minstrel/internal/api/catalogue.go

package api

import (
	"context"
	"errors"
	"net/http"
	"net/url"
	"slices"
	"strings"
	"sync"
	"time"

	"github.com/go-chi/chi/v5"

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

// catalogueSearchLimit is how many results one search shows.
const catalogueSearchLimit = 25

// catalogueSearchResult is one row of GET /api/catalogue/search, read by the
// Discover page and request rows. artist_mbid and album_mbid are the parents a
// request needs: empty on an artist, the artist on an album, both on a track.
// An album is a MusicBrainz release group.
type catalogueSearchResult struct {
	MBID          string `json:"mbid"`
	Name          string `json:"name"`
	SecondaryText string `json:"secondary_text"`
	ImageURL      string `json:"image_url"`
	ArtistMBID    string `json:"artist_mbid"`
	AlbumMBID     string `json:"album_mbid"`
	InLibrary     bool   `json:"in_library"`
	Requested     bool   `json:"requested"`
}

// handleCatalogueSearch implements GET
// /api/catalogue/search?q=&kind=artist|album|track asking MusicBrainz directly.
// An unreachable MusicBrainz is a 503 the page shows as such, not an empty
// result.
func (h *handlers) handleCatalogueSearch(w http.ResponseWriter, r *http.Request) {
	kind := strings.TrimSpace(r.URL.Query().Get("kind"))
	switch kind {
	case "artist", "album", "track":
	default:
		writeErr(w, apierror.BadRequest("bad_kind", "kind must be artist, album, or track"))
		return
	}
	q := strings.TrimSpace(r.URL.Query().Get("q"))
	if q == "" {
		writeErr(w, apierror.BadRequest("missing_query", "q is required"))
		return
	}

	out, err := h.catalogueSearches.get(r.Context(), kind, q, h.searchCatalogue)
	if err != nil {
		switch {
		case errors.Is(err, musicbrainz.ErrUnreachable), errors.Is(err, musicbrainz.ErrBadResponse):
			writeErr(w, &apierror.Error{Status: 503, Code: "musicbrainz_unreachable", Message: "MusicBrainz can't be reached", Cause: err})
		case r.Context().Err() != nil:
			return
		default:
			h.logger.Error("api: catalogue search", "kind", kind, "err", err)
			writeErr(w, apierror.InternalMsg("search failed", err))
		}
		return
	}

	dbQ := dbq.New(h.pool)
	for i := range out {
		inLib, err := h.catalogueInLibrary(r.Context(), kind, out[i].MBID)
		if err != nil {
			writeErr(w, apierror.InternalMsg("library check failed", err))
			return
		}
		requested, err := dbQ.HasNonTerminalRequestForMBID(r.Context(), out[i].MBID)
		if err != nil {
			writeErr(w, apierror.InternalMsg("request check failed", err))
			return
		}
		out[i].InLibrary, out[i].Requested = inLib, requested
	}
	writeJSON(w, http.StatusOK, out)
}

func (h *handlers) searchCatalogue(ctx context.Context, kind, q string) ([]catalogueSearchResult, error) {
	mb := h.catalogue.MusicBrainz()
	out := []catalogueSearchResult{}
	switch kind {
	case "artist":
		artists, err := mb.SearchArtists(ctx, q, catalogueSearchLimit)
		if err != nil {
			return nil, err
		}
		for _, a := range artists {
			out = append(out, catalogueSearchResult{
				MBID: a.MBID, Name: a.Name, SecondaryText: artistLine(a),
				ImageURL: artistArtURL(a.MBID, a.Name),
			})
		}
	case "album":
		groups, err := mb.SearchReleaseGroups(ctx, q, catalogueSearchLimit)
		if err != nil {
			return nil, err
		}
		for _, g := range groups {
			out = append(out, catalogueSearchResult{
				MBID: g.MBID, Name: g.Title, SecondaryText: joinNonEmpty(g.ArtistCredit, g.Year(), groupType(g)),
				ImageURL: groupArtURL(g), ArtistMBID: first(g.ArtistMBIDs),
			})
		}
	case "track":
		recs, err := mb.SearchRecordings(ctx, q, catalogueSearchLimit)
		if err != nil {
			return nil, err
		}
		for _, rec := range recs {
			res := catalogueSearchResult{
				MBID: rec.MBID, Name: rec.Title,
				SecondaryText: joinNonEmpty(rec.ReleaseGroup.Title, rec.ArtistCredit),
				ArtistMBID:    first(rec.ArtistMBIDs), AlbumMBID: rec.ReleaseGroup.MBID,
			}
			if rec.ReleaseGroup.MBID != "" {
				res.ImageURL = groupArtURL(rec.ReleaseGroup)
			}
			out = append(out, res)
		}
	}
	return out, nil
}

// catalogueSearchTTL is how long a search's MusicBrainz answer is reused.
// MusicBrainz allows a request a second, and Discover searches as the user
// types, so the same words are often asked again within moments.
const catalogueSearchTTL = 10 * time.Minute

// catalogueSearchCacheMax bounds the cache; past it, the cache starts over.
const catalogueSearchCacheMax = 500

