Initial

MareSynchronosServer/MareSynchronosStaticFilesServer/Services/ColdTouchHashService.cs

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+using MareSynchronosShared.Services;
+using MareSynchronosShared.Utils.Configuration;
+using MareSynchronosStaticFilesServer.Utils;
+using System.Collections.Concurrent;
+
+namespace MareSynchronosStaticFilesServer.Services;
+
+// Perform access time updates for cold cache files accessed via hot cache or shard servers
+public class ColdTouchHashService : ITouchHashService
+{
+    private readonly ILogger<ColdTouchHashService> _logger;
+    private readonly IConfigurationService<StaticFilesServerConfiguration> _configuration;
+
+    private readonly bool _useColdStorage;
+    private readonly string _coldStoragePath;
+
+    // Debounce multiple updates towards the same file
+    private readonly ConcurrentDictionary<string, DateTime> _lastUpdateTimesUtc = new(StringComparer.Ordinal);
+    private int _cleanupCounter = 0;
+    private object _cleanupLockObj = new();
+    private const double _debounceTimeSecs = 900.0;
+
+    public ColdTouchHashService(ILogger<ColdTouchHashService> logger, IConfigurationService<StaticFilesServerConfiguration> configuration)
+    {
+        _logger = logger;
+        _configuration = configuration;
+        _useColdStorage = configuration.GetValueOrDefault(nameof(StaticFilesServerConfiguration.UseColdStorage), false);
+        _coldStoragePath = configuration.GetValue<string>(nameof(StaticFilesServerConfiguration.ColdStorageDirectory));
+    }
+
+    public Task StartAsync(CancellationToken cancellationToken)
+    {
+        return Task.CompletedTask;
+    }
+
+    public Task StopAsync(CancellationToken cancellationToken)
+    {
+        return Task.CompletedTask;
+    }
+
+    public void TouchColdHash(string hash)
+    {
+        if (!_useColdStorage)
+            return;
+
+        var nowUtc = DateTime.UtcNow;
+
+        // Clean up debounce dictionary regularly
+        if (_cleanupCounter++ >= 1000)
+        {
+            _cleanupCounter = 0;
+            if (Monitor.TryEnter(_cleanupLockObj))
+            {
+                try
+                {
+                    foreach (var entry in _lastUpdateTimesUtc.Where(entry => (nowUtc - entry.Value).TotalSeconds >= _debounceTimeSecs).ToList())
+                        _lastUpdateTimesUtc.TryRemove(entry.Key, out _);
+                }
+                finally
+                {
+                    Monitor.Exit(_cleanupLockObj);
+                }
+            }
+        }
+
+        // Ignore multiple updates within a time window of the first
+        if (_lastUpdateTimesUtc.TryGetValue(hash, out var lastUpdateTimeUtc) && (nowUtc - lastUpdateTimeUtc).TotalSeconds < _debounceTimeSecs)
+            return;
+
+        var fileInfo = FilePathUtil.GetFileInfoForHash(_coldStoragePath, hash);
+        if (fileInfo != null)
+        {
+            _logger.LogTrace("Touching {fileName}", fileInfo.Name);
+            try
+            {
+                fileInfo.LastAccessTimeUtc = nowUtc;
+            }
+            catch (IOException) { return; }
+            _lastUpdateTimesUtc.TryAdd(hash, nowUtc);
+        }
+    }
+}