#!/usr/bin/env perl

use warnings;

sub usage {
  my ($program, $error) = @_;
  print "Error: $error\n";
  print "Usage:\n";
  print "\tcat filename | $program --smudge filename";
  print "\tcat filename | $program --clean";
}

sub expand {
  my ($filename) = @_;
  my $sha1 = `git log --pretty=format:"%H" -1 -- $filename`;
  while($_ = <STDIN>) {
    s{\$ Header \$}{\$Header $sha1 Exp \$}xms;
    print;
  }
}

sub collapse {
  while ($_ = <STDIN>) {
    s{\$ Header [^\$]* \$}{\$Header\$}xms;
    print;
  }
}

my $program = $^X;
my ($option, $filename) = @ARGV;
$program =~ s{^.*/}{};

if ($option eq "--smudge") {
  usage($program, "please provide a filename with --smudge") if !$filename;
  expand($filename);
}
elsif ($option eq "--clean") {
  collapse();
}
else {
  usage($program, "unknown command-line option: $option");
}