#!usr/bin/perl
use strict;
use warnings;

my $sequence='ABCD';
my @headings= qw/ Tags Frequency /;
my $headings=join("\t",@headings);
my @input_files=<*.seq>;

foreach my $input_file (@input_files)
{
    open INPUT, "<", $input_file or die "Cannot open file \"$input_file\". $!";
    (my $outfile = $input_file) =~ s/.seq/\.tag\.txt/i;
    my %freq;
    
    while (my $line=<INPUT>)
    {
        
        if ($line=~m/$sequence(.{11})(.{11})$sequence/i){
	    my $revcomp=reverse($1);
	    $revcomp=~tr/ACGTacgt/TGCAtgca/;

             $freq{$_}++ for $revcomp, $2;
           }
        
    }
    close INPUT or die "Cannot close file \"$input_file\". $!";
    open OUTPUT, ">", $outfile or die "Cannot open file \"$outfile\".
+ $!";
    
    print OUTPUT $headings, "\n";
    for my $tag (sort {$freq{$b} <=> $freq{$a}} keys %freq) {
        	print OUTPUT $tag,"\t",$freq{$tag},"\n"; 
    }

    close OUTPUT or die "Unable to close \"$outfile\". $!";
}