#!/usr/bin/perl

# Routine to find and remove the spurious FITS headers from some of the 
# NNSN FITS files, add a block of nulls to make the byte counts work, and
# insert an explanatory NOTE into the corresponding PDS labels.
#
# Format:  fixshort [fits_file_list]
#
# 23 Aug 2006, acr.
#
#============================================================================

$TMPFILE = "__bob.tmp";
$FMT     = "%-78.78s\r\n";  # Label line output format

# Initialize a block of nulls to write on the end of affected FITS files:

for ($i=0; $i<2880; $i++)
  { substr($nullbuff,$i,1) = "\x00"; }

# Loop through the input files:

while ($file = shift @ARGV)
  { open (FIT,"$file")    || die "Could not open $file ($!)";
    open (TMP,">$TMPFILE") || die "Could not open $TMPFITS ($!)";

    # Transfer the first two blocks, which are always OK:

    read(FIT,$block,5760);
    syswrite(TMP,$block,5760);

    # Read the third block and look for a spurious label:

    read(FIT,$block,2880);
    if (substr($block,0,10) ne "SIMPLE  = ")  # Not a label - nothing to do
      { close(FIT);
        close(TMP);
        unlink $TMPFILE;
        printf "$file is OK\n";
        next;
      }

    # All right, we know a couple things: We have a file that needs
    # correcting; and the spurious FITS header is only one block long.
    # So, we'll begin by transferring the rest of the existing FITS 
    # blocks to the temp file:

    while (!eof FIT)
      { read(FIT,$block,2880); 
        syswrite(TMP,$block,2880);
      }
    close(FIT);

    # Now add the block of null bytes, to balance the byte counts:

    syswrite(TMP,$nullbuff,2880);

    # And we're done with the FITS file:

    close(TMP);
    rename $TMPFILE, $file;

    # Now, we need to find the corresponding PDS label and add a note:

    $labelfile = $file;
    $labelfile =~ s/fit$/lbl/;

    open(LBL,$labelfile) || die "Could not open $labelfile ($!)";
    open(TMP,">$TMPFILE") || die "Could not open $TMPFILE ($!)";

    # We want to insert a NOTE just above the "END_OBJECT = IMAGE" line
    # in the label (because it's easy to find), so we read through the
    # label until we find that line:

    $line = <LBL>;
    while ($line !~ /END_OBJECT\s*=\s*IMAGE/)
      { printf TMP $line;
        $line = <LBL>;
      }

    # Now we insert the note:

    printf TMP $FMT,"  NOTE                     = \"";
    printf TMP $FMT,"    This file was damaged during reprocessing in 1990.";
    printf TMP $FMT,"    As a result, the last 3.5 records in the image ";
    printf TMP $FMT,"    contain null bytes.";
    printf TMP $FMT,"    \"";

    # And transfer the rest of the label:

    printf TMP $line;
    while (!eof LBL)
      { $line = <LBL>;
        printf TMP $line;
      }

    close(TMP);
    close(LBL);

    rename $TMPFILE, $labelfile;
  }