && eventData.nature !== set.nature && !canMint) {
			if (fastReturn) return true;
			problems.push(`${name} must have a ${eventData.nature} nature${etc} - Mints are only available starting gen 8.`);
		}
		let requiredIVs = 0;
		if (eventData.ivs) {
			/** In Gen 7+, IVs can be changed to 31 */
			const canBottleCap = dex.gen >= 7 && set.level >= (dex.gen < 9 ? 100 : 50);

			if (!set.ivs) set.ivs = { hp: 31, atk: 31, def: 31, spa: 31, spd: 31, spe: 31 };
			let statName: StatID;
			for (statName in eventData.ivs) {
				if (canBottleCap && set.ivs[statName] === 31) continue;
				if (set.ivs[statName] !== eventData.ivs[statName]) {
					if (fastReturn) return true;
					problems.push(`${name} must have ${eventData.ivs[statName]} ${Dex.stats.names[statName]} IVs${etc}.`);
				}
			}

			if (canBottleCap) {
				// IVs can be overridden but Hidden Power type can't
				if (Object.keys(eventData.ivs).length >= 6) {
					const requiredHpType = dex.getHiddenPower(eventData.ivs as StatsTable).type;
					if (set.hpType && set.hpType !== requiredHpType) {
						if (fastReturn) return true;
						problems.push(`${name} can only have Hidden Power ${requiredHpType}${etc}.`);
					}
					set.hpType = requiredHpType;
				}
			}
		} else {
			requiredIVs = eventData.perfectIVs || 0;
		}
		if (requiredIVs && set.ivs) {
			// Legendary Pokemon must have at least 3 perfect IVs in gen 6
			// Events can also have a certain amount of guaranteed perfect IVs
			let perfectIVs = 0;
			let statName: StatID;
			for (statName in set.ivs) {
				if (set.ivs[statName] >= 31) perfectIVs++;
			}
			if (perfectIVs < requiredIVs) {
				if (fastReturn) return true;
				if (eventData.perfectIVs) {
					problems.push(`${name} must have at least ${requiredIVs} perfect IVs${etc}.`);
				}
			}
			// The perfect IV count affects Hidden Power availability
			if (dex.gen >= 3 && requiredIVs >= 3 && set.hpType === 'Fighting') {
				if (fastReturn) return true;
				problems.push(`${name} can't use Hidden Power Fighting because it must have at least three perfect IVs${etc}.`);
			} else if (
				dex.gen >= 3 && requiredIVs >= 5 && set.hpType &&
				!['Dark', 'Dragon', 'Electric', 'Steel', 'Ice'].includes(set.hpType)
			) {
				if (fastReturn) return true;
				problems.push(`${name} can only use Hidden Power Dark/Dragon/Electric/Steel/Ice because it must have at least 5 perfect IVs${etc}.`);
			}
		}
		const ruleTable = this.ruleTable;
		if (ruleTable.has('obtainablemoves')) {
			const ssMaxSourceGen = setSources.maxSourceGen();
			const tradebackEligible = dex.gen === 2 && (species.gen === 1 || eventSpecies.gen === 1);
			if (ssMaxSourceGen && eventData.generation > ssMaxSourceGen && !tradebackEligible) {
				if (fastReturn) return true;
				problems.push(`${name} must not have moves only learnable in gen ${ssMaxSourceGen}${etc}.`);
			}

			if (eventData.from === "Gen 5 Dream World" && setSources.dreamWorldMoveCount > 1) {
				problems.push(`${name} can only have one Dream World move.`);
			}
		}
		if (ruleTable.has('obtainableabilities')) {
			if (dex.gen <= 5 && eventData.abilities && eventData.abilities.length === 1 && !eventData.isHidden) {
				if (species.name === eventSpecies.name) {
					// has not evolved, abilities must match
					const requiredAbility = dex.abilities.get(eventData.abilities[0]).name;
					if (set.ability !== requiredAbility) {
						if (fastReturn) return true;
						problems.push(`${name} must have ${requiredAbility}${etc}.`);
					}
				} else {
					// has evolved
					const ability1 = dex.abilities.get(eventSpecies.abilities['1']);
					if (ability1.gen && eventData.generation >= ability1.gen) {
						// pokemon had 2 available abilities in the gen the event happened
						// ability is restricted to a single ability slot
						const requiredAbilitySlot = (toID(eventData.abilities[0]) === ability1.id ? 1 : 0);
						const requiredAbility = dex.abilities.get(species.abilities[requiredAbilitySlot] || species.abilities['0']).name;
						if (set.ability !== requiredAbility) {
							const originalAbility = dex.abilities.get(eventData.abilities[0]).name;
							if (fastReturn) return true;
							problems.push(`${name} must have ${requiredAbility}${because} from a ${originalAbility} ${eventSpecies.name} event.`);
						}
					}
				}
			}
			if (species.abilities['H']) {
				const isHidden = (set.ability === species.abilities['H']);
				if (!isHidden && eventData.isHidden && dex.gen <= 8) {
					if (fastReturn) return true;
					problems.push(`${name} must have its Hidden Ability${etc}.`);
				}

