minstrel/internal/wanted/match.go

package wanted

import (
	"context"
	"errors"
	"fmt"
	"slices"
	"strings"
	"time"

	"git.fabledsword.com/bvandeusen/minstrel/internal/catalogue"
	"git.fabledsword.com/bvandeusen/minstrel/internal/db/dbq"
	"git.fabledsword.com/bvandeusen/minstrel/internal/musicbrainz"
	"git.fabledsword.com/bvandeusen/minstrel/internal/release"
	"git.fabledsword.com/bvandeusen/minstrel/internal/tags"
)

// Matching a library album to its MusicBrainz release group (#5569).
//
// Everything in the library came from a service that matched it against
// MusicBrainz (operator, 2026-10-10: "they should all exist in music brainz
// we need to use their meta data or a search system to link them up"), so
// every album should have a group. The ids its tags carry are taken as
// they are. Without them, the groups called what the album is called, from
// the artist's discography and then from a search, are checked against the
// album's own tracks, and the one its tracks agree with is taken.

// Match methods, as library_album_matches records them.
const (
	matchTags        = "tags"
	matchRelease     = "release"
	matchDiscography = "discography"
	matchSearch      = "search"
)

// matchAgreement is the share of an album's tracks, in tenths, an edition
// must agree with: most, not all, since a rip's track may carry a typo or a
// hidden track's length.
const matchAgreement = 8

// matchCandidates bounds how many groups one album is checked against: each
// costs a MusicBrainz read the first time.
const matchCandidates = 8

// matchDiscographyAge is how old a held discography may be and still be
// read for matching: a name does not change, and a new release is not in
// the library.
const matchDiscographyAge = 90 * 24 * time.Hour

// errMusicBrainzAway: MusicBrainz did not answer, so the album is left for
// the next pass rather than decided on half the evidence.
var errMusicBrainzAway = errors.New("wanted: MusicBrainz did not answer")

// libraryTrack is what one of an album's tracks says about itself.
type libraryTrack struct {
	Disc, Number int
	Title        string
	LengthMs     int
	Recording    string
}

// editionTrack is one track of a MusicBrainz edition.
type editionTrack struct {
	Medium, Position int
	Title            string
	LengthMs         int
	Recording        string
}

// candidate is a release group an album may be.
type candidate struct {
	Group            string
	Title            string
	PrimaryType      string
	FirstReleaseDate string
	ArtistMBID       string
	ArtistName       string
	Method           string
}

// albumMatch is what matching decided: a group, or why there is none.
type albumMatch struct {
	candidate
	OK     bool
	Detail string
}

func tracksToMatch(rows []dbq.ListAlbumTracksToMatchRow) []libraryTrack {
	out := make([]libraryTrack, 0, len(rows))
	for _, r := range rows {
		t := libraryTrack{Title: r.Title, LengthMs: int(r.DurationMs), Recording: deref(r.Mbid)}
		if r.DiscNumber != nil {
			t.Disc = int(*r.DiscNumber)
		}
		if r.TrackNumber != nil {
			t.Number = int(*r.TrackNumber)
		}
		out = append(out, t)
	}
	return out
}

// trackAgreement counts the album's tracks an edition agrees with: the same
// recording, or a length that fits and a title that agrees. A track is
// paired by its disc and number first, then by title, so an album missing
// some tracks still pairs the ones it has.
func trackAgreement(tracks []libraryTrack, edition []editionTrack) int {
	byPos := make(map[[2]int]int, len(edition))
	for i, e := range edition {
		byPos[[2]int{max(e.Medium, 1), e.Position}] = i
	}
	agree := func(t libraryTrack, e editionTrack) bool {
		if t.Recording != "" && strings.EqualFold(t.Recording, e.Recording) {
			return true
		}
		return release.LengthFits(t.LengthMs, e.LengthMs) && release.TitleAgrees(t.Title, e.Title)
	}
	used := make([]bool, len(edition))
	n := 0
	for _, t := range tracks {
		if t.Number > 0 {
			if i, ok := byPos[[2]int{max(t.Disc, 1), t.Number}]; ok && !used[i] && agree(t, edition[i]) {
				used[i] = true
				n++
				continue
			}
		}
		for i, e := range edition {
			if !used[i] && agree(t, e) {
				used[i] = true
				n++
				break
			}
		}
	}
	return n
}

// agrees: enough of the album's tracks agree for the edition to be it.
func agrees(n, tracks int) bool {
	return tracks > 0 && n*10 >= tracks*matchAgreement
}

