using System;
using System.Diagnostics;
using System.Threading;
using System.Threading.Tasks;
using AMWD.Common.Utilities;
using Microsoft.VisualStudio.TestTools.UnitTesting;

namespace AMWD.Common.Tests.Utilities
{
	[TestClass]
	[System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverage]
	public class DelayedTaskWithResultTests
	{
		[TestMethod]
		public void ShouldCreateNewDelayedTaskNotStarting()
		{
			// arrange
			int executionCount = 0;
			var delay = TimeSpan.FromMilliseconds(100);
			var function = () => { executionCount++; return new[] { 42, 21 }; };

			// act
			var cts = new CancellationTokenSource(delay.Add(TimeSpan.FromSeconds(1)));
			var delayedTaskWithResult = DelayedTask.Create(function, delay);
			SpinWait.SpinUntil(() => executionCount > 0 || cts.IsCancellationRequested);

			// assert
			Assert.IsNotNull(delayedTaskWithResult);
			Assert.AreEqual(delay, delayedTaskWithResult.Delay);
			Assert.IsFalse(delayedTaskWithResult.IsRunning);
			Assert.IsFalse(delayedTaskWithResult.IsWaitingToRun);
			Assert.IsNull(delayedTaskWithResult.Exception);
			Assert.AreEqual(0, executionCount);
		}

		[TestMethod]
		public async Task ShouldCreateNewDelayedTaskStarting()
		{
			// arrange
			int executionCount = 0;
			var delay = TimeSpan.FromMilliseconds(100);
			var function = () => { executionCount++; return new[] { 42, 21 }; };

			// act
			var delayedTaskWithResult = DelayedTask.Run(function, delay);
			int[] result = await delayedTaskWithResult;

			// assert
			Assert.IsNotNull(delayedTaskWithResult);
			Assert.AreEqual(delay, delayedTaskWithResult.Delay);
			Assert.IsFalse(delayedTaskWithResult.IsRunning);
			Assert.IsFalse(delayedTaskWithResult.IsWaitingToRun);
			Assert.IsNull(delayedTaskWithResult.Exception);
			Assert.AreEqual(1, executionCount);
			CollectionAssert.AreEqual(new[] { 42, 21 }, result);
		}

		[TestMethod]
		public void ShouldHaveAnExceptionSet()
		{
			// arrange
			var delay = TimeSpan.FromMilliseconds(100);
#pragma warning disable CS0162 // Unreachable Code detected.
			var function = () => { throw new Exception("TEST :D"); return new[] { 42, 21 }; };
#pragma warning restore CS0162 // Unreachable Code detected

			// act
			var delayedTaskWithResult = DelayedTask.Run(function, delay);

			var awaiter = delayedTaskWithResult.GetAwaiter();
			SpinWait.SpinUntil(() => awaiter.IsCompleted);

			// assert
			Assert.IsNotNull(delayedTaskWithResult);
			Assert.IsFalse(delayedTaskWithResult.IsRunning);
			Assert.IsFalse(delayedTaskWithResult.IsWaitingToRun);
			Assert.IsNotNull(delayedTaskWithResult.Exception);
		}

		[TestMethod]
		public void ShouldUseExceptionHandler()
		{
			// arrange
			string exceptionText = null;
			var delay = TimeSpan.FromMilliseconds(100);
#pragma warning disable CS0162 // Unreachable Code detected.
			var function = () => { throw new Exception("TEST :D"); return new[] { 42, 21 }; };
#pragma warning restore CS0162 // Unreachable Code detected
			var exceptionHandler = (Exception ex) =>
			{
				exceptionText = ex.Message;
			};

			// act
			var delayedTaskWithResult = DelayedTask.Run(function, delay)
				.WithExceptionHandler(exceptionHandler);

			var awaiter = delayedTaskWithResult.GetAwaiter();
			SpinWait.SpinUntil(() => awaiter.IsCompleted);

			// assert
			Assert.IsNotNull(delayedTaskWithResult);
			Assert.IsFalse(delayedTaskWithResult.IsRunning);
			Assert.IsFalse(delayedTaskWithResult.IsWaitingToRun);
			Assert.IsNotNull(delayedTaskWithResult.Exception);
			Assert.AreEqual("TEST :D", exceptionText);
		}

		[TestMethod]
		public async Task ShouldReturnNormalTask()
		{
			// arrange
			int executionCount = 0;
			var delay = TimeSpan.FromMilliseconds(100);
			var function = () => { executionCount++; return new[] { 42, 21 }; };
			var delayedTaskWithResult = DelayedTask.Create(function, delay);

			// act
			delayedTaskWithResult.Reset();
			var task = delayedTaskWithResult.Task;
			int[] result = await task;

			// assert
			Assert.IsNotNull(delayedTaskWithResult);
			Assert.IsNotNull(task);
			Assert.IsInstanceOfType(task, typeof(Task));
			Assert.IsFalse(delayedTaskWithResult.IsRunning);
			Assert.IsFalse(delayedTaskWithResult.IsWaitingToRun);
			Assert.AreEqual(1, executionCount);
			Assert.AreEqual(TaskStatus.RanToCompletion, task.Status);
			CollectionAssert.AreEqual(new int[] { 42, 21 }, result);
		}
	}
}