				const canUseAbilityPatch = dex.gen >= 8 && this.format.mod !== 'gen8dlc1';
				if (isHidden && !eventData.isHidden && !canUseAbilityPatch) {
					if (fastReturn) return true;
					problems.push(`${name} must not have its Hidden Ability${etc}.`);
				}
			}
		}
		if (problems.length) return problems;
		if (eventData.gender) set.gender = eventData.gender;
	}

	allSources(species?: Species) {
		let minSourceGen = this.minSourceGen;
		if (this.dex.gen >= 3 && minSourceGen < 3) minSourceGen = 3;
		if (species) minSourceGen = Math.max(minSourceGen, species.gen);
		const maxSourceGen = this.ruleTable.has('allowtradeback') ? Utils.clampIntRange(this.dex.gen + 1, 1, 8) : this.dex.gen;
		return new PokemonSources(maxSourceGen, minSourceGen);
	}

	validateMoves(
		species: Species, moves: string[], setSources: PokemonSources, set?: Partial<PokemonSet>,
		name: string = species.name, moveLegalityWhitelist: { [k: string]: true | undefined } = {}
	) {
		const dex = this.dex;
		const ruleTable = this.ruleTable;

		const problems = [];

		const checkCanLearn = (ruleTable.checkCanLearn?.[0] || this.checkCanLearn);
		for (const moveName of moves) {
			const move = dex.moves.get(moveName);
			if (moveLegalityWhitelist[move.id]) continue;
			const problem = checkCanLearn.call(this, move, species, setSources, set);
			if (problem) {
				problems.push(`${name}${problem}`);
				break;
			}
		}

		if (setSources.size() && setSources.moveEvoCarryCount > 3) {
			if (setSources.sourcesBefore < 6) setSources.sourcesBefore = 0;
			setSources.sources = setSources.sources.filter(
				source => source.charAt(1) === 'E' && parseInt(source.charAt(0)) >= 6
			);
			if (!setSources.size()) {
				problems.push(`${name} needs to know ${species.evoMove || 'a Fairy-type move'} to evolve, so it can only know 3 other moves from ${species.prevo}.`);
			}
		}

		if (problems.length) return problems;

		if (setSources.isHidden) {
			setSources.sources = setSources.sources.filter(
				source => parseInt(source.charAt(0)) >= 5
			);
			if (setSources.sourcesBefore < 5) setSources.sourcesBefore = 0;
			const canUseAbilityPatch = dex.gen >= 8 && this.format.mod !== 'gen8dlc1';
			if (!setSources.size() && !canUseAbilityPatch) {
				problems.push(`${name} has a hidden ability - it can't have moves only learned before gen 5.`);
				return problems;
			}
		}

		if (setSources.babyOnly && setSources.sources.length) {
			const baby = dex.species.get(setSources.babyOnly);
			const babyEvo = toID(baby.evos[0]);
			setSources.sources = setSources.sources.filter(source => {
				if (source.charAt(1) === 'S') {
					const sourceId = source.split(' ')[1];
					if (sourceId !== baby.id) return false;
				}
				if (source.charAt(1) === 'E') {
					if (babyEvo && source.slice(2) === babyEvo) return false;
				}
				if (source.charAt(1) === 'D') {
					if (babyEvo && source.slice(2) === babyEvo) return false;
				}
				return true;
			});
			if (!setSources.size()) {
				problems.push(`${name}'s event/egg moves are from an evolution, and are incompatible with its moves from ${baby.name}.`);
			}
		}
		if (setSources.babyOnly && setSources.size() && this.gen > 2) {
			// there do theoretically exist evo/tradeback incompatibilities in
			// gen 2, but those are very complicated to validate and should be
			// handled separately anyway, so for now we just treat them all as
			// legal (competitively relevant ones can be manually banned)
			const baby = dex.species.get(setSources.babyOnly);
			setSources.sources = setSources.sources.filter(source => {
				if (baby.gen > parseInt(source.charAt(0)) && !source.startsWith('1ST')) return false;
				if (baby.gen > 2 && source === '7V') return false;
				return true;
			});
			if (setSources.sourcesBefore < baby.gen) setSources.sourcesBefore = 0;
			if (!setSources.size()) {
				problems.push(`${name} has moves from before Gen ${baby.gen}, which are incompatible with its moves from ${baby.name}.`);
			}
		}

