package DateTime::Event::Easter; use DateTime; use DateTime::Set; use Carp; use Params::Validate qw( validate SCALAR BOOLEAN OBJECT ); use strict; use vars qw( $VERSION @ISA @EXPORT @EXPORT_OK ); require Exporter; @ISA = qw(Exporter); @EXPORT_OK = qw(easter); $VERSION = '1.04'; sub new { my $class = shift; my %args = validate( @_, { easter => { type => SCALAR, default=>'western', optional=>1, regex => qr/^(western|eastern)$/i }, day => { type => SCALAR, default=>'sunday', optional=>1 }, as => { type => SCALAR, default=>'point', optional=>1 }, } ); my %self; my $offset; if ($args{day} =~/^palm/i) { $offset = -7; } elsif ($args{day} =~/saturday/i) { $offset = -1; } elsif ($args{day} =~/friday/i) { $offset = -2; } elsif ($args{day} =~/thursday/i) { $offset = -3; } elsif ($args{day} =~/^\-?\d+$/i) { $offset = $args{day}; } else { $offset = 0; } $self{offset} = DateTime::Duration->new(days=>$offset); $self{easter} = lc $args{easter}; if ($self{easter} eq 'eastern') { require DateTime::Calendar::Julian; } # Set to return points or spans die("Argument 'as' must be 'point' or 'span'.") unless $args{as}=~/^(point|span)s?$/i; $self{as} = lc $1; return bless \%self, $class; } sub following { my $self = shift; my $dt = shift; my $class = ref($dt); if ($self->{easter} eq 'eastern' && $class ne 'DateTime::Calendar::Julian') { croak ("Dates need to be datetime objects") unless ($dt->can('utc_rd_values')); $dt = DateTime::Calendar::Julian->from_object(object=>$dt); } elsif ($class ne 'DateTime') { croak ("Dates need to be datetime objects") unless ($dt->can('utc_rd_values')); $dt = DateTime->from_object(object=>$dt); } my $easter_this_year = $self->_easter($dt->year)+$self->{offset}; my $easter = ($easter_this_year > $dt) ? $easter_this_year : $self->_easter($dt->year+1)+$self->{offset}; $easter = $class->from_object(object=>$easter) if (ref($easter) ne $class); return ($self->{as} eq 'span') ? _tospan($easter) : $easter; } sub previous { my $self = shift; my $dt = shift; my $class = ref($dt); if ($self->{easter} eq 'eastern' && $class ne 'DateTime::Calendar::Julian') { croak ("Dates need to be datetime objects") unless ($dt->can('utc_rd_values')); $dt = DateTime::Calendar::Julian->from_object(object=>$dt); } elsif ($class ne 'DateTime') { croak ("Dates need to be datetime objects") unless ($dt->can('utc_rd_values')); $dt = DateTime->from_object(object=>$dt); } my $easter_this_year = $self->_easter($dt->year)+$self->{offset}; my $easter = ($easter_this_year->ymd lt $dt->ymd) ? $easter_this_year : $self->_easter($dt->year-1)+$self->{offset}; $easter = $class->from_object(object=>$easter) if (ref($easter) ne $class); return ($self->{as} eq 'span') ? _tospan($easter) : $easter; } sub closest { my $self = shift; my $dt = shift; my $class = ref($dt); if ($class ne 'DateTime') { croak ("Dates need to be datetime objects") unless ($dt->can('utc_rd_values')); $dt = DateTime->from_object(object=>$dt); } if ($self->is($dt)) { my $easter = $dt->clone->truncate(to=>'day'); $easter = $class->from_object(object=>$easter) if (ref($easter) ne $class); return ($self->{as} eq 'span') ? _tospan($easter) : $easter; } my $following_easter = $self->following($dt); my $following_delta = $following_easter - $dt; my $previous_easter = $self->previous($dt); my $easter = ($previous_easter + $following_delta < $dt) ? $following_easter : $previous_easter; $easter = $class->from_object(object=>$easter) if (ref($easter) ne $class); return ($self->{as} eq 'span') ? _tospan($easter) : $easter; } sub is { my $self = shift; my $dt = shift; my $class = ref($dt); if ($class ne 'DateTime') { croak ("Dates need to be datetime objects") unless ($dt->can('utc_rd_values')); $dt = DateTime->from_object(object=>$dt); } if ($self->{easter} eq 'eastern') { $dt = DateTime::Calendar::Julian->from_object(object=>$dt) } my $easter_this_year = $self->_easter($dt->year)+$self->{offset}; return ($easter_this_year->ymd eq $dt->ymd) ? 1 : 0; } sub as_list { my $self = shift; my %args = validate( @_, { from => { type => OBJECT }, to => { type => OBJECT }, inclusive => { type => SCALAR, default=>0 }, } ); # Make sure our args are in the right order ($args{from}, $args{to}) = sort ($args{from}, $args{to}); my @set = (); if ($args{inclusive}) { if ($self->is($args{from})) { push(@set,$args{from}); } if ($self->is($args{to})) { push(@set,$args{to}); } } my $checkdate = $args{from}; while ($checkdate < $args{to}) { $checkdate = $self->following($checkdate); push(@set,$checkdate) if ($checkdate < $args{to}); } return sort @set; } sub as_old_set { my $self = shift; return DateTime::Set->from_datetimes( dates => [ $self->as_list(@_) ] ); } sub as_set { my $self = shift; my %args = @_; if (exists $args{inclusive}) { croak("You must specify both a 'from' and a 'to' datetime") unless ref($args{to})=~/DateTime/ and