/*
** ppmr3.c - redact portions of a PPM picture
** Written by Harry Sintonen <sintonen@iki.fi>
**
** Compile:
** % gcc -Wall -O2 ppmr3.c -o ppmr3
**
** Usage:
** Redact two rectangles:
** % echo -e '5 8 90 24\n5 32 90 48' | ./ppmr3 secret.ppm > out.ppm
** Redact the whole picture:
** % echo '0 0 99999 99999' | ./ppmr3 secret.ppm > out.ppm
*/

#include <sys/time.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>

enum { D_RECT, D_VERBOSE, NUMDEBUGFLAGS };
static int debug[NUMDEBUGFLAGS];

int ftime(time_t *);
#ifdef __GNUC__
static void fail(const char *fmt, ...) __attribute__ ((noreturn));
#endif
static void fail(const char *fmt, ...)
{
  va_list args;
  va_start(args, fmt);
  vfprintf(stderr, fmt, args);
  va_end(args);
  exit(EXIT_FAILURE);
}

/* Read number from a file, PPM header style, return -1 for an EOF */
static int readval(FILE *fh)
{
  int state = 0, val = 0, c;
  while ((c = fgetc(fh)) != EOF)
  {
    if (debug[D_VERBOSE]) printf("# state=%d c=%d\n", state, c);
    switch (state)
    {
      case 0: /* skipping whitespaces */
        if (c == ' ' || c == '\t' || c == '\r' || c == '\n') break;
        state = 1;
      case 1: /* checking for possible comment start */
        if (c == '#') { state = 3; break; }
        state = 2;
      case 2: /* parsing digits */
        if (c < '0' || c > '9') return val;
        val = val * 10 + c - '0'; break;
      case 3: /* skipping comment */
        if (c == '\n') state = 0;
    }
  }
  return state == 2 ? val : -1;
}

static __inline void clip(int *valptr, int maxval)
{
  if (*valptr < 0) *valptr = 0;
  else if (*valptr > maxval) *valptr = maxval;
}

int main(int argc, char **argv)
{
  static time_t seed;
  int optind = 1, cols, rows, maxval, bpp, bpr;
  int minx, miny, maxx, maxy, x, y;
  unsigned char id[2], *pixels;
  FILE *fh;

  if (ftime(&seed)) srand(seed);

  if (argc > 1 && argv[1][0] == '-' && argv[1][1] == 'd')
  {
    debug[D_RECT] = 1; debug[D_VERBOSE] = 1;
    argc--; optind++;
  }
  if (argc < 2)
    fail("usage: %s [-d] in.ppm < redactions.txt > out.ppm\n", argv[0]);

  if (!(fh = fopen(argv[optind], "r")))
    fail("could not open file \"%s\"\n", argv[optind]);

  if (fread(id, 1, 2, fh) != 2 || id[0] != 'P' || id[1] != '6' ||
      (cols = readval(fh)) < 0 || (rows = readval(fh)) < 0 ||
      (maxval = readval(fh)) < 0 || maxval > 65535)
    fail("invalid or unsupported PPM file \"%s\"\n", argv[optind]);

  bpp = maxval < 256 ? 1 : 2;
  bpr = cols * bpp * 3;
  if (debug[D_VERBOSE]) printf("# cols=%d rows=%d maxval=%d bpp=%d bpr=%d\n",
                               cols, rows, maxval, bpp, bpr);
  if (!(pixels = malloc(bpr * rows)))
    fail("out of memory\n"); 

  if (fread(pixels, bpr, rows, fh) != rows)
    fail("could not read file \"%s\"\n", argv[optind]);

  fclose(fh);

  if (printf("P6\n%d %d\n", cols, rows) < 0)
    fail("could not write PPM file header\n");

  while ((minx = readval(stdin)) >= 0 && (miny = readval(stdin)) >= 0 &&
         (maxx = readval(stdin)) >= 0 && (maxy = readval(stdin)) >= 0)
  {
    clip(&minx, cols); clip(&maxx, cols);
    clip(&miny, rows); clip(&maxy, rows);
    if (debug[D_RECT]) printf("# %d,%d to %d,%d\n", minx, miny, maxx, maxy);

    minx *= 3; maxx *= 3 * bpp;
    for (y = miny; y < maxy; y++)
    {
      unsigned char *ptr = &pixels[y * bpr + minx * bpp];
      for (x = minx; x < maxx; x++) *ptr++ ^= rand();
    }
  }

  if (printf("%d\n", maxval) < 0 ||
      fwrite(pixels, bpr, rows, stdout) != rows)
    fail("could not write PPM file pixel data\n");

  return EXIT_SUCCESS;
}