package RPN;

use strict;
use warnings;
use Math::Trig;

require Exporter;

our @ISA = qw(Exporter);

# Items to export into callers namespace by default. Note: do not export
# names by default without a very good reason. Use EXPORT_OK instead.
# Do not simply export all your public functions/methods/constants.

# This allows declaration	use RPN ':all';
# If you do not need this, moving things directly into @EXPORT or @EXPORT_OK
# will save memory.
our %EXPORT_TAGS = ( 'all' => [ qw( rpn ) ] );

our @EXPORT_OK = ( @{ $EXPORT_TAGS{'all'} } );

our @EXPORT = qw( );

our $VERSION = '1.0';


# Preloaded methods go here.

my %operations = (
    "POP"  => (
		sub {
			my ($stackRef) = @_;

			if (scalar @{$stackRef} < 1)
			{
				return undef;
			}	

			pop @$stackRef;
		}
	),
    "DUP" => (
		sub {
			my ($stackRef) = @_;

			if (scalar @{$stackRef} < 1)
			{
				return undef;
			}	

			push (@$stackRef, @$stackRef[-1]);
		}
	),
    "PI" => (
		sub {
			my ($stackRef) = @_;

			if (scalar @{$stackRef} < 0)
			{
				return undef;
			}	

			push (@$stackRef, 4.0*atan2(1.0,1.0));
		}
	),
    "++" => (
		sub {
			my ($stackRef) = @_;

			if (scalar @{$stackRef} < 1)
			{
				return undef;
			}	

			@$stackRef[-1]++;
		}
	),
    "--" => (
		sub {
			my ($stackRef) = @_;

			if (scalar @{$stackRef} < 1)
			{
				return undef;
			}	
			
			@$stackRef[-1]--;
		}
	),
    "ABS" => (
		sub {
			my ($stackRef) = @_;

			if (scalar @{$stackRef} < 1)
			{
				return undef;
			}	

			push (@$stackRef, abs pop (@$stackRef));
		}
	),
    "COS" => (
		sub {
			my ($stackRef) = @_;

			if (scalar @{$stackRef} < 1)
			{
				return undef;
			}	

			push (@$stackRef, cos pop (@$stackRef));
		}
	),
    "EXP" => (
		sub {
			my ($stackRef) = @_;

			if (scalar @{$stackRef} < 1)
			{
				return undef;
			}	

			push (@$stackRef, exp pop (@$stackRef));
		}
	),
    "INT" => (
		sub {
			my ($stackRef) = @_;

			if (scalar @{$stackRef} < 1)
			{
				return undef;
			}	

			push (@$stackRef, int pop (@$stackRef));
		}
	),
    "LOG" => (
		sub {
			my ($stackRef) = @_;

			if (scalar @{$stackRef} < 1)
			{
				return undef;
			}	

			push (@$stackRef, log pop (@$stackRef));
		}
	),
    "ROUND" => (
		sub {
			my ($stackRef) = @_;

			if (scalar @{$stackRef} < 1)
			{
				return undef;
			}	

			push (@$stackRef, sprintf ("%.0f", pop (@$stackRef)));
		}
	),
    "SIN" => (
		sub {
			my ($stackRef) = @_;

			if (scalar @{$stackRef} < 1)
			{
				return undef;
			}	

			push (@$stackRef, sin pop (@$stackRef));
		}
	),
    "SQRT" => (
		sub {
			my ($stackRef) = @_;

			if (scalar @{$stackRef} < 1)
			{
				return undef;
			}	

			push (@$stackRef, sqrt pop (@$stackRef));
		}
	),
    "TAN" => (
		sub {
			my ($stackRef) = @_;

			if (scalar @{$stackRef} < 1)
			{
				return undef;
			}	

			push (@$stackRef, tan pop (@$stackRef));
		}
	),
    "%" => (
		sub {
			my ($stackRef) = @_;

			if (scalar @{$stackRef} < 2)
			{
				return undef;
			}	
			
			my $var2 = pop (@$stackRef);
			my $var1 = pop (@$stackRef);

			push (@$stackRef, $var1 % $var2);
		}
	),
    "*" => (
		sub {
			my ($stackRef) = @_;

			if (scalar @{$stackRef} < 2)
			{
				return undef;
			}	

			my $var2 = pop (@$stackRef);
			my $var1 = pop (@$stackRef);

			push (@$stackRef, $var1 * $var2);
		}
	),
    "+" => (
		sub {
			my ($stackRef) = @_;

