package library

// MusicBrainz tag keys vary by audio format. dhowden/tag's Raw() map exposes
// the format-specific entries as-is — so we look up multiple candidates and
// take the first non-empty match.
//
// References:
//   - ID3v2 (MP3):       TXXX frames keyed by description.
//   - Vorbis (FLAC/OGG): all-caps comment names.
//   - MP4 (M4A):         iTunes freeform atoms ("----:com.apple.iTunes:...").

var albumMBIDKeys = []string{
	"TXXX:MusicBrainz Album Id",
	"MUSICBRAINZ_ALBUMID",
	"----:com.apple.iTunes:MusicBrainz Album Id",
}

var artistMBIDKeys = []string{
	"TXXX:MusicBrainz Artist Id",
	"MUSICBRAINZ_ARTISTID",
	"----:com.apple.iTunes:MusicBrainz Artist Id",
}

// extractMBIDs reads MusicBrainz album and artist IDs from a tag.Metadata
// Raw() map. Returns ("", "") when the keys are absent. Multi-value keys
// (some formats list multiple artist IDs for collaborations) take only the
// first value — Minstrel uses the primary release artist for MBCAA lookup.
func extractMBIDs(raw map[string]interface{}) (albumMBID, artistMBID string) {
	albumMBID = firstStringValue(raw, albumMBIDKeys)
	artistMBID = firstStringValue(raw, artistMBIDKeys)
	return
}

func firstStringValue(raw map[string]interface{}, keys []string) string {
	for _, k := range keys {
		v, ok := raw[k]
		if !ok || v == nil {
			continue
		}
		switch x := v.(type) {
		case string:
			if x != "" {
				return x
			}
		case []string:
			if len(x) > 0 && x[0] != "" {
				return x[0]
			}
		case []interface{}:
			if len(x) == 0 {
				continue
			}
			if s, ok := x[0].(string); ok && s != "" {
				return s
			}
		}
	}
	return ""
}