		return problems;
	}
	/**
	 * Returns a list of problems regarding a Pokemon's availability in Pokemon GO (empty list if no problems)
	 * If the Pokemon cannot be obtained from Pokemon GO, returns null
	 */
	validatePokemonGo(
		species: Species, set: PokemonSet, setSources: PokemonSources, name: string = species.name,
	): string[] | null {
		let problems = [];
		let minLevel = 50; // maximum level a Pokemon can be in Pokemon GO
		let minIVs = 15; // IVs range from 0 to 15 in Pokemon GO
		const dex = this.dex;
		const pokemonGoData = dex.species.getPokemonGoData(species.id);
		if (dex.gen < 8 || this.format.mod === 'gen8dlc1') return null;
		if (!pokemonGoData) {
			// Handles forms and evolutions not obtainable from Pokemon GO
			const otherSpecies = this.dex.species.get(species.changesFrom || species.prevo);
			// If a Pokemon is somehow not obtainable from Pokemon GO and it must be leveled up to be evolved,
			// validation for the game should stop because it's more optimal to get the Pokemon outside of the game
			if (otherSpecies.name && !species.evoLevel) {
				const otherProblems = this.validatePokemonGo(otherSpecies, set, setSources, name);
				if (otherProblems) {
					problems = otherProblems;
				} else {
					return null;
				}
			} else {
				return null;
			}
		} else {
			const pokemonGoSources = pokemonGoData.encounters;
			// should never happen
			if (!pokemonGoSources) throw new Error(`Species with no Pokemon GO data: ${species.id}`);
			if (set.shiny) name = "Shiny " + name;
			if (set.shiny && pokemonGoSources.includes('noshiny')) {
				problems.push(`${name} is not obtainable from Pokemon GO.`);
			} else {
				if (pokemonGoSources.includes('wild')) {
					minLevel = 1;
					minIVs = 0;
				}
				if (pokemonGoSources.includes('egg')) {
					/**
					 * A Pokemon's level when hatched is determined by the trainer's level when it is obtained
					 * It is no longer possible for new accounts to obtain eggs at level 1 because they will have reached
					 * level 2 by the time they can spin a PokeStop. However, it might be possible for a sleeper account
					 * from before XP changes to get a level 1 egg from spinning a PokeStop that sends the account to
					 * level 2, but this needs research
					*/
					minLevel = Math.min(minLevel, 2);
					minIVs = Math.min(minIVs, 10);
				}
				if (pokemonGoSources.includes('12kmegg')) {
					minLevel = Math.min(minLevel, 8);
					minIVs = Math.min(minIVs, 10);
				}
				if (pokemonGoSources.includes('raid')) {
					minLevel = Math.min(minLevel, 20);
					minIVs = Math.min(minIVs, 10);
				}
				if (species.id === 'mewtwo' && set.level >= 20) {
					// A bug allowed Mewtwo to be encountered with an IV floor of 0 from GO Battle League
					minIVs = Math.min(minIVs, 0);
				}
				if (pokemonGoSources.includes('research')) {
					if (species.id === 'cresselia') {
						// For some reason, Cresselia from research has a possible level 10 source
						minLevel = Math.min(minLevel, 10);
					} else {
						minLevel = Math.min(minLevel, 15);
					}
					minIVs = Math.min(minIVs, 10);
				}
				if (pokemonGoSources.includes('giovanni') && !set.shiny) {
					/**
					 * Purified Pokemon can be leveled down to level 8 after trading; they are forced to
					 * special trades, but currently all Giovanni Shadow Pokemon are already forced special trades
					*/
					minLevel = Math.min(minLevel, 8);
					minIVs = Math.min(minIVs, 1);
					if (set.level < 12) setSources.pokemonGoSource = "purified";
				}
				// Attempt to trade the Pokemon to reduce level and IVs
				if (!pokemonGoSources.includes('notrade')) {
					// Special trades require a good friend
					// Trading with a friend of this level has an IV floor of 1
					// Note that (non-shiny) Deoxys could be traded for a short time when it was introduced
					if (!set.shiny || species.id !== 'deoxys') {
						const specialTrade = pokemonGoSources.includes('specialtrade') || set.shiny;
						minLevel = Math.min(minLevel, 12);
						minIVs = Math.min(minIVs, specialTrade ? 1 : 0);
					}
				}
				if (set.level < minLevel) {
					problems.push(`${name} must be at least level ${minLevel} to be from Pokemon GO.`);
				}
				const ivs = set.ivs || TeamValidator.fillStats(null, 31);
				const postTransferMinIVs = minIVs * 2 + 1;
				let IVsTooLow = false;
				let hasEvenIVs = false;
				for (const stat in ivs) {
					if (stat === 'spe') continue;
					if (ivs[stat as 'hp'] < postTransferMinIVs) IVsTooLow = true;
					if (ivs[stat as 'hp'] % 2 === 0) hasEvenIVs = true;
				}
				if (IVsTooLow) {
					problems.push(`${name} must have at least ${postTransferMinIVs} ` +
						(postTransferMinIVs === 1 ? `IV` : `IVs`) + ` in non-Speed stats to be from Pokemon GO.`);
				}
				if (hasEvenIVs) {
					problems.push(`${name} must have odd non-Speed IVs to be from Pokemon GO.`);
				}
				const canBottleCap = dex.gen >= 7 && set.level >= (dex.gen < 9 ? 100 : 50);
				if (ivs.atk !== ivs.spa && !(canBottleCap && (ivs.atk === 31 || ivs.spa === 31))) {
					problems.push(`${name}'s Atk and Sp. Atk IVs must match to be from Pokemon GO.`);
				}
				if (ivs.def !== ivs.spd && !(canBottleCap && (ivs.def === 31 || ivs.spd === 31))) {
					problems.push(`${name}'s Def and Sp. Def IVs must match to be from Pokemon GO.`);
				}
			}
		}
		return problems;
	}

