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

unless (@ARGV){
    #part A
    print "Enter the name of an input file: \n";
    chomp (my $in_file = <STDIN>);
    -e $in_file and -s _ and -r _ or
	die "File doesn't exist, is empty, or isn't readable\n";

    open my $in_fh, '<', $in_file or die "Could not open $in_file: $!\n";
    
    chomp (my $line = <$in_fh>);
    my ($n1, $n2) = split ' ', $line;
    
    print "Enter the name of an output file:\n";
    chomp (my $out_file = <STDIN>);
    
    open my $out_fh, '>', $out_file or die "Could not open $out_file: $!\n";

    my $old_fh = select $out_fh;
    print "$n1 + $n2 = ", $n1 + $n2, "\n";
    print "$n1 - $n2 = ", $n1 - $n2, "\n";
    print "$n1 * $n2 = ", $n1 * $n2, "\n";
    print "$n1 / $n2 = ", $n1 / $n2, "\n";

    close $out_fh or die "Could not close $out_file: $!\n";

} else {

    my %files_starting_with;
    my %files_named;

    for my $directory (@ARGV){
	unless (-e $directory and -d _){
	    warn "$directory doesn't exist or isn't a directory.  Moving on\n";
	    next;
	}
	opendir my $dir_handle, $directory or die "Can't open $directory: $!\n";
	while (my $filename = readdir $dir_handle){
	    if (-f "$directory/$filename"){
		$files_named{$filename}++;
		$files_starting_with{lc substr($filename, 0, 1)}++;
	    }
	}
    }

    for my $filename (keys %files_named){
	print "There were $files_named{$filename} files named $filename\n";
    }

    print "\n\n";
    for my $letter ('a'..'z'){
	if (exists $files_starting_with{$letter}){
	    print "There were $files_starting_with{$letter} files starting with $letter\n";
	} else {
	    print "There were not any files starting with $letter\n";
	}
    }
}