pipu-music/services/api/internal/musicbrainz/client.go

// Package musicbrainz adapts MusicBrainz and Cover Art Archive without receiving audio files.
package musicbrainz

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"sort"
	"strings"
	"sync"
	"time"

	"github.com/google/uuid"
)

type Track struct {
	RecordingID string `json:"recording_id"`
	Title       string `json:"title"`
	Artist      string `json:"artist"`
	Disc        int    `json:"disc"`
	Position    int    `json:"position"`
	DurationMs  int    `json:"duration_ms"`
}
type Release struct {
	ID       string  `json:"id"`
	GroupID  string  `json:"group_id"`
	Title    string  `json:"title"`
	Artist   string  `json:"artist"`
	Type     string  `json:"type"`
	Date     string  `json:"date"`
	Country  string  `json:"country"`
	Comment  string  `json:"comment"`
	HasCover bool    `json:"has_cover"`
	Tracks   []Track `json:"tracks"`
}
type Query struct {
	GroupID      string   `json:"group_id,omitempty"`
	Artist       string   `json:"artist"`
	Album        string   `json:"album"`
	ReleaseID    string   `json:"release_id"`
	Audio        bool     `json:"audio,omitempty"`
	RecordingIDs []string `json:"-"`
}
type Cover struct {
	Data  []byte
	MIME  string
	URL   string
	Exact bool
}
type Cache interface {
	GetMetadataCache(context.Context, string) ([]byte, bool, error)
	PutMetadataCache(context.Context, string, []byte, time.Duration) error
}
type Client struct {
	http      *http.Client
	cache     Cache
	mu        sync.Mutex
	next      time.Time
	base      string
	coverBase string
	interval  time.Duration
	userAgent string
}

func New(cache Cache, userAgent string) *Client {
	return &Client{cache: cache, base: "https://musicbrainz.org/ws/2", coverBase: "https://coverartarchive.org", interval: 1100 * time.Millisecond,
		userAgent: userAgent, http: &http.Client{Timeout: 20 * time.Second, CheckRedirect: func(req *http.Request, via []*http.Request) error {
			h := req.URL.Hostname()
			if len(via) > 5 || req.URL.Scheme != "https" || req.URL.Port() != "" || req.URL.User != nil ||
				!(h == "musicbrainz.org" || h == "coverartarchive.org" || h == "archive.org" || strings.HasSuffix(h, ".archive.org")) {
				return errors.New("metadata: redirect outside provider")
			}
			return nil
		}}}
}
func (c *Client) wait(ctx context.Context) error {
	c.mu.Lock()
	defer c.mu.Unlock()
	if delay := time.Until(c.next); delay > 0 {
		t := time.NewTimer(delay)
		defer t.Stop()
		select {
		case <-ctx.Done():
			return ctx.Err()
		case <-t.C:
		}
	}
	c.next = time.Now().Add(c.interval)
	return nil
}

var ErrNotFound = errors.New("metadata: not found")

func (c *Client) get(ctx context.Context, address string, limited bool, maxBytes int64) ([]byte, error) {
	if data, ok, err := c.cache.GetMetadataCache(ctx, address); err == nil && ok {
		return data, nil
	}
	if limited {
		if err := c.wait(ctx); err != nil {
			return nil, err
		}
	}
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, address, nil)
	if err != nil {
		return nil, err
	}
	req.Header.Set("User-Agent", c.userAgent)
	req.Header.Set("Accept", "application/json, image/jpeg, image/png, image/webp")
	res, err := c.http.Do(req)
	if err != nil {
		return nil, err
	}
	defer res.Body.Close()
	if res.StatusCode == http.StatusNotFound {
		return nil, ErrNotFound
	}
	if res.StatusCode != http.StatusOK {
		return nil, fmt.Errorf("metadata: HTTP %d", res.StatusCode)
	}
	data, err := io.ReadAll(io.LimitReader(res.Body, maxBytes+1))
	if err != nil {
		return nil, err
	}
	if int64(len(data)) > maxBytes {
		return nil, errors.New("metadata: response too large")
	}
	if limited && !json.Valid(data) {
		return nil, errors.New("metadata: invalid JSON response")
	}
	if !limited {
		mime := http.DetectContentType(data)
		if mime != "image/jpeg" && mime != "image/png" && mime != "image/webp" {
			return nil, errors.New("metadata: unsupported cover")
		}
	}
	_ = c.cache.PutMetadataCache(ctx, address, data, 7*24*time.Hour)
	return data, nil
}

type credit struct {
	Name   string `json:"name"`
	Join   string `json:"joinphrase"`
	Artist struct {
		Name string `json:"name"`
	} `json:"artist"`
}

func artist(credits []credit) string {
	var s strings.Builder
	for _, a := range credits {
		name := a.Name
		if name == "" {
			name = a.Artist.Name
		}
		s.WriteString(name)
		s.WriteString(a.Join)
	}
	return s.String()
}

type releaseJSON struct {
	ID      string   `json:"id"`
	Title   string   `json:"title"`
	Date    string   `json:"date"`
	Country string   `json:"country"`
	Comment string   `json:"disambiguation"`
	Credits []credit `json:"artist-credit"`
	Group   struct {
		ID   string `json:"id"`
		Type string `json:"primary-type"`
	} `json:"release-group"`
	Cover struct {
		Front bool `json:"front"`
	} `json:"cover-art-archive"`
	Media []struct {
		Position int `json:"position"`
		Tracks   []struct {
			Position  int      `json:"position"`
			Title     string   `json:"title"`
			Length    int      `json:"length"`
			Credits   []credit `json:"artist-credit"`
			Recording struct {
				ID      string   `json:"id"`
				Title   string   `json:"title"`
				Length  int      `json:"length"`
				Credits []credit `json:"artist-credit"`
			} `json:"recording"`
		} `json:"tracks"`
	} `json:"media"`
}

