#define _POSIX_C_SOURCE 202511L

#include <string.h>
#include <stdlib.h>
#include <time.h>

#include "wrmr.h"
#include "vui.h"

/* input buffer */

int inbuf[32] = { 0 };
#define INBUF_MASK 0x1f
u32 inbuf_start = 0, inbuf_end = 0;

int pop_input(void) {
	/*
	int k = inbuf[inbuf_start];
	inbuf[inbuf_start] = 0;
	if (k) inbuf_start = (inbuf_start + 1) & INBUF_MASK;
	return k;
	*/
	if (inbuf_start == inbuf_end) return 0;
	int k = inbuf[inbuf_start++];
	inbuf_start &= INBUF_MASK;
	return k;
}

void push_input(int i) {
	inbuf[inbuf_end++] = i;
	inbuf_end &= INBUF_MASK;
}

u32 poll_input_iter = 0;
int poll_input(u32 ms) {
	struct timespec start;
	clock_gettime(CLOCK_MONOTONIC, &start);
	u64 n = start.tv_nsec + (ms * 1000000);
	struct timespec stop = {
		.tv_sec = start.tv_sec + n / 1000000000,
		.tv_nsec = n % 1000000000
	};
	poll_input_iter = 0;
	for (;;) {
		poll_input_iter++;
		struct timespec now;
		clock_gettime(CLOCK_MONOTONIC, &now);
		i64 ns_rem = (stop.tv_sec - now.tv_sec) * 1000000000 + (i64)stop.tv_nsec - (i64)now.tv_nsec;
		i64 ms_rem = ns_rem / 1000000;
		if (ns_rem < 1) break;
		if (vui_wait_for_input(ms_rem)) push_input(vui_key());
		else break;
	}
	return 0;
}

/* program */

#define WIDTH  32
#define HEIGHT 32

typedef enum {
	TILE_FLOOR,
	TILE_SNK_ODD,
	TILE_SNK_EVEN,
	TILE_APPLE,
	TILE_MAX
} Tile;

const VuiAttr tile_attr[TILE_MAX][2] = {
	{ FG_BLUE   | BG_BLACK, FG_BLUE   | BG_BLACK },
	{ FG_YELLOW | BG_BLACK, FG_BYELLOW | BG_BLACK },
	{ FG_GREEN  | BG_BLACK, FG_BGREEN  | BG_BLACK },
	{ FG_BGREEN | BG_BLACK, FG_BRED    | BG_BLACK },
};

const VuiChar tile_chr[TILE_MAX][2] = {
	{ ' ', '.' },
	{ '[', ']' },
	{ '[', ']' },
	{ '`', 'o' }
};

Tile board[HEIGHT][WIDTH];

typedef enum {
	DIR_LEFT,
	DIR_UP,
	DIR_RIGHT,
	DIR_DOWN
} Dir;

#define DIR_IS_Y(d) ((d)&1)
#define DIR_IS_X(d) (~(d)&1)
#define DIR_SIGN(d) ((d)&2 ? 1 : -1)
#define DIR_FLIP(d) (((d) + 2) & 3)
#define DIR_DX(d) (DIR_IS_X(d) * DIR_SIGN(d))
#define DIR_DY(d) (DIR_IS_Y(d) * DIR_SIGN(d))

typedef struct {
	i16 x, y;
} SnkSeg;

#define SNK_SEG_MAX (WIDTH * HEIGHT)

typedef struct {
	Dir dir;
	u32 len;
	SnkSeg seg[SNK_SEG_MAX];
} Snake;

Snake snk = { 0 };

typedef struct {
	i16 x, y;
} Apple;

#define APPLE_MAX 32
Apple apple[APPLE_MAX];

void replace_apple(u32 i) {
	Apple *a = &apple[i];
	do {
		a->x = rand() % WIDTH;
		a->y = rand() % HEIGHT;
	} while (board[a->y][a->x] != TILE_FLOOR);
}

void place_apple(void) {
	for (u32 i = 0; i < APPLE_MAX; i++) {
		replace_apple(i);
	}
}

void brd_clear(void) {
	for (u32 y = 0; y < HEIGHT; y++) {
		for (u32 x = 0; x < WIDTH; x++) {
			board[y][x] = TILE_FLOOR;
		}
	}
}

void brd_draw(void) {
	/*
	u32 left = COLS / 2 - WIDTH;
	u32 top = LINES / 2 - HEIGHT / 2;
	*/
	u32 left = COLS / 2 - snk.seg->x * 2;
	u32 top = LINES / 2 - snk.seg->y;

