/* ppm.c */

/* This is a general parser for reading ppm files. */

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

int main()
{
   char id[3] = {0, 0, 0};
   int  vals[6];
   int  count = 0;
   char *buf = malloc(256);
   int  rc;
   unsigned char *base;
   unsigned char *im1;
   unsigned char *im2;
   int  size;
   int  i;

/* Acquire first line of text */

   fgets(buf, 256, stdin);

/* Extract the P5 or P6 tag */

   memcpy(id, buf, 2);

/* Try to get any numeric values that follow the tag */

   rc = sscanf(buf + 2, "%d %d %d", vals, vals + 1, vals + 2);

/* Update count if any were obtained */

   if (rc > 0)
      count = rc;

/* Loop until we have 3 values or run out of data */

   while (count < 3)
   {

   /* Break out of loop on end of file */

      if (fgets(buf, 256, stdin) <= 0)
          break;

   /* Try again to get three values */
   /* Its important to read them into the array starting */
   /* at the proper offset which is the value of count.  */

      rc = sscanf(buf, "%d %d %d", &vals[count],
                          &vals[count + 1], &vals[count + 2]);

   /* If values were obtained update count */

      if (rc > 0)
         count += rc;

   }

/* With any luck we have now processed a complete header   */
/* vals[0] has number of image columns, vals[1] the number */
/* of rows. Save total number of pixels in "size"          */

   size = vals[0] * vals[1];

/* Allocate input and output pixel arrays .. need 3 bytes */
/* per pixel in the input image.. only 1 byte per pix in  */
/* the output.                                            */

   im1 = (unsigned char *)malloc(3 * size);
   im2 = (unsigned char *)malloc(    size);

/* Need to remember the start address of the output array */
/* so we can write it out after we fill it in.            */

   base = im2;

   count = fread(im1, 3, size, stdin);

/* If it didn't work warn the customer */

   if (count != size)
   {
       fprintf(stderr, "Tried to read %d but read %d \n",
                                             size, count);
       perror("Error was");
       exit(1);
   }

   for (i = 0; i < size; i++)
   {
      float sum = 0.0;

   /* Build output value */

      sum += 0.30 * *im1;
      sum += 0.59 * *(im1 + 1);
      sum += 0.11 * *(im1 + 2);

   /* Store it in the output pixel array */

      *im2 = sum + 0.5;

   /* Advance both ptrs to next pixel */

      im2 += 1;
      im1 += 3;
   }

/* Write the P5 header... Don't want extra spaces after 3rd value */
/* MUST have \n after last value                                  */

   fprintf(stdout, "P5 %d %d %d\n", vals[0], vals[1], vals[2]);

/* Write output image */

   count = fwrite(base, 1, size, stdout);

/* If it didn't work warn the customer */

   if (count != size)
   {
       fprintf(stderr, "Tried to write %d but wrote %d \n",
                        size, count);
       perror("Error was");
   }
   fclose(stdout);

   return(0);
}