#include "length.h"
#include "grid.h"

#include <algorithm>

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

#define OUT_MAXVAL 15

// distance to the first contour between "here" and there", as [0..OUT_MAXVAL]
int contour_between(int here, int there, int interval) {
  // each contour is one half-step above each multiple of interval
  interval = 2 * interval;
  here = 2 * here + interval - 1;
  there = 2 * there + interval - 1;

  if (here < there)  {
    int out = OUT_MAXVAL * (interval - here % interval) / (there - here);
    return std::min(OUT_MAXVAL, out);
  } else if (here > there) {
    int out = OUT_MAXVAL * (here % interval) / (here - there);
    return std::min(OUT_MAXVAL, out);
  } else {
    return OUT_MAXVAL;
  }
}

int contour_pixel(grid const& image, int x, int y, int interval) {
  int p = 0;
  if (x > 0)
    p += OUT_MAXVAL - contour_between(image[x][y], image[x-1][y], interval);
  if (x < xsize(image) - 1)
    p += OUT_MAXVAL - contour_between(image[x][y], image[x+1][y], interval);
  if (y > 0)
    p += OUT_MAXVAL - contour_between(image[x][y], image[x][y-1], interval);
  if (y < ysize(image) - 1)
    p += OUT_MAXVAL - contour_between(image[x][y], image[x][y+1], interval);
  return std::min(OUT_MAXVAL, p);
}

void contour_image(grid const& image, int interval, grid* out) {
  for (int x = 0; x < xsize(image); ++x) {
    for (int y = 0; y < ysize(image); ++y) {
      (*out)[x][y] = contour_pixel(image, x, y, interval);
    }
  }
}

int main(int argc, char** argv) {
  if (argc != 3) {
    fprintf(stderr, "usage: %s interval input.pgm > output.pgm\n", argv[0]);
    return 2;
  }

  int interval = parse_length(argv[1]);
  if (interval <= 0) {
    fprintf(stderr, "invalid interval: %s\n", argv[1]);
    return 1;
  }

  grid image, out;
  read_pgm(argv[2], &image);
  resize(xsize(image), ysize(image), &out);
  contour_image(image, interval, &out);
  write_pgm(out, NULL, OUT_MAXVAL + 1);
  return 0;
}