Windows Services Made Simple

using System;
using System.Collections.Generic;
using System.Threading;

using Pegasus.Diagnostics;
using Pegasus.Threading;

namespace Pegasus.Workflow.Service.DefaultServices
{
	/// <summary>
	/// Implements the message service using the Pegasus AppThreadPool class.  
	/// Each message is dispatched to a worker thread.
	/// </summary>
	public class ThreadedMessageService : WorkflowMessageService, IDispatchTimerTask
	{
		// Local Instance Values
		private Dictionary<int, TimerTask> m_taskTable = new Dictionary<int, TimerTask>();
		private AppThreadPool m_threadPool;

		/// <summary>
		/// Initializes a new instance of the <see cref="T:ThreadedMessageService"/> class.
		/// </summary>
		public ThreadedMessageService()
		{
			m_threadPool = new AppThreadPool();
			m_threadPool.UnhandledException += new AppThreadPool.UnhandledExceptionHandler( ThreadPool_UnhandledException );
		}

		/// <summary>
		/// Gets the underlying thread pool.
		/// </summary>
		/// <value>The thread pool.</value>
		public AppThreadPool ThreadPool
		{
			get
			{
				return m_threadPool;
			}
		}

		/// <summary>
		/// Starts this instance of the service.
		/// </summary>
		/// <param name="workflowService"></param>
		public override void Start( WorkflowService workflowService )
		{
			base.Start( workflowService );
		}

		/// <summary>
		/// Stops this instance of the service.
		/// </summary>
		public override void Stop()
		{
			base.Stop();

			// Stop all pending tasks
			foreach( TimerTask task in m_taskTable.Values )
			{
				AppScheduler2.AppScheduler.UnscheduleTask( task );
			}
			
			m_taskTable.Clear();
			m_threadPool.JoinWorkers();
		}

		/// <summary>
		/// Dispatches the timer event that was fired from the timer task.
		/// </summary>
		/// <param name="task">The task.</param>
		/// <param name="parameters">The parameters.</param>
		void IDispatchTimerTask.DispatchTimerTask( TimerTask task, WorkflowEventParameters parameters )
		{
			// Check Parameters
			ParamCode.AssertNotNull( task, "task" );
			ParamCode.AssertNotNull( parameters, "parameters" );

			// Remove the task from our table.
			lock( m_taskTable )
			{
				m_taskTable.Remove( task.GetHashCode() );
			}

			// Queue the message to be executed
			m_threadPool.QueueUserWorkItem( new WaitCallback( ThreadWorkflowEventMessage ), parameters );
		}

		/// <summary>
		/// Processes the workflow start message.
		/// </summary>
		/// <param name="workflowId">The workflow id.</param>
		/// <returns>
		/// True if the message was process, False if the message should be recycled and processed later.
		/// </returns>
		protected override bool ProcessWorkflowStartMessage( int workflowId )
		{
			// Check Parameters
			ParamCode.AssertRange( workflowId, 1, int.MaxValue, "workflowId" );

			m_threadPool.QueueUserWorkItem( new WaitCallback( ThreadStartMessage ), workflowId );
			return true;
		}

		/// <summary>
		/// Processes the workflow start message.
		/// </summary>
		/// <param name="workflowId">The workflow id.</param>
		/// <param name="startState">The start state.</param>
		/// <returns>
		/// True if the message was process, False if the message should be recycled and processed later.
		/// </returns>
		protected override bool ProcessWorkflowRestartMessage( int workflowId, string startState )
		{
			// Check Parameters
			ParamCode.AssertRange( workflowId, 1, int.MaxValue, "workflowId" );
			ParamCode.AssertNotEmpty( startState, "startState" );

			RestartParameters parameters = new RestartParameters();
			parameters.WorkflowId = workflowId;
			parameters.StartState = startState;

			m_threadPool.QueueUserWorkItem( new WaitCallback( ThreadRestartMessage ), parameters );
			return true;
		}

		/// <summary>
		/// Processes the data exchange message.
		/// </summary>
		/// <param name="message">The message.</param>
		/// <returns>
		/// True if the message was process, False if the message should be recycled and processed later.
		/// </returns>
		protected override bool ProcessDataExchangeMessage( DataExchangeMessage message )
		{
			// Check Parameters
			ParamCode.AssertNotNull( message, "message" );

			m_threadPool.QueueUserWorkItem( new WaitCallback( ThreadDataExchangeMessage ), message );
			return true;
		}

		/// <summary>
		/// Processes the workflow event message.
		/// </summary>
		/// <param name="message">The message.</param>
		/// <param name="sender">The sender.</param>
		/// <param name="args">The <see cref="T:Pegasus.Workflow.Service2.WorkflowEventArgs"/> instance containing the event data.</param>
		/// <returns>
		/// True if the message was process, False if the message should be recycled and processed later.
		/// </returns>
		protected override bool ProcessWorkflowEventMessage( WorkflowMessageService.WorkflowEventMessage message, object sender, WorkflowEventArgs args )
		{
			// Check Parameters
			ParamCode.AssertNotNull( message, "message" );
			// sender can be null
			ParamCode.AssertNotNull( args, "args" );

