Add database

Author: ajeetdsouza

db.go

@@ -0,0 +1,82 @@
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"os"
+	"path/filepath"
+
+	"github.com/adrg/xdg"
+	"github.com/google/renameio/maybe"
+	"github.com/pkg/errors"
+)
+
+// dbPath is the path to the database file.
+// This is usually set to ~/.local/share/clidle/db.json on most UNIX systems.
+var dbPath = filepath.Join(xdg.DataHome, "clidle", "db.json")
+
+// db is the file where the game statistics are stored.
+type db struct {
+	// Guesses stores the win statistics of each game. Guesses[0] is the number
+	// of games that were lost, Guesses[1] is the number of games that were won
+	// with 1 guess, etc.
+	Guesses [numGuesses + 1]int `json:"guesses"`
+}
+
+// loadDb reads the database from dbPath.
+func loadDb() (*db, error) {
+	file, err := os.Open(dbPath)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return &db{}, nil
+		}
+		return nil, errors.Wrap(err, "could not find database")
+	}
+	var db db
+	if err := json.NewDecoder(file).Decode(&db); err != nil {
+		return nil, errors.Wrap(err, "could not read from database")
+	}
+	return &db, nil
+}
+
+// save atomically (best effort) writes the database to dbPath.
+func (db *db) save() error {
+	dir := filepath.Dir(dbPath)
+	if err := os.MkdirAll(dir, 0755); err != nil {
+		return errors.Wrapf(err, "could not create data directory: %s", dir)
+	}
+	data, err := json.MarshalIndent(&db, "", "  ")
+	if err != nil {
+		return errors.Wrap(err, "could not serialize database")
+	}
+	if err := maybe.WriteFile(dbPath, data, 0o644); err != nil {
+		return errors.Wrapf(err, "could not write to database: %s", dbPath)
+	}
+	return nil
+}
+
+// addWin adds a win to the game statistics. It also stores the number of
+// guesses it took, in the range [1,numGuesses].
+func (db *db) addWin(guesses int) {
+	if !(1 <= guesses && guesses <= numGuesses) {
+		panic(fmt.Sprintf("guesses out of range: %d", guesses))
+	}
+	db.Guesses[guesses]++
+}
+
+// addLoss adds a loss to the game statistics.
+func (db *db) addLoss() {
+	db.Guesses[0]++
+}
+
+// score returns the current total score based on the statistics.
+//
+// A game that was lost provides 0 points. A game that was won provides 50
+// points, plus an extra 10 points for each remaining guess.
+func (db *db) score() int {
+	score := 0
+	for i, guess := range db.Guesses[1:] {
+		score += (100 - 10*i) * guess
+	}
+	return score
+}