	omCheckCanLearn(
		move: Move,
		s: Species,
		setSources = this.allSources(s),
		set: Partial<PokemonSet> = {},
		problem = `${set.name || s.name} can't learn ${move.name}`,
	): string | null {
		if (!this.ruleTable.checkCanLearn?.[0]) return problem;
		const baseCheckCanLearn = this.checkCanLearn;
		// tell the custom move legality check that the move is illegal by default
		this.checkCanLearn = () => problem;
		const omVerdict = this.ruleTable.checkCanLearn[0].call(this, move, s, setSources, set);
		this.checkCanLearn = baseCheckCanLearn;
		return omVerdict;
	}

	/** Returns null if you can learn the move, or a string explaining why you can't learn it */
	checkCanLearn(
		move: Move,
		originalSpecies: Species,
		setSources = this.allSources(originalSpecies),
		set: Partial<PokemonSet> = {}
	): string | null {
		const dex = this.dex;
		if (!setSources.size()) throw new Error(`Bad sources passed to checkCanLearn`);

		move = dex.moves.get(move);
		const moveid = move.id;
		const baseSpecies = dex.species.get(originalSpecies);

		const format = this.format;
		const ruleTable = this.ruleTable;
		const level = set.level || 100;
		const canLearnSpecies: ID[] = [];

		let cantLearnReason = null;

		let limit1 = true;
		let sketch = false;
		let blockedHM = false;

		let babyOnly = '';
		let minLearnGen = dex.gen;

		// This is a pretty complicated algorithm

		// Abstractly, what it does is construct the union of sets of all
		// possible ways this pokemon could be obtained, and then intersect
		// it with a the pokemon's existing set of all possible ways it could
		// be obtained. If this intersection is non-empty, the move is legal.

		// set of possible sources of a pokemon with this move
		const moveSources = new PokemonSources();

		/**
		 * The format doesn't allow Pokemon traded from the future
		 * (This is everything except in Gen 1 Tradeback)
		 */
		const noFutureGen = !ruleTable.has('allowtradeback');
		/**
		 * The format allows Sketch to copy moves in Gen 8
		 */
		const canSketchPostGen7Moves = ruleTable.has('sketchpostgen7moves') || this.dex.currentMod === 'gen8bdsp';

		let tradebackEligible = false;
		const fullLearnset = dex.species.getFullLearnset(originalSpecies.id);
		if (!fullLearnset.length) {
			// It's normal for a nonstandard species not to have learnset data

