Add caching for lrclib lyrics

backend/lrclib.go

@@ -2,10 +2,15 @@ package backend
 
 import (
 	"context"
+	"crypto/md5"
+	"encoding/hex"
 	"encoding/json"
 	"errors"
 	"fmt"
+	"log"
 	"net/http"
+	"os"
+	"path/filepath"
 	"regexp"
 	"strconv"
 	"strings"
@@ -14,6 +19,38 @@ import (
 	"github.com/dweymouth/supersonic/backend/mediaprovider"
 )
 
+func FetchLrcLibLyricsCached(name, artist, album string, durationSecs int, cacheDir string) (*mediaprovider.Lyrics, error) {
+	hash := makeTrackIdHash(name, artist, album)
+	cacheFilePath := filepath.Join(cacheDir, fmt.Sprintf("%s_lyrics.txt", hash))
+
+	// File is cached. Try to use it
+	if _, err := os.Stat(cacheFilePath); err == nil {
+		lyrics, err := readCachedLyrics(cacheFilePath)
+		if err == nil {
+			return lyrics, nil
+		}
+
+		// On an error, remove the file.
+		if !os.IsNotExist(err) {
+			os.Remove(cacheFilePath)
+		}
+	}
+
+	// Fetch the lyrics
+	lyrics, err := FetchLrcLibLyrics(name, artist, album, durationSecs)
+	if err != nil {
+		return nil, err
+	}
+
+	// Try to write it into cache
+	err = writeCachedLyrics(cacheFilePath, lyrics)
+	if err != nil {
+		log.Printf("Failed to serialize fetched lyrics: %s", err)
+	}
+
+	return lyrics, nil
+}
+
 // FetchLrcLibLyrics is a static function to search and fetch lyrics from lrclib.net
 func FetchLrcLibLyrics(name, artist, album string, durationSecs int) (*mediaprovider.Lyrics, error) {
 	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
@@ -105,3 +142,46 @@ type lrcLibResponse struct {
 	PlainLyrics  string  `json:"plainLyrics"`
 	SyncedLyrics string  `json:"syncedLyrics"`
 }
+
+// Write lyrics to the given file.
+func writeCachedLyrics(cacheFile string, lyrics *mediaprovider.Lyrics) error {
+	serialized, err := json.Marshal(lyrics)
+	if err != nil {
+		return err
+	}
+
+	f, err := os.Create(cacheFile)
+	if err != nil {
+		return nil
+	}
+	defer f.Close()
+
+	f.Write(serialized)
+
+	return nil
+}
+
+// Read lyrics from the given cache file.
+func readCachedLyrics(cacheFile string) (*mediaprovider.Lyrics, error) {
+	cachedBytes, err := os.ReadFile(cacheFile)
+	if err != nil {
+		return nil, err
+	}
+
+	var lyrics mediaprovider.Lyrics
+
+	err = json.Unmarshal(cachedBytes, &lyrics)
+	if err != nil {
+		return nil, err
+	}
+
+	return &lyrics, nil
+}
+
+// Create a "unique" hash for a song to identify it.
+func makeTrackIdHash(name, artist, album string) string {
+	hasher := md5.New()
+	identifier := fmt.Sprintf("%s;%s;%s", name, artist, album)
+	hasher.Write([]byte(identifier))
+	return hex.EncodeToString(hasher.Sum(nil))
+}