package i18n;
$i18n::VERSION = '0.07';

=head1 NAME

i18n - Perl Internationalization Pragma

=head1 VERSION

This document describes version 0.07 of i18n, released November 4, 2004.

=head1 SYNOPSIS

In one-liners:

    % export LANG=sp
    % perl -Mi18n=/path/to/po-files/ -le 'print ~~"Hello, world"';
    Hola, mundo

In your module:

    use i18n "/path/to/po-files";
    my $place = ~~'world';
    print ~~"Hello, $world";

=head1 DESCRIPTION

Internationalization (abbreviated C<i18n>) is the process of designing an
application so that it can be adapted to various languages and regions.
The most basic task is to let your program know which strings are meant
for human consumption and which strings are intended for the computer.

Strings for humans need to get localized (translated to the language of
the human using your program) and strings for computers B<must not> get
translated.

=head2 Syntax

The C<i18n> module gives you a remarkably simple way to mark strings
that are intended for humans. All you do is put two tilde signs (C<~~>)
in front of every string that is intended to be translated.  That's it.
All the other details of localization are handled outside the program.
Here are some examples:

    my $str1 = ~~'The time is now';
    my $str2 = ~~"$str1 for having a cow";
    my $str3 = ~~qq{Wow! $str2};
    my $str4 = ~~<<END;
    How now.
    Brown cow.
    END

Think of the tilde signs as an indicator that you are looking for things
that B<approximates> the string in the user's language.  To turn off the
magic of C<~~> lexically, just say:

    no i18n;

One nice thing about this particular markup, is that you can completely
turn off internationalization, by simply removing the C<use i18n;> statement.
The C<~~> signs are actually valid Perl that just happen to not do anything
in this context, and thus are constant-optimized away at compile time.

=head2 Implementation

When you say:

    my $string = ~~"Bob is your uncle";

then C<$string> really is an C<i18n::string> object that is overloaded to
stringify as a localized translation.

Currently, the magic is just a thin wrapper on C<Locale::Maketext::Simple>,
which makes it equivalent to this call:

    my $string = loc("Bob is your uncle");

Similarly, this line:

    my $string = ~~"$person is your uncle";

will be turned into this at runtime:

    my $string = loc("[_1] is your uncle", $person);

=head1 CAVEATS

The authors of this module are not linguists.  If you would like to help us
define suitable C<i18n> magic for your language, please send us an email.

One thing we plan to do next is to provide collaborative, just-in-time lexicon
creation tools.  So Joe American could write his wonderful Perl script in
English, with the appropriate C<~~> notation, and 24 hours later it would "just
work" in Swahili.

=cut

use strict;
use constant DATA     => 0;
use constant LINE     => 1;
use constant PACKAGE  => 2;
use constant NEGATED  => 3;
use warnings::register;
use overload (
    '~'  => \&_negate,
    '.'	 => \&_concat,
    '""' => \&_stringify,
    fallback => 1,
);

sub import {
    my $class = shift;
    my $caller = caller;

    eval { require Locale::Maketext::Simple; 1 } or return;

    overload::constant(
	q => sub {
	    shift; pop;
	    bless([
		\@_,		# DATA
		(caller(1))[2],	# LINE
		$caller,	# PACKAGE
	    ], $class);
	},
    );

    {
	no strict 'refs';
	no warnings 'redefine';

	delete ${"$class\::"}{loc};
	delete ${"$class\::"}{loc_lang};

        unshift @_, 'Path' if @_ % 2;
	Locale::Maketext::Simple->import(@_);

	*{"$caller\::loc"} = $class->can('loc');
	*{"$caller\::loc_lang"} = $class->can('loc_lang');

	*{"$class\::loc"} = \&_loc;
	*{"$class\::loc_lang"} = \&_loc_lang;
    }

    @_ = (warnings => $class);
    goto &warnings::import;
}

sub unimport {
    my $class = shift;
    overload::remove_constant('q');

    @_ = (warnings => $class);
    goto &warnings::unimport;
}

sub loc { goto \&_loc }
sub loc_lang { goto \&_loc_lang }

sub _loc {
    my $class = shift;
    return $_[0] unless UNIVERSAL::can($_[0], '_negate');
    goto &_do_loc;
}

sub _loc_lang {
    my $class = shift;
    my $caller = caller;
    my $loc_lang = $caller->can('loc_lang') or return;
    goto &$loc_lang;
}

sub _negate {
    my $class = ref $_[0];

    return ~_stringify($_[0]) unless warnings::enabled($class);

    goto &_do_loc if $_[0][NEGATED];

    bless([
	[@{$_[0][DATA]}],   # DATA
	$_[0][LINE],	    # LINE
	$_[0][PACKAGE],	    # PACKAGE
	1,		    # NEGATED
    ], $class);
}

sub _concat {
    my $class = ref $_[0];
    my $pkg = $_[0][PACKAGE];

    @_ = reverse(@_) if pop;
    return join('', @_) unless warnings::enabled($class);

    my $line = (caller)[2];
    my ($seen, @data);

    foreach (@_) {
	(push(@data, bless(\\$_, "$class\::var")), next)
	    unless ref($_) and UNIVERSAL::isa($_, $class);
	$seen++;

	(push(@data, bless(\\$_, "$class\::var")), next)
	    unless $_->[LINE] == $line and !$_->[NEGATED];
	$seen++;

	$pkg = $_->[PACKAGE];
	push @data, @{$_->[DATA]};
    }

    return join('', @data) if $seen < 2;

    return bless([
	\@data,	    # DATA
	$line,	    # LINE
	$pkg,	    # PACKAGE
    ], $class);
}

sub _stringify {
    ($_[0][NEGATED])
	? ~join('', map { (ref $_) ? "$$$_" : "$_" } @{$_[0][DATA]})
	:  join('', map { (ref $_) ? "$$$_" : "$_" } @{$_[0][DATA]});
}

sub _do_loc {
    my $class = ref $_[0];
    my $pkg = $_[0][PACKAGE];

    ($pkg eq caller) and my $loc = $pkg->can('loc') 
	or return ~"$_[0]";

    my @vars;
    my $format = join('', map {
	UNIVERSAL::isa($_, "$class\::var")
	    ? do { push(@vars, $$$_); "[_".@vars."]" }
	    : do { my $str = $_; $str =~ s/(?=[\[\]~])/~/g; $str };
    } @{$_[0][DATA]});

    # Defeat constant folding
    return bless([$loc => $format], 'i18n::string') if !@vars;

    @_ = ($format, @vars);
    goto &$loc;
}

package i18n::string;

use overload (
    '""' => \&_stringify,
    '0+' => \&_stringify,
    fallback => 1,
);

sub _stringify {
    $_[0][0]->($_[0][1]);
}

package i18n::var;

use overload (
    '""' => \&_stringify,
    '0+' => \&_stringify,
    fallback => 1,
);

sub _stringify { ${${$_[0]}} }

1;

=head1 SEE ALSO

L<Locale::Maketext::Simple>, L<Locale::Maketext::Lexicon>

=head1 AUTHORS

Autrijus Tang E<lt>autrijus@autrijus.orgE<gt>,
Brian Ingerson E<lt>INGY@cpan.orgE<gt>.

=head1 COPYRIGHT

Copyright 2004 by
Autrijus Tang E<lt>autrijus@autrijus.orgE<gt>,
Brian Ingerson E<lt>INGY@cpan.orgE<gt>.

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

See L<http://www.perl.com/perl/misc/Artistic.html>

=cut