#include <stdint.h>
#include <stdlib.h>

#define width 512
#define height 512

static uint8_t field[width * height];
static uint8_t nextField[width * height];
static uint8_t pixels[width * height * 4];

static uint8_t rand8(void);
static int countNeighbours(int x, int y);

EXPORT(getWidth) int get_width(void) { return width; }
EXPORT(getHeight) int get_height(void) { return height; }
EXPORT(getPixels) uint8_t* get_pixels(void) { return pixels; }

EXPORT(step) void step(void) 
{
    for (int y = 0; y < height; y++) {
        for (int x = 0; x < width; x++) {
            int count = countNeighbours(x, y);
            uint8_t currentCell = field[x + y * width];
            int nextCell = currentCell;
            if (currentCell && count < 2) nextCell = 0;
            else if (currentCell && count > 3) nextCell = 0;
            else if (!currentCell && count == 3) nextCell = 1;

            nextField[x + y * width] = nextCell;
        }
    }

    for (int i = 0; i < width * height; i++) {
        field[i] = nextField[i];
        uint8_t px = field[i];

        if (px) {
            pixels[(i << 2) + 0] = 0;
            pixels[(i << 2) + 1] = 0;
            pixels[(i << 2) + 2] = 0;
        } else {
            pixels[(i << 2) + 0] = 255;
            pixels[(i << 2) + 1] = 255;
            pixels[(i << 2) + 2] = 255;
        }
        pixels[(i << 2) + 3] = 255;
    }
}

static int countNeighbours(int x, int y) 
{
    int count = 0;
    for (int i = -1; i <= 1; i++) {
        for (int j = -1; j <= 1; j++) {
            if (i == 0 && j == 0) continue;

            int xx = (x + i + width) % width;
            int yy = (y + j + height) % height;

            if (field[xx + yy * width]) {
                count++;
            }
        }
    }
    return count;
}

/** Random generator implementation from https://stackoverflow.com/a/16761955 */
#define STATE_BYTES 7
#define MULT 0x13B /* for STATE_BYTES==6 only */
#define MULT_LO (MULT & 255)
#define MULT_HI (MULT & 256)

static uint8_t rand_state[STATE_BYTES] = { 0x87, 0xdd, 0xdc, 0x10, 0x35, 0xbc, 0x5c };

static uint8_t rand8(void)
{
    static uint16_t c = 0x42;
    static uint32_t i = 0;
    uint16_t t;
    uint8_t x;

    x = rand_state[i];
    t = (uint16_t)x * MULT_LO + c;
    c = t >> 8;
#if MULT_HI
    c += x;
#endif
    x = t & 255;
    rand_state[i] = x;
    if (++i >= sizeof(rand_state))
        i = 0;
    return x;
}

EXPORT(initField) void init_field(uint32_t randomSeed)
{
    *((uint32_t*)&rand_state[STATE_BYTES - sizeof(uint32_t)]) = randomSeed; // Voodoo

    for (int i = 0; i < width * height; i++) {
        field[i] = rand8() & 1;
    }
}