/*
 *  libstdgb - library of useful Game Boy operations
 *  Copyright (C) 2016-2017 Delwink, LLC
 *
 *  This program is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU Affero General Public License as published by
 *  the Free Software Foundation, version 3 only.
 *
 *  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 Affero General Public License for more details.
 *
 *  You should have received a copy of the GNU Affero General Public License
 *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include "stdgb.h"

uint8_t (* const GB_OBJECTS)[GB_BYTES_PER_OBJ] = (void *) 0xDF00;
static uint8_t * const DPAD_STATE = (void *) 0xDFA0;
static uint8_t * const BTN_STATE = (void *) 0xDFA1;

void
gb_mbc5_select_rombank(uint16_t bank)
{
	uint8_t upper = (bank & 0xFF00) >> 8;
	uint8_t lower = bank & 0x00FF;

	*((uint8_t *) 0x3000) = upper;
	*((uint8_t *) 0x2000) = lower;
}

static void
invert_state(uint8_t *state)
{
	*state = (~(*state)) & 0x0F;
}

void
gb_update_input_state()
{
	// this routine is copied from the official Nintendo programming manual
	__asm__("ld a, #0x20\n\t"     // load flag to read d-pad input
		"ld (#0xFF00), a\n\t" // make input request
		"ld a, (#0xFF00)\n\t" // read input ports
		"ld a, (#0xFF00)\n\t" // do this twice for necessary delay
		"ld (#0xDFA0), a\n\t" // save it in *DPAD_STATE

		"ld a, #0x10\n\t"     // load flag to read button input
		"ld (#0xFF00), a\n\t" // make input request
		"ld a, (#0xFF00)\n\t" // read input ports
		"ld a, (#0xFF00)\n\t" // do this six times for necessary delay
		"ld a, (#0xFF00)\n\t"
		"ld a, (#0xFF00)\n\t"
		"ld a, (#0xFF00)\n\t"
		"ld a, (#0xFF00)\n\t"
		"ld (#0xDFA1), a\n\t" // save it in *BTN_STATE

		"ld a, #0x30\n\t"     // load flag to read nothing
		"ld (#0xFF00), a");   // disable input reads

	invert_state(DPAD_STATE);
	invert_state(BTN_STATE);
}

uint8_t
gb_dpad_down(uint8_t direction)
{
	return *DPAD_STATE & direction;
}

uint8_t
gb_button_down(uint8_t button)
{
	return *BTN_STATE & button;
}

void
gb_enable_vblank()
{
	*GB_INT_ENABLE |= GB_INT_VBLANK;
	gb_enable_interrupts();
}

void
gb_wait_vblank()
{
	do
	{
		gb_halt();
	} while (!gb_have_vblank());
}

void
gb_define_tile(uint8_t start, const uint8_t *data)
{
	uint8_t *tiles = GB_TILE_DATA;
	gb_memcpy(&tiles[start * GB_BYTES_PER_TILE], data, GB_BYTES_PER_TILE);
}

void
gb_set_view(uint8_t x, uint8_t y)
{
	*GB_SCROLL_X = x;
	*GB_SCROLL_Y = y;
}

void
gb_shift_view(int8_t x, int8_t y)
{
	*GB_SCROLL_X += x;
	*GB_SCROLL_Y += y;
}

static void
copy_objects()
{
	__asm__("ld a,#0xDF\n\t"        // specify that objects are at 0xDF00
		"ld (0xFF46),a\n\t"     // start DMA copy
		"ld a,#0x28\n"          // set wait counter to 40
		"obj_copy_wait:\n\t"
		"dec a\n\t"             // decrement counter
		"jr nz,obj_copy_wait"); // wait until counter is zero
}

void
gb_init_objects()
{
	gb_memcpy(GB_HRAM, (uint8_t *) copy_objects, 12);
	memset(GB_OBJECTS, 0, GB_NUM_OBJECTS * GB_BYTES_PER_OBJ);
	gb_update_objects();
}

void
gb_update_objects()
{
	__asm__("jp 0xFF80"); // real function is at HRAM
}

void
gb_memcpy(uint8_t *dest, const uint8_t *src, uint8_t n)
{
	while (n--)
		*(dest++) = *(src++);
}