#include <stdio.h>
#include <gb.h>
#include <r_io.h>

static ut64 __lseek(RIO* io, RIODesc *desc, ut64 offset, int whence) {
	GBTimers *timers = (GBTimers *)desc->data;
	switch (whence) {
	case R_IO_SEEK_SET:
		return timers->seek = R_MIN (4, offset);
	case R_IO_SEEK_CUR:
		return timers->seek = R_MIN (4, timers->seek + offset);
	case R_IO_SEEK_END:
		return timers->seek = 4;
	}
	return timers->seek;
}

static int __read(RIO *io, RIODesc *desc, ut8 *buf, int len) {
	GBTimers *timers = (GBTimers *)desc->data;
	if (timers->seek > 3 || len < 1) {
		return 0;
	}
	len = R_MIN (len, 4 - timers->seek);
	memcpy (buf, &timers->buf[timers->seek], len);
	timers->seek += len;
	return len;
}

static bool __check(RIO *io, const char *pathname, bool many) {
	return r_str_startswith (pathname, "gb_timers://");
}

static RIODesc *__open(RIO *io, const char *pathname, int rw, int mode) {
	if (!r_str_startswith (pathname, "gb_timers://")) {
		return NULL;
	}
	GBTimers *timers = NULL;
	sscanf (pathname, "gb_timers://%p", &timers);
	RIODesc *desc = r_io_desc_new (io, &r_io_plugin_gb_timers, pathname,
		R_PERM_RWX, mode, timers);
	return desc;
}

static bool __close(RIODesc *desc) {
	return true;
}

static int __write(RIO *io, RIODesc *desc, const ut8 *buf, int len) {
	GBTimers *timers = (GBTimers *)desc->data;
	if (timers->seek == 4) {
		return 0;
	}
	int wlen = R_MIN (len, 4 - timers->seek);
	ut64 endseek = timers->seek + wlen;
	ut32 i;
	for (i = 0; timers->seek < endseek; timers->seek++) {
		switch (timers->seek) {
		case GB_TIMERS_DIV:
			timers->buf[GB_TIMERS_DIV] = 0;
			timers->div = 0;
			break;
		case GB_TIMERS_TIMA:
			timers->buf[GB_TIMERS_TIMA] = buf[i];
#if 0
			if (timers->tima_wait > 1) {
				timers->tima_wait = 0;
			}
#else
			timers->tima_wait = 0;
#endif
			break;
		case GB_TIMERS_TMA:
			timers->otma = timers->buf[GB_TIMERS_TMA];
			timers->buf[GB_TIMERS_TMA] = buf[i];
			break;
		case GB_TIMERS_TAC:
			timers->check_fedge = !!(timers->buf[GB_TIMERS_TAC] & 0x4);
			timers->buf[GB_TIMERS_TAC] = buf[i];
			if (!!(buf[i] & 0x4)) {
				timers->check_fedge = false;;
			}
			break;
		}
		i++;
	}
	return wlen;
}

RIOPlugin r_io_plugin_gb_timers = {
	.meta = {
		.name = "gb_timers",
		.desc = "gb_timers",
		.license = "LGPL",
	},
	.uris = "gb_timers://",
	.open = __open,
	.close = __close,
	.read = __read,
	.check = __check,
	.seek = __lseek,
	.write = __write,
};

bool gb_timers_init (GBTimers *timers, RIO *io) {
	if (!timers || !io) {
		return false;
	}
	timers[0] = (const GBTimers){0};
	char uri[64];
	memset (uri, 0x00, sizeof (char) * 64);
	sprintf (uri, "gb_timers://%p", timers);
	RIODesc *desc = r_io_desc_open_plugin (io, &r_io_plugin_gb_timers,
		uri, R_PERM_RWX, 0);
	if (!desc) {
		return false;
	}
	if (!r_io_map_add (io, desc->fd, R_PERM_RWX, 0, 0xff04, 4)) {
		r_io_desc_close (desc);
		return false;
	}
	timers->fd = desc->fd;
	return true;
}

void gb_timers_fini (GBTimers *timers, RIO *io) {
	if (!timers || !io) {
		return;
	}
	r_io_fd_close (io, timers->fd);
}

void gb_timers_continue (GB *gb, ut32 cycles) {
	GBTimers *timers = &gb->timers;
	bool request_interrupt = false;
	do {
		//ensure all falling edges are detected
		ut32 _cycles = R_MIN (((~timers->div) & 0x7) + 1, cycles);
		timers->odiv = timers->div;
		timers->div += _cycles;
		timers->buf[GB_TIMERS_DIV] = (timers->div >> 8) & 0xff;

		if (timers->tima_wait) {
			timers->tima_wait -= _cycles;
			if (timers->tima_wait <= 0) {
				timers->tima_wait = 0;
				timers->buf[GB_TIMERS_TIMA] = timers->otma;
				request_interrupt = true;
			}
		}
		if ((timers->buf[GB_TIMERS_TAC] & 0x4) || timers->check_fedge) {
			timers->otma = timers->buf[GB_TIMERS_TMA];
			ut32 mask;
			switch (timers->buf[GB_TIMERS_TAC] & 0x3) {
			case 0:
				mask = 0x1 << 9;
				break;
			case 1:
				mask = 0x1 << 3;
				break;
			case 2:
				mask = 0x1 << 5;
				break;
			case 3:
				mask = 0x1 << 7;
				break;
			}
			if (((timers->odiv & mask) && !(timers->div & mask)) ||
				((timers->odiv & mask) && (timers->div & mask) && timers->check_fedge)) {
				if (timers->buf[GB_TIMERS_TIMA] == 0xff) {
					timers->tima_wait = 4;
					timers->buf[GB_TIMERS_TIMA] = 0x00;
				} else {
					timers->buf[GB_TIMERS_TIMA]++;
				}
			}
			timers->check_fedge = false;
		}
		cycles -= _cycles;
	} while (cycles);
	if (request_interrupt) {
		gb_interrupts_request (gb, GB_INTERRUPT_TIMER);
	}
}

void gb_timers_reset_div (GBTimers *timers) {
	timers->buf[GB_TIMERS_DIV] = 0;
	timers->div = 0;
}