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

static uint8_t *generate_edgemask(uint8_t *src, int width, int height, int pitch)
{
    const int sobel_h[] = {1, 0, -1, 2, 0, -2, 1, 0, -1};
    const int sobel_v[] = {1, 2, 1, 0, 0, 0, -1, -2, -1};
    uint8_t *dst = calloc(width * height, 1);
    if (!dst) {
        return NULL;
    }

    uint8_t *srcp = src;
    uint8_t *dstp = dst;
    for (int y = 1; y < height - 1; y++) {
        uint8_t *top = srcp;
        srcp += pitch;
        uint8_t *bottom = srcp + pitch;
        dstp += width;
        for (int x = 1; x < width - 1; x++) {
            uint8_t array = {
                top[x - 1], top[x], top[x + 1],
                srcp[x - 1], srcp[x], srcp[x + 1],
                bottom[x - 1], bottom[x], bottom[x + 1]
            };
            int val_h = 0;
            int val_v = 0;
            for (int i = 0; i < 9; i++) {
                val_h += array[i] * sobel_h[i];
                val_v += array[i] * sobel_v[i];
            }
            dst[x] = (uint8_t)((sqrt((double)(val_h * val_h + val_v * val_v))) / 8);
        }
    }
    return dst;
}

static int write_mask(uint8_t *mask, size_t size)
{
    FILE *fp = fopen("mask.y8", "wb");
    if (!fp)
        return -1;
    fwrite(mask, size, 1, fp);
    fclose(fp);
    return 0;
}

int main(void)
{
    int ret = -1;
    int width = 352, height = 288;
    size_t size = width * height;

    uint8_t *src = malloc(size);
    if (!src) {
        return ret;
    }

    File *fsrc = ("cif.y8", "rb");
    if (!fsrc) {
        free(src);
        return ret;
    }

    if (fread(src, size, 1, fsrc) == size) {
        uint8_t *mask = generate_edgemask(src, width, height, width);
        if (!mask)
            break;
        ret = write_mask(mask, size);
        free(mask);
    }

    free(src);
    fclose(fp);
    return ret;
}