fix: sync mounted Emby favourites across web and Emby clients (#21)

Unify favourite writes through SyncUserFavorite so remote mounted media is
stored locally and proxied to the upstream Emby server. Emby clients now
query favourites from the local table (including remote pseudo IDs), and
remote item payloads merge local IsFavorite state.

Co-authored-by: Cursor Agent <cursoragent@cursor.com>
Co-authored-by: truewhile <truewhile@users.noreply.github.com>

internal/service/favorites_sync.go

@@ -0,0 +1,74 @@
+package service
+
+import (
+	"context"
+	"errors"
+
+	"gorm.io/gorm"
+
+	"github.com/truewhile/MeBox/internal/model"
+	"github.com/truewhile/MeBox/internal/repository"
+)
+
+// SyncUserFavorite keeps favourite state aligned across the local favourites table
+// and the upstream remote Emby server for mounted items.
+func SyncUserFavorite(ctx context.Context, repo *repository.Container, remote *EmbyRemoteService, userID, mediaID string, favorite bool) error {
+	if repo == nil || userID == "" || mediaID == "" {
+		return errors.New("missing favourite sync inputs")
+	}
+	if err := setLocalFavorite(ctx, repo, userID, mediaID, favorite); err != nil {
+		return err
+	}
+	if favorite || IsEmbyRemoteID(mediaID) {
+		if err := proxyRemoteFavorite(ctx, remote, mediaID, favorite); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// IsUserFavorite reports whether the user has favourited mediaID locally.
+func IsUserFavorite(ctx context.Context, repo *repository.Container, userID, mediaID string) (bool, error) {
+	if repo == nil || userID == "" || mediaID == "" {
+		return false, nil
+	}
+	var count int64
+	err := repo.DB.WithContext(ctx).Model(&model.Favorite{}).
+		Where("user_id = ? AND media_id = ?", userID, mediaID).
+		Count(&count).Error
+	return count > 0, err
+}
+
+func setLocalFavorite(ctx context.Context, repo *repository.Container, userID, mediaID string, favorite bool) error {
+	if favorite {
+		var existing model.Favorite
+		err := repo.DB.WithContext(ctx).
+			Where("user_id = ? AND media_id = ?", userID, mediaID).
+			First(&existing).Error
+		if errors.Is(err, gorm.ErrRecordNotFound) {
+			return repo.DB.WithContext(ctx).Create(&model.Favorite{
+				UserID:  userID,
+				MediaID: mediaID,
+			}).Error
+		}
+		return err
+	}
+	return repo.DB.WithContext(ctx).
+		Where("user_id = ? AND media_id = ?", userID, mediaID).
+		Delete(&model.Favorite{}).Error
+}
+
+func proxyRemoteFavorite(ctx context.Context, remote *EmbyRemoteService, mediaID string, favorite bool) error {
+	if remote == nil || !IsEmbyRemoteID(mediaID) {
+		return nil
+	}
+	mountID, remoteItemID, ok := DecodeEmbyRemoteID(mediaID)
+	if !ok {
+		return nil
+	}
+	_, acct, err := remote.ResolveMount(ctx, mountID)
+	if err != nil {
+		return err
+	}
+	return remote.ProxySetFavorite(ctx, acct, remoteItemID, favorite)
+}