// emoji_favorites.go handles persistence of the user's favorite emoji list,
// stored as a JSON file in the cache directory.
package chat

import (
	"encoding/json"
	"log/slog"
	"os"
	"path/filepath"
	"sync"

	"github.com/ayn2op/discordo/internal/consts"
)

const maxFavoriteEmoji = 10

// maxFavoritesFileSize is the upper bound on the emoji favorites JSON file (4 KiB).
const maxFavoritesFileSize = 4096

// maxFavoriteEmojiLen is the maximum byte length of a single emoji favorite string.
const maxFavoriteEmojiLen = 64

type emojiFavorites struct {
	Favorites []string `json:"favorites"`
	mu        sync.RWMutex
}

var emojiFavoritesPath = filepath.Join(consts.CacheDir(), "emoji_favorites.json")

func loadEmojiFavorites() *emojiFavorites {
	ef := &emojiFavorites{}
	data, err := os.ReadFile(emojiFavoritesPath)
	if err != nil {
		return ef
	}
	if len(data) > maxFavoritesFileSize {
		slog.Warn("emoji favorites file too large, ignoring", "size", len(data))
		return ef
	}
	if err := json.Unmarshal(data, ef); err != nil {
		slog.Warn("failed to parse emoji favorites", "err", err)
		return &emojiFavorites{}
	}
	// Reject any favorite strings that exceed the length limit.
	valid := ef.Favorites[:0]
	for _, e := range ef.Favorites {
		if len(e) <= maxFavoriteEmojiLen {
			valid = append(valid, e)
		} else {
			slog.Warn("emoji favorite too long, skipping", "len", len(e))
		}
	}
	ef.Favorites = valid
	return ef
}

// save persists favorites to disk. The caller must hold ef.mu.
func (ef *emojiFavorites) save() {
	atomicSaveJSON(emojiFavoritesPath, ef)
}

func (ef *emojiFavorites) toggle(emoji string) {
	ef.mu.Lock()
	defer ef.mu.Unlock()
	for i, e := range ef.Favorites {
		if e == emoji {
			ef.Favorites = append(ef.Favorites[:i], ef.Favorites[i+1:]...)
			ef.save()
			return
		}
	}
	if len(ef.Favorites) >= maxFavoriteEmoji {
		return
	}
	ef.Favorites = append(ef.Favorites, emoji)
	ef.save()
}

func (ef *emojiFavorites) list() []string {
	ef.mu.RLock()
	defer ef.mu.RUnlock()
	out := make([]string, len(ef.Favorites))
	copy(out, ef.Favorites)
	return out
}