using System;
using System.Threading;
using System.Collections.Concurrent;

namespace BizHawk.Client.EmuHawk
{
	public class RewindThreader : IDisposable
	{
		// adelikat: tweak this to test performance with threading or not with threading
		// natt: IEmulator.SaveStateBinary() returns a byte[] but you're not allowed to modify it,
		// and if the method is called again, the data from a previous call could be invalidated.
		// GPGX and N64 make use of this property.  if you set IsThreaded = true, you'll need to Clone() in many cases,
		// which will kill N64 for sure...
		public static bool IsThreaded = false;

		private readonly ConcurrentQueue<Job> Jobs = new ConcurrentQueue<Job>();
		private EventWaitHandle _ewh, _ewh2;
		private Thread _thread;

		// TODO: this is bad design!
		private Rewinder _rewinder;

		public RewindThreader(Rewinder rewinder, bool isThreaded)
		{
			IsThreaded = isThreaded;
			_rewinder = rewinder;

			if (IsThreaded)
			{
				_ewh = new EventWaitHandle(false, EventResetMode.AutoReset);
				_ewh2 = new EventWaitHandle(false, EventResetMode.AutoReset);
				_thread = new Thread(ThreadProc);
				_thread.IsBackground = true;
				_thread.Start();
			}
		}

		public void Dispose()
		{
			if (!IsThreaded)
			{
				return;
			}

			var job = new Job();
			job.Type = JobType.Abort;
			Jobs.Enqueue(job);
			_ewh.Set();

			_thread.Join();
			_ewh.Dispose();
			_ewh2.Dispose();
		}

		void ThreadProc()
		{
			for (; ; )
			{
				_ewh.WaitOne();
				while (Jobs.Count != 0)
				{
					Job job = null;
					if (Jobs.TryDequeue(out job))
					{
						if (job.Type == JobType.Abort)
						{
							return;
						}

						if (job.Type == JobType.Capture)
						{
							_rewinder.RunCapture(job.CoreState);
						}

						if (job.Type == JobType.Rewind)
						{
							_rewinder._RunRewind(job.Frames);
							_ewh2.Set();
						}
					}
				}
			}
		}

		public void Rewind(int frames)
		{
			if (!IsThreaded)
			{
				_rewinder._RunRewind(frames);
				return;
			}

			var job = new Job();
			job.Type = JobType.Rewind;
			job.Frames = frames;
			Jobs.Enqueue(job);
			_ewh.Set();
			_ewh2.WaitOne();
		}

		void DoSafeEnqueue(Job job)
		{
			Jobs.Enqueue(job);
			_ewh.Set();

			//just in case... we're getting really behind.. slow it down here
			//if this gets backed up too much, then the rewind will seem to malfunction since it requires all the captures in the queue to complete first
			while (Jobs.Count > 15)
			{
				Thread.Sleep(0);
			}
		}

		public void Capture(byte[] coreSavestate)
		{
			if (!IsThreaded)
			{
				_rewinder.RunCapture(coreSavestate);
				return;
			}

			var job = new Job();
			job.Type = JobType.Capture;
			job.CoreState = coreSavestate;
			DoSafeEnqueue(job);
		}

		private enum JobType
		{
			Capture, Rewind, Abort
		}

		private class Job
		{
			public JobType Type;
			public byte[] CoreState;
			public int Frames;
		}
	}
}