#include <stddef.h>
#include <stdint.h>

#if SDL
#include <string.h>
#define xmemcpy memcpy
#else
#define xmemcpy __builtin_memcpy
#endif


typedef struct {
	unsigned char r, g, b, a;
} Color;

typedef struct {
	int x, y, w, h;
	Color fill;
	Color border;
} DrawElement;

typedef struct {
	int len;
	DrawElement els[512];
} DrawList;

#define MEM_SIZE (1<<16)
#define GRIDWIDTH 16
#define GRIDHEIGHT 16
#define TICK_LENGTH 200

typedef struct {
	char *start;
	char *end;
} Arena;

#define new(a, c, t) ((t *) alloc(a, c, sizeof(t), _Alignof(t)))
#define affirm(c) while (!(c)) *(volatile int *)0 = 0

static void *alloc(Arena *a, ptrdiff_t count, ptrdiff_t size, ptrdiff_t align) {
	ptrdiff_t pad = -(size_t) a->start & (align - 1);
	affirm(count < (a->end - a->start - pad) / size);
	char *r = a->start + pad;
	a->start += pad + size * count;
	for (ptrdiff_t i = 0; i < count * size; i++) {
		r[i] = 0;
	}

	return r;
}

typedef struct {
	int width, height;
} UI;

typedef struct {
	uint64_t lastTick;
	char playing;
	int grid[GRIDWIDTH * GRIDHEIGHT];
} State;

// Mirror these in src/index.html.in
enum {
	INPUT_NONE,
	INPUT_CLICK,
	INPUT_PAUSE_PLAY,
};

typedef struct {
	State state;
	UI ui;
	int input;
	int mousex, mousey;
} Game;

enum {
	EMPTY,
	BLACK,
	RED,
	YELLOW,
	N_COLORS,
};

static const Color colors[N_COLORS] = {
	{255, 255, 255, 255},
	{0, 0, 0, 255},
	{255, 0, 0, 255},
	{255, 255, 0, 255}
};

static DrawList *render(State *state, UI *ui, Arena *a) {
	(void) ui;

	DrawList *drawList = new(a, 1, DrawList);

	int cellWidth = ui->width / GRIDWIDTH;
	int cellHeight = ui->height / GRIDHEIGHT;

	for (int x = 0; x < GRIDWIDTH; x++) {
		for (int y = 0; y < GRIDHEIGHT; y++) {
			drawList->els[drawList->len++] = (DrawElement) {
				.x = cellWidth * x,
				.y = cellHeight * y,
				.w = cellWidth,
				.h = cellHeight,
				.fill = colors[state->grid[x + GRIDWIDTH * y]],
				.border = {0, 0, 0, 255},
			};
		}
	}

	return drawList;
}

static void update(Game *game, uint64_t now, Arena a) {
	switch (game->input) {
		int x, y;
		case INPUT_CLICK:
			x = game->mousex * GRIDWIDTH / game->ui.width;
			y = game->mousey * GRIDHEIGHT / game->ui.height;
			game->state.grid[x + y * GRIDWIDTH] = (game->state.grid[x + y * GRIDWIDTH] + 1) % (sizeof(colors) / sizeof(colors[0]));
			break;
		case INPUT_PAUSE_PLAY:
			game->state.playing = !game->state.playing;
			break;
		default:
			break;
	}

	if (game->state.playing && game->state.lastTick + TICK_LENGTH <= now) {
		game->state.lastTick = now;
		State *lastState = new(&a, 1, State);
		xmemcpy(lastState, game, sizeof(State));

		for (int x = 0; x < GRIDWIDTH; x++) {
			for (int y = 0; y < GRIDHEIGHT; y++) {
				if (
					lastState->grid[x + y * GRIDWIDTH] == BLACK && (
						(x > 0 && lastState->grid[x - 1 + y * GRIDWIDTH] == RED) ||
						(x < GRIDWIDTH - 1 && lastState->grid[x + 1 + y * GRIDWIDTH] == RED) ||
						(y > 0 && lastState->grid[x + (y - 1) * GRIDWIDTH] == RED) ||
						(y < GRIDHEIGHT - 1 && lastState->grid[x + (y + 1) * GRIDWIDTH] == RED)
					)
				) {
					game->state.grid[x + y * GRIDWIDTH] = RED;
				}

				if (lastState->grid[x + y * GRIDWIDTH] == RED) {
					game->state.grid[x + y * GRIDWIDTH] = YELLOW;
				}

				if (lastState->grid[x + y * GRIDWIDTH] == YELLOW) {
					game->state.grid[x + y * GRIDWIDTH] = BLACK;
				}
			}
		}
	}
}