// sameTitle: the same words, not merely one holding the other.
func sameTitle(a, b string) bool {
	return slices.Equal(release.Tokens(a), release.Tokens(b))
}

// matchAlbum finds the release group a library album is. A MusicBrainz
// that does not answer is errMusicBrainzAway; anything else MusicBrainz
// says is evidence, and an album with none is an albumMatch that is not OK.
func (s *Service) matchAlbum(ctx context.Context, a dbq.ListAlbumsToMatchRow, tracks []libraryTrack) (albumMatch, error) {
	// The ids the tags carry name it.
	if group := deref(a.ReleaseGroupMbid); group != "" {
		if c, err := s.groupCandidate(ctx, group, matchTags, a); err != nil || c.Group != "" {
			return albumMatch{candidate: c, OK: err == nil}, err
		}
	}
	if rel := deref(a.Mbid); rel != "" {
		group, err := s.releaseGroup(ctx, rel)
		switch {
		case errors.Is(err, tags.ErrNotFound): // includes MusicBrainz switched off for tags
		case err != nil:
			return albumMatch{}, fmt.Errorf("%w: %v", errMusicBrainzAway, err)
		default:
			if c, err := s.groupCandidate(ctx, group, matchRelease, a); err != nil || c.Group != "" {
				return albumMatch{candidate: c, OK: err == nil}, err
			}
		}
	}

	// Otherwise its name, checked against its tracks: the artist's own
	// discography first, then a search.
	tried := map[string]bool{}
	var best albumMatch
	bestN, bestEdition, considered := -1, 0, 0
	check := func(cands []candidate) error {
		for _, c := range cands {
			if tried[c.Group] || len(tried) >= matchCandidates {
				continue
			}
			tried[c.Group] = true
			n, size, err := s.agreementWith(ctx, c.Group, tracks)
			if err != nil {
				return err
			}
			considered++
			// More tracks agreeing wins; then the same title over a longer
			// one; then the edition nearest the album's length.
			st, bt := sameTitle(c.Title, a.Title), sameTitle(best.Title, a.Title)
			if n > bestN || (n == bestN && ((st && !bt) || (st == bt && abs(size-len(tracks)) < abs(bestEdition-len(tracks))))) {
				best, bestN, bestEdition = albumMatch{candidate: c}, n, size
			}
		}
		return nil
	}
	discography, err := s.discographyCandidates(ctx, a)
	if err != nil {
		return albumMatch{}, err
	}
	if err := check(discography); err != nil {
		return albumMatch{}, err
	}
	if !agrees(bestN, len(tracks)) {
		found, err := s.searchCandidates(ctx, a)
		if err != nil {
			return albumMatch{}, err
		}
		if err := check(found); err != nil {
			return albumMatch{}, err
		}
	}
	if agrees(bestN, len(tracks)) {
		best.OK = true
		return best, nil
	}
	if considered == 0 {
		return albumMatch{Detail: fmt.Sprintf("MusicBrainz has no album called %q by %s.", a.Title, a.ArtistName)}, nil
	}
	return albumMatch{Detail: fmt.Sprintf(
		"MusicBrainz has %d %s called %q by %s, but none has its tracks: the closest, %q, agrees on %d of its %d.",
		considered, plural(considered, "album", "albums"), a.Title, a.ArtistName, best.Title, max(bestN, 0), len(tracks))}, nil
}

// groupCandidate reads a group the tags name. A group MusicBrainz does not
// have is a zero candidate, so the album is matched by name instead.
func (s *Service) groupCandidate(ctx context.Context, group, method string, a dbq.ListAlbumsToMatchRow) (candidate, error) {
	g, err := s.cat.MusicBrainz().ReleaseGroup(ctx, group)
	switch {
	case errors.Is(err, musicbrainz.ErrNotFound):
		return candidate{}, nil
	case err != nil:
		return candidate{}, fmt.Errorf("%w: %v", errMusicBrainzAway, err)
	}
	artist := creditedArtist(g.ArtistMBIDs, deref(a.ArtistMbid))
	if artist == "" {
		return candidate{}, nil
	}
	return candidate{Group: g.MBID, Title: g.Title, PrimaryType: g.PrimaryType, FirstReleaseDate: g.FirstReleaseDate,
		ArtistMBID: artist, ArtistName: g.ArtistCredit, Method: method}, nil
}

