#include "drain.h"
#include "ops.h"
#include <stdio.h>
#include <stdint.h>
#include <SDL2/SDL.h>

#define MEM_SIZE 0xffff

static const uint16_t buttons[SDL_NUM_SCANCODES] = {
	[SDL_SCANCODE_BACKSPACE] = 1 << 2,
	[SDL_SCANCODE_RETURN] = 1 << 3,
	/* WASD JK */
	[SDL_SCANCODE_J] = 1 << 0,
	[SDL_SCANCODE_K] = 1 << 1,
	[SDL_SCANCODE_W] = 1 << 4,
	[SDL_SCANCODE_S] = 1 << 5,
	[SDL_SCANCODE_A] = 1 << 6,
	[SDL_SCANCODE_D] = 1 << 7,
	/* arrows XC */
	[SDL_SCANCODE_X] = 1 << 0,
	[SDL_SCANCODE_C] = 1 << 1,
	[SDL_SCANCODE_UP] = 1 << 4,
	[SDL_SCANCODE_DOWN] = 1 << 5,
	[SDL_SCANCODE_LEFT] = 1 << 6,
	[SDL_SCANCODE_RIGHT] = 1 << 7,
};

static uint16_t *mem = NULL, *stack = NULL, *rstack = NULL;
static size_t stack_ptr = 0, rstack_ptr = 0;
static SDL_Window *window = NULL;
static SDL_Renderer *renderer = NULL;
static SDL_Texture *target = NULL;
static Uint64 next_time = 0;

static int
fail(void)
{
	if (target != NULL)
		SDL_DestroyTexture(target);
	if (renderer != NULL)
		SDL_DestroyRenderer(renderer);
	if (window != NULL)
		SDL_DestroyWindow(window);
	SDL_Quit();
	if (mem != NULL)
		free(mem);
	if (stack != NULL)
		free(stack);
	if (rstack != NULL)
		free(rstack);
	return 1;
}

static uint16_t
get_short(const unsigned char *s)
{
	return s[0] | (s[1] * 0x0100);
}

static int
cycle_events(uint16_t *input)
{
	SDL_Event e;
	while (SDL_PollEvent(&e)) {
		switch (e.type) {
		case SDL_QUIT:
			return 1;
		case SDL_KEYDOWN:
			if (e.key.repeat)
				break;
			if (e.key.keysym.scancode == SDL_SCANCODE_F) {
				static int fullscreen = 0;
				fullscreen = !fullscreen;
				SDL_SetWindowFullscreen(window, fullscreen);
			}
			*input |= buttons[e.key.keysym.scancode];
			break;
		case SDL_KEYUP:
			*input &= ~(buttons[e.key.keysym.scancode]);
			break;
		default:
			break;
		}
	}
	return 0;
}

static void
render(uint16_t *mem)
{
	int win_w, win_h;
	SDL_GetWindowSize(window, &win_w, &win_h);
	win_w = win_w ? win_w : 1;
	win_h = win_h ? win_h : 1;
	const float ratio_w = win_w / 128.0;
	const float ratio_h = win_h / 128.0;
	float scale = (ratio_w < ratio_h) ? ratio_w : ratio_h;
	if (scale > 1.0)
		scale = (int)scale;
	const int off_x = (win_w - 128 * scale) / 2;
	const int off_y = (win_h - 128 * scale) / 2;
	const SDL_Rect dest = { off_x, off_y, 128 * scale, 128 * scale };

