add features

2026-07-29 04:35:25 -05:00
parent 23c6113b33
commit cab5a987b0
29 changed files with 1179 additions and 89 deletions
@@ -0,0 +1,147 @@
+package backend
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"net/url"
+	"strings"
+	"sync"
+	"time"
+)
+
+const (
+	musicBrainzAPIBase = "https://musicbrainz.org/ws/2"
+	coverArtAPIBase    = "https://coverartarchive.org"
+)
+
+// musicBrainzArtworkResolver resolves public album artwork URLs while obeying
+// MusicBrainz's one-request-per-second client limit.
+type musicBrainzArtworkResolver struct {
+	ctx       context.Context
+	client    *http.Client
+	userAgent string
+	mu        sync.Mutex
+	lastCall  time.Time
+	cache     map[string]string
+	inFlight  map[string][]chan string
+}
+
+func newMusicBrainzArtworkResolver(ctx context.Context, userAgent string) *musicBrainzArtworkResolver {
+	return &musicBrainzArtworkResolver{
+		ctx: ctx, client: &http.Client{Timeout: 10 * time.Second}, userAgent: userAgent,
+		cache: make(map[string]string), inFlight: make(map[string][]chan string),
+	}
+}
+
+func (r *musicBrainzArtworkResolver) Resolve(artist, album string) string {
+	artist, album = strings.TrimSpace(artist), strings.TrimSpace(album)
+	if artist == "" || album == "" {
+		return ""
+	}
+	key := strings.ToLower(artist + "\x00" + album)
+	r.mu.Lock()
+	if result, ok := r.cache[key]; ok {
+		r.mu.Unlock()
+		return result
+	}
+	if waiters, ok := r.inFlight[key]; ok {
+		wait := make(chan string, 1)
+		r.inFlight[key] = append(waiters, wait)
+		r.mu.Unlock()
+		select {
+		case result := <-wait:
+			return result
+		case <-r.ctx.Done():
+			return ""
+		}
+	}
+	r.inFlight[key] = nil
+	r.mu.Unlock()
+
+	result := r.lookup(artist, album)
+	r.mu.Lock()
+	r.cache[key] = result
+	for _, waiter := range r.inFlight[key] {
+		waiter <- result
+		close(waiter)
+	}
+	delete(r.inFlight, key)
+	r.mu.Unlock()
+	return result
+}
+
+func (r *musicBrainzArtworkResolver) lookup(artist, album string) string {
+	if !r.waitForRateLimit() {
+		return ""
+	}
+	query := fmt.Sprintf(`releasegroup:"%s" AND artist:"%s"`, luceneEscape(album), luceneEscape(artist))
+	endpoint := musicBrainzAPIBase + "/release-group/?fmt=json&limit=1&query=" + url.QueryEscape(query)
+	req, err := http.NewRequestWithContext(r.ctx, http.MethodGet, endpoint, nil)
+	if err != nil {
+		return ""
+	}
+	req.Header.Set("Accept", "application/json")
+	req.Header.Set("User-Agent", r.userAgent)
+	resp, err := r.client.Do(req)
+	if err != nil {
+		return ""
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		return ""
+	}
+	var result struct {
+		ReleaseGroups []struct {
+			ID string `json:"id"`
+		} `json:"release-groups"`
+	}
+	if json.NewDecoder(resp.Body).Decode(&result) != nil || len(result.ReleaseGroups) == 0 {
+		return ""
+	}
+
+	artURL := coverArtAPIBase + "/release-group/" + result.ReleaseGroups[0].ID + "/front-500"
+	artReq, err := http.NewRequestWithContext(r.ctx, http.MethodHead, artURL, nil)
+	if err != nil {
+		return ""
+	}
+	// Validate the Cover Art Archive endpoint itself without following the
+	// redirect to an archive.org image host. Some archive mirrors reject HEAD
+	// even though Discord can fetch the redirected image normally.
+	artClient := *r.client
+	artClient.CheckRedirect = func(_ *http.Request, _ []*http.Request) error { return http.ErrUseLastResponse }
+	artResp, err := artClient.Do(artReq)
+	if err != nil {
+		return ""
+	}
+	artResp.Body.Close()
+	validRedirect := artResp.StatusCode >= 300 && artResp.StatusCode < 400 && artResp.Header.Get("Location") != ""
+	if (artResp.StatusCode < 200 || artResp.StatusCode >= 300) && !validRedirect {
+		return ""
+	}
+	return artURL
+}
+
+func (r *musicBrainzArtworkResolver) waitForRateLimit() bool {
+	r.mu.Lock()
+	wait := time.Until(r.lastCall.Add(time.Second))
+	if wait < 0 {
+		wait = 0
+	}
+	r.lastCall = time.Now().Add(wait)
+	r.mu.Unlock()
+	timer := time.NewTimer(wait)
+	defer timer.Stop()
+	select {
+	case <-timer.C:
+		return true
+	case <-r.ctx.Done():
+		return false
+	}
+}
+
+func luceneEscape(value string) string {
+	value = strings.ReplaceAll(value, `\`, `\\`)
+	return strings.ReplaceAll(value, `"`, `\"`)
+}