package Class::MOP::Immutable;

use strict;
use warnings;

use Class::MOP::Method::Constructor;

use Carp         'confess';
use Scalar::Util 'blessed';

our $VERSION   = '0.04';
our $AUTHORITY = 'cpan:STEVAN';

sub new {
    my ($class, $metaclass, $options) = @_;

    my $self = bless {
        '$!metaclass'           => $metaclass,
        '%!options'             => $options,
        '$!immutable_metaclass' => undef,
    } => $class;

    # NOTE:
    # we initialize the immutable
    # version of the metaclass here
    $self->create_immutable_metaclass;

    return $self;
}

sub immutable_metaclass { (shift)->{'$!immutable_metaclass'} }
sub metaclass           { (shift)->{'$!metaclass'}           }
sub options             { (shift)->{'%!options'}             }

sub create_immutable_metaclass {
    my $self = shift;

    # NOTE:
    # The immutable version of the
    # metaclass is just a anon-class
    # which shadows the methods
    # appropriately
    $self->{'$!immutable_metaclass'} = Class::MOP::Class->create_anon_class(
        superclasses => [ blessed($self->metaclass) ],
        methods      => $self->create_methods_for_immutable_metaclass,
    );
}


my %DEFAULT_METHODS = (
    # I don't really understand this, but removing it breaks tests (groditi)
    meta => sub {
        my $self = shift;
        # if it is not blessed, then someone is asking
        # for the meta of Class::MOP::Immutable
        return Class::MOP::Class->initialize($self) unless blessed($self);
        # otherwise, they are asking for the metaclass
        # which has been made immutable, which is itself
        return $self;
    },
    is_mutable     => sub { 0  },
    is_immutable   => sub { 1  },
    make_immutable => sub { () },
);

# NOTE:
# this will actually convert the
# existing metaclass to an immutable
# version of itself
sub make_metaclass_immutable {
    my ($self, $metaclass, $options) = @_;

    foreach my $pair (
            [ inline_accessors   => 1     ],
            [ inline_constructor => 1     ],
            [ inline_destructor  => 0     ],
            [ constructor_name   => 'new' ],
            [ debug              => 0     ],
        ) {
        $options->{$pair->[0]} = $pair->[1] unless exists $options->{$pair->[0]};
    }

    my %options = %$options;

    if ($options{inline_accessors}) {
        foreach my $attr_name ($metaclass->get_attribute_list) {
            # inline the accessors
            $metaclass->get_attribute($attr_name)
                      ->install_accessors(1);
        }
    }

    if ($options{inline_constructor}) {
        my $constructor_class = $options{constructor_class} || 'Class::MOP::Method::Constructor';
        $metaclass->add_method(
            $options{constructor_name},
            $constructor_class->new(
                options   => \%options,
                metaclass => $metaclass,
                is_inline => 1,
            )
        ) unless $metaclass->has_method($options{constructor_name});
    }

    if ($options{inline_destructor}) {
        (exists $options{destructor_class})
            || confess "The 'inline_destructor' option is present, but "
                     . "no destructor class was specified";

        my $destructor_class = $options{destructor_class};

        my $destructor = $destructor_class->new(
            options   => \%options,
            metaclass => $metaclass,
        );

        $metaclass->add_method('DESTROY' => $destructor)
            # NOTE:
            # we allow the destructor to determine
            # if it is needed or not, it can perform
            # all sorts of checks because it has the
            # metaclass instance
            if $destructor->is_needed;
    }

    my $memoized_methods = $self->options->{memoize};
    foreach my $method_name (keys %{$memoized_methods}) {
        my $type = $memoized_methods->{$method_name};

        ($metaclass->can($method_name))
            || confess "Could not find the method '$method_name' in " . $metaclass->name;

        if ($type eq 'ARRAY') {
            $metaclass->{'___' . $method_name} = [ $metaclass->$method_name ];
        }
        elsif ($type eq 'HASH') {
            $metaclass->{'___' . $method_name} = { $metaclass->$method_name };
        }
        elsif ($type eq 'SCALAR') {
            $metaclass->{'___' . $method_name} = $metaclass->$method_name;
        }
    }

    $metaclass->{'___original_class'} = blessed($metaclass);
    bless $metaclass => $self->immutable_metaclass->name;
}

sub make_metaclass_mutable {
    my ($self, $immutable, $options) = @_;

    my %options = %$options;

    my $original_class = $immutable->get_mutable_metaclass_name;
    delete $immutable->{'___original_class'} ;
    bless $immutable => $original_class;

    my $memoized_methods = $self->options->{memoize};
    foreach my $method_name (keys %{$memoized_methods}) {
        my $type = $memoized_methods->{$method_name};

        ($immutable->can($method_name))
          || confess "Could not find the method '$method_name' in " . $immutable->name;
        if ($type eq 'SCALAR' || $type eq 'ARRAY' ||  $type eq 'HASH' ) {
            delete $immutable->{'___' . $method_name};
        }
    }

    if ($options{inline_destructor} && $immutable->has_method('DESTROY')) {
        $immutable->remove_method('DESTROY')
          if $immutable->get_method('DESTROY')->blessed eq $options{destructor_class};
    }

