minstrel/internal/library/mbids.go

package library

import (
	"strings"

	"github.com/dhowden/tag"
	"github.com/dhowden/tag/mbz"
)

// TagMBIDs is what a file's MusicBrainz Picard tags name. Empty means the
// tag is absent.
type TagMBIDs struct {
	// Release is musicbrainz_albumid: one edition, what albums.mbid stores.
	Release string
	Artist  string
	// ReleaseGroup is musicbrainz_releasegroupid. Wants name albums by
	// release group, so re-acquisition and request completion key on it
	// (#5241).
	ReleaseGroup string
	// Recording is what tracks.mbid stores and the ListenBrainz Labs
	// similar-recordings API keys on.
	Recording string
}

// ReadTagMBIDs reads a file's MusicBrainz IDs, for the scanner, the MBID
// backfills and the importer alike.
//
// Delegates to dhowden/tag/mbz, which knows the per-format Raw() conventions:
//   - Vorbis (FLAC/OGG/Opus) keys are lowercased by the parser.
//   - ID3v2 (MP3) TXXX frames are stored under "TXXX"/"TXXX_N" with
//     a *tag.Comm value whose Description holds the Picard tag name.
//   - MP4 (M4A) freeform iTunes atoms are stored under their bare sub-name.
//
// mbz maps keys by name alone, and Picard names the recording differently
// in Vorbis: MUSICBRAINZ_TRACKID there is the recording (the release track
// is MUSICBRAINZ_RELEASETRACKID), so mbz files it under mbz.Track, its name
// for the release track. Read mbz.Recording alone and every FLAC has no
// recording id (#5637).
func ReadTagMBIDs(m tag.Metadata) TagMBIDs {
	info := mbz.Extract(m)
	ids := TagMBIDs{
		Release:      cleanMBID(info.Get(mbz.Album)),
		Artist:       cleanMBID(info.Get(mbz.Artist)),
		ReleaseGroup: cleanMBID(info.Get(mbz.ReleaseGroup)),
		Recording:    cleanMBID(info.Get(mbz.Recording)),
	}
	if ids.Recording == "" && m.Format() == tag.VORBIS {
		ids.Recording = cleanMBID(info.Get(mbz.Track))
	}
	return ids
}

// cleanMBID takes the first non-empty NUL-separated value. dhowden's
// readTextWithDescrFrame (used for ID3v2 TXXX) does NOT strip the
// trailing/embedded NUL bytes that ID3v2.4 uses as frame terminator and
// multi-value separator — so the Text often comes out as "uuid\x00" or
// "uuid1\x00uuid2". Postgres rejects NULs in text columns (SQLSTATE 22021).
// Minstrel uses the primary release artist for MBCAA lookup, so first-wins
// matches the original semantics.
func cleanMBID(s string) string {
	for _, part := range strings.Split(s, "\x00") {
		if t := strings.TrimSpace(part); t != "" {
			return t
		}
	}
	return ""
}