	u32 right = left + WIDTH * 2;
	u32 bottom = top + HEIGHT;
	for (u32 y = 0; y < HEIGHT; y++) {
		vui_chr(left - 1, top + y, u'║');
		vui_chr(right + 1, top + y, u'║');
		for (u32 x = 0; x < WIDTH; x++) {
			Tile t = board[y][x];
			vui_chra(left + 2 * x,     top + y, tile_chr[t][0], tile_attr[t][0]);
			vui_chra(left + 2 * x + 1, top + y, tile_chr[t][1], tile_attr[t][1]);
			vui_puts(left + 2 * x,     top - 1, "══");
			vui_puts(left + 2 * x,     bottom,  "══");
		}
	}
	vui_chr(left  - 1, top - 1, u'╔');
	vui_chr(right + 1, top - 1, u'╗');
	vui_chr(left  - 1, bottom,  u'╚');
	vui_chr(right + 1, bottom,  u'╝');
	vui_chr(right, bottom,  u'═');
	vui_chr(right, top - 1,  u'═');
	/*
	u32 x = 0;
	u32 y = 1;
	for (u32 i = 0; i < sizeof inbuf / sizeof *inbuf; i++) {
		int within = (i >= inbuf_start && i < inbuf_end);
		if (inbuf_end < inbuf_start) {
			within = i >= inbuf_start || i < inbuf_end;
		}
		VuiAttr a = within ? FG_BCYAN : FG_BBLACK;
		if (i == inbuf_start) vui_chra(x,     bottom + y - 1, 'v', FG_BCYAN);
		if (i == inbuf_end)   vui_chra(x + 1, bottom + y - 1, 'v', FG_BMAGENTA);
		x += vui_aprintf(x, bottom + y, a, "%6X ", inbuf[i]);
		if (x >= COLS - 24) {
			x = 0;
			y += 2;
		}
	}
	*/
}

void snk_draw(Snake *s) {
	for (u32 i = 0; i < s->len; i++) {
		board[s->seg[i].y][s->seg[i].x] = (i / 4) & 1 ? TILE_SNK_ODD : TILE_SNK_EVEN;
	}
}

void apple_draw(void) {
	for (u32 i = 0; i < APPLE_MAX; i++) {
		board[apple[i].y][apple[i].x] = TILE_APPLE;
	}
}

int alive, paused;

void draw(void *ctx) {
	(void)ctx;
	vui_clear();

	brd_clear();
	snk_draw(&snk);
	apple_draw();
	brd_draw();

	if (!alive) {
		vui_puts(COLS/2 - 4, LINES/2, "YOU DIED!");
	}
	vui_printf(0, 0, "input polling iterations: %u", poll_input_iter);
}

void update(void) {
	for (u32 i = 0; i < APPLE_MAX; i++) {
		if (snk.seg[0].x == apple[i].x && snk.seg[0].y == apple[i].y) {
			replace_apple(i);
			snk.len++;
			break;
		}
	}

	memmove(snk.seg + 1, snk.seg, (SNK_SEG_MAX - 1) * sizeof(SnkSeg));

	i16 x = snk.seg[0].x + DIR_DX(snk.dir);
	i16 y = snk.seg[0].y + DIR_DY(snk.dir);

	if (x < 0 || y < 0 || x >= WIDTH || y >= HEIGHT) {
		alive = 0;
		return;
	}

	for (u32 i = 1; i < snk.len; i++) {
		if (snk.seg[i].x == x && snk.seg[i].y == y) {
			alive = 0;
			return;
		}
	}

	snk.seg[0].x = x;
	snk.seg[0].y = y;
	vui_scroll(-DIR_DX(snk.dir) * 2, -DIR_DY(snk.dir));
}

void snk_chg_dir(Snake *s, Dir d) {
	if (s->len < 2 || d != DIR_FLIP(s->dir)) {
		s->dir = d;
	}
}

/* game */

int main(void) {
	srand(time(NULL));
	vui_init();
	snk.dir = DIR_RIGHT;
	snk.seg[snk.len++] = (SnkSeg) { 0, 0 };
	alive = 1;
	paused = 0;
	vui_redraw_fn(draw);
	place_apple();
	while (alive) {
		poll_input(30);
		draw(NULL);
		vui_blit();
		switch (pop_input()) {
		case 0: break;
		case KEY_ESC: goto done;
		case KEY_LEFT : case 'j': snk_chg_dir(&snk, DIR_LEFT); break;
		case KEY_UP   : case 'i': snk_chg_dir(&snk, DIR_UP); break;
		case KEY_RIGHT: case 'l': snk_chg_dir(&snk, DIR_RIGHT); break;
		case KEY_DOWN : case 'k': snk_chg_dir(&snk, DIR_DOWN); break;
		case ' ': paused = !paused; break;
		}
		if (!paused) update();
	}
	draw(NULL);
	vui_blit();
	(void)vui_key();
done:
	vui_fini();
	return 0;
}