Initial upload

api/server/RateLimit.cs

@@ -0,0 +1,40 @@
+using System.Collections.Concurrent;
+
+public static class RateLimit
+{
+    private static readonly ConcurrentDictionary<string, DateTime> _requests = new();
+
+    public static bool TryConsume(
+        string key,
+        int cooldownSeconds,
+        out int retryAfterSeconds)
+    {
+        retryAfterSeconds = 0;
+        var now = DateTime.UtcNow;
+
+        var last = _requests.GetOrAdd(key, _ => DateTime.MinValue);
+        var elapsed = (now - last).TotalSeconds;
+
+        if (elapsed < cooldownSeconds)
+        {
+            retryAfterSeconds = (int)Math.Ceiling(cooldownSeconds - elapsed);
+            return false;
+        }
+
+        _requests[key] = now;
+
+        Cleanup(now);
+        return true;
+    }
+
+    private static void Cleanup(DateTime now)
+    {
+        if (_requests.Count < 10_000) return;
+
+        foreach (var kv in _requests)
+        {
+            if ((now - kv.Value).TotalMinutes > 10)
+                _requests.TryRemove(kv.Key, out _);
+        }
+    }
+}