sigma update

LightlessSync/WebAPI/Files/FileDownloadDeduplicator.cs

@@ -0,0 +1,48 @@
+using System.Collections.Concurrent;
+
+namespace LightlessSync.WebAPI.Files;
+
+public readonly record struct DownloadClaim(bool IsOwner, Task<bool> Completion);
+
+public sealed class FileDownloadDeduplicator
+{
+    private readonly ConcurrentDictionary<string, TaskCompletionSource<bool>> _inFlight =
+        new(StringComparer.OrdinalIgnoreCase);
+
+    public DownloadClaim Claim(string hash)
+    {
+        if (string.IsNullOrWhiteSpace(hash))
+        {
+            return new DownloadClaim(false, Task.FromResult(true));
+        }
+
+        var tcs = new TaskCompletionSource<bool>(TaskCreationOptions.RunContinuationsAsynchronously);
+        var existing = _inFlight.GetOrAdd(hash, tcs);
+        var isOwner = ReferenceEquals(existing, tcs);
+        return new DownloadClaim(isOwner, existing.Task);
+    }
+
+    public void Complete(string hash, bool success)
+    {
+        if (string.IsNullOrWhiteSpace(hash))
+        {
+            return;
+        }
+
+        if (_inFlight.TryRemove(hash, out var tcs))
+        {
+            tcs.TrySetResult(success);
+        }
+    }
+
+    public void CompleteAll(bool success)
+    {
+        foreach (var entry in _inFlight.ToArray())
+        {
+            if (_inFlight.TryRemove(entry.Key, out var tcs))
+            {
+                tcs.TrySetResult(success);
+            }
+        }
+    }
+}