func (c *Client) release(ctx context.Context, id string) (Release, error) {
	if _, err := uuid.Parse(id); err != nil {
		return Release{}, errors.New("metadata: invalid release ID")
	}
	data, err := c.get(ctx, c.base+"/release/"+id+"?fmt=json&inc=recordings%2Bartist-credits%2Brelease-groups", true, 8<<20)
	if err != nil {
		return Release{}, err
	}
	var raw releaseJSON
	if err = json.Unmarshal(data, &raw); err != nil {
		return Release{}, err
	}
	r := Release{ID: raw.ID, GroupID: raw.Group.ID, Title: raw.Title, Artist: artist(raw.Credits), Type: raw.Group.Type, Date: raw.Date, Country: raw.Country, Comment: raw.Comment, HasCover: raw.Cover.Front, Tracks: []Track{}}
	if _, err = uuid.Parse(r.ID); err != nil {
		return Release{}, errors.New("metadata: invalid release response")
	}
	for _, m := range raw.Media {
		for _, t := range m.Tracks {
			title := t.Title
			if title == "" {
				title = t.Recording.Title
			}
			a := artist(t.Credits)
			if a == "" {
				a = artist(t.Recording.Credits)
			}
			if a == "" {
				a = r.Artist
			}
			length := t.Length
			if length == 0 {
				length = t.Recording.Length
			}
			r.Tracks = append(r.Tracks, Track{RecordingID: t.Recording.ID, Title: title, Artist: a, Disc: m.Position, Position: t.Position, DurationMs: length})
		}
	}
	if len(r.Tracks) == 0 || len(r.Tracks) > 1000 {
		return Release{}, errors.New("metadata: invalid track list")
	}
	return r, nil
}
func quote(s string) string { return `"` + strings.NewReplacer(`\`, `\\`, `"`, `\"`).Replace(s) + `"` }
func (c *Client) Search(ctx context.Context, q Query) ([]Release, error) {
	if len(q.RecordingIDs) > 0 {
		return c.byRecordings(ctx, q.RecordingIDs)
	}
	if q.ReleaseID != "" {
		r, err := c.release(ctx, q.ReleaseID)
		if errors.Is(err, ErrNotFound) {
			return []Release{}, nil
		}
		return []Release{r}, err
	}
	params := url.Values{"fmt": {"json"}, "limit": {"5"}, "query": {"release:" + quote(q.Album) + " AND artist:" + quote(q.Artist)}}
	data, err := c.get(ctx, c.base+"/release?"+params.Encode(), true, 4<<20)
	if err != nil {
		return nil, err
	}
	var found struct {
		Releases []struct {
			ID string `json:"id"`
		} `json:"releases"`
	}
	if err = json.Unmarshal(data, &found); err != nil {
		return nil, err
	}
	out := []Release{}
	for _, candidate := range found.Releases {
		r, err := c.release(ctx, candidate.ID)
		if err != nil {
			return nil, err
		}
		out = append(out, r)
	}
	return out, nil
}

// byRecordings discovers editions from a bounded sample; all batch files are matched afterwards.
func (c *Client) byRecordings(ctx context.Context, ids []string) ([]Release, error) {
	votes := map[string]int{}
	seen := map[string]bool{}
	for _, id := range ids {
		if _, err := uuid.Parse(id); err != nil {
			return nil, errors.New("metadata: invalid recording ID")
		}
		if seen[id] {
			continue
		}
		if len(seen) == 8 {
			break
		}
		seen[id] = true
		params := url.Values{"fmt": {"json"}, "recording": {id}, "limit": {"100"}}
		data, err := c.get(ctx, c.base+"/release?"+params.Encode(), true, 4<<20)
		if err != nil {
			return nil, err
		}
		var found struct {
			Releases []struct {
				ID string `json:"id"`
			} `json:"releases"`
		}
		if err = json.Unmarshal(data, &found); err != nil {
			return nil, err
		}
		perRecording := map[string]bool{}
		for _, r := range found.Releases {
			if _, err := uuid.Parse(r.ID); err == nil && !perRecording[r.ID] {
				votes[r.ID]++
				perRecording[r.ID] = true
			}
		}
	}
	candidates := []string{}
	for id := range votes {
		candidates = append(candidates, id)
	}
	sort.Slice(candidates, func(i, j int) bool {
		if votes[candidates[i]] == votes[candidates[j]] {
			return candidates[i] < candidates[j]
		}
		return votes[candidates[i]] > votes[candidates[j]]
	})
	out := []Release{}
	for _, id := range candidates[:min(5, len(candidates))] {
		r, err := c.release(ctx, id)
		if err != nil {
			return nil, err
		}
		out = append(out, r)
	}
	return out, nil
}
func (c *Client) Cover(ctx context.Context, r Release) (Cover, error) {
	for i, id := range []string{r.ID, r.GroupID} {
		if _, err := uuid.Parse(id); err != nil {
			continue
		}
		kind := "release"
		if i == 1 {
			kind = "release-group"
		}
		address := c.coverBase + "/" + kind + "/" + id + "/front-1200"
		data, err := c.get(ctx, address, false, 8<<20)
		if errors.Is(err, ErrNotFound) {
			continue
		}
		if err != nil {
			return Cover{}, err
		}
		mime := http.DetectContentType(data)
		if mime != "image/jpeg" && mime != "image/png" && mime != "image/webp" {
			return Cover{}, errors.New("metadata: unsupported cover")
		}
		return Cover{Data: data, MIME: mime, URL: address, Exact: i == 0}, nil
	}
	return Cover{}, ErrNotFound
}