	SDL_SetRenderTarget(renderer, target);
	SDL_SetRenderDrawColor(renderer, 0, 0, 0, 255);
	SDL_RenderClear(renderer);
	for (int y = 0; y < 128; y++) {
		for (int x = 0; x < 128; x++) {
			const uint16_t pixel = mem[x + y * 128];
			if (!pixel)
				continue;
			const uint16_t r = (pixel & 0x1f) << 3;
			const uint16_t g = ((pixel >> 5) & 0x3f) << 2;
			const uint16_t b = ((pixel >> 11) & 0x1f) << 3;
			SDL_SetRenderDrawColor(renderer, r, g, b, 255);
			SDL_RenderDrawPoint(renderer, x, y);
		}
	}
	SDL_SetRenderTarget(renderer, NULL);
	SDL_SetRenderDrawColor(renderer, 0, 0, 0, 255);
	SDL_RenderClear(renderer);
	SDL_RenderCopy(renderer, target, NULL, &dest);

	next_time += 1000 / 30;
	const Uint64 cur_time = SDL_GetTicks64();
	if (next_time <= cur_time) {
		fprintf(stderr, "lagging %lu\n", cur_time - next_time);
		next_time = cur_time;
	} else
		SDL_Delay(next_time - cur_time);

	SDL_RenderPresent(renderer);
}

static void
push(uint16_t v)
{
	stack[stack_ptr] = v;
	stack_ptr += 1;
	if (stack_ptr >= MEM_SIZE) {
		fprintf(stderr, "stack overflow\n");
		exit(fail());
	}
}

static uint16_t
pop(void)
{
	if (stack_ptr == 0) {
		fprintf(stderr, "stack underflow\n");
		exit(fail());
	}
	stack_ptr -= 1;
	return stack[stack_ptr];
}

static void
push_rs(uint16_t v)
{
	rstack[rstack_ptr] = v;
	rstack_ptr += 1;
	if (rstack_ptr >= MEM_SIZE) {
		fprintf(stderr, "return stack overflow\n");
		exit(fail());
	}
}
 
static uint16_t
pop_rs(void)
{
	if (rstack_ptr == 0) {
		fprintf(stderr, "return stack underflow\n");
		exit(fail());
	}
	rstack_ptr -= 1;
	return rstack[rstack_ptr];
}

static long
exec_op(uint16_t *mem, long pc)
{
	switch (mem[pc]) {
	case OP_NOP:
		return pc + 1;
	case OP_LIT:
		push(mem[pc + 1]);
		return pc + 2;
	case OP_POP:
		pop();
		return pc + 1;
	case OP_NIP: {
		const uint16_t a = pop();
		pop();
		push(a);
		return pc + 1;
	}
	case OP_SWP: {
		const uint16_t a = pop();
		const uint16_t b = pop();
		push(a);
		push(b);
		return pc + 1;
	}
	case OP_ROT: {
		const uint16_t a = pop();
		const uint16_t b = pop();
		const uint16_t c = pop();
		push(b);
		push(a);
		push(c);
	} return pc + 1;
	case OP_DUP: {
		const uint16_t a = pop();
		push(a);
		push(a);
		return pc + 1;
	}
	case OP_OVR: {
		const uint16_t a = pop();
		const uint16_t b = pop();
		push(b);
		push(a);
		push(b);
		return pc + 1;
	}
	case OP_EQU:
		push(pop() == pop());
		return pc + 1;
	case OP_NEQ:
		push(pop() != pop());
		return pc + 1;
	case OP_GTH: {
		const uint16_t b = pop();
		const uint16_t a = pop();
		push(a > b);
		return pc + 1;
	}
	case OP_LTH: {
		const uint16_t b = pop();
		const uint16_t a = pop();
		push(a < b);
		return pc + 1;
	}
	case OP_JEZ:
		if (pop() == 0)
			return mem[pc + 1];
		return pc + 2;
	case OP_JNZ:
		if (pop() != 0)
			return mem[pc + 1];
		return pc + 2;
	case OP_JMP:
		return mem[pc + 1];
	case OP_JRT:
		push_rs(pc + 2);
		return mem[pc + 1];
	case OP_RET:
		if (rstack_ptr > 0)
			return pop_rs();
		return MEM_SIZE;
	case OP_LDA:
		push(mem[pop()]);
		return pc + 1;
	case OP_STA: {
		const uint16_t a = pop();
		const uint16_t b = pop();
		mem[a] = b;
		return pc + 1;
	}
	case OP_RED:
		push(getchar());
		return pc + 1;
	case OP_WRT:
		putchar(pop());
		return pc + 1;
	case OP_ADD:
		push(pop() + pop());
		return pc + 1;
	case OP_SUB: {
		const uint16_t b = pop();
		const uint16_t a = pop();
		push(a - b);
		return pc + 1;
	}
	case OP_MUL:
		push(pop() * pop());
		return pc + 1;
	case OP_DIV: {
		const uint16_t b = pop();
		const uint16_t a = pop();
		push(a / b);
		return pc + 1;
	}
	case OP_AND:
		push(pop() & pop());
		return pc + 1;
	case OP_ORA:
		push(pop() | pop());
		return pc + 1;
	case OP_XOR:
		push(pop() ^ pop());
		return pc + 1;
	case OP_LSF: {
		const uint16_t shift = pop();
		const uint16_t a = pop();
		push(a << shift);
		return pc + 1;
	}
	case OP_RSF: {
		const uint16_t shift = pop();
		const uint16_t a = pop();
		push(a >> shift);
		return pc + 1;
	}
	case OP_SLP:
		if (cycle_events(mem + 0xbffe))
			return MEM_SIZE;
		render(mem + 0xbfff);
		return pc + 1;
	case OP_INC:
		push(pop() + 1);
		return pc + 1;
	case OP_DEC:
		push(pop() - 1);
		return pc + 1;
	case OP_DBG:
		fprintf(stderr, "<%04x> ", (unsigned)stack_ptr);
		for (size_t i = 0; i < stack_ptr; i++)
			fprintf(stderr, "%04x ", stack[i]);
		fputc('\n', stderr);
		return pc + 1;
	default:
		fprintf(stderr, "unhandled opcode %04x\n", mem[pc]);
		if (mem[pc] <= OP_SLP)
			fprintf(stderr, "(%s)\n", ops[mem[pc]]);
		exit(fail());
	}
}

