/* This program searches the header of the fits file, which is specified on
   the command line.  It then changes the header to the value specified on 
   the command line:

   ch_head <field> <value> <fits file>
   
   */

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

char *field;             /*  Standard length of a FITS field name */
char *value;      /*  Standard length of the value (I hope)*/
char *new_value;  /* what we want instead of the read-in value */

main(int argc, char **argv)
{
    int i;
    float max, min;
    FILE *file;

    if (argc < 3) {   /*  No file specified !  */
       fprintf(stderr, "Usage:  fits_head <field> <value> <file specs>\n");
       fprintf(stderr, "    field:       The field to modify\n");
       fprintf(stderr, "    value:       The new value of the field\n");
       fprintf(stderr, "    file specs:  The fits files to examine\n");
       exit(1);
    }
    else {
       field = argv[1];
       new_value = argv[2];
    }

    for (i = 0 ; i < argc - 3 ; ++i) {
       file = fopen(argv[i+3], "rb");
       read_header(file);
    }
}

read_header(FILE *fp)
{
    static unsigned char fcard[80]; /* basic FITS card, 36 to a block of 2880 bytes */
    static unsigned char new_fcard[80];
    char *trailer;
    int end = 0; /* assume the worst! */
    int length = 0;
    while( fread(fcard,1,80,fp) == 80 ) {
        length = strlen(field); 
        if( strncasecmp(fcard,field,length) == 0 ) { 
           /* fprintf(stderr,"%p\n", fcard+9); */
           value = fcard+9;
           trailer = fcard+30;
           sprintf(fcard, "%-8s=%21s%50s", field, new_value, trailer);
           fwrite(fcard,1,80,stdout);
        }
/*        else if( strncasecmp(fcard,"END",3) == 0 ) { 
           fwrite(fcard,1,80,stdout); 
           end = 1; break; 
        }*/
        else {
           fwrite(fcard,1,80,stdout);
        }
    }
    return;
}