    # NOTE:
    # 14:01 <@stevan> nah,. you shouldnt
    # 14:01 <@stevan> they are just inlined
    # 14:01 <@stevan> which is the default in Moose anyway
    # 14:02 <@stevan> and adding new attributes will just DWIM
    # 14:02 <@stevan> and you really cant change an attribute anyway
    # if ($options{inline_accessors}) {
    #     foreach my $attr_name ($immutable->get_attribute_list) {
    #         my $attr = $immutable->get_attribute($attr_name);
    #         $attr->remove_accessors;
    #         $attr->install_accessors(0);
    #     }
    # }

    # 14:26 <@stevan> the only user of ::Method::Constructor is immutable
    # 14:27 <@stevan> if someone uses it outside of immutable,.. they are either: mst or groditi
    # 14:27 <@stevan> so I am not worried
    if ($options{inline_constructor}) {
        my $constructor_class = $options{constructor_class} || 'Class::MOP::Method::Constructor';
        $immutable->remove_method( $options{constructor_name}  )
          if $immutable->get_method($options{constructor_name})->blessed eq $constructor_class;
    }
}

sub create_methods_for_immutable_metaclass {
    my $self = shift;

    my %methods = %DEFAULT_METHODS;

    foreach my $read_only_method (@{$self->options->{read_only}}) {
        my $method = $self->metaclass->meta->find_method_by_name($read_only_method);

        (defined $method)
            || confess "Could not find the method '$read_only_method' in " . $self->metaclass->name;

        $methods{$read_only_method} = sub {
            confess "This method is read-only" if scalar @_ > 1;
            goto &{$method->body}
        };
    }

    foreach my $cannot_call_method (@{$self->options->{cannot_call}}) {
        $methods{$cannot_call_method} = sub {
            confess "This method ($cannot_call_method) cannot be called on an immutable instance";
        };
    }

    my $memoized_methods = $self->options->{memoize};
    foreach my $method_name (keys %{$memoized_methods}) {
        my $type = $memoized_methods->{$method_name};
        if ($type eq 'ARRAY') {
            $methods{$method_name} = sub { @{$_[0]->{'___' . $method_name}} };
        }
        elsif ($type eq 'HASH') {
            $methods{$method_name} = sub { %{$_[0]->{'___' . $method_name}} };
        }
        elsif ($type eq 'SCALAR') {
            $methods{$method_name} = sub { $_[0]->{'___' . $method_name} };
        }
    }

    $methods{get_mutable_metaclass_name} = sub { (shift)->{'___original_class'} };

    $methods{immutable_transformer} = sub { $self };

    return \%methods;
}

1;

__END__

=pod

=head1 NAME

Class::MOP::Immutable - A class to transform Class::MOP::Class metaclasses

=head1 SYNOPSIS

    use Class::MOP::Immutable;

    my $immutable_metaclass = Class::MOP::Immutable->new($metaclass, {
        read_only   => [qw/superclasses/],
        cannot_call => [qw/
            add_method
            alias_method
            remove_method
            add_attribute
            remove_attribute
            add_package_symbol
            remove_package_symbol
        /],
        memoize     => {
            class_precedence_list             => 'ARRAY',
            compute_all_applicable_attributes => 'ARRAY',
            get_meta_instance                 => 'SCALAR',
            get_method_map                    => 'SCALAR',
        }
    });

    $immutable_metaclass->make_metaclass_immutable(@_)

=head1 DESCRIPTION

This is basically a module for applying a transformation on a given
metaclass. Current features include making methods read-only,
making methods un-callable and memoizing methods (in a type specific
way too).

This module is not for the feint of heart, it does some whacky things
to the metaclass in order to make it immutable. If you are just curious, 
I suggest you turn back now, there is nothing to see here.

=head1 METHODS

=over 4

=item B<new ($metaclass, \%options)>

Given a C<$metaclass> and a set of C<%options> this module will
prepare an immutable version of the C<$metaclass>, which can then
be applied to the C<$metaclass> using the C<make_metaclass_immutable>
method.

=item B<options>

Returns the options HASH set in C<new>.

=item B<metaclass>

Returns the metaclass set in C<new>.

=item B<immutable_metaclass>

Returns the immutable metaclass created within C<new>.

=back

=over 4

=item B<create_immutable_metaclass>

This will create the immutable version of the C<$metaclass>, but will
not actually change the original metaclass.

=item B<create_methods_for_immutable_metaclass>

This will create all the methods for the immutable metaclass based
on the C<%options> passed into C<new>.

=item B<make_metaclass_immutable (%options)>

This will actually change the C<$metaclass> into the immutable version.

=item B<make_metaclass_mutable (%options)>

This will change the C<$metaclass> into the mutable version by reversing
the immutable process. C<%options> should be the same options that were
given to make_metaclass_immutable.

=back

=head1 AUTHORS

Stevan Little E<lt>stevan@iinteractive.comE<gt>

=head1 COPYRIGHT AND LICENSE

Copyright 2006-2008 by Infinity Interactive, Inc.

L<http://www.iinteractive.com>

This library is free software; you can redistribute it and/or modify
it under the same terms as Perl itself.

=cut