using System;
using System.Threading;

namespace Spider
{
	/// <summary>
	/// This is a very simple object that
	/// allows the spider to determine when
	/// it is done. This object implements
	/// a simple lock that the spider class
	/// can wait on to determine completion.
	/// Done is defined as the spider having
	/// no more work to complete.
	/// 
	/// This spider is copyright 2003 by Jeff Heaton. However, it is
	/// released under a Limited GNU Public License (LGPL). You may 
	/// use it freely in your own programs. For the latest version visit
	/// http://www.jeffheaton.com.
	///
	/// </summary>
	public class Done 
	{

		/// <summary>
		/// The number of SpiderWorker object
		/// threads that are currently working
		/// on something.
		/// </summary>
		private int m_activeThreads = 0;

		/// <summary>
		/// This boolean keeps track of if
		/// the very first thread has started
		/// or not. This prevents this object
		/// from falsely reporting that the spider
		/// is done, just because the first thread
		/// has not yet started.
		/// </summary>
		private bool m_started = false;


		
		/// <summary>
		/// This method can be called to block
		/// the current thread until the spider
		/// is done.
		/// </summary>
		public void WaitDone()
		{
			Monitor.Enter(this);
			while ( m_activeThreads>0 ) 
			{
				Monitor.Wait(this);
			}
			Monitor.Exit(this);
		}

		/// <summary>
		/// Called to wait for the first thread to
		/// start. Once this method returns the
		/// spidering process has begun.
		/// </summary>
		public void WaitBegin()
		{
			Monitor.Enter(this);
			while ( !m_started ) 
			{
				Monitor.Wait(this);
			}
			Monitor.Exit(this);
		}


		/// <summary>
		/// Called by a SpiderWorker object
		/// to indicate that it has begun
		/// working on a workload.
		/// </summary>
		public void WorkerBegin()
		{
			Monitor.Enter(this);
			m_activeThreads++;
			m_started = true;
			Monitor.Pulse(this);
			Monitor.Exit(this);
		}

		/// <summary>
		/// Called by a SpiderWorker object to
		/// indicate that it has completed a
		/// workload.
		/// </summary>
		public void WorkerEnd()
		{
			Monitor.Enter(this);
			m_activeThreads--;
			Monitor.Pulse(this);
			Monitor.Exit(this);
		}

		/// <summary>
		/// Called to reset this object to
		/// its initial state.
		/// </summary>
		public void Reset()
		{
			Monitor.Enter(this);
			m_activeThreads = 0;
			Monitor.Exit(this);
		}
	}
}