// Amplify Motion - Full-scene Motion Blur for Unity Pro
// Copyright (c) Amplify Creations, Lda <info@amplify.pt>

using System;
using System.Threading;
#if NETFX_CORE
using Windows.System.Threading;
using System.Threading.Tasks;
#endif
using System.Collections.Generic;
using UnityEngine;

namespace AmplifyMotion
{
internal class WorkerThreadPool
{
#if !NETFX_CORE && !UNITY_WEBGL
	private const int ThreadStateQueueCapacity = 1024;
	internal Queue<AmplifyMotion.MotionState>[] m_threadStateQueues = null;
	internal object[] m_threadStateQueueLocks = null;

	private int m_threadPoolSize = 0;
	private ManualResetEvent m_threadPoolTerminateSignal;
	private AutoResetEvent[] m_threadPoolContinueSignals;
	private Thread[] m_threadPool = null;
	private bool m_threadPoolFallback = false;
	internal object m_threadPoolLock = null;
	internal int m_threadPoolIndex = 0;
#endif

	internal void InitializeAsyncUpdateThreads( int threadCount, bool systemThreadPool )
	{
	#if !NETFX_CORE && !UNITY_WEBGL
		if ( systemThreadPool )
		{
			m_threadPoolFallback = true;
			return;
		}

		try
		{
			m_threadPoolSize = threadCount;
			m_threadStateQueues = new Queue<AmplifyMotion.MotionState>[ m_threadPoolSize ];
			m_threadStateQueueLocks = new object[ m_threadPoolSize ];
			m_threadPool = new Thread[ m_threadPoolSize ];

			m_threadPoolTerminateSignal = new ManualResetEvent( false );
			m_threadPoolContinueSignals = new AutoResetEvent[ m_threadPoolSize ];
			m_threadPoolLock = new object();
			m_threadPoolIndex = 0;

			for ( int id = 0; id < m_threadPoolSize; id++ )
			{
				m_threadStateQueues[ id ] = new Queue<AmplifyMotion.MotionState>( ThreadStateQueueCapacity );
				m_threadStateQueueLocks[ id ] = new object();

				m_threadPoolContinueSignals[ id ] = new AutoResetEvent( false );

				m_threadPool[ id ] = new Thread( new ParameterizedThreadStart( AsyncUpdateThread ) );
				m_threadPool[ id ].Start( new KeyValuePair<object, int>( this, id ) );
			}
		}
		catch ( Exception e )
		{
			// fallback to ThreadPool
			Debug.LogWarning( "[AmplifyMotion] Non-critical error while initializing WorkerThreads. Falling back to using System.Threading.ThreadPool().\n" + e.Message );
			m_threadPoolFallback = true;
		}
	#endif
	}

	internal void FinalizeAsyncUpdateThreads()
	{
	#if !NETFX_CORE && !UNITY_WEBGL
		if ( !m_threadPoolFallback )
		{
			m_threadPoolTerminateSignal.Set();

			for ( int i = 0; i < m_threadPoolSize; i++ )
			{
				if ( m_threadPool[ i ].IsAlive )
				{
					m_threadPoolContinueSignals[ i ].Set();
					m_threadPool[ i ].Join();
	
					// making sure these marked for disposal
					m_threadPool[ i ] = null;
				}

				lock ( m_threadStateQueueLocks[ i ] )
				{
					while ( m_threadStateQueues[ i ].Count > 0 )
						m_threadStateQueues[ i ].Dequeue().AsyncUpdate();
				}
			}

			m_threadStateQueues = null;
			m_threadStateQueueLocks = null;

			m_threadPoolSize = 0;
			m_threadPool = null;
			m_threadPoolTerminateSignal = null;
			m_threadPoolContinueSignals = null;
			m_threadPoolLock = null;
			m_threadPoolIndex = 0;
		}
	#endif
	}

	internal void EnqueueAsyncUpdate( AmplifyMotion.MotionState state )
	{
	#if NETFX_CORE
		Task.Run( () => AsyncUpdateCallback( state ) );
	#elif UNITY_WEBGL
		AsyncUpdateCallback( state );
	#else
		if ( !m_threadPoolFallback )
		{
			lock ( m_threadStateQueueLocks[ m_threadPoolIndex ] )
			{
				m_threadStateQueues[ m_threadPoolIndex ].Enqueue( state );
			}

			m_threadPoolContinueSignals[ m_threadPoolIndex ].Set();

			m_threadPoolIndex++;
			if ( m_threadPoolIndex >= m_threadPoolSize )
				m_threadPoolIndex = 0;
		}
		else
			ThreadPool.QueueUserWorkItem( new WaitCallback( AsyncUpdateCallback ), state );
	#endif
	}

	private static void AsyncUpdateCallback( object obj )
	{
		AmplifyMotion.MotionState state = ( AmplifyMotion.MotionState ) obj;
		state.AsyncUpdate();
	}

	private static void AsyncUpdateThread( object obj )
	{
	#if !NETFX_CORE && !UNITY_WEBGL
		KeyValuePair<object, int> pair = ( KeyValuePair<object, int> ) obj;
		WorkerThreadPool pool = ( WorkerThreadPool ) pair.Key;
		int id = ( int ) pair.Value;

		while ( true )
		{
			try
			{
				pool.m_threadPoolContinueSignals[ id ].WaitOne();

				if ( pool.m_threadPoolTerminateSignal.WaitOne( 0 ) )
					break;

				while ( true )
				{
					AmplifyMotion.MotionState state = null;

					lock ( pool.m_threadStateQueueLocks[ id ] )
					{
						if ( pool.m_threadStateQueues[ id ].Count > 0 )
							state = pool.m_threadStateQueues[ id ].Dequeue();
					}

					if ( state != null )
						state.AsyncUpdate();
					else
						break;
				}
			}
			catch ( System.Exception e )
			{
				if ( e.GetType() != typeof( ThreadAbortException ) )
					Debug.LogWarning( e );
			}
		}
	#endif
	}
}
}