			// Formats should replace the `Obtainable Moves` rule if they want to
			// allow pokemon without learnsets.
			return ` can't learn any moves at all.`;
		}

		for (const { species, learnset } of fullLearnset) {
			if (dex.gen <= 2 && species.gen === 1) tradebackEligible = true;
			const checkingPrevo = species.baseSpecies !== originalSpecies.baseSpecies;
			if (checkingPrevo && !moveSources.size()) {
				if (!setSources.babyOnly || !species.prevo) {
					babyOnly = species.id;
				}
			}

			const formeCantInherit = dex.species.eggMovesOnly(species, baseSpecies);
			if (formeCantInherit && dex.gen < 9) break;

			let sources = learnset[moveid] || [];
			if (moveid === 'sketch') {
				sketch = true;
			} else if (learnset['sketch']) {
				if (move.flags['nosketch'] || move.isZ || move.isMax) {
					cantLearnReason = `can't be Sketched.`;
				} else if (move.gen > 7 && !canSketchPostGen7Moves &&
					(dex.gen === 8 ||
						(dex.gen === 9 && ['gen9dlc1', 'gen9predlc'].includes(format.mod)))) {
					cantLearnReason = `can't be Sketched because it's a Gen ${move.gen} move and Sketch isn't available in Gen ${move.gen}.`;
				} else {
					if (!sources.length || !moveSources.size()) sketch = true;
					sources = [...learnset['sketch'], ...sources];
				}
			}

			let canUseHomeRelearner = false;
			for (let learned of sources) {
				// Every `learned` represents a single way a pokemon might
				// learn a move. This can be handled one of several ways:
				// `continue`
				//   means we can't learn it
				// `return null`
				//   means we can learn it with no restrictions
				//   (there's a way to just teach any pokemon of this species
				//   the move in the current gen, like a TM.)
				// `moveSources.add(source)`
				//   means we can learn it only if obtained that exact way described
				//   in source
				// `moveSources.addGen(learnedGen)`
				//   means we can learn it only if obtained at or before learnedGen
				//   (i.e. get the pokemon however you want, transfer to that gen,
				//   teach it, and transfer it to the current gen.)

				const learnedGen = parseInt(learned.charAt(0));
				if (formeCantInherit && (learned.charAt(1) !== 'E' || learnedGen < 9)) continue;
				if (setSources.learnsetDomain && !setSources.learnsetDomain.includes(`${learnedGen}${toID(species.baseSpecies)}`) &&
					(learned.charAt(1) !== 'E' || learnedGen < 8)
				) {
					if (!cantLearnReason) {
						cantLearnReason = `is incompatible with ${(setSources.restrictiveMoves || []).join(', ')}.`;
					}
					continue;
				}
				if (learnedGen < this.minSourceGen && !canUseHomeRelearner) {
					if (!cantLearnReason) {
						cantLearnReason = `can't be transferred from Gen ${learnedGen} to ${this.minSourceGen}.`;
					}
					continue;
				}
				if (noFutureGen && learnedGen > dex.gen) {
					if (!cantLearnReason) {
						cantLearnReason = `can't be transferred from Gen ${learnedGen} to ${dex.gen}.`;
					}
					continue;
				}

				if (learnedGen === 9 && learned.charAt(1) !== 'S') canUseHomeRelearner = true;

				if (
					baseSpecies.evoRegion === 'Alola' && checkingPrevo && learnedGen >= 8 &&
					(dex.gen < 9 || learned.charAt(1) !== 'E')
				) {
					cantLearnReason = `is from a ${species.name} that can't be transferred to USUM to evolve into ${baseSpecies.name}.`;
					continue;
				}

				const canUseAbilityPatch = dex.gen >= 8 && format.mod !== 'gen8dlc1';
				if (
					learnedGen < 7 && setSources.isHidden && !canUseAbilityPatch &&
					!dex.mod(`gen${learnedGen}`).species.get(baseSpecies.name).abilities['H']
				) {
					cantLearnReason = `can only be learned in gens without Hidden Abilities.`;
					continue;
				}

				const ability = dex.abilities.get(set.ability);
				if (dex.gen < 6 && ability.gen > learnedGen && !checkingPrevo) {
					// You can evolve a transferred mon to reroll for its new Ability.
					cantLearnReason = `is learned in gen ${learnedGen}, but the Ability ${ability.name} did not exist then.`;
					continue;
				}