// discographyCandidates are the artist's release groups called what the
// album is called.
func (s *Service) discographyCandidates(ctx context.Context, a dbq.ListAlbumsToMatchRow) ([]candidate, error) {
	artist := deref(a.ArtistMbid)
	if !Followable(artist, a.ArtistName) {
		return nil, nil // no artist, or Various Artists: thousands of groups
	}
	d, err := s.cat.DiscographyWithin(ctx, artist, matchDiscographyAge)
	switch {
	case errors.Is(err, catalogue.ErrNotFound):
		return nil, nil
	case err != nil:
		return nil, fmt.Errorf("%w: %v", errMusicBrainzAway, err)
	}
	var out []candidate
	for _, g := range d.Groups {
		if release.TitleAgrees(g.Title, a.Title) {
			out = append(out, candidate{Group: g.Mbid, Title: g.Title, PrimaryType: g.PrimaryType,
				FirstReleaseDate: g.FirstReleaseDate, ArtistMBID: artist, ArtistName: d.Artist.Name, Method: matchDiscography})
		}
	}
	sortSameTitleFirst(out, a.Title)
	return out, nil
}

// searchCandidates are the groups MusicBrainz's search finds by the album's
// artist and title, whose title and artist both agree.
func (s *Service) searchCandidates(ctx context.Context, a dbq.ListAlbumsToMatchRow) ([]candidate, error) {
	found, err := s.cat.MusicBrainz().SearchReleaseGroupsBy(ctx, a.ArtistName, a.Title, 10)
	switch {
	case errors.Is(err, musicbrainz.ErrNotFound):
		return nil, nil
	case errors.Is(err, musicbrainz.ErrBadResponse):
		// A query MusicBrainz will not read is not a reason to wait.
		s.logger.Warn("wanted: MusicBrainz refused a search", "album", a.Title, "artist", a.ArtistName, "err", err)
		return nil, nil
	case err != nil:
		return nil, fmt.Errorf("%w: %v", errMusicBrainzAway, err)
	}
	var out []candidate
	for _, g := range found {
		artist := creditedArtist(g.ArtistMBIDs, deref(a.ArtistMbid))
		if artist == "" || !release.TitleAgrees(g.Title, a.Title) {
			continue
		}
		if !slices.Contains(g.ArtistMBIDs, deref(a.ArtistMbid)) && !release.TitleAgrees(g.ArtistCredit, a.ArtistName) {
			continue
		}
		out = append(out, candidate{Group: g.MBID, Title: g.Title, PrimaryType: g.PrimaryType,
			FirstReleaseDate: g.FirstReleaseDate, ArtistMBID: artist, ArtistName: g.ArtistCredit, Method: matchSearch})
	}
	sortSameTitleFirst(out, a.Title)
	return out, nil
}

// agreementWith is how many of the album's tracks the group's best edition
// agrees with, and that edition's length. A group MusicBrainz no longer has
// agrees with none.
func (s *Service) agreementWith(ctx context.Context, group string, tracks []libraryTrack) (n, size int, err error) {
	eds, err := s.cat.Releases(ctx, group)
	switch {
	case errors.Is(err, catalogue.ErrNotFound):
		return -1, 0, nil
	case err != nil:
		return 0, 0, fmt.Errorf("%w: %v", errMusicBrainzAway, err)
	}
	n = -1
	for _, e := range eds.Editions {
		edition := make([]editionTrack, 0, len(e.Tracks))
		for _, t := range e.Tracks {
			edition = append(edition, editionTrack{Medium: int(t.MediumPosition), Position: int(t.Position),
				Title: t.Title, LengthMs: int(t.LengthMs), Recording: t.RecordingMbid})
		}
		if got := trackAgreement(tracks, edition); got > n || (got == n && abs(len(edition)-len(tracks)) < abs(size-len(tracks))) {
			n, size = got, len(edition)
		}
	}
	return n, size, nil
}

// creditedArtist is the artist a want is filed under: the library's own
// artist when MusicBrainz credits them, else the first credited.
func creditedArtist(credited []string, own string) string {
	if own != "" && (len(credited) == 0 || slices.Contains(credited, own)) {
		return own
	}
	if len(credited) > 0 {
		return credited[0]
	}
	return ""
}

func sortSameTitleFirst(cs []candidate, title string) {
	slices.SortStableFunc(cs, func(x, y candidate) int {
		switch sx, sy := sameTitle(x.Title, title), sameTitle(y.Title, title); {
		case sx && !sy:
			return -1
		case sy && !sx:
			return 1
		}
		return 0
	})
}

func abs(n int) int {
	if n < 0 {
		return -n
	}
	return n
}

func plural(n int, one, many string) string {
	if n == 1 {
		return one
	}
	return many
}