NAME
    DateTime::TimeZone - Time zone object base class and factory

SYNOPSIS
      use DateTime;
      use DateTime::TimeZone;

      my $tz = DateTime::TimeZone->new( name => 'America/Chicago' );

      my $dt = DateTime->now();
      my $offset = $tz->offset_for_datetime($dt);

DESCRIPTION
    This class is the base class for all time zone objects. A time zone is
    represented internally as a set of observances, each of which describes
    the offset from GMT for a given time period.

    Note that without the "DateTime.pm" module, this module does not do
    much. It's primary interface is through a "DateTime" object, and most
    users will not need to directly use "DateTime::TimeZone" methods.

USAGE
    This class has the following methods:

  DateTime::TimeZone->new( name => $tz_name )
    Given a valid time zone name, this method returns a new time zone
    blessed into the appropriate subclass. Subclasses are named for the
    given time zone, so that the time zone "America/Chicago" is the
    DateTime::TimeZone::America::Chicago class.

    If the name given is a "link" name in the Olson database, the object
    created may have a different name. For example, there is a link from the
    old "EST5EDT" name to "America/New_York".

    When loading a time zone from the Olson database, the constructor checks
    the version of the loaded class to make sure it matches the version of
    the current DateTime::TimeZone installation. If they do not match it
    will issue a warning. This is useful because time zone names may fall
    out of use, but you may have an old module file installed for that time
    zone.

    There are also several special values that can be given as names.

    If the "name" parameter is "floating", then a
    "DateTime::TimeZone::Floating" object is returned. A floating time zone
    does have *any* offset, and is always the same time. This is useful for
    calendaring applications, which may need to specify that a given event
    happens at the same *local* time, regardless of where it occurs. See RFC
    2445 for more details.

    If the "name" parameter is "UTC", then a "DateTime::TimeZone::UTC"
    object is returned.

    If the "name" is an offset string, it is converted to a number, and a
    "DateTime::TimeZone::OffsetOnly" object is returned.

   The "local" time zone
    If the "name" parameter is "local", then the module attempts to
    determine the local time zone for the system.

    First it checks $ENV for keys named "TZ", "SYS$TIMEZONE_RULE",
    "SYS$TIMEZONE_NAME", "UCX$TZ", or "TCPIP$TZC" (the last 4 are for VMS).
    If this is defined, and it is not the string "local", then it is treated
    as any other valid name (including "floating"), and the constructor
    tries to create a time zone based on that name.

    Next, it checks for the existence of a symlink at /etc/localtime. It
    follows this link to the real file and figures out what the file's name
    is. It then tries to turn this name into a valid time zone. For example,
    if this file is linked to /usr/share/zoneinfo/US/Central, it will end up
    trying "US/Central", which will then be converted to "America/Chicago"
    internally.

    Some systems just copy the relevant file to /etc/localtime instead of
    making a symlink. In this case, we look in /usr/share/zoneinfo for a
    file that has the same size and content as /etc/localtime to determine
    the local time zone.

    Then it checks for a file called /etc/timezone or /etc/TIMEZONE. If one
    of these exists, it is read and it tries to create a time zone with the
    name contained in the file.

    Finally, it checks for a file called /etc/sysconfig/clock. If this file
    exists, it looks for a line inside the file matching
    "/^(?:TIME)?ZONE="([^"]+)"/". If this line exists, it tries the value as
    a time zone name.

    If none of these methods work, it gives up and dies.

  $tz->offset_for_datetime( $dt )
    Given a "DateTime" object, this method returns the offset in seconds for
    the given datetime. This takes into account historical time zone
    information, as well as Daylight Saving Time. The offset is determined
    by looking at the object's UTC Rata Die days and seconds.

  $tz->offset_for_local_datetime( $dt )
    Given a "DateTime" object, this method returns the offset in seconds for
    the given datetime. Unlike the previous method, this method uses the
    local time's Rata Die days and seconds. This should only be done when
    the corresponding UTC time is not yet known, because local times can be
    ambiguous due to Daylight Saving Time rules.

  $tz->name
    Returns the name of the time zone. If this value is passed to the
    "new()" method, it is guaranteed to create the same object.

  $tz->short_name_for_datetime( $dt )
    Given a "DateTime" object, this method returns the "short name" for the
    current observance and rule this datetime is in. These are names like
    "EST", "GMT", etc.

