using Sandbox.Engine;
using Sandbox.Tasks;
using System;
using System.Threading;

namespace Misc
{
	[TestClass]
	public class AsyncTasks
	{
		private TaskSource TaskSource;

		[TestInitialize]
		public void TestInitialize()
		{
			SyncContext.Init();
			SyncContext.Reset();

			TaskSource = new TaskSource( 0 );
		}

		private void Reset()
		{
			GlobalContext.Current.Reset();

			SyncContext.Reset();

			// Give tasks time to handle being cancelled

			for ( var i = 1; i <= 10; ++i )
			{
				Console.WriteLine( $"Reset + {i * 10}ms" );
				Thread.Sleep( 10 );
				SyncContext.MainThread.ProcessQueue();
			}
		}

		[TestMethod]
		public void TaskCancel1()
		{
			var task = ExampleTask1Async();

			Reset();

			Assert.IsTrue( task.IsCanceled );
		}

		private Task<string> TaskWithResultAsync()
		{
			return Task.FromResult( "Hello world!" );
		}

		private async Task ExampleTask1Async( int initialDelay = 50 )
		{
			await TaskSource.DelayRealtime( initialDelay );

			while ( true )
			{
				await TaskWithResultAsync();
				await TaskSource.DelayRealtime( 50 );
			}
		}

		[TestMethod]
		public void TaskCancel2()
		{
			Assert.AreEqual( SyncContext.MainThread, SynchronizationContext.Current );

			var tasks = Enumerable.Range( 0, 1_000 ).Select( x => ExampleTask2Async( x * 10 ) ).ToArray();

			for ( var i = 0; i < 20; ++i )
			{
				Thread.Sleep( 10 );
				SyncContext.MainThread.ProcessQueue();
			}

			Reset();

			foreach ( var task in tasks )
			{
				Assert.IsTrue( task.IsCompleted );
				Assert.IsTrue( task.IsCompletedSuccessfully );
				Assert.IsTrue( task.Result );
			}
		}

		private async Task<bool> ExampleTask2Async( int initialDelay )
		{
			while ( true )
			{
				try
				{
					await ExampleTask1Async( initialDelay );
				}
				catch ( TaskCanceledException )
				{
					Console.WriteLine( $"  Cancelled: {initialDelay}" );
					return true;
				}
			}
		}

		[TestMethod]
		public void TaskCancel3()
		{
			var task = ExampleTask3Async();

			Reset();

			Assert.IsFalse( task.IsCanceled );
		}

		private async Task ExampleTask3Async()
		{
			while ( true )
			{
				try
				{
					await Task.Yield();
					await ExampleTask1Async();
				}
				catch ( TaskCanceledException )
				{
					Console.WriteLine( "I was cancelled!" );
				}
			}
		}

		private static int _counter = 0;

		[TestMethod]
		public void TaskCancel4()
		{
			var task = ExampleTask4Async();

			Reset();

			var counterValue = _counter;

			Assert.IsFalse( task.Wait( 1000 ) );
			Assert.IsTrue( _counter <= counterValue + 1 );
		}

		private async Task ExampleTask4Async()
		{
			var src = TaskSource;

			while ( true )
			{
				try
				{
					await Task.Run( async () =>
					{
						++_counter;
						await src.DelayRealtime( 10 );
					} );
				}
				catch ( TaskCanceledException )
				{
					Console.WriteLine( "I was cancelled!" );
				}
			}
		}

		[TestMethod]
		public void SwitchThreads1()
		{
			var task = ExampleTask5Async();

			for ( var i = 0; i < 100 && !task.IsCompleted; ++i )
			{
				Thread.Sleep( 10 );
				SyncContext.MainThread.ProcessQueue();
			}

			if ( task.Exception != null )
			{
				throw task.Exception;
			}

			Assert.IsTrue( task.IsCompletedSuccessfully );
		}

		private async Task ExampleTask5Async()
		{
			Console.WriteLine( $"Hello from {(ThreadSafe.IsMainThread ? "the main thread" : "a worker thread")}!" );
			ThreadSafe.AssertIsMainThread();

			await GameTask.WorkerThread();

			Console.WriteLine( $"Hello from {(ThreadSafe.IsMainThread ? "the main thread" : "a worker thread")}!" );
			ThreadSafe.AssertIsNotMainThread();

			await GameTask.MainThread();

			Console.WriteLine( $"Hello from {(ThreadSafe.IsMainThread ? "the main thread" : "a worker thread")}!" );
			ThreadSafe.AssertIsMainThread();
		}
	}
}