			if (scalar @{$stackRef} < 2)
			{
				return undef;
			}	
	
			my $var2 = pop (@$stackRef);
			my $var1 = pop (@$stackRef);

			push (@$stackRef, $var1 + $var2);
		}
	),
    "-" => (
		sub {
			my ($stackRef) = @_;

			if (scalar @{$stackRef} < 2)
			{
				return undef;
			}	
	
			my $var2 = pop (@$stackRef);
			my $var1 = pop (@$stackRef);

			push (@$stackRef, $var1 - $var2);
		}
	),
    "/" => (
		sub {
			my ($stackRef) = @_;

			if (scalar @{$stackRef} < 2)
			{
				return undef;
			}	
	
			my $var2 = pop (@$stackRef);
			my $var1 = pop (@$stackRef);

			push (@$stackRef, $var1 / $var2);
		}
	),
    "ATAN2" => (
		sub {
			my ($stackRef) = @_;

			if (scalar @{$stackRef} < 2)
			{
				return undef;
			}	
	
			my $var2 = pop (@$stackRef);
			my $var1 = pop (@$stackRef);

			push (@$stackRef, atan2 $var1, $var2);
		}
	),
    "EXCH" => (
		sub {
			my ($stackRef) = @_;

			if (scalar @{$stackRef} < 2)
			{
				return undef;
			}	
	
			push (@$stackRef, (pop (@$stackRef), pop (@$stackRef)));
		}
	),
    "MAX" => (
		sub {
			my ($stackRef) = @_;

			if (scalar @{$stackRef} < 2)
			{
				return undef;
			}	
	
			my $var2 = pop (@$stackRef);
			my $var1 = pop (@$stackRef);

			push (@$stackRef, $var1 > $var2 ? $var1 : $var2);
		}
	),
    "MIN" => (
		sub {
			my ($stackRef) = @_;

			if (scalar @{$stackRef} < 2)
			{
				return undef;
			}	
	
			my $var2 = pop (@$stackRef);
			my $var1 = pop (@$stackRef);

			push (@$stackRef, $var1 < $var2 ? $var1 : $var2);
		}
	),
    "POW"  => (
		sub {
			my ($stackRef) = @_;

			if (scalar @{$stackRef} < 2)
			{
				return undef;
			}	
	
			my $var2 = pop (@$stackRef);
			my $var1 = pop (@$stackRef);

			push (@$stackRef, $var1 ** $var2);
		}
	)
);

sub rpn {
	my ( $RpnString ) = @_;

	# Check if RPN String is supplied.
	if(!defined $RpnString)
	{
		printf STDERR "RpnString needs to be supplied.\n";
		return undef;
	}

	# RPN value stack
	my @stack;

	for my $operand (split /\s+/, $RpnString)
	{
		if (defined $operations{$operand})
		{
			if(!defined($operations{$operand}->(\@stack)))
			{
				return undef;
			}
		}
		else
		{
			if ($operand =~ /^[-+]?[0-9]*\.?[0-9]+([eE][-+]?[0-9]+)?$/)
			{
				push (@stack, $operand);
			}
			else
			{
				print STDERR "RpnString contains a value that is not numeric or an operand.\n";
				return undef;
			}
		}
	}

	if (scalar @stack != 1)
	{
		print STDERR "After calculation there is not one value on stack.\n";
		return undef;
	}

	return $stack[0];
}

1;
__END__
# Below is stub documentation for your module. You'd better edit it!

=head1 NAME

RPN - Perl extension for blah blah blah

=head1 SYNOPSIS

  use RPN;
  blah blah blah

=head1 DESCRIPTION

Stub documentation for RPN, created by h2xs. It looks like the
author of the extension was negligent enough to leave the stub
unedited.

Blah blah blah.

=head2 EXPORT

None by default.



=head1 SEE ALSO

Mention other useful documentation such as the documentation of
related modules or operating system documentation (such as man pages
in UNIX), or any relevant external documentation such as RFCs or
standards.

If you have a mailing list set up for your module, mention it here.

If you have a web site set up for your module, mention it here.

=head1 AUTHOR

Stefan Suhren, E<lt>suhren.stefan@fh-swf.deE<gt>

=head1 COPYRIGHT AND LICENSE

Copyright (C) 2015 by Stefan Suhren

This library is free software; you can redistribute it and/or modify
it under the same terms as Perl itself, either Perl version 5.22.0 or,
at your option, any later version of Perl 5 you may have available.


=cut