Date::Calendar(3)

NAME
Date::Calendar - Calendar objects for different holiday schemes

MOTTO
There is more than one way to do it - this is just one of them!

PREFACE
Basically, Date::Calendar is just a caching proxy class for Date::Calendar::Year objects, which are embedded in each Date::Calendar object.

However, and in contrast to Date::Calendar::Year methods, Date::Calendar methods permit calculations spanning an arbitrary number of years, without loss of efficiency.

So you should usually use Date::Calendar and not Date::Calendar::Year, since that way you don't have to worry about calculations crossing year boundaries.

Note however that Date::Calendar and Date::Calendar::Year can only deal with years lying within the range [1583..2299].

SYNOPSIS
  use Date::Calendar::Profiles qw( $Profiles );
  use Date::Calendar;

  $calendar_US_AZ  = Date::Calendar->new( $Profiles->{'US-AZ'} [,LANG[,WEEKEND]] );
  $calendar_DE_SN  = Date::Calendar->new( $Profiles->{'DE-SN'} [,LANG[,WEEKEND]] );

  $year_2000_US_AZ = $calendar_US_AZ->year( 2000 );
  $year_2001_DE_SN = $calendar_DE_SN->year( 2001 );

  @years = $calendar->cache_keys(); # returns list of year numbers
  @years = $calendar->cache_vals(); # returns list of year objects

  $calendar->cache_clr();
  $calendar->cache_add(YEAR|DATE,...);
  $calendar->cache_del(YEAR|DATE,...);

  $index        = $calendar->date2index(YEAR,MONTH,DAY|DATE);

  @names        = $calendar->labels(YEAR,MONTH,DAY|DATE);
  @holidays     = $calendar->labels();
  $holidays     = $calendar->labels();

  @dates        = $calendar->search(PATTERN);
  $dates        = $calendar->search(PATTERN);

  $hashref      = $calendar->tags(YEAR,MONTH,DAY|DATE);

  $days         = $calendar->delta_workdays(YEAR1,MONTH1,DAY1|DATE1
                                           ,YEAR2,MONTH2,DAY2|DATE2
                                           ,FLAG1,FLAG2);

  ($date,$rest) = $calendar->add_delta_workdays(YEAR,MONTH,DAY|DATE
                                               ,DELTA);
  $date         = $calendar->add_delta_workdays(YEAR,MONTH,DAY|DATE
                                               ,DELTA);

  $flag         = $calendar->is_full(YEAR,MONTH,DAY|DATE);
  $flag         = $calendar->is_half(YEAR,MONTH,DAY|DATE);
  $flag         = $calendar->is_work(YEAR,MONTH,DAY|DATE);

INTERFACE
Note that whenever a year number, a date, a time or a combined date and time are expected as input parameters by one of the methods of this class, you can always pass a Date::Calc[::Object] date object or an array reference (of an array of appropriate length) instead!

See Date::Calc::Object(3) for more details.

So instead of calling a given method like this:

  $object->method1( $year,$month,$day );
  $object->method2( $year1,$month1,$day1, $year2,$month2,$day2 );
  $object->method3( $year1, $year2, $year3 );

You can also call it like so:

  $object->method1( $date );
  $object->method1( [1964,1,3] );

  $object->method2( $year1,$month1,$day1, $date2 );
  $object->method2( $date1, $year2,$month2,$day2 );
  $object->method2( $date1, $date2 );
  $object->method2( $year1,$month1,$day1, [2001,3,17] );
  $object->method2( [1964,1,3], $year2,$month2,$day2 );
  $object->method2( [1964,1,3], [2001,3,17] );
  $object->method2( $date1, [2001,3,17] );
  $object->method2( [1964,1,3], $date2 );

  $object->method3( $year1, $date2, [2001,3,17] );

And similarly if a time or a combined date and time are expected.

If you substitute an expected year number by an anonymous array (this is the recommended way of writing date constants, for increased readability of your programs), it must contain three values, nevertheless (otherwise the use of an anonymous array would be pointless).

Don't confuse year numbers and their substitutes (a date object or an array reference) with Date::Calendar::Year objects, which are a totally different thing!

But incidentally ":-)", you may also pass a Date::Calendar::Year object whenever a year number is expected. However, and perhaps against your expectations at times, especially in conjunction with the method "cache_add()", only the year number from that object will be used, not the year object itself (the year object in question might be using the wrong profile!).

Moreover, whenever a method of this class returns a date, it does so by returning a Date::Calc[::Object] date object.

