Add startup cache warming service

- Proactively loads all file caches into Redis on container startup
- Warms genre cache (30-day expiration)
- Warms playlist items cache (24-hour expiration)
- Logs warming progress and duration
- Ensures fast access immediately after restart
- Cleans up expired genre cache files automatically
- All 225 tests passing

allstarr/Program.cs

@@ -482,6 +482,9 @@ builder.Services.AddHostedService<StartupValidationOrchestrator>();
 // Register cache cleanup service (only runs when StorageMode is Cache)
 builder.Services.AddHostedService<CacheCleanupService>();
 
+// Register cache warming service (loads file caches into Redis on startup)
+builder.Services.AddHostedService<CacheWarmingService>();
+
 // Register Spotify API client, lyrics service, and settings for direct API access
 // Configure from environment variables with SPOTIFY_API_ prefix
 builder.Services.Configure<allstarr.Models.Settings.SpotifyApiSettings>(options =>

allstarr/Services/Common/CacheWarmingService.cs

@@ -0,0 +1,172 @@
+using System.Text.Json;
+
+namespace allstarr.Services.Common;
+
+/// <summary>
+/// Background service that warms up Redis cache from file system on startup.
+/// Ensures fast access to cached data after container restarts.
+/// </summary>
+public class CacheWarmingService : IHostedService
+{
+    private readonly RedisCacheService _cache;
+    private readonly ILogger<CacheWarmingService> _logger;
+    private const string GenreCacheDirectory = "/app/cache/genres";
+    private const string PlaylistCacheDirectory = "/app/cache/spotify";
+
+    public CacheWarmingService(
+        RedisCacheService cache,
+        ILogger<CacheWarmingService> logger)
+    {
+        _cache = cache;
+        _logger = logger;
+    }
+
+    public async Task StartAsync(CancellationToken cancellationToken)
+    {
+        _logger.LogInformation("🔥 Starting cache warming from file system...");
+
+        var startTime = DateTime.UtcNow;
+        var genresWarmed = 0;
+        var playlistsWarmed = 0;
+
+        try
+        {
+            // Warm genre cache
+            genresWarmed = await WarmGenreCacheAsync(cancellationToken);
+
+            // Warm playlist cache
+            playlistsWarmed = await WarmPlaylistCacheAsync(cancellationToken);
+
+            var duration = DateTime.UtcNow - startTime;
+            _logger.LogInformation(
+                "✅ Cache warming complete in {Duration:F1}s: {Genres} genres, {Playlists} playlists",
+                duration.TotalSeconds, genresWarmed, playlistsWarmed);
+        }
+        catch (Exception ex)
+        {
+            _logger.LogError(ex, "Failed to warm cache from file system");
+        }
+    }
+
+    public Task StopAsync(CancellationToken cancellationToken)
+    {
+        return Task.CompletedTask;
+    }
+
+    /// <summary>
+    /// Warms genre cache from file system.
+    /// </summary>
+    private async Task<int> WarmGenreCacheAsync(CancellationToken cancellationToken)
+    {
+        if (!Directory.Exists(GenreCacheDirectory))
+        {
+            return 0;
+        }
+
+        var files = Directory.GetFiles(GenreCacheDirectory, "*.json");
+        var warmedCount = 0;
+
+        foreach (var file in files)
+        {
+            if (cancellationToken.IsCancellationRequested)
+                break;
+
+            try
+            {
+                // Check if cache is expired (30 days)
+                var fileInfo = new FileInfo(file);
+                if (DateTime.UtcNow - fileInfo.LastWriteTimeUtc > TimeSpan.FromDays(30))
+                {
+                    File.Delete(file);
+                    continue;
+                }
+
+                var json = await File.ReadAllTextAsync(file, cancellationToken);
+                var cacheEntry = JsonSerializer.Deserialize<GenreCacheEntry>(json);
+
+                if (cacheEntry != null && !string.IsNullOrEmpty(cacheEntry.CacheKey))
+                {
+                    var redisKey = $"genre:{cacheEntry.CacheKey}";
+                    await _cache.SetAsync(redisKey, cacheEntry.Genre, TimeSpan.FromDays(30));
+                    warmedCount++;
+                }
+            }
+            catch (Exception ex)
+            {
+                _logger.LogWarning(ex, "Failed to warm genre cache from file: {File}", file);
+            }
+        }
+
+        if (warmedCount > 0)
+        {
+            _logger.LogInformation("🔥 Warmed {Count} genre entries from file cache", warmedCount);
+        }
+
+        return warmedCount;
+    }
+
+    /// <summary>
+    /// Warms playlist cache from file system.
+    /// </summary>
+    private async Task<int> WarmPlaylistCacheAsync(CancellationToken cancellationToken)
+    {
+        if (!Directory.Exists(PlaylistCacheDirectory))
+        {
+            return 0;
+        }
+
+        var files = Directory.GetFiles(PlaylistCacheDirectory, "*_items.json");
+        var warmedCount = 0;
+
+        foreach (var file in files)
+        {
+            if (cancellationToken.IsCancellationRequested)
+                break;
+
+            try
+            {
+                // Check if cache is expired (24 hours)
+                var fileInfo = new FileInfo(file);
+                if (DateTime.UtcNow - fileInfo.LastWriteTimeUtc > TimeSpan.FromHours(24))
+                {
+                    continue; // Don't delete, let the normal flow handle it
+                }
+
+                var json = await File.ReadAllTextAsync(file, cancellationToken);
+                var items = JsonSerializer.Deserialize<List<Dictionary<string, object?>>>(json);
+
+                if (items != null && items.Count > 0)
+                {
+                    // Extract playlist name from filename
+                    var fileName = Path.GetFileNameWithoutExtension(file);
+                    var playlistName = fileName.Replace("_items", "");
+
+                    var redisKey = $"spotify:playlist:items:{playlistName}";
+                    await _cache.SetAsync(redisKey, items, TimeSpan.FromHours(24));
+                    warmedCount++;
+
+                    _logger.LogDebug("🔥 Warmed playlist cache for {Playlist} ({Count} items)", 
+                        playlistName, items.Count);
+                }
+            }
+            catch (Exception ex)
+            {
+                _logger.LogWarning(ex, "Failed to warm playlist cache from file: {File}", file);
+            }
+        }
+
+        if (warmedCount > 0)
+        {
+            _logger.LogInformation("🔥 Warmed {Count} playlist caches from file system", warmedCount);
+        }
+
+        return warmedCount;
+    }
+
+    private class GenreCacheEntry
+    {
+        public string CacheKey { get; set; } = "";
+        public string Genre { get; set; } = "";
+        public DateTime CachedAt { get; set; }
+    }
+}