package Math::Name::To::Be::Determined;

use warnings;
use strict;

our $VERSION = '0.01';

use vars qw(@ISA @EXPORT_OK %EXPORT_TAGS);
use Exporter;
@ISA = 'Exporter';

@EXPORT_OK = qw(
  clear_prime_cache
  is_prime
  primes_upto
);

%EXPORT_TAGS = (
    all => \@EXPORT_OK,
);

{
    my ( @PRIMES, %IS_PRIME );
    clear_prime_cache();

    sub is_prime {
        my $number = shift;
        return 1 if $IS_PRIME{$number};
        return   if $number < $PRIMES[-1];

        my $is_prime;
        for ( $PRIMES[-1] + 1 .. $number ) {

            # cache prime numbers
            if ( $is_prime = _is_prime($_) ) {
                push @PRIMES => $_;
            }
        }
        return $is_prime;
    }

    sub _is_prime {
        my $number = shift;
        return unless _is_integer($number);
        return 1 if $IS_PRIME{$number};
        return unless $number > 2 and $number % 2;

        my $max = 1 + int $number**.5;
        for ( my $divisor = 3; $divisor < $max; $divisor += 2 ) {
            return unless $number % $divisor;
        }
        $IS_PRIME{$number} = 1;    # cache it
        return 1;
    }

    sub primes_upto {
        my $number = shift;
        if ( $number > $PRIMES[-1] ) {

            # extend cache
            is_prime($number);
        }

        my (@primes);
        foreach my $i ( 0 .. @PRIMES ) {
            next if $number > $PRIMES[$i];
            @primes = @PRIMES[ 0 .. $i - 1 ] if $i;
            last;
        }
        return wantarray ? @primes : \@primes;
    }

    sub clear_prime_cache {
        @PRIMES = _get_primes();
        %IS_PRIME = map { $_ => 1 } @PRIMES;
        return;
    }
}

sub _is_integer {
    return shift =~ /^[-+]?\d+$/;
}

sub _get_primes {

    # list from Crypt::Primes
    # http://search.cpan.org/dist/Crypt-Primes/
    return (
        # huge list of all primes < 2^16
    );
}

1;