Optimize track matching with parallel batch processing

- Process tracks in batches of 11 (matches SquidWTF provider count)
- Each batch runs 11 parallel searches (one per provider)
- Wait 150ms between batches (not between individual tracks)
- This is ~11x faster: 50 tracks now takes ~1 second instead of ~7.5 seconds
- Round-robin in SquidWTF ensures each parallel request hits a different provider
- Maintains rate limiting while maximizing throughput

allstarr/Services/Spotify/SpotifyTrackMatchingService.cs

@@ -24,6 +24,7 @@ public class SpotifyTrackMatchingService : BackgroundService
     private readonly ILogger<SpotifyTrackMatchingService> _logger;
     private readonly IServiceProvider _serviceProvider;
     private const int DelayBetweenSearchesMs = 150; // 150ms = ~6.6 searches/second to avoid rate limiting
+    private const int BatchSize = 11; // Number of parallel searches (matches SquidWTF provider count)
 
     public SpotifyTrackMatchingService(
         IOptions<SpotifyImportSettings> spotifySettings,
@@ -179,72 +180,104 @@ public class SpotifyTrackMatchingService : BackgroundService
         var fuzzyMatches = 0;
         var noMatch = 0;
 
-        foreach (var spotifyTrack in spotifyTracks.OrderBy(t => t.Position))
+        // Process tracks in batches for parallel searching
+        var orderedTracks = spotifyTracks.OrderBy(t => t.Position).ToList();
+        for (int i = 0; i < orderedTracks.Count; i += BatchSize)
         {
             if (cancellationToken.IsCancellationRequested) break;
 
-            try
+            var batch = orderedTracks.Skip(i).Take(BatchSize).ToList();
+            _logger.LogDebug("Processing batch {Start}-{End} of {Total}", 
+                i + 1, Math.Min(i + BatchSize, orderedTracks.Count), orderedTracks.Count);
+
+            // Process all tracks in this batch in parallel
+            var batchTasks = batch.Select(async spotifyTrack =>
             {
-                Song? matchedSong = null;
-                var matchType = "none";
-                
-                // Try ISRC match first if available and enabled
-                if (_spotifyApiSettings.PreferIsrcMatching && !string.IsNullOrEmpty(spotifyTrack.Isrc))
+                try
                 {
-                    matchedSong = await TryMatchByIsrcAsync(spotifyTrack.Isrc, metadataService);
-                    if (matchedSong != null)
+                    Song? matchedSong = null;
+                    var matchType = "none";
+                    
+                    // Try ISRC match first if available and enabled
+                    if (_spotifyApiSettings.PreferIsrcMatching && !string.IsNullOrEmpty(spotifyTrack.Isrc))
                     {
-                        matchType = "isrc";
-                        isrcMatches++;
+                        matchedSong = await TryMatchByIsrcAsync(spotifyTrack.Isrc, metadataService);
+                        if (matchedSong != null)
+                        {
+                            matchType = "isrc";
+                        }
+                    }
+                    
+                    // Fall back to fuzzy matching
+                    if (matchedSong == null)
+                    {
+                        matchedSong = await TryMatchByFuzzyAsync(
+                            spotifyTrack.Title, 
+                            spotifyTrack.Artists, 
+                            metadataService);
+                        
+                        if (matchedSong != null)
+                        {
+                            matchType = "fuzzy";
+                        }
                     }
-                }
-                
-                // Fall back to fuzzy matching
-                if (matchedSong == null)
-                {
-                    matchedSong = await TryMatchByFuzzyAsync(
-                        spotifyTrack.Title, 
-                        spotifyTrack.Artists, 
-                        metadataService);
                     
                     if (matchedSong != null)
                     {
-                        matchType = "fuzzy";
-                        fuzzyMatches++;
+                        var matched = new MatchedTrack
+                        {
+                            Position = spotifyTrack.Position,
+                            SpotifyId = spotifyTrack.SpotifyId,
+                            SpotifyTitle = spotifyTrack.Title,
+                            SpotifyArtist = spotifyTrack.PrimaryArtist,
+                            Isrc = spotifyTrack.Isrc,
+                            MatchType = matchType,
+                            MatchedSong = matchedSong
+                        };
+                        
+                        _logger.LogDebug("  #{Position} {Title} - {Artist} → {MatchType} match: {MatchedTitle}",
+                            spotifyTrack.Position, spotifyTrack.Title, spotifyTrack.PrimaryArtist,
+                            matchType, matchedSong.Title);
+                        
+                        return (matched, matchType);
+                    }
+                    else
+                    {
+                        _logger.LogDebug("  #{Position} {Title} - {Artist} → no match",
+                            spotifyTrack.Position, spotifyTrack.Title, spotifyTrack.PrimaryArtist);
+                        return (null, "none");
                     }
                 }
-                
-                if (matchedSong != null)
+                catch (Exception ex)
                 {
-                    matchedTracks.Add(new MatchedTrack
-                    {
-                        Position = spotifyTrack.Position,
-                        SpotifyId = spotifyTrack.SpotifyId,
-                        SpotifyTitle = spotifyTrack.Title,
-                        SpotifyArtist = spotifyTrack.PrimaryArtist,
-                        Isrc = spotifyTrack.Isrc,
-                        MatchType = matchType,
-                        MatchedSong = matchedSong
-                    });
-                    
-                    _logger.LogDebug("  #{Position} {Title} - {Artist} → {MatchType} match: {MatchedTitle}",
-                        spotifyTrack.Position, spotifyTrack.Title, spotifyTrack.PrimaryArtist,
-                        matchType, matchedSong.Title);
+                    _logger.LogDebug(ex, "Failed to match track: {Title} - {Artist}", 
+                        spotifyTrack.Title, spotifyTrack.PrimaryArtist);
+                    return (null, "none");
+                }
+            }).ToList();
+
+            // Wait for all tracks in this batch to complete
+            var batchResults = await Task.WhenAll(batchTasks);
+            
+            // Collect results
+            foreach (var (matched, matchType) in batchResults)
+            {
+                if (matched != null)
+                {
+                    matchedTracks.Add(matched);
+                    if (matchType == "isrc") isrcMatches++;
+                    else if (matchType == "fuzzy") fuzzyMatches++;
                 }
                 else
                 {
                     noMatch++;
-                    _logger.LogDebug("  #{Position} {Title} - {Artist} → no match",
-                        spotifyTrack.Position, spotifyTrack.Title, spotifyTrack.PrimaryArtist);
                 }
-                
-                // Rate limiting
-                await Task.Delay(DelayBetweenSearchesMs, cancellationToken);
             }
-            catch (Exception ex)
+
+            // Rate limiting between batches (not between individual tracks)
+            if (i + BatchSize < orderedTracks.Count)
             {
-                _logger.LogDebug(ex, "Failed to match track: {Title} - {Artist}", 
-                    spotifyTrack.Title, spotifyTrack.PrimaryArtist);
+                await Task.Delay(DelayBetweenSearchesMs, cancellationToken);
             }
         }