package CodeGenerator;

use strict;
use warnings;

sub new {
    my $class = shift;
    my $self = bless {}, $class;
    $self->{string_size} = shift;
    $self->{digits_used} = [ @_ ];
    $self->{seen} = {};  # Not necessary, but helpful to 
                         # those reading the code.
    return $self;
}

sub generate {
    my $self = shift;
    my $rand_string;
    do{
        $rand_string = '';
        $rand_string .= 
            $self->{digits_used}[ rand @{$self->{digits_used}} ] 
                for 1 .. $self->{string_size};
    } while( $self->{seen}{$rand_string}++ );
    return $rand_string;
}

1;

package main;

use strict;
use warnings;
use autodie;
use v5.10;  #  For "say".

# Some criteria.  
my @digits_used = ( 'a' .. 'z', 3, 4, 6, 7, 9 );
my $string_length = 10;
my $need = 6_000_000;
my $filename = 'testfile.txt';

my $codegen = CodeGenerator->new( $string_length, @digits_used );

open my $out_fh, '>', $filename;

for( my $count = 0; $count < $need; $count++ ) {
    say $out_fh $codegen->generate();
}


close $out_fh;