implement a few interfaces from the specification

Author: pedep

packages/kitsu-core/src/resources/attributes.ts

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+// https://jsonapi.org/format/#document-resource-object-attributes
+//
+// The value of the attributes key MUST be an object (an “attributes object”). Members of the attributes object (“attributes”) represent information about the resource object in which it’s defined.
+// Attributes may contain any valid JSON value, including complex data structures involving JSON objects and arrays.
+// Keys that reference related resources (e.g. author_id) SHOULD NOT appear as attributes. Instead, relationships SHOULD be used.
+
+// Valid JSON values
+// https://datatracker.ietf.org/doc/html/rfc8259#section-3
+export type JsonValues = object | number | string | false | null | true | Array<JsonValues>;
+
+// https://datatracker.ietf.org/doc/html/rfc8259#section-4
+// "A name is a string"
+export interface Attributes {
+  [name: string]: JsonValues;
+}
+
+export function isAttributes(attrs: any): attrs is Attributes {
+  return typeof attrs.attributes === 'object' &&
+    attrs.attributes !== null &&
+    !Array.isArray(attrs.attributes)
+}

packages/kitsu-core/src/resources/resource-identifier.ts

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+// https://jsonapi.org/format/#document-resource-object-identification
+//
+// > As noted above, every resource object MUST contain a type member.
+// > Every resource object MUST also contain an id member, except when the resource object originates at the client and represents a new resource to be created on the server.
+// > If id is omitted due to this exception, a lid member MAY be included to uniquely identify the resource by type locally within the document.
+// > The value of the lid member MUST be identical for every representation of the resource in the document, including resource identifier objects.
+
+export interface LocalResourceIdentifier {
+  lid: string;
+  type: string;
+}
+
+export interface RemoteResourceIdentifier {
+  id: string;
+  type: string;
+}
+
+export type ResourceIdentifier = LocalResourceIdentifier | RemoteResourceIdentifier;

packages/kitsu-core/src/resources/resource-object.ts

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+import { Attributes } from "./attributes.js";
+import { ResourceIdentifier } from "./resource-identifier.js";
+
+type Relationships = void;
+type Links = void;
+type Meta = void;
+
+export interface _ResourceObject {
+  attributes?: Attributes;
+  relationships?: Relationships;
+  links?: Links;
+  meta?: Meta;
+}
+
+export type ResourceObject = _ResourceObject & ResourceIdentifier;