				if (species.isNonstandard !== 'CAP') {
					// HMs can't be transferred
					if (dex.gen >= 4 && learnedGen <= 3 && [
						'cut', 'fly', 'surf', 'strength', 'flash', 'rocksmash', 'waterfall', 'dive',
					].includes(moveid)) {
						cantLearnReason = `can't be transferred from Gen 3 to 4 because it's an HM move.`;
						continue;
					}
					if (dex.gen >= 5 && learnedGen <= 4 && [
						'cut', 'fly', 'surf', 'strength', 'rocksmash', 'waterfall', 'rockclimb',
					].includes(moveid)) {
						cantLearnReason = `can't be transferred from Gen 4 to 5 because it's an HM move.`;
						continue;
					}
					// Defog and Whirlpool can't be transferred together
					if (dex.gen >= 5 && ['defog', 'whirlpool'].includes(moveid) && learnedGen <= 4) blockedHM = true;
				}

				if (learned.charAt(1) === 'L') {
					// special checking for level-up moves
					if (level >= parseInt(learned.substr(2)) || learnedGen === 7) {
						// we're past the required level to learn it
						// (gen 7 level-up moves can be relearnered at any level)
						// falls through to LMT check below
					} else if (level >= 5 && learnedGen === 3 && species.canHatch) {
						// Pomeg Glitch
						learned = `${learnedGen}Epomeg` as MoveSource;
					} else if (species.gender !== 'N' &&
						learnedGen >= 2 && species.canHatch && !setSources.isFromPokemonGo) {
						// available as egg move
						if (species.gender === 'M' && !this.motherCanLearn(toID(species.mother), moveid)) {
							// male-only Pokemon can have level-up egg moves if it can have a mother that learns the move
							cantLearnReason = `is learned at level ${parseInt(learned.substr(2))}.`;
							continue;
						}
						learned = `${learnedGen}Eany` as MoveSource;
						// falls through to E check below
					} else {
						// this move is unavailable, skip it
						cantLearnReason = `is learned at level ${parseInt(learned.substr(2))}.`;
						continue;
					}
				}

				// Gen 8+ egg moves can be taught to any pokemon from any source
				if (learnedGen >= 8 && learned.charAt(1) === 'E' && learned.slice(1) !== 'Eany' &&
					learned.slice(1) !== 'Epomeg' || 'LMTR'.includes(learned.charAt(1))) {
					if (learnedGen === dex.gen && learned.charAt(1) !== 'R') {
						// current-gen level-up, TM or tutor moves:
						//   always available
						if (!(learnedGen >= 8 && learned.charAt(1) === 'E') && babyOnly &&
							setSources.isFromPokemonGo && species.evoLevel) {
							cantLearnReason = `is from a prevo, which is incompatible with its Pokemon GO origin.`;
							continue;
						}
						if (!moveSources.moveEvoCarryCount && !babyOnly) return null;
					}
					// past-gen level-up, TM, or tutor moves:
					//   available as long as the source gen was or was before this gen
					if (learned.charAt(1) === 'R') {
						moveSources.restrictedMove = moveid;
					}
					limit1 = false;
					moveSources.addGen(learnedGen);
				} else if (learned.charAt(1) === 'E') {
					// egg moves:
					//   only if hatched from an egg
					let limitedEggMove: ID | null | undefined = undefined;
					if (learned.slice(1) === 'Eany') {
						if (species.gender === 'F') {
							limitedEggMove = move.id;
							moveSources.levelUpEggMoves = [move.id];
						} else {
							limitedEggMove = null;
						}
					} else if (learned.slice(1) === 'Epomeg') {
						// Pomeg glitched moves have to be from an egg but since they aren't true egg moves,
						// there should be no breeding restrictions
						moveSources.pomegEggMoves = [move.id];
