/*
** ppmr5.c - redact portions of a PPM picture
** Written by Harry Sintonen <sintonen@iki.fi>
**
** Compile:
** % gcc -Wall -O2 ppmr5.c -o ppmr5
**
** Usage:
** Redact two rectangles:
** % echo -e '5 8 90 24\n5 32 90 48' | ./ppmr5 secret.ppm > out.ppm
** Redact the whole picture:
** % echo '0 0 99999 99999' | ./ppmr5 secret.ppm > out.ppm
*/

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

#define iswhite(c) ((c) == ' ' || (c) == '\t' || (c) == '\r' || (c) == '\n')
struct rect {
  int x1, y1, x2, y2;
};

static void fail(const char *fmt, ...)
{
  va_list args;
  va_start(args, fmt);
  vfprintf(stderr, fmt, args);
  va_end(args);
  exit(EXIT_FAILURE);
}

int main(int argc, char **argv)
{
  int state = 0, c, var[3] = {0}, vindex = 0, numrects, x = 0, y = 0;
  struct rect *rects, rect, *r;
  long dataoffs = 0, offs = 0;
  FILE *fh;

  if (argc != 2)
    fail("usage: %s in.ppm < redactions.txt > out.ppm\n", argv[0]);

  if (!(fh = fopen(argv[1], "r")))
    fail("could not open file \"%s\"\n", argv[1]);

  for (rects = 0, numrects = 0;
       scanf("%d %d %d %d", &rect.x1, &rect.y1, &rect.x2, &rect.y2) == 4 &&
       (rects = realloc(rects, ++numrects * sizeof(struct rect)));)
    rects[numrects - 1] = rect;

  while ((c = fgetc(fh)) != EOF)
  {
    switch (state)
    {
      case 0: case 1:          /* check file header ID */
        if (c != "P6"[state++]) fail("unsupported file format\n");
        break;
      case 2: case 5: case 8:  /* skip whitespaces/check for comment */
        if (iswhite(c)) break;
        if (c == '#') { state += 2; break; }
        state++; /* fall thru */
      case 3: case 6: case 9:  /* parse decimal number */
        if (c < '0' || c > '9')
        {
          if (var[vindex] == 0) fail("unsupported file format\n");
          state += 2; vindex++; ungetc(c, fh); break;
        }
        var[vindex] = var[vindex] * 10 + c - '0';
        break;
      case 4: case 7: case 10: /* skip comment until newline */
        if (c == '\n') state -= 2;
        break;
      case 11:                 /* check final delimiter, store data start */
        if (!iswhite(c)) fail("unsupported file format\n");
        if ((dataoffs = ftell(fh)) < 0) fail("ftell error\n");
        state++;
        break;
      case 12: case 15:        /* seek to file beginning to clone header */
        if (fseek(fh, 0, SEEK_SET) < 0) fail("fseek error\n");
        state++;
        break;
      case 14:                 /* process data, redacting pixels */
        for (r = rects; r < &rects[numrects]; r++)
          if (x >= r->x1 * 3 && x < r->x2 * 3 && y >= r->y1 && y < r->y2)
            { c = 0; break; }
        if (++x == var[0] * 3) { x = 0; y++; }
        /* fall thru */
      default:                 /* write char */
        putchar(c);
        if (++offs >= dataoffs)
        {
          dataoffs += var[0] * 3 * var[1];
          state++;
        }
    }
  }
  return EXIT_SUCCESS;
}