using System;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;
using System.Linq;
namespace sharp.extensions
{
	public delegate void TaskDelegate();

	public class ExtendableThreadPool
	{
		Stack<ExtendableThread> availableThreads = new Stack<ExtendableThread>();
		List<ExtendableThread> activeThreads = new List<ExtendableThread>();

		Queue<TaskDelegate> queuedTasks = new Queue<TaskDelegate>();

		public static ThreadLocal<ExtendableThread> CurrentExtendedThread { get; private set; } = new ThreadLocal<ExtendableThread>();

		public int MaximumConcurrentThreads { get; set; } = -1;

		public ExtendableThreadPool()
		{
		}

		public void QueueTask(TaskDelegate task){
			lock(this)
			{
				queuedTasks.Enqueue(task);
				SignalQueue();
			}
		}

		private void SignalQueue(){
			ExtendableThread st;

			lock (this){
				if (availableThreads.Count > 0){
					st = availableThreads.Pop();
					Monitor.Enter(st);
					Monitor.Pulse(st);
					Monitor.Exit(st);
				} else {
					st = new ExtendableThread(this);
				}
			}
		}

		private TaskDelegate fetchTask(){
			lock (this){
				if (queuedTasks.Count == 0){
					return null;
				} else {
					return queuedTasks.Dequeue();
				}
			}
		}

		protected void InvokeTaskDelegate(TaskDelegate task)
		{
			try
			{
				task.Invoke();
			}
			catch (Exception e)
			{
				Console.WriteLine("InvokeTaskDelegate:t Task threw exception: {0}", e.ToString());
			}
		}

		public class ExtendableThread
		{
			Thread thread;
			bool requestExit;
			bool isReady;

			public ExtendableThreadPool Pool { get; private set; }

			public ExtendableThread(ExtendableThreadPool pool)
			{
				Pool = pool;
				thread = new Thread(worker);
				thread.Start();
			}

			public bool IsReady {
				get 
				{
					lock (this){
						return isReady;
					}
				}
			}

			public bool ExitRequested {
				get { lock(this) { return requestExit; } }
			}

			protected void InvokeTaskDelegate(TaskDelegate task)
			{
				Pool.InvokeTaskDelegate(task);
			}

			private void worker(){
				ExtendableThreadPool.CurrentExtendedThread.Value = this;

				bool taskAvailable = true;

				while (!ExitRequested){
					TaskDelegate t;

					while ((t = Pool.fetchTask()) != null)
					{
						if (t != null)
						{
							InvokeTaskDelegate(t);
						}
					}


					lock(Pool)
					{
						Pool.activeThreads.Remove(this);
						Pool.availableThreads.Push(this);
					}


					lock(this)
					{
						isReady = true;

						while (!Monitor.Wait(this, 250) && !ExitRequested) { }

						if (ExitRequested)
						{
							break;
						}
					}
					lock (Pool)
					{
						Pool.activeThreads.Add(this);
					}

				}

				lock(this){
					Monitor.Pulse(this);
					isReady = false;
				}
			}

			public void Stop()
			{
				lock (this)
				{
					requestExit = true;
				}
			}
			public void Stop(int timeoutms)
			{
				lock (this)
				{
					requestExit = true;
					Monitor.Wait(this, timeoutms);
					if (thread.IsAlive){
						thread.Abort();
					}
				}
			}

		}


	}
}