ref($args{from})=~/DateTime/; if ($args{inclusive}) { $args{start} = delete $args{from}; $args{end} = delete $args{to}; } else { $args{after} = delete $args{from}; $args{before} = delete $args{to}; } delete $args{inclusive}; } elsif (exists $args{from} or exists $args{to}) { croak("You must specify both a 'from' and a 'to' datetime") unless ref($args{to})=~/DateTime/ and ref($args{from})=~/DateTime/; $args{after} = delete $args{from}; $args{before} = delete $args{to}; } return DateTime::Set->from_recurrence( next => sub { return $_[0] if $_[0]->is_infinite; $self->following( $_[0] ) }, previous => sub { return $_[0] if $_[0]->is_infinite; $self->previous( $_[0] ) }, %args ); } sub as_span { my $self = shift; $self->{as} = 'span'; return $self; } sub as_point { my $self = shift; $self->{as} = 'point'; return $self; } sub _tospan { return DateTime::Span->from_datetime_and_duration( start => $_[0], hours => 24, ); } sub _easter { my $self = shift; my $year = shift; return ($self->{easter} eq 'eastern') ? eastern_easter($year) : western_easter($year); } sub western_easter { my $year = shift; croak "Year value '$year' should be numeric." if $year!~/^\-?\d+$/; my $golden_number = $year % 19; #quasicentury is so named because its a century, only its # the number of full centuries rather than the current century my $quasicentury = int($year / 100); my $epact = ($quasicentury - int($quasicentury/4) - int(($quasicentury * 8 + 13)/25) + ($golden_number*19) + 15) % 30; my $interval = $epact - int($epact/28)*(1 - int(29/($epact+1)) * int((21 - $golden_number)/11) ); my $weekday = ($year + int($year/4) + $interval + 2 - $quasicentury + int($quasicentury/4)) % 7; my $offset = $interval - $weekday; my $month = 3 + int(($offset+40)/44); my $day = $offset + 28 - 31* int($month/4); return DateTime->new(year=>$year, month=>$month, day=>$day); } *easter = \&western_easter; #alias so people can call 'easter($year)' externally sub eastern_easter { my $year = shift; croak "Year value '$year' should be numeric." if $year!~/^\-?\d+$/; my $golden_number = $year % 19; my $interval = ($golden_number * 19 + 15) % 30; my $weekday = ($year + int($year/4) + $interval) % 7; my $offset = $interval - $weekday; my $month = 3 + int(($offset+40)/44); my $day = $offset + 28 - 31* int($month/4); return DateTime::Calendar::Julian->new(year=>$year, month=>$month, day=>$day); } sub _floor { my $x = shift; my $ix = int $x; if ($ix <= $x) { return $ix; } else { return $ix - 1; } } 1; __END__ =head1 NAME DateTime::Event::Easter - Returns Easter events for DateTime objects =head1 SYNOPSIS use DateTime::Event::Easter; $dt = DateTime->new( year => 2002, month => 3, day => 31, ); $easter_sunday = DateTime::Event::Easter->new(); $previous_easter_sunday = $easter_sunday->previous($dt); # Sun, 15 Apr 2001 00:00:00 UTC $following_easter_sunday = $easter_sunday->following($dt); # Sun, 20 Apr 2003 00:00:00 UTC $closest_easter_sunday = $easter_sunday->closest($dt); # Sun, 31 Mar 2002 00:00:00 UTC $is_easter_sunday = $easter_sunday->is($dt); # 1 $palm_sunday = DateTime::Event::Easter->new(day=>'Palm Sunday'); $dt2 = DateTime->new( year => 2060, month => 4, day => 30, ); @set = $palm_sunday->as_list(from=>$dt, to=>$dt2, inclusive=>1); # Sun, 13 Apr 2003 00:00:00 UTC # Sun, 04 Apr 2004 00:00:00 UTC # Sun, 20 Mar 2005 00:00:00 UTC # Sun, 09 Apr 2006 00:00:00 UTC $datetime_set = $palm_sunday->as_set; # A set of every Palm Sunday ever. See C for more information. =head1 DESCRIPTION The DateTime::Event::Easter module returns Easter events for DateTime objects. From a given datetime, it can tell you the previous, the following and the closest Easter event. The 'is' method will tell you if the given DateTime is an Easter Event. Easter Events can be Palm Sunday, Maundy Thursday, Good Friday, Black Saturday and Easter Sunday. If that's not enough, the module will also accept an offset so you can get the date for Pentecost (49 days after Easter Sunday) by passing 49. =head1 BACKGROUND Easter Sunday is the Sunday following the first full moon on or following the Official Vernal Equinox. The Official Vernal Equinox is March 21st. Easter Sunday is never on the full moon. Thus the earliest Easter can be is March 22nd. In the orthodox world, although they now use the Gregorian Calendar rather than the Julian, they still take the first full moon after the Julian March 21st. As the Julian calendar is slowly getting further and further out of sync with the Gregorian, the first full moon after this date can be a completely different one than for the western Easter. This is why the Orthodox churches celebrate Easter later than western churches. =head1 CONSTRUCTOR This class accepts the following options to its 'new' constructor: =over 4 =item * easter => ([western]|eastern) DateTime::Event::Easter understands two calculations for Easter. For