					} else if (learnedGen < 6 || (species.mother && !this.motherCanLearn(toID(species.mother), moveid))) {
						limitedEggMove = move.id;
					}
					learned = `${learnedGen}E${species.prevo ? species.id : ''}` as MoveSource;
					if (tradebackEligible && learnedGen === 2 && move.gen <= 1) {
						// can tradeback
						moveSources.add(`1ET${learned.slice(2)}`, limitedEggMove);
					}
					moveSources.add(learned, limitedEggMove);
				} else if (learned.charAt(1) === 'S') {
					// event moves:
					//   only if that was the source
					// Event Pokémon:
					// 	Available as long as the past gen can get the Pokémon and then trade it back.
					if (tradebackEligible && learnedGen === 2 && move.gen <= 1) {
						// can tradeback
						moveSources.add(`1ST${learned.slice(2)} ${species.id}`);
					}
					moveSources.add(`${learned} ${species.id}`);
					const eventLearnset = dex.species.getLearnsetData(species.id);
					if (eventLearnset.eventData?.[parseInt(learned.charAt(2))].emeraldEventEgg && learnedGen === 3) {
						moveSources.pomegEventEgg = `${learned} ${species.id}`;
					}
				} else if (learned.charAt(1) === 'D') {
					// DW moves:
					//   only if that was the source
					moveSources.add(`${learned}${species.id}`);
					// If a DW move can be learned through some means other than DW,
					// it should not be treated as a DW move
					if (!moveSources.sourcesBefore) moveSources.dreamWorldMoveCount++;
				} else if (learned.charAt(1) === 'V' && this.minSourceGen < learnedGen) {
					// Virtual Console or Let's Go transfer moves:
					//   only if that was the source
					if (learned === '8V' && setSources.isFromPokemonGo && babyOnly && species.evoLevel) {
						cantLearnReason = `is from a prevo, which is incompatible with its Pokemon GO origin.`;
						continue;
					}
					moveSources.add(learned);
				}
				if (learned.charAt(1) === 'E' && learnedGen >= 8 && !canLearnSpecies.includes(toID(baseSpecies.baseSpecies))) {
					canLearnSpecies.push(toID(baseSpecies.baseSpecies));
				}
				if (!canLearnSpecies.includes(toID(species.baseSpecies))) canLearnSpecies.push(toID(species.baseSpecies));
				minLearnGen = Math.min(minLearnGen, learnedGen);
			}
			if (canUseHomeRelearner) {
				const fullSources = [];
				let learnsetData = this.getExternalLearnsetData(species.id, 'gen8bdsp');
				if (!['nincada', 'spinda'].includes(species.id) && learnsetData?.learnset?.[move.id]) {
					fullSources.push(...learnsetData.learnset[move.id]);
				}
				learnsetData = this.getExternalLearnsetData(species.id, 'gen8legends');
				if (learnsetData?.learnset?.[move.id]) {
					fullSources.push(...learnsetData.learnset[move.id]);
				}
				for (const source of fullSources) {
					// Non-event sources from BDSP/LA should always be legal through HOME relearner,
					// assuming the Pokemon's level is high enough
					if (source.charAt(1) === 'S') continue;
					if (source.charAt(1) === 'L' && level < parseInt(source.substr(2))) continue;
					return null;
				}
			}
			if (ruleTable.has('mimicglitch') && species.gen < 5) {
				// include the Mimic Glitch when checking this mon's learnset
				const glitchMoves = ['metronome', 'copycat', 'transform', 'mimic', 'assist'];
				let getGlitch = false;
				for (const i of glitchMoves) {
					if (learnset[i]) {
						if (!(i === 'mimic' && dex.abilities.get(set.ability).gen === 4 && !species.prevo)) {
							getGlitch = true;
							break;
						}
					}
				}
				if (getGlitch) {
					moveSources.addGen(4);
					if (move.gen < 5) {
						limit1 = false;
					}
				}
			}

