minstrel/internal/library/mbids.go

package library

import (
	"strings"

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

// extractMBIDs reads MusicBrainz album and artist IDs from a tag.Metadata.
//
// Delegates to dhowden/tag/mbz, which knows the per-format Raw() conventions:
//   - Vorbis (FLAC/OGG) 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.
//
// Then sanitizes: 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). We split on NUL and take the first non-empty
// segment — Minstrel uses the primary release artist for MBCAA lookup,
// so first-wins matches the original semantics.
func extractMBIDs(m tag.Metadata) (albumMBID, artistMBID string) {
	info := mbz.Extract(m)
	return cleanMBID(info.Get(mbz.Album)), cleanMBID(info.Get(mbz.Artist))
}

// extractRecordingMBID reads the MusicBrainz *recording* ID — Picard's
// musicbrainz_recordingid, surfaced by dhowden/tag as mbz.Recording
// (tag display name "MusicBrainz Track Id"). This is the id the
// ListenBrainz Labs similar-recordings API keys on and what tracks.mbid
// stores.
//
// Deliberately NOT mbz.Track ("MusicBrainz Release Track Id"): that is
// per-release-track, whereas similarity is per-recording. Kept separate
// from extractMBIDs so its existing (album, artist) signature and unit
// tests stay untouched.
func extractRecordingMBID(m tag.Metadata) string {
	return cleanMBID(mbz.Extract(m).Get(mbz.Recording))
}

// extractReleaseGroupMBID reads the MusicBrainz *release-group* ID —
// Picard's musicbrainz_releasegroupid, surfaced by dhowden/tag as
// mbz.ReleaseGroup. mbz.Album (what albums.mbid stores) is the release: one
// edition. Wants name albums by release group, so re-acquisition and
// request completion key on this one (#5241). Separate from extractMBIDs for
// the same reason extractRecordingMBID is.
func extractReleaseGroupMBID(m tag.Metadata) string {
	return cleanMBID(mbz.Extract(m).Get(mbz.ReleaseGroup))
}

func cleanMBID(s string) string {
	if s == "" {
		return ""
	}
	for _, part := range strings.Split(s, "\x00") {
		if t := strings.TrimSpace(part); t != "" {
			return t
		}
	}
	return ""
}