    It is strongly recommended that you do not rely on these names for
    anything other than display. These names are not official, and many of
    them are simply the invention of the Olson database maintainers.
    Moreover, these names are not unique. For example, there is an "EST" at
    both -0500 and +1000/+1100.

  $tz->is_floating
    Returns a boolean indicating whether or not this object represents a
    floating time zone, as defined by RFC 2445.

  $tz->is_utc
    Indicates whether or not this object represents the UTC (GMT) time zone.

  $tz->has_dst_changes
    Indicates whether or not this zone has *ever* had a change to and from
    DST, either in the past or future.

  $tz->is_olson
    Returns true if the time zone is a named time zone from the Olson
    database.

  $tz->category
    Returns the part of the time zone name before the first slash. For
    example, the "America/Chicago" time zone would return "America".

  DateTime::TimeZone->is_valid_name($name)
    Given a string, this method returns a boolean value indicating whether
    or not the string is a valid time zone name. If you are using
    "DateTime::TimeZone::Alias", any aliases you've created will be valid.

  DateTime::TimeZone->all_names
    This returns a pre-sorted list of all the time zone names. This list
    does not include link names. In scalar context, it returns an array
    reference, while in list context it returns an array.

  DateTime::TimeZone->categories
    This returns a list of all time zone categories. In scalar context, it
    returns an array reference, while in list context it returns an array.

  DateTime::TimeZone->links
    This returns a hash of all time zone links, where the keys are the old,
    deprecated names, and the values are the new names. In scalar context,
    it returns a hash reference, while in list context it returns a hash.

  DateTime::TimeZone->names_in_category( $category )
    Given a valid category, this method returns a list of the names in that
    category, without the category portion. So the list for the "America"
    category would include the strings "Chicago", "Kentucky/Monticello", and
    "New_York". In scalar context, it returns an array reference, while in
    list context it returns an array.

    The list is returned in order of population by zone, which should mean
    that this order will be the best to use for most UIs.

  DateTime::TimeZone->countries()
    Returns a sorted list of all the valid country codes (in lower-case)
    which can be passed to "names_in_country()". In scalar context, it
    returns an array reference, while in list context it returns an array.

    If you need to convert country codes to names or vice versa you can use
    "Locale::Country" to do so.

  DateTime::TimeZone->names_in_country( $country_code )
    Given a two-letter ISO3066 country code, this method returns a list of
    time zones used in that country. The country code may be of any case. In
    scalar context, it returns an array reference, while in list context it
    returns an array.

  DateTime::TimeZone->offset_as_seconds( $offset )
    Given an offset as a string, this returns the number of seconds
    represented by the offset as a positive or negative number. Returns
    "undef" if $offset is not in the range "-99:59:59" to "+99:59:59".

    The offset is expected to match either
    "/^([\+\-])?(\d\d?):(\d\d)(?::(\d\d))?$/" or
    "/^([\+\-])?(\d\d)(\d\d)(\d\d)?$/". If it doesn't match either of these,
    "undef" will be returned.

    This means that if you want to specify hours as a single digit, then
    each element of the offset must be separated by a colon (:).

  DateTime::TimeZone->offset_as_string( $offset )
    Given an offset as a number, this returns the offset as a string.
    Returns "undef" if $offset is not in the range -359999 to 359999.

  Storable Hooks
    This module provides freeze and thaw hooks for "Storable" so that the
    huge data structures for Olson time zones are not actually stored in the
    serialized structure.

    If you subclass "DateTime::TimeZone", you will inherit its hooks, which
    may not work for your module, so please test the interaction of your
    module with Storable.

SUPPORT
    Support for this module is provided via the datetime@perl.org email
    list. See http://datetime.perl.org/?MailingList for details.

    Please submit bugs to the CPAN RT system at
    http://rt.cpan.org/NoAuth/ReportBug.html?Queue=datetime%3A%3Atimezone or
    via email at bug-datetime-timezone@rt.cpan.org.

AUTHOR
    Dave Rolsky <autarch@urth.org>

CREDITS
    This module was inspired by Jesse Vincent's work on
    Date::ICal::Timezone, and written with much help from the
    datetime@perl.org list.

COPYRIGHT
    Copyright (c) 2003-2008 David Rolsky. 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.

SEE ALSO
    datetime@perl.org mailing list

    http://datetime.perl.org/

    The tools directory of the DateTime::TimeZone distribution includes two
    scripts that may be of interest to some people. They are parse_olson and
    tests_from_zdump. Please run them with the --help flag to see what they
    can be used for.

