#!/usr/bin/env perl

#program to generate 6 Million unique codes, Oct 15, 2011.

use strict;
use warnings;
use autodie;
use v5.10;  # Just for feature "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';



# Takes a string length, and a list of digits allowed, and returns an
# iterator function that on each call returns a unique string.

sub create_random_string_generator {

    # Our bind values:
    my $size = shift;
    my @contains = @_;

    # Our duplicate cache.
    my %found;

    # Here's where we create an iterator function with bound criteria.

    return sub {
        my $rand_string;
        do{
            my @rand_digits;
            push @rand_digits, 
                 $contains[ rand @contains ] for 1 .. $size;
            $rand_string = join '', @rand_digits;
        } while( $found{$rand_string}++ );  
        return $rand_string;
    }

}



# Now we bind our criteria and create a generator iterator function.
my $string_gen = 
    create_random_string_generator( $string_length, @digits_used );


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

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


close $out_fh;


##</code><code>##

# Verify that there are no duplicates.
perl -nE 'say $_ if $seen{$_}++;' testfile.txt
# We want no output.


# Verify that there are 6000000 lines.
perl -nE '$count++; END{ say $count; }' testfile.txt
# We want 6000000 as the output.


# Verify that we only have digits between a..z and 3, 4, 6, 7, 9.
perl -nE 'say "$. : $_" if m/[^a-z34679\n]/' testfile.txt
# We want no output.

##</code><code>##

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;