/*
** ppmr4.c - redact portions of a PPM picture
** Written by Harry Sintonen <sintonen@iki.fi>
**
** Compile:
** % gcc -Wall -O2 ppmr4.c -o ppmr4
**
** Usage:
** Redact two rectangles:
** % echo -e '5 8 90 24\n5 32 90 48' | ./ppmr4 secret.ppm > out.ppm
** Redact the whole picture:
** % echo '0 0 99999 99999' | ./ppmr4 secret.ppm > out.ppm
*/

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

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, c;
  while ((c = fgetc(fh)) != EOF)
    if (state) state = c != '\n';
    else if (c == '#') state = 1;
         else if (c != ' ' && c != '\t' && c != '\r' && c != '\n')
         { ungetc(c, fh); break; }
  return fscanf(fh, "%u ", &val) == 1 ? val : -1;
}

struct rect {
  int           minx, miny, maxx, maxy;
};
struct region {
  int           size, numrects;
  struct rect  *rects;
};
struct data {
  FILE         *fh;
  struct region region;
  int           bpp, bpr, ypos;
};

static void addregionrect(struct region *r, const struct rect *rect)
{
  if (++r->numrects > r->size)
  {
    r->size += 16;
    if (!(r->rects = realloc(r->rects, r->size * sizeof(struct rect))))
      fail("out of memory\n");
  }
  r->rects[r->numrects - 1] = *rect;
}

static void redact(struct data *d)
{
  unsigned char in[d->bpr], out[d->bpr];
  while (fread(in, 1, d->bpr, d->fh) == d->bpr)
  {
    struct rect *r = d->region.rects;
    int x, y = d->ypos++;
    for (x = 0; x < d->bpr; x++)
      out[x] = in[x];
    for (; r < &d->region.rects[d->region.numrects]; r++)
      if (y >= r->miny && y < r->maxy)
        for (x = r->minx * d->bpp; x < r->maxx * d->bpp; x++)
          out[x] = 0;
    if (fwrite(out, 1, d->bpr, stdout) != d->bpr)
      fail("error writing output\n");
    else redact(d); fwrite(in, 1, d->bpr, stdout); break;
  }
}

int main(int argc, char **argv)
{
  int cols = 0, rows = 0, maxval = 0;
  unsigned char id[2];
  struct data data = {0};
  struct rect r;

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

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

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

  while (scanf("%d %d %d %d", &r.minx, &r.miny, &r.maxx, &r.maxy) == 4)
  {
    if (r.maxx > cols) r.maxx = cols; /* clip to image width */
    addregionrect(&data.region, &r);
  }

  printf("P6\n%d %d\n%d\n", cols, rows, maxval);
  data.bpp = 3 * (maxval < 256 ? 1 : 2);
  data.bpr = cols * data.bpp;
  redact(&data);

  return EXIT_SUCCESS;
}