/*
 * This program source code file is part of KiCad, a free EDA CAD application.
 *
 * Copyright (C) 2013 CERN
 * @author Tomasz Wlostowski <tomasz.wlostowski@cern.ch>
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, you may find one here:
 * http://www.gnu.org/licenses/old-licenses/gpl-2.0.html
 * or you may search the http://www.gnu.org website for the version 2 license,
 * or you may write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA
 */

#ifndef __COROUTINE_H
#define __COROUTINE_H

#include <cstdlib>

#include <boost/context/fcontext.hpp>

#include "delegate.h"

/**
  Class COROUNTINE.
  Implements a coroutine. Wikipedia has a good explanation:
  
  "Coroutines are computer program components that generalize subroutines to 
  allow multiple entry points for suspending and resuming execution at certain locations. 
  Coroutines are well-suited for implementing more familiar program components such as cooperative 
  tasks, exceptions, event loop, iterators, infinite lists and pipes."

  In other words, a coroutine can be considered a lightweight thread - which can be 
  preempted only when it deliberately yields the control to the caller. This way,
  we avoid concurrency problems such as locking / race conditions.

  Uses boost::context library to do the actual context switching.

  This particular version takes a DELEGATE as an entry point, so it can invoke
  methods within a given object as separate coroutines.

  See coroutine_example.cpp for sample code.
 */

template<class ReturnType, class ArgType>
class COROUTINE
{
public:
	COROUTINE()
	{
		m_stackSize = c_defaultStackSize;
		m_stack = NULL;		
		m_saved = NULL;
	}
	
	/**
	 * Constructor
	 * Creates a coroutine from a member method of an object 
	 */
	template<class T>
	COROUTINE( T* object, ReturnType (T::*ptr)( ArgType ) ) :
		m_func( object, ptr ), m_saved( NULL ), m_stack( NULL ), m_stackSize( c_defaultStackSize )
	{
	}

	/**
	 * Constructor
	 * Creates a coroutine from a delegate object
	 */
	COROUTINE( DELEGATE<ReturnType, ArgType> aEntry ) :
            m_func( aEntry ), m_saved( NULL ), m_stack( NULL ), m_stackSize( c_defaultStackSize )
	{};

	~COROUTINE()
	{
        if( m_saved )
            delete m_saved;
        if( m_stack )
            free( m_stack );
	}

	/**
	 * Function Yield()
	 *
	 * Stops execution of the coroutine and returns control to the caller.
	 * After a yield, Call() or Resume() methods invoked by the caller will 
	 * immediately return true, indicating that we are not done yet, just asleep.
	 */
	void Yield()
	{
		jump_fcontext( m_self, m_saved, 0 );
	}

	/**
	 * Function Yield() 
	 *
	 * Yield with a value - passes a value of given type to the caller.
	 * Useful for implementing generator objects.
	 */
	void Yield( ReturnType& retVal )
	{
		m_retVal = retVal;
		jump_fcontext( m_self, m_saved, 0 );
	}

	/**
	 * Function SetEntry()
	 * 
	 * Defines the entry point for the coroutine, if not set in the constructor.
	 */
	void SetEntry( DELEGATE<ReturnType, ArgType> aEntry )
	{
		m_func = aEntry;
	}

	/* Function Call()
	 *
	 * Starts execution of a coroutine, passing args as its arguments.
	 * @return true, if the coroutine has yielded and false if it has finished its
	 * execution (returned).
	 */
	bool Call( ArgType args )
	{
		// fixme: Clean up stack stuff. Add a guard 
        m_stack = malloc( c_defaultStackSize );

        // align to 16 bytes
        void *sp = (void *) ( ( ( (ptrdiff_t) m_stack ) + m_stackSize - 0xf ) & 0xfffffff0 );

        m_args = &args;
        m_self = boost::context::make_fcontext( sp, m_stackSize, callerStub );
        m_saved = new boost::context::fcontext_t();

        m_running = true;
        // off we go!
        boost::context::jump_fcontext( m_saved, m_self, reinterpret_cast<intptr_t>( this ) );
        return m_running;
	}

	/**
	 * Function Resume()
	 * 
	 * Resumes execution of a previously yielded coroutine.
	 * @return true, if the coroutine has yielded again and false if it has finished its
	 * execution (returned).
	 */
	bool Resume()
	{
        jump_fcontext( m_saved, m_self, 0 );
        return m_running;
	}

	/**
	 * Function ReturnValue()
	 * 
	 * Returns the yielded value (the argument Yield() was called with)
	 */
	const ReturnType& ReturnValue() const
	{
		return m_retVal;
	}

	/** 
	 * Function Running()
	 *
	 * @return true, if the coroutine is active
	 */
	bool Running() const
	{
		return m_running;
	}

private:
	static const int c_defaultStackSize = 2000000;

	/* real entry point of the coroutine */
	static void callerStub( intptr_t data )
	{
		// get pointer to self 
		COROUTINE<ReturnType, ArgType>* cor = reinterpret_cast<COROUTINE<ReturnType, ArgType>*>( data );

		// call the coroutine method
		cor->m_retVal = cor->m_func( *cor->m_args );
		cor->m_running = false;		

		// go back to wherever we came from.
		boost::context::jump_fcontext( cor->m_self, cor->m_saved, 0 ); //reinterpret_cast<intptr_t>( this ));
	}

	template <typename T> struct strip_ref
	{
  		typedef T result;
	};

	template <typename T> struct strip_ref<T&>
	{
  		typedef T result;
	};

	DELEGATE<ReturnType, ArgType> m_func;
	
	///< pointer to coroutine entry arguments. Stripped of references
	///< to avoid compiler errors.
	typename strip_ref<ArgType>::result* m_args;
	ReturnType m_retVal;
	
	///< saved caller context
	boost::context::fcontext_t* m_saved;
	
	///< saved coroutine context
	boost::context::fcontext_t* m_self;

	///< coroutine stack
	void* m_stack;

	size_t m_stackSize;

	bool m_running;
};

#endif