simplicity we've called them 'western' and 'eastern'. Western Easter is the day celebrated by the Catholic and Protestant churches. It falls on the first Sunday on or after the the first Full Moon after March 21st. Eastern Easter, as celebrated by the Eastern Orthodox Churches similarly falls on the first Sunday on or after the the first Full Moon after March 21st. However Eastern Easter uses March 21st in the Julian Calendar. By default this module uses the Western Easter. Even if you pass a Julian DateTime to the module, you'll get back Western Easter unless you specifically ask for Eastern. If this parameter is not supplied, the western Easter will be used. =item * day => ([Easter Sunday]|Palm Sunday|Maundy Thursday|Good Friday|Black Saturday|I) When constructed with a day parameter, the method can return associated Easter days other than Easter Sunday. The constructor also allows an integer to be passed here as an offset. For example, Maundy Thursday is the same as an offset of -3 (Three days before Easter Sunday) When constructed without a day parameter, the method uses the date for Easter Sunday (which is the churches' official day for 'Easter', think of it a 'Easter Day' if you want) This parameter also allows the following abreviations: day => ([Sunday]|Palm|Thursday|Friday|Saturday) =item * as => ([point]|span) By default, all returns are single points in time. Namely they are the moment of midnight for the day in question. If you want Easter 2003 then you actually get back midnight of April 20th 2003. If you specify C 'span'> in your constructor, you'll now receive 24 hour spans rather than moments (or 'points'). I and C methods below> =back =head1 METHODS For all these methods, unless otherwise noted, $dt is a plain vanila DateTime object or a DateTime object from any DateTime::Calendar module that can handle calls to from_object and utc_rd_values (which should be all of them, but there's nothing stopping someone making a bad egg). This class offers the following methods. =over 4 =item * following($dt) Returns the DateTime object for the Easter Event after $dt. This will not return $dt. =item * previous($dt) Returns the DateTime object for the Easter Event before $dt. This will not return $dt. =item * closest($dt) Returns the DateTime object for the Easter Event closest to $dt. This will return midnight of $dt if $dt is the Easter Event. =item * is($dt) Return positive (1) if $dt is the Easter Event, otherwise returns false (0) =item * as_list(from => $dt, to => $dt2, inclusive=>I<([0]|1)>) Returns a list of Easter Events between I and I. If the optional I parameter is true (non-zero), the to and from dates will be included if they are the Easter Event. If you do not include an I parameter, we assume you do not want to include these dates (the same behaviour as supplying a false value) =item * as_set() Returns a DateTime::Set of Easter Events. In the past this method used the same syntax as 'as_list' above. However we now allow both the above syntax as well as the full options allowable when creating sets with C. This means you can call C<$datetime_set = $palm_sunday->as_set;> and it will return a C of all Palm Sundays. See C for more information. =item * as_span() This method switches output to spans rather than points. See the 'as' attribute of the constructor for more information. The method returns the object for easy chaining. =item * as_point() This method switches output to points rather than spans. See the 'as' attribute of the constructor for more information. The method returns the object for easy chaining. =back =head1 EXPORTS This class does not export any methods by default, however the following exports are supported. =over 4 =item * easter($year) Given a Gregorian year, this method will return a DateTime object for Western Easter Sunday in that year. =back =head1 THE SMALL PRINT =head2 REFERENCES =over 4 =item * http://datetime.perl.org - The official home of the DateTime project =item * http://www.tondering.dk/claus/calendar.html - Claus Tøndering's calendar FAQ =back =head2 SUPPORT Support for this module, and for all DateTime modules will be given through the DateTime mailing list - datetime@perl.org. Bugs should be reported through rt.cpan.org. =head2 AUTHOR Rick Measham =head2 CREDITS Much help from the DateTime mailing list, especially from: B - who pointed out flaws causing errors on gregorian years with no eastern easter (like 35000) and who came up with a patch to make the module accept any calendar's DateTime object B - who picked nits, designed DateTime itself and leads the project B - who pointed out the posibility of memory leak with an early beta =head2 COPYRIGHT (c) Copyright 2003 Rick Measham. 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. =head2 SEE ALSO L, L, perl(1), http://datetime.perl.org.