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

// Package acoustid identifies recordings using Chromaprint, never audio files.
package acoustid

import (
	"context"
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"strings"
	"sync"
	"time"

	"github.com/google/uuid"
)

type Match struct {
	RecordingID string
	Score       float64
}
type Cache interface {
	GetMetadataCache(context.Context, string) ([]byte, bool, error)
	PutMetadataCache(context.Context, string, []byte, time.Duration) error
}
type Client struct {
	key, endpoint string
	cache         Cache
	http          *http.Client
	mu            sync.Mutex
	next          time.Time
	interval      time.Duration
}

func New(key string, cache Cache) *Client {
	return &Client{key: key, endpoint: "https://api.acoustid.org/v2/lookup", cache: cache, interval: 350 * time.Millisecond,
		http: &http.Client{Timeout: 20 * time.Second, CheckRedirect: func(*http.Request, []*http.Request) error { return http.ErrUseLastResponse }}}
}
func (c *Client) wait(ctx context.Context) error {
	c.mu.Lock()
	defer c.mu.Unlock()
	t := time.NewTimer(max(time.Duration(0), time.Until(c.next)))
	defer t.Stop()
	select {
	case <-ctx.Done():
		return ctx.Err()
	case <-t.C:
	}
	c.next = time.Now().Add(c.interval)
	return nil
}
func (c *Client) Lookup(ctx context.Context, fingerprint string, duration int) ([]Match, error) {
	if c.key == "" || duration <= 0 || len(fingerprint) == 0 || len(fingerprint) > 65536 {
		return nil, errors.New("acoustid: invalid lookup input")
	}
	hash := sha256.Sum256([]byte(fmt.Sprint(duration) + ":" + fingerprint))
	key := "acoustid:" + hex.EncodeToString(hash[:])
	if data, ok, err := c.cache.GetMetadataCache(ctx, key); err == nil && ok {
		return parse(data)
	}
	if err := c.wait(ctx); err != nil {
		return nil, err
	}
	body := url.Values{"client": {c.key}, "duration": {fmt.Sprint(duration)}, "fingerprint": {fingerprint}, "meta": {"recordingids"}, "format": {"json"}}
	req, err := http.NewRequestWithContext(ctx, http.MethodPost, c.endpoint, strings.NewReader(body.Encode()))
	if err != nil {
		return nil, err
	}
	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
	req.Header.Set("User-Agent", "PipuMusic (https://gitea.hsrv.site/mrleo1nid/pipu-music)")
	res, err := c.http.Do(req)
	if err != nil {
		return nil, errors.New("acoustid: request failed")
	}
	defer res.Body.Close()
	if res.StatusCode != http.StatusOK {
		return nil, fmt.Errorf("acoustid: HTTP %d", res.StatusCode)
	}
	data, err := io.ReadAll(io.LimitReader(res.Body, (2<<20)+1))
	if err != nil || len(data) > 2<<20 {
		return nil, errors.New("acoustid: invalid response size")
	}
	matches, err := parse(data)
	if err != nil {
		return nil, err
	}
	_ = c.cache.PutMetadataCache(ctx, key, data, 7*24*time.Hour)
	return matches, nil
}
func parse(data []byte) ([]Match, error) {
	var response struct {
		Status  string `json:"status"`
		Results []struct {
			Score      float64 `json:"score"`
			Recordings []struct {
				ID string `json:"id"`
			} `json:"recordings"`
		} `json:"results"`
	}
	if err := json.Unmarshal(data, &response); err != nil {
		return nil, errors.New("acoustid: invalid response")
	}
	if response.Status != "ok" {
		return nil, errors.New("acoustid: lookup rejected; check application key")
	}
	best := map[string]float64{}
	for _, result := range response.Results {
		if result.Score <= 0 || result.Score > 1 {
			continue
		}
		for _, recording := range result.Recordings {
			id, err := uuid.Parse(recording.ID)
			if err == nil && id != uuid.Nil && result.Score > best[id.String()] {
				best[id.String()] = result.Score
			}
		}
	}
	out := []Match{}
	for id, score := range best {
		out = append(out, Match{RecordingID: id, Score: score})
	}
	return out, nil
}