New: Rebuilt Completed/Failed download handling from scratch

src/NzbDrone.Common/NzbDrone.Common.csproj

@@ -182,6 +182,7 @@
     <Compile Include="ServiceProvider.cs" />
     <Compile Include="Extensions\StringExtensions.cs" />
     <Compile Include="TinyIoC.cs" />
+    <Compile Include="TPL\Debouncer.cs" />
     <Compile Include="TPL\LimitedConcurrencyLevelTaskScheduler.cs" />
     <Compile Include="TPL\TaskExtensions.cs" />
     <Compile Include="Extensions\TryParseExtensions.cs" />

src/NzbDrone.Common/TPL/Debouncer.cs

@@ -0,0 +1,28 @@
+using System;
+
+namespace NzbDrone.Common.TPL
+{
+    public class Debouncer
+    {
+        private readonly Action _action;
+        private readonly System.Timers.Timer _timer;
+
+        public Debouncer(Action action, TimeSpan debounceDuration)
+        {
+            _action = action;
+            _timer = new System.Timers.Timer(debounceDuration.TotalMilliseconds);
+            _timer.Elapsed += timer_Elapsed;
+        }
+
+        void timer_Elapsed(object sender, System.Timers.ElapsedEventArgs e)
+        {
+            _timer.Stop();
+            _action();
+        }
+
+        public void Execute()
+        {
+            _timer.Start();
+        }
+    }
+}