renamed Cache to Cached, and refactored many events to use Cached

src/Discord.Net.Core/Utils/Cache.cs

@@ -1,23 +0,0 @@
-using System;
-using System.Reflection;
-using System.Threading.Tasks;
-using TId = Discord.IEntity<ulong>;
-
-
-namespace Discord
-{
-    public abstract class Cache<T> where T : IEntity<ulong> 
-    {
-        public bool IsCached => Value != null;
-        public TId Id { get; }
-        public T Value { get; }
-
-        protected Cache(TId id)
-        {
-            Id = id;
-        }
-
-        public async Task<T> DownloadAsync() => typeof(T).GetRuntimeMethod("DownloadAsync",{ulong id});
-        public async Task<T> GetOrDownloadAsync() => IsCached ? Value : await DownloadAsync();
-    }
-}

src/Discord.Net.Core/Utils/Cached.cs

@@ -0,0 +1,33 @@
+using Discord.WebSocket;
+using System;
+using System.Collections.Generic;
+using System.Threading.Tasks;
+
+namespace Discord
+{
+    public struct Cached<T> where T : IMessage
+    {
+        public bool IsCached => !EqualityComparer<T>.Default.Equals(Value, default(T));
+        public bool IsDownloadable { get; }
+        public ulong Id { get; }
+        public T Value { get; }
+        public ISocketMessageChannel Channel { get; }
+
+        public Cached(ulong id, T value, ISocketMessageChannel channel, bool isDownloadable = true)
+        {
+            Id = id;
+            Value = value;
+            Channel = channel;
+            IsDownloadable = isDownloadable;
+        }
+
+        public async Task<T> DownloadAsync()
+        {
+            if (IsDownloadable)
+                return (T) await Channel.GetMessageAsync(Id);
+            throw new InvalidOperationException("This message cannot be downloaded.");
+        }
+
+        public async Task<T> GetOrDownloadAsync() => IsCached ? Value : await DownloadAsync();
+    }
+}