DESCRIPTION

•   "$calendar = Date::Calendar->new(PROFILE[,LANG[,WEEKEND]]);"

    The first argument must be the reference of a hash, which contains a holiday scheme or "profile" to be used in all calculations involving the new calendar object.

    The second argument is optional, and must consist of the valid name or number of a language as provided by the Date::Calc(3) module if given.

    After the second argument, a list of day numbers which will constitute the "weekend" can optionally be specified, where 1=Monday, 2=Tuesday, 3=Wednesday, 4=Thursday, 5=Friday, 6=Saturday and 7=Sunday.

    If no values are given, 6 and 7 (Saturday and Sunday) are automatically taken as default.

    If values outside of the range 1..7 are given, they will be ignored.

    This can be used to switch off this feature and to have no regularly recurring holidays at all when for instance a zero is given.

    See Date::Calendar::Profiles(3) and Date::Calendar::Year(3) for more details about these arguments and about how to roll your own calendar profiles.

    The method creates a new calendar object for a given profile, i.e., a given location and its scheme of holidays (or a scheme of your own).

    This calendar object is a caching proxy object; it stores the reference of the given profile and contains a hash (the cache) of Date::Calendar::Year objects.

•   "$year = $calendar->year(YEAR|DATE);"

    This method returns a Date::Calendar::Year object for the given year and the profile that was associated with the given calendar object.

    If the cache in the given calendar object already contains an object for the requested year, the corresponding object reference is simply returned.

    If not, a new Date::Calendar::Year object is created using the profile that has been associated with the given calendar object. The new Date::Calendar::Year object is then stored in the calendar object's cache and its object reference is returned.

    A fatal "given year out of range" error will occur if the given year number lies outside the valid range of [1583..2299].

•   "@years = $calendar->cache_keys();"

    This method returns the list of YEAR NUMBERS of the Date::Calendar::Year objects contained in the given calendar object's cache.

•   "@years = $calendar->cache_vals();"

    This method returns the list of OBJECT REFERENCES of the Date::Calendar::Year objects contained in the given calendar object's cache.

•   "$calendar->cache_clr();"

    This method clears the entire cache of the given calendar object (by destroying the cache hash and creating a new one).

•   "$calendar->cache_add(YEAR|DATE,...);"

    Roughly, this method is a shortcut for

      for $year (@list)
      {
          $calendar->year($year);
      }

•   "$calendar->cache_del(YEAR|DATE,...);"

    This method removes the Date::Calendar::Year objects whose year numbers are given from the cache of the given calendar object.

    Year numbers for which the calendar object's cache doesn't contain an entry are simply ignored.

•   "$index = $calendar->date2index(YEAR,MONTH,DAY|DATE);"

    This method converts a given date into the number of the day in that year (this is sometimes also referred to as the "julian" date), i.e., a number between 0 (for January 1st) and the number of days in the given year minus one, i.e., 364 or 365 (for December 31st).

    You may need this in order to access the bit vectors returned by the Date::Calendar::Year methods "vec_full()", "vec_half()" and "vec_work()".

    If the Date::Calendar::Year object for the given YEAR is not in the $calendar's cache yet, it will be created and added.

    An exception ("invalid date") is thrown if the given arguments do not constitute a valid date, or ("given year out of range [1583..2299]") if the given year lies outside of the permitted range.

•   "@names = $calendar->labels(YEAR,MONTH,DAY|DATE);"

    "@holidays = $calendar->labels();"

    "$holidays = $calendar->labels();"

    If any arguments are given, they are supposed to represent a date. In that case, a list of all labels (= names of holidays) associated with that date are returned. The first item returned is always the name of the day of week for that date. The corresponding year object for the given date's year is added to the calendar's cache first if necessary.

    If no arguments are given, the list of all available labels in all years that have previously been accessed in the given calendar (i.e., the years which are already in the given calendar's cache) is constructed. Note that this means that the returned list will be empty if there are no year objects in the given calendar's cache yet (!). The returned list does NOT include any names of the days of week (which would be pointless in this case).

    Multiple labels are reported only once.

    Usually all years have the same set of labels, so it may seem superfluous to scan all the years in the cache instead of just one. But there may be exceptions, because it is possible to define calendar profiles which do not contain all possible holidays in every year. See Date::Calendar::Profiles(3) and Date::Calendar::Year(3) for more details.

    In list context, the resulting list itself is returned. In scalar context, the number of items in the resulting list is returned.

