Simplify waiting for a single event.

Add method to EventEmitter that allows you to await a single event type
to be raised. No more dealing with TaskCompletionSource and setting
event handlers.

Pusher/EventEmitter.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Threading.Tasks;
 
 namespace Pusher
 {
@@ -46,5 +47,34 @@ public void TryConvertEvent(object sender, IIncomingEvent e)
 				}
 			}
 		}
+
+		/// <summary>
+		/// Wait for a single incoming event of a certain type.
+		/// </summary>
+		/// <typeparam name="TResult">The type of the value you want to extract from the event</typeparam>
+		/// <typeparam name="TEventArgs">The expected event type arguments</typeparam>
+		/// <param name="resultDelegate">A function that produces the result from the event data.</param>
+		/// <returns>The return value produced by resultDelegate</returns>
+		protected async Task<TResult> WaitForSingleEventAsync<TResult, TEventArgs>(
+			Func<object, IIncomingEvent<TEventArgs>, TResult> resultDelegate)
+		{
+			var completionSource = new TaskCompletionSource<TResult>();
+			GenericEventEmittedHandler<TEventArgs> eventHandler =
+				(sender, e) => completionSource.SetResult(resultDelegate(sender, e));
+			var eventSubscription = GetEventSubscription<TEventArgs>();
+			eventSubscription.EventEmitted += eventHandler;
+			var result = await completionSource.Task;
+			eventSubscription.EventEmitted -= eventHandler;
+			return result;
+		}
+
+		/// <summary>
+		/// Wait for a single event of a certain type.
+		/// </summary>
+		/// <returns>An empty task.</returns>
+		protected Task WaitForSingleEventAsync<TEventArgs>()
+		{
+			return WaitForSingleEventAsync<object, TEventArgs>((sender, e) => null);
+		}
 	}
 }

Pusher/Pusher.cs

@@ -77,14 +77,8 @@ public async Task ConnectAsync()
 					                      ApplicationKey)));
 			_connection.OnData += ReceivedEvent;
 			await _connection.Open();
-
-			// wait for the connection established event before returning
-			var completionSource = new TaskCompletionSource<string>();
-			GenericEventEmittedHandler<ConnectionEstablishedEventArgs> eventHandler =
-				(sender, e) => completionSource.SetResult(e.DataObject.SocketId);
-			GetEventSubscription<ConnectionEstablishedEventArgs>().EventEmitted += eventHandler;
-			await completionSource.Task;
-			GetEventSubscription<ConnectionEstablishedEventArgs>().EventEmitted -= eventHandler;
+
+			await WaitForSingleEventAsync<ConnectionEstablishedEventArgs>();
 		}
 
 		public void AddContract(IEventContract contract)
@@ -104,14 +98,8 @@ private async Task<string> GetSocketIdAsync()
 				return SocketId;
 			}
 
-			// wait for ConnectionEstablishedEvent, and use socket ID
-			var completionSource = new TaskCompletionSource<string>();
-			GenericEventEmittedHandler<ConnectionEstablishedEventArgs> eventHandler =
-				(sender, e) => completionSource.SetResult(e.DataObject.SocketId);
-			GetEventSubscription<ConnectionEstablishedEventArgs>().EventEmitted += eventHandler;
-			await completionSource.Task;
-			GetEventSubscription<ConnectionEstablishedEventArgs>().EventEmitted -= eventHandler;
-			return completionSource.Task.Result;
+			return await WaitForSingleEventAsync<string, ConnectionEstablishedEventArgs>(
+				(sender, e) => e.DataObject.SocketId);
 		}
 
 		private void ReceivedEvent(object sender, DataReceivedEventArgs dataReceivedEventArgs)