=pod

=head1 NAME

DateTime::TimeZone::Alias - Create aliases for DateTime timezones

=head1 SYNOPSIS

    use DateTime::TimeZone::Alias Hawaii => 'Pacific/Honolulu',
                                  EST => 'Australia/Melbourne';

    or

    DateTime::TimeZone::Alias->add( Fun => 'America/Tijuana', %hash );

    or

    DateTime::TimeZone::Alias->set( Pain => 'America/Dawson_Creek', %hash );
    DateTime::TimeZone::Alias->set( boat => 'floating' );
    DateTime::TimeZone::Alias->set( home => 'local' );
    DateTime::TimeZone::Alias->set( lulu => 'Z' );
    DateTime::TimeZone::Alias->set( cut => 'UTC' );
    DateTime::TimeZone::Alias->set( nowhere => '-09:30' );

    or

    DateTime::TimeZone::Alias->remove( qw( Hawaii EST Pain Fun ) );

    or

    DateTime::TimeZone::Alias->value( 'EST' );

    or

    DateTime::TimeZone::Alias->is_defined( 'Hawaii' )
    DateTime::TimeZone::Alias->is_alias( 'EST' )
    DateTime::TimeZone::Alias->is_timezone( 'Antarctica/Vostok' )

    or

    DateTime::TimeZone::Alias->aliases
    DateTime::TimeZone::Alias->timezones

=head1 DESCRIPTION

Creates and destroys aliases for DateTime timezones.  This module violates 
the encapsulation of the DateTime internals.  User _Beware_.

=head1 IMPORT PARAMETERS

Accepts a hash representing an alias and the timezone it should map too.
Import has the exact same behaviors as the C<set> method.

=head1 METHODS

=over 4

=item * set( alias => timezone, ... ) 

Accepts a hash representing an alias and the timezone it should map too.
If an invalid timezone value or no parameters are passed an exception is thrown.
It is possible to create an alias to another alias.  This method will
redefine an existing alias or add a new alias that overrides an existing
timezone.

What may be aliased:

    aliases
    floating
    local
    OffsetOnly
    Olson time zones
    UTC
    Z

=item * add( alias => timezone, ... ) 

Accepts a hash representing an alias and the timezone it should map too.
If an invalid timezone value or no parameters are passed an exception is thrown.
It is possible to create an alias to another alias.
This method will _not_ redefine an existing alias or allow you remap a
timezone.  For redefinitions see the C<set> method.

=item * remove( alias, ... )

Accepts a list of aliases to be removed.  If an the name of an aliases that
doesn't exist is passed in then an exception is thrown.  It's important to 
note that you can remove aliases but not timezones.  However, a redefined timezone
is actually an alias and can be removed.

=item * value( $str )

If $str is a known alias then the timezone being aliased is returned, otherwise undef.

=item * is_defined( $str )

If $str is a known timezone or alias this method returns 1, otherwise undef is returned. 

=item * is_alias( $str )

If $str is a known alias this method returns 1, otherwise undef is returned. 

=item * is_timezone( $str )

If $str is a known timezone this method returns 1, otherwise undef is returned. 

=item * aliases

In list context a hash of all known aliases and their values is returned.
In scalar context a reference to a hash is returned.

=item * timezones

In list context an array of all known timezones is returned.
In scalar context a reference to an array is returned.

=back

=head1 GOTCHAS

=head2 Import

Multiple C<use DateTime::TimeZone::Alias> statements in the same package may
not have the desired result if attempting to redefine existing aliases.  If
you want to redefine an alias use the C<set> method instead.

=head2 Aliasing

You can _not_ create circular aliases.  E.g.

    # TSH actually points to value of HST - 'Pacific/Honolulu'
    # if HST wasn't already defined this would be an exception
    DateTime::TimeZone::Alias->set( TSH => HST );

    # HST still points to 'Pacific/Honolulu'
    DateTime::TimeZone::Alias->set( HST => TSH );

Sorry - no evil here, move along.

=head2 Global Behavior

It's important to remember that aliases are global in scope. E.g.

    package Foo;

    DateTime::TimeZone::Alias->set( EST => 'US/Eastern' );

    Bar->bar();

    # this will fail because EST is no longer defined
    my $dt = DateTime->now( time_zone => 'EST' );

    package Bar;

    sub bar {
        DateTime::TimeZone::Alias->set( EST => 'US/Eastern' );
        .
        .

        DateTime::TimeZone::Alias->remove( qw( EST ) );
    }

There are many possible ways to avoid this trap.  The best solution is to
simply not write code like this.  If you insist on this style then you can try
one of the suggested work arounds.

=head3 Poor Man's DateTime::TimeZone::Alias

Sometimes DateTime::TimeZone::Alias may not be the best solution to your
problem.  Particularly if your in an environment that has poor C<sand-boxing>
such as C<mod_perl>.  E.g.

    use constant EST => 'US/Eastern';

    or

    sub EST () { 'US/Eastern' }
    .
    .

    my $dt = DateTime->new( %params, time_zone => EST );

=head3 store/restore

This probably isn't thread safe.  E.g.

    sub bar {
        my $my_alias = DateTime::TimeZone::Alias->value( 'EST' );
        DateTime::TimeZone::Alias->set( EST => 'US/Eastern' );
        .
        .

        DateTime::TimeZone::Alias->set( EST => $my_alias );
    }

If C<$my_alias> is undefined then the C<set> will fail as an alias must point to a
valid timezone.

=head1 DEVELOPER NOTES

The C<aliases> and C<timezones> methods preserve encapsulation by returning a
reference to a copy of the internal data structures instead of a direct
reference.

=head1 CREDITS

Ben Bennett (BBENNETT) for a bug report, some API suggestions,
documentation suggestions, and being so darn enthusiastic.
(not necessary in that order)

Everyone at the DateTime C<Asylum>.

=head1 SUPPORT
  
Support for this module is provided via the datetime@perl.org email
list. See http://lists.perl.org/ for more details.
 
=head1 AUTHOR

Joshua Hoblitt <jhoblitt@cpan.org>

=head1 COPYRIGHT

Copyright (c) 2003 Joshua Hoblitt.  All rights reserved.  This program
is free software; you can redistribute it and/or modify it under the
same terms as Perl itself.

The full text of the license can be found in the LICENSE file included
with this module.

=head1 SEE ALSO

datetime@perl.org mailing list

http://datetime.perl.org/

=cut