Use DelegatingHandler for RateLimits

API/MangaDownloadClients/RateLimitHandler.cs

@@ -0,0 +1,31 @@
+using System.Net;
+using System.Threading.RateLimiting;
+using log4net;
+
+namespace API.MangaDownloadClients;
+
+public class RateLimitHandler() : DelegatingHandler(new HttpClientHandler())
+{
+    private ILog Log { get; init; } = LogManager.GetLogger(typeof(RateLimitHandler));
+
+    private readonly RateLimiter _limiter = new SlidingWindowRateLimiter(new ()
+    {
+        AutoReplenishment = true,
+        PermitLimit = 240,
+        QueueLimit = 120,
+        QueueProcessingOrder = QueueProcessingOrder.OldestFirst,
+        SegmentsPerWindow = 60,
+        Window = TimeSpan.FromSeconds(60)
+    });
+    
+    protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
+    {
+        Log.Debug($"Requesting lease {request.RequestUri}");
+        using RateLimitLease lease = await _limiter.AcquireAsync(permitCount: 1, cancellationToken);
+        Log.Debug($"lease {lease.IsAcquired} {request.RequestUri}");
+
+        return lease.IsAcquired
+            ? await base.SendAsync(request, cancellationToken)
+            : new (HttpStatusCode.TooManyRequests);
+    }
+}