			WorkflowEventParameters parameters = new WorkflowEventParameters();
			parameters.Message = message;
			parameters.Sender = sender;
			parameters.Args = args;

			m_threadPool.QueueUserWorkItem( new WaitCallback( ThreadWorkflowEventMessage ), parameters );
			return true;
		}

		/// <summary>
		/// Processes the register workflow event message.
		/// </summary>
		/// <param name="time">The time.</param>
		/// <param name="message">The message.</param>
		/// <param name="sender">The sender.</param>
		/// <param name="args">The <see cref="T:Pegasus.Workflow.Service2.WorkflowEventArgs"/> instance containing the event data.</param>
		/// <returns></returns>
		protected override int ProcessRegisterWorkflowEventMessage( DateTime time, WorkflowEventMessage message, object sender, WorkflowEventArgs args )
		{
			// Check Parameters 
			// time can be any valid date time
			ParamCode.AssertNotNull( message, "message" );
			// sender can be null
			ParamCode.AssertNotNull( args, "args" );
			
			WorkflowEventParameters parameters = new WorkflowEventParameters();
			parameters.Message = message;
			parameters.Sender = sender;
			parameters.Args = args;

			TimerTask task = new TimerTask( this, time, parameters );
			int messageId = task.GetHashCode();

			m_taskTable.Add( messageId, task );
			AppScheduler2.AppScheduler.ScheduleTask( task );

			return messageId;
		}

		/// <summary>
		/// Processes the unregister workflow event message.
		/// </summary>
		/// <param name="messageId">The message id.</param>
		protected override void ProcessReleaseWorkflowEventMessage( int messageId )
		{
			// Check Parameters
			// messageId is any value int

			if( m_taskTable.ContainsKey( messageId ) )
			{
				TimerTask task = m_taskTable[ messageId ];
				m_taskTable.Remove( messageId );

				AppScheduler2.AppScheduler.UnscheduleTask( task );
			}
		}

		/// <summary>
		/// Process unhandled exception from the thread pool.
		/// </summary>
		/// <param name="callback">The callback.</param>
		/// <param name="state">The state.</param>
		/// <param name="e">The e.</param>
		private void ThreadPool_UnhandledException( WaitCallback callback, object state, Exception e )
		{
			// Check Parameters
			// callback could be null
			// state could be null
			ParamCode.AssertNotNull( e, "e" );

			WorkflowService.FireUnhandledException( this, e );
		}

		/// <summary>
		/// ThreadProc to process the workflow start message.
		/// </summary>
		/// <param name="parameter">The parameter.</param>
		private void ThreadStartMessage( object parameter )
		{
			// Check Parameters
			ParamCode.AssertNotNull( parameter, "parameter" );
			ParamCode.Assert( parameter is int, "parameter", "Parameter is wrong type, expected WorkflowId (int), received {0}", parameter.GetType() );

			DispatchWorkflowStartMessage( (int) parameter );
		}

		/// <summary>
		/// ThreadProc to process the workflow restart message.
		/// </summary>
		/// <param name="parameter">The parameter.</param>
		private void ThreadRestartMessage( object parameter )
		{
			// Check Parameters
			ParamCode.AssertNotNull( parameter, "parameter" );
			ParamCode.Assert( parameter is RestartParameters, "parameter", "Parameter is wrong type, expected RestartParameters, received {0}", parameter.GetType() );

			RestartParameters restartParams = (RestartParameters) parameter;

			DispatchWorkflowRestartMessage( restartParams.WorkflowId, restartParams.StartState );
		}

		/// <summary>
		/// Threads the data exchange message.
		/// </summary>
		/// <param name="parameter">The parameter.</param>
		private void ThreadDataExchangeMessage( object parameter )
		{
			// Check Parameters
			ParamCode.AssertNotNull( parameter, "parameter" );
			ParamCode.Assert( parameter is WorkflowMessageService.DataExchangeMessage, "parameter", "Parameter is wrong type, expected WorkflowMessageService.DataExchangeMessage, received {0}", parameter.GetType() );

			DispatchDataExchangeMessage( (WorkflowMessageService.DataExchangeMessage) parameter );
		}

		/// <summary>
		/// Threads the workflow event message.
		/// </summary>
		/// <param name="parameter">The parameter.</param>
		private void ThreadWorkflowEventMessage( object parameter )
		{
			// Check Parameters
			ParamCode.AssertNotNull( parameter, "parameter" );
			ParamCode.Assert( parameter is WorkflowEventParameters, "parameter", "Parameter is wrong type, expected WorkflowEventParameters, received {0}", parameter.GetType() );

			WorkflowEventParameters parameters = (WorkflowEventParameters) parameter;

			DispatchWorkflowEventMessage( parameters.Message, parameters.Sender, parameters.Args );
		}
	}
}