#include <string.h>
#include <stdio.h>
#include "fitsio.h"

int main(int argc, char *argv[])
{
    fitsfile *fptr;         /* FITS file pointer, defined in fitsio.h */
    char card[FLEN_CARD], newcard[FLEN_CARD];
    char oldvalue[FLEN_VALUE], comment[FLEN_COMMENT];
    int status = 0;   /*  CFITSIO status value MUST be initialized to zero!  */
    int iomode, keytype;

    if (argc == 3) 
      iomode = READONLY;
    else if (argc == 4)
      iomode = READWRITE;
    else {
      printf("Usage:  modhead filename[ext] keyword newvalue\n");
      printf("\n");
      printf("Write or modify the value of a header keyword.\n");
      printf("If 'newvalue' is not specified then just print \n");
      printf("the current value. \n");
      printf("\n");
      printf("Examples: \n");
      printf("  modhead file.fits dec      - list the DEC keyword \n");
      printf("  modhead file.fits dec 30.0 - set DEC = 30.0 \n");
      return(0);
    }

    if (!fits_open_file(&fptr, argv[1], iomode, &status))
    {
      if (fits_read_card(fptr,argv[2], card, &status))
      {
        printf("Keyword does not exist\n");
        card[0] = '\0';
        comment[0] = '\0';
        status = 0;  /* reset status after error */
      }
      else
        printf("%s\n",card);

      if (argc == 4)  /* write or overwrite the keyword */
      {
          /* check if this is a protected keyword that must not be changed */
          if (*card && fits_get_keyclass(card) == TYP_STRUC_KEY)
          {
            printf("Protected keyword cannot be modified.\n");
          }
          else
          {
            /* get the comment string */
            if (*card)fits_parse_value(card, oldvalue, comment, &status);

            /* construct template for new keyword */
            strcpy(newcard, argv[2]);     /* copy keyword name */
            strcat(newcard, " = ");       /* '=' value delimiter */
            strcat(newcard, argv[3]);     /* new value */
            if (*comment) {
              strcat(newcard, " / ");  /* comment delimiter */
              strcat(newcard, comment);     /* append the comment */
            }

            /* reformat the keyword string to conform to FITS rules */
            fits_parse_template(newcard, card, &keytype, &status);

            /* overwrite the keyword with the new value */
            fits_update_card(fptr, argv[2], card, &status);

            printf("Keyword has been changed to:\n");
            printf("%s\n",card);
          }
      }  /* if argc == 4 */
      fits_close_file(fptr, &status);
    }    /* open_file */

    /* if error occured, print out error message */
    if (status) fits_report_error(stderr, status);
    return(status);
}