/* Copyright notice for this file:
 * Copyright (C) 2018
 *
 * 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, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 *
 * This mapper was added by retrowertz for Libretro port of QuickNES.
 * 3/24/18
 *
 * VRC-3 Konami, Salamander
 */

#include "Nes_Mapper.h"

struct vrc3_state_t
{
	bool     irq_enable;
	bool     irq_awk;
	uint16_t irq_latch;
	uint16_t irq_counter;

	uint8_t  irq_pending;
	uint16_t next_time;
};

class Mapper_VRC3 : public Nes_Mapper, vrc3_state_t {
public:
	Mapper_VRC3()
	{
		vrc3_state_t * state = this;
		register_state( state, sizeof * state );
	}

	void reset_state()
	{
	}

	void apply_mapping()
	{
		enable_sram();
		mirror_vert();
	}

	virtual void run_until( nes_time_t end_time )
	{
		if ( irq_enable )
		{
			long counter = irq_counter + ( end_time - next_time );

			if ( counter > 0xFFFF )
			{
				irq_pending = true;
				irq_enable  = irq_awk;
				irq_counter = irq_latch;
			}
			else
				irq_counter = counter;
		}

		next_time = end_time;
	}

	virtual void end_frame( nes_time_t end_time )
	{
		if ( end_time > next_time )
			run_until( end_time );

		next_time -= end_time;
	}

	virtual nes_time_t next_irq( nes_time_t present )
	{
		if ( irq_pending )
			return present;

		if ( !irq_enable )
			return no_irq;

		return 0x10000 - irq_counter + next_time;
	}

	void write_irq_counter( int shift, int data )
	{
		irq_latch &= ~( 0xF << shift );
		irq_latch |= data << shift;
	}

	void write( nes_time_t time, nes_addr_t addr, int data )
	{
		data &= 0xF;

		switch ( addr >> 12 )
		{
			case 0xF: set_prg_bank( 0x8000, bank_16k, data ); break;
			case 0x8: write_irq_counter(  0, data ); break;
			case 0x9: write_irq_counter(  4, data ); break;
			case 0xA: write_irq_counter(  8, data ); break;
			case 0xB: write_irq_counter( 12, data ); break;
			case 0xC:
				irq_pending = false;
				irq_awk     = data & 1;
				irq_enable  = data & 2;

				if ( irq_enable )
					irq_counter = irq_latch;

				break;
			case 0xD:
				irq_pending = false;
				irq_enable  = irq_awk;
				break;
		}

		irq_changed();
	}
};

void register_vrc3_mapper();
void register_vrc3_mapper()
{
	register_mapper< Mapper_VRC3> ( 73 );
}