#if SDL

#include <SDL3/SDL.h>

int main(int argc, char **argv) {
	(void) argc;
	(void) argv;

	char *mem = SDL_malloc(MEM_SIZE);
	Arena a = {
		.start = mem,
		.end = mem + MEM_SIZE,
	};

	Game *game = new(&a, 1, Game);
	game->state.grid[0] = 0;
	game->state.playing = 0;
	game->ui = (UI) {
		.width = 640,
		.height = 480,
	};

	SDL_Init(SDL_INIT_VIDEO);
	SDL_Window *w = SDL_CreateWindow(
		"LDJam 57",
		game->ui.width,
		game->ui.height,
		SDL_WINDOW_RESIZABLE
	);
	SDL_PropertiesID renderProps = SDL_CreateProperties();
	SDL_SetPointerProperty(renderProps, SDL_PROP_RENDERER_CREATE_WINDOW_POINTER, w);
	SDL_SetNumberProperty(renderProps, SDL_PROP_RENDERER_CREATE_PRESENT_VSYNC_NUMBER, 1);
	SDL_Renderer *r = SDL_CreateRendererWithProperties(renderProps);
	SDL_DestroyProperties(renderProps);
	
	for (;;) {
		uint64_t now = SDL_GetTicks();
		game->input = INPUT_NONE;
		SDL_Event e = {0};
		while (SDL_PollEvent(&e)) {
			switch (e.type) {
				case SDL_EVENT_QUIT:
					return 0;
				case SDL_EVENT_MOUSE_BUTTON_DOWN:
					game->input = INPUT_CLICK;
					game->mousex = (int) e.button.x;
					game->mousey = (int) e.button.y;
					break;
				case SDL_EVENT_KEY_DOWN:
					switch (e.key.key) {
						case SDLK_SPACE:
							game->input = INPUT_PAUSE_PLAY;
							break;
					}
					break;
				case SDL_EVENT_WINDOW_RESIZED:
					SDL_GetWindowSize(w, &game->ui.width, &game->ui.height);
					break;
			}
		}

		Arena scratch = a;
		DrawList *drawList = render(&game->state, &game->ui, &scratch);
		SDL_SetRenderDrawColor(r, 0, 0, 0, 255);
		SDL_RenderFillRect(r, NULL);
		for (int i = 0; i < drawList->len; i++) {
			SDL_FRect rect = {
				.x = (float) drawList->els[i].x,
				.y = (float) drawList->els[i].y,
				.w = (float) drawList->els[i].w,
				.h = (float) drawList->els[i].h
			};

			SDL_SetRenderDrawColor(
				r,
				drawList->els[i].fill.r,
				drawList->els[i].fill.g,
				drawList->els[i].fill.b,
				drawList->els[i].fill.a
			);
			SDL_RenderFillRect(r, &rect);

			SDL_SetRenderDrawColor(
				r,
				drawList->els[i].border.r,
				drawList->els[i].border.g,
				drawList->els[i].border.b,
				drawList->els[i].border.a
			);
			SDL_RenderRect(r, &rect);
		}

		update(game, now, a);

		SDL_RenderPresent(r);
	}

	return 0;
}

#elif WASM

static Game *game;
static Arena perm;

__attribute((export_name("game_init")))
void game_init(void) {
	static char heap[MEM_SIZE];
	perm.start = heap;
	perm.end = heap + MEM_SIZE;

	game = new(&perm, 1, Game);
	game->state.grid[0] = 1;
}

__attribute((export_name("game_render")))
DrawList *game_render(int width, int height) {
	game->ui.width = width;
	game->ui.height = height;
	Arena scratch = perm;
	return render(&game->state, &game->ui, &scratch);
}

__attribute((export_name("game_update")))
void game_update(int input, int mousex, int mousey) {
	game->input = input;
	game->mousex = mousex;
	game->mousey = mousey;
	update(game, perm);
}

#endif