			if (!moveSources.size()) {
				if (
					(species.evoType === 'levelMove' && species.evoMove !== move.name) ||
					(species.id === 'sylveon' && move.type !== 'Fairy')
				) {
					moveSources.moveEvoCarryCount = 1;
				}
			}
		}

		if (limit1 && sketch) {
			// limit 1 sketch move
			if (setSources.sketchMove) {
				return ` can't Sketch ${move.name} and ${setSources.sketchMove} because it can only Sketch 1 move.`;
			}
			setSources.sketchMove = move.name;
		}

		if (blockedHM) {
			// Limit one of Defog/Whirlpool to be transferred
			if (setSources.hm) return ` can't simultaneously transfer Defog and Whirlpool from Gen 4 to 5.`;
			setSources.hm = moveid;
		}

		if (!setSources.restrictiveMoves) {
			setSources.restrictiveMoves = [];
		}
		if (!setSources.restrictiveMoves.includes(move.name)) {
			setSources.restrictiveMoves.push(move.name);
		}

		const checkedSpecies = babyOnly ? fullLearnset[fullLearnset.length - 1].species : baseSpecies;
		if (checkedSpecies && setSources.isFromPokemonGo &&
			(setSources.pokemonGoSource === 'purified' || checkedSpecies.id === 'mew')) {
			// Pokemon that cannot be sent from Pokemon GO to Let's Go can only access Let's Go moves through HOME
			// It can only obtain a chain of four level up moves and cannot have TM moves
			const pokemonGoData = dex.species.getPokemonGoData(checkedSpecies.id);
			if (pokemonGoData?.LGPERestrictiveMoves) {
				let levelUpMoveCount = 0;
				const restrictiveMovesToID = [];
				for (const moveName of setSources.restrictiveMoves) {
					restrictiveMovesToID.push(toID(moveName));
				}
				for (const restrictiveMove in pokemonGoData.LGPERestrictiveMoves) {
					const moveLevel = pokemonGoData.LGPERestrictiveMoves[restrictiveMove];
					if (toID(move) === restrictiveMove) {
						if (!moveLevel) {
							return `'s move ${move.name} is incompatible with its Pokemon GO origin.`;
						} else if (set.level && set.level < moveLevel) {
							return ` must be at least level ${moveLevel} to learn ${move.name} due to its Pokemon GO origin.`;
						}
					}
					if (levelUpMoveCount) levelUpMoveCount++;
					if (restrictiveMovesToID.includes(restrictiveMove)) {
						if (!levelUpMoveCount) {
							levelUpMoveCount++;
						} else if (levelUpMoveCount > 4) {
							return `'s moves ${(setSources.restrictiveMoves || []).join(', ')} are incompatible with its Pokemon GO origin.`;
						}
					}
				}
			}
		}

		let nextSpecies;
		nextSpecies = baseSpecies;
		let speciesCount = 0;
		if (!tradebackEligible) {
			if (!dex.species.getLearnsetData(nextSpecies.id).learnset) {
				nextSpecies = dex.species.get(nextSpecies.changesFrom || nextSpecies.baseSpecies);
			}
			while (nextSpecies.name) {
				for (let gen = nextSpecies.gen; gen <= dex.gen; gen++) {
					/**
					 * Case 1: The species can learn the move - allow moves of the species from all gens
					 * Case 2: Both prevo and evo can learn the move - same as case 1
					 * Case 3: Prevo-only move - allow moves of the species from the min gen and later
					 * Case 4: Evo-only move - allow moves of the species from the max gen and before
					*/
					const baseSpeciesID = toID(nextSpecies.baseSpecies);
					if (canLearnSpecies.includes(baseSpeciesID) ||
						(0 < speciesCount && speciesCount < canLearnSpecies.length) ||
						(speciesCount === 0 && gen >= minLearnGen) ||
						(speciesCount === canLearnSpecies.length && gen <= moveSources.sourcesBefore)
					) {
						if (!moveSources.learnsetDomain) moveSources.learnsetDomain = [];
						moveSources.learnsetDomain.push(`${gen}${baseSpeciesID}`);
					}
				}
				if (canLearnSpecies.includes(nextSpecies.id)) speciesCount++;
				nextSpecies = dex.species.get(nextSpecies.prevo);
			}
		}

		// Now that we have our list of possible sources, intersect it with the current list
		if (!moveSources.size()) {
			if (cantLearnReason) return `'s move ${move.name} ${cantLearnReason}`;
			return ` can't learn ${move.name}.`;
		}
		const eggSources = moveSources.sources.filter(source => source.charAt(1) === 'E');
		if (dex.gen >= 3 && eggSources.length && moveSources.limitedEggMoves === null && moveSources.sourcesBefore) {
			moveSources.possiblyLimitedEggMoves = [toID(`${moveSources.sourcesBefore}${move.id}`)];
		}
		const backupSources = setSources.sources;
		const backupSourcesBefore = setSources.sourcesBefore;
		setSources.intersectWith(moveSources);
		if (!setSources.size()) {
			// pretend this pokemon didn't have this move:
			// prevents a crash if OMs override `checkCanLearn` to keep validating after an error
			setSources.sources = backupSources;
			setSources.sourcesBefore = backupSourcesBefore;
			if (setSources.isFromPokemonGo) return `'s move ${move.name} is incompatible with its Pokemon GO origin.`;
			return `'s moves ${(setSources.restrictiveMoves || []).join(', ')} are incompatible.`;
		}

		if (babyOnly) setSources.babyOnly = babyOnly;
		return null;
	}

	getExternalLearnsetData(species: ID, mod: string) {
		const moddedDex = this.dex.mod(mod);
		if (moddedDex.species.get(species).isNonstandard) return null;
		return moddedDex.species.getLearnsetData(species);
	}

	static fillStats(stats: SparseStatsTable | null, fillNum = 0): StatsTable {
		const filledStats: StatsTable = { hp: fillNum, atk: fillNum, def: fillNum, spa: fillNum, spd: fillNum, spe: fillNum };
		if (stats) {
			let statName: StatID;
			for (statName in filledStats) {
				const stat = stats[statName];
				if (typeof stat === 'number') filledStats[statName] = stat;
			}
		}
		return filledStats;
	}

	static get(format: string | Format) {
		return new TeamValidator(format);
	}
}