static void
exec_data(uint16_t *mem)
{
	long pc = 0;
	do
		pc = exec_op(mem, pc);
	while (pc < MEM_SIZE);
}

int
main(int argc, char **argv)
{
	if (argc != 2) {
		fprintf(stderr, "usage: %s <rom>\n", argv[0]);
		return 1;
	}

	FILE *file = fopen(argv[1], "rb");
	if (file == NULL) {
		perror(argv[1]);
		return 1;
	}

	long size;
	unsigned char *const data = (unsigned char*)drain(file, &size);
	fclose(file);
	if (data == NULL)
		return 1;

	mem = calloc(MEM_SIZE, sizeof(uint16_t));
	if (mem == NULL) {
		perror("main:calloc");
		free(data);
		return 1;
	}

	for (long i = 0; i < size; i += 2)
		mem[i / 2] = get_short(data + i);
	free(data);

	stack = calloc(MEM_SIZE, sizeof(uint16_t));
	if (stack == NULL) {
		perror("main:calloc");
		return fail();
	}

	rstack = calloc(MEM_SIZE, sizeof(uint16_t));
	if (rstack == NULL) {
		perror("main:calloc");
		return fail();
	}

	if (SDL_Init(SDL_INIT_VIDEO) < 0) {
		fprintf(stderr, "%s\n", SDL_GetError());
		return fail();
	}
	if (SDL_CreateWindowAndRenderer(384, 384, SDL_WINDOW_RESIZABLE,
	                                &window, &renderer) < 0) {
		fprintf(stderr, "%s\n", SDL_GetError());
		return fail();
	}
	target = SDL_CreateTexture(renderer, SDL_PIXELFORMAT_RGB888,
	                           SDL_TEXTUREACCESS_TARGET, 128, 128);
	if (target == NULL) {
		fprintf(stderr, "%s\n", SDL_GetError());
		return fail();
	}
	next_time = SDL_GetTicks64();

	exec_data(mem);
	return fail(), 0;
}