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

#define LINEPIX 2100
#define XW 50
#define YW 100
#define KMAX 1000

void printerror( int status );

int main(int argc, char *argv[])
{
  fitsfile *fp;
  int i,j,status,nfound,anynull,bitpix=-32;
  long fpixel, nelements,naxis=2;
  long naxes[2]={LINEPIX, LINEPIX},nbuffer;
  float nullval;
  static float buffer[LINEPIX],z[LINEPIX][LINEPIX];
  int k;
  float zod[4][KMAX],ztmp;
  double lev,ave[4];

  if(argc!=3 && argc!=4){
    fprintf(stderr,"Usage : %s input_file output_file [lev]\n",argv[0]);
    exit(0);
  }

  fprintf(stderr,"Read %s  ... ",argv[1]);

  status=0;
  if(fits_open_file(&fp,argv[1], READONLY, &status))
    printerror(status);
  if(fits_read_keys_lng(fp, "NAXIS", 1, 2, naxes, &nfound, &status))
    printerror(status);
  fprintf(stderr,"%ld x %ld format ",naxes[0],naxes[1]);
  if((naxes[0]>LINEPIX)||(naxes[1]>LINEPIX)){
    fprintf(stderr,"\nIllegal image format\n");
    exit(0);
  }
  fpixel = 1;
  nullval = 0;
  nbuffer = naxes[0];
  for(i=0;i<naxes[1];i++){
    if (fits_read_img(fp, TFLOAT, fpixel, nbuffer, &nullval,
                      buffer, &anynull, &status))
      printerror(status);
    for(j=0;j<naxes[0];j++) z[i][j]=buffer[j];
    fpixel+=naxes[0];
  }
  if(fits_close_file(fp, &status))
    printerror(status);
  fprintf(stderr,"OK\n");

  if(argc==4) sscanf(argv[3],"%lf",&lev);
  else{
    for(i=0;i<4;i++){
      for(k=0;k<KMAX;k++) zod[i][k]=0;
    }
    for(i=0;i<YW;i++){
      for(j=naxes[0]/2-XW;j<naxes[0]/2;j++){
	if(zod[0][0]<z[i][j]){
	  zod[0][0]=z[i][j];
	  for(k=1;k<KMAX;k++){
	    if(zod[0][k]<zod[0][k-1]){
	      ztmp=zod[0][k];
	      zod[0][k]=zod[0][k-1];
	      zod[0][k-1]=ztmp;
	    }else break;
	  }
	}
      }
      for(j=naxes[0]/2;j<naxes[0]/2+XW;j++){
	if(zod[1][0]<z[i][j]){
	  zod[1][0]=z[i][j];
	  for(k=1;k<KMAX;k++){
	    if(zod[1][k]<zod[1][k-1]){
	      ztmp=zod[1][k];
	      zod[1][k]=zod[1][k-1];
	      zod[1][k-1]=ztmp;
	    }else break;
	  }
	}
      }
    }
    for(i=naxes[1]-YW;i<naxes[1];i++){
      for(j=naxes[0]/2-XW;j<naxes[0]/2;j++){
	if(zod[2][0]<z[i][j]){
	  zod[2][0]=z[i][j];
	  for(k=1;k<KMAX;k++){
	    if(zod[2][k]<zod[2][k-1]){
	      ztmp=zod[2][k];
	      zod[2][k]=zod[2][k-1];
	      zod[2][k-1]=ztmp;
	    }else break;
	  }
	}
      }
      for(j=naxes[0]/2;j<naxes[0]/2+XW;j++){
	if(zod[3][0]<z[i][j]){
	  zod[3][0]=z[i][j];
	  for(k=1;k<KMAX;k++){
	    if(zod[3][k]<zod[3][k-1]){
	      ztmp=zod[3][k];
	      zod[3][k]=zod[3][k-1];
	      zod[3][k-1]=ztmp;
	    }else break;
	  }
	}
      }
    }
    for(i=0;i<4;i++){
      ave[i]=0;
      for(k=KMAX/10;k<KMAX;k++) ave[i]+=zod[i][k]/KMAX/0.9;
    }
    fprintf(stderr,"%g %g %g %g\n",ave[0],ave[1],ave[2],ave[3]);
    lev=(ave[1]-ave[0]+ave[2]-ave[3])/2/(1-(double)YW/naxes[1]);
  }
  fprintf(stderr,"fixed level=%g\n",lev);

  for(i=0;i<naxes[1]/2;i++){
    for(j=0;j<naxes[0]/2;j++) z[i][j]-=lev*(naxes[0]-2*j)/naxes[0];
  }
  for(i=0;i<naxes[1]/2;i++){
    for(j=0;j<naxes[0]/2;j++) z[i][j+naxes[0]/2]-=lev*(naxes[1]-2*i)/naxes[1];
  }
  for(i=0;i<naxes[1]/2;i++){
    for(j=0;j<naxes[0]/2;j++) z[i+naxes[1]/2][j]-=lev*(2*i)/naxes[1];
  }
  for(i=0;i<naxes[1]/2;i++){
    for(j=0;j<naxes[0]/2;j++) z[i+naxes[1]/2][j+naxes[0]/2]-=lev*(2*j)/naxes[0];
  }

  fprintf(stderr,"Write %s  ... ",argv[2]);
  status=0;
  if (fits_create_file(&fp, argv[2], &status))
    printerror(status);
  if (fits_create_img(fp, bitpix, naxis, naxes, &status))
    printerror(status);
  fpixel=1;
  nelements=naxes[0];
  for(i=0;i<naxes[1];i++){
    if (fits_write_img(fp, TFLOAT, fpixel, nelements, z[i], &status))
      printerror(status);
    fpixel+=naxes[0];
  }
  if (fits_close_file(fp, &status))
    printerror(status);
  fprintf(stderr,"OK\n");
  return(0);
}

void printerror( int status)
{
    /*****************************************************/
    /* Print out cfitsio error messages and exit program */
    /*****************************************************/

    char status_str[FLEN_STATUS], errmsg[FLEN_ERRMSG];

    if (status)
      fprintf(stderr, "\n*** Error occurred during program execution ***\n");

    fits_get_errstatus(status, status_str);   /* get the error description */
    fprintf(stderr, "\nstatus = %d: %s\n", status, status_str);

    /* get first message; null if stack is empty */
    if ( fits_read_errmsg(errmsg) )
    {
         fprintf(stderr, "\nError message stack:\n");
         fprintf(stderr, " %s\n", errmsg);

         while ( fits_read_errmsg(errmsg) )  /* get remaining messages */
             fprintf(stderr, " %s\n", errmsg);
    }

    exit( status );       /* terminate the program, returning error status */
}