// searchCache keeps recent MusicBrainz answers by kind and query. A nil
// cache asks every time. Whether a result is held or requested is not
// cached: the handler works that out on every request.
type searchCache struct {
	mu      sync.Mutex
	entries map[string]searchEntry
	now     func() time.Time
}

type searchEntry struct {
	at      time.Time
	results []catalogueSearchResult
}

func newSearchCache() *searchCache {
	return &searchCache{entries: map[string]searchEntry{}, now: time.Now}
}

func (c *searchCache) get(ctx context.Context, kind, q string,
	ask func(context.Context, string, string) ([]catalogueSearchResult, error),
) ([]catalogueSearchResult, error) {
	if c == nil {
		return ask(ctx, kind, q)
	}
	key := kind + "\x00" + strings.ToLower(q)
	c.mu.Lock()
	e, ok := c.entries[key]
	c.mu.Unlock()
	if ok && c.now().Sub(e.at) < catalogueSearchTTL {
		return slices.Clone(e.results), nil
	}
	results, err := ask(ctx, kind, q)
	if err != nil {
		return nil, err
	}
	c.mu.Lock()
	if len(c.entries) >= catalogueSearchCacheMax {
		c.entries = map[string]searchEntry{}
	}
	c.entries[key] = searchEntry{at: c.now(), results: slices.Clone(results)}
	c.mu.Unlock()
	return results, nil
}

// artistLine is what tells two artists of one name apart: MusicBrainz's own
// disambiguation when it has one, else the kind of artist and the country.
func artistLine(a musicbrainz.Artist) string {
	if a.Disambiguation != "" {
		return a.Disambiguation
	}
	return joinNonEmpty(a.Type, a.Country)
}

// groupType names an album's kind the way people do: "Album", "EP",
// "Album · Live", "Single · Remix".
func groupType(g musicbrainz.ReleaseGroup) string {
	return joinNonEmpty(append([]string{g.PrimaryType}, g.SecondaryTypes...)...)
}

func joinNonEmpty(parts ...string) string {
	kept := parts[:0:0]
	for _, p := range parts {
		if p != "" {
			kept = append(kept, p)
		}
	}
	return strings.Join(kept, " · ")
}

func first(s []string) string {
	if len(s) == 0 {
		return ""
	}
	return s[0]
}

// artistArtURL and groupArtURL point at Minstrel's own art endpoints. The
// names ride along for the sources that look art up by name.
func artistArtURL(mbid, name string) string {
	if mbid == "" {
		return ""
	}
	return "/api/catalogue/art/artist/" + mbid + "?" + url.Values{"name": {name}}.Encode()
}

func groupArtURL(g musicbrainz.ReleaseGroup) string {
	return "/api/catalogue/art/release-group/" + g.MBID + "?" +
		url.Values{"artist": {g.ArtistCredit}, "title": {g.Title}}.Encode()
}

// catalogueInLibrary reports whether a result is already held: an artist by
// its MBID, an album by its release group (or a release id that happens to be
// the same), a track by its recording.
func (h *handlers) catalogueInLibrary(ctx context.Context, kind, mbid string) (bool, error) {
	var query string
	switch kind {
	case "artist":
		query = `SELECT EXISTS(SELECT 1 FROM artists WHERE mbid = $1)`
	case "album":
		query = `SELECT EXISTS(SELECT 1 FROM albums WHERE release_group_mbid = $1 OR mbid = $1)`
	case "track":
		query = `SELECT EXISTS(SELECT 1 FROM tracks WHERE mbid = $1)`
	default:
		return false, nil
	}
	var exists bool
	err := h.pool.QueryRow(ctx, query, mbid).Scan(&exists)
	return exists, err
}

// handleCatalogueArt implements GET /api/catalogue/art/{kind}/{mbid} for an
// artist or a release group Minstrel doesn't hold. The image comes from the
// enabled cover-art sources and is kept on disk, so the browser
// never fetches a third-party host. A 404 shows the placeholder.
func (h *handlers) handleCatalogueArt(w http.ResponseWriter, r *http.Request) {
	kind, mbid := chi.URLParam(r, "kind"), chi.URLParam(r, "mbid")
	if !catalogue.ValidMBID(mbid) {
		writeErr(w, apierror.NotFound("art"))
		return
	}
	var (
		body []byte
		err  error
	)
	switch kind {
	case "artist":
		body, err = h.catalogueArt.Artist(r.Context(), mbid, r.URL.Query().Get("name"))
	case "release-group":
		body, err = h.catalogueArt.ReleaseGroup(r.Context(), mbid, r.URL.Query().Get("artist"), r.URL.Query().Get("title"))
	default:
		writeErr(w, apierror.NotFound("art"))
		return
	}
	if err != nil {
		if r.Context().Err() == nil {
			writeErr(w, apierror.NotFound("art"))
		}
		return
	}
	w.Header().Set("Content-Type", http.DetectContentType(body))
	w.Header().Set("Cache-Control", "private, max-age=86400")
	_, _ = w.Write(body)
}