•   "@dates = $calendar->search(PATTERN);"

    "$dates = $calendar->search(PATTERN);"

    This method searches through all the labels in all years that have previously been accessed in the given calendar (i.e., the years which are already in the given calendar's cache) and returns a list of date objects with all dates whose labels match the given pattern.

    (Use the methods "cache_clr()", "cache_add()" and "cache_del()" in order to put the year numbers you want into the calendar object's cache, or to make sure it only contains the year numbers you want to search.)

    Note that this is a simple, case-insensitive substring search, NOT a full-fledged regular expression search!

    The result is guaranteed to be sorted chronologically.

    In scalar context, only the number of items in the resulting list is returned, instead of the resulting list itself (as in list context).

•   "$hashref = $calendar->tags(YEAR,MONTH,DAY|DATE);"

    This method returns a hash reference for the given calendar and date. The hash it refers to is a copy of the calendar profile's internal hash which contains the names for the given date as keys and 0, 1, 2, or 3 as their corresponding values meaning the following:

        0    =>    commemorative day
        1    =>    "half" holiday
        2    =>    "full" holiday
        3    =>    both a "half" and a "full" holiday

    The value "3" should only occur if a date has been redefined by the underlying profile using the same key (i.e., the same name) but with a different type of holiday.

•   "$days = $calendar->delta_workdays(YEAR1,MONTH1,DAY1, YEAR2,MONTH2,DAY2, FLAG1,FLAG2);"

    "$days = $calendar->delta_workdays(DATE1,DATE2,FLAG1,FLAG2);"

    This method calculates the number of work days (i.e., the number of days, but excluding all holidays) between two dates.

    In other words, this method is equivalent to the "Delta_Days()" function of the Date::Calc module, except that it disregards holidays in its counting.

    The two flags indicate whether the start and end dates should be included in the counting (that is, of course, only in case they aren't holidays), or not.

    It is common, for example, that you want to know how many work days are left between the current date and a given deadline.

    Typically, you will want to count the current date but not the deadline's date. So you would specify "true" ("1") for FLAG1 and "false" ("0") for FLAG2 in order to achieve that.

    In other words, a value of "true" means "including this date", a value of "false" means "excluding this date".

    As with the "Delta_Days()" function from the Date::Calc module, the dates have to be given in chronological order to yield a positive result. If the dates are reversed, the result will be negative.

    The parameter FLAG1 is associated with the first given date, the parameter FLAG2 with the second given date (regardless of whether the dates are in chronological order or not).

    An exception ("invalid date") is raised if either of the two date arguments does not constitute a valid date.

•   "($date,$rest) = $calendar->add_delta_workdays(YEAR,MONTH,DAY, DELTA);"

    "($date,$rest) = $calendar->add_delta_workdays(DATE,DELTA);"

    "$date = $calendar->add_delta_workdays(YEAR,MONTH,DAY, DELTA);"

    "$date = $calendar->add_delta_workdays(DATE,DELTA);"

    This method is the equivalent of the "Add_Delta_Days()" function from the Date::Calc module, except that it adds work days and skips holidays.

    In other words, you can add or subtract a number of work days "DELTA" to/from a given date and get a new date as the result (as a Date::Calc object).

    You add days (i.e., you go forward in time) with a positive offset "DELTA", and you subtract days (i.e., you go backwards in time) with a negative offset.

    Note that an exception ("invalid date") is raised if the given date argument does not constitute a valid date.

    In scalar context, the method just returns the resulting date object, whereas in list context the method not only returns the new date, but also a "rest". This rest is useful for cases in which your profile contains "half" holidays, or when you add or subtract fractions of a day.

    Sometimes it is not possible to accomodate the requested number of work days, and a rest remains.

    This rest can currently only assume the value "0.0" (zero), "-0.5" (minus one half) or "0.5" (one half), provided you use only integral or multiples of 0.5 as offsets. A rest of zero indicates that the calculation yielded an exact result. If the rest is 0.5 or -0.5, this is to be interpreted as "the resulting date at 12:00 o'clock", instead of as "the resulting date at 0:00 o'clock".

    The rest is always positive (or zero) if the offset "DELTA" is positive (or zero), and always negative (or zero) if the offset is negative (or zero).

    Example:

      #!perl
      use Date::Calendar;
      use Date::Calendar::Profiles qw( $Profiles );
      $year = shift;
      $cal = Date::Calendar->new( $Profiles->{'sdm-MUC'} );
      ($date,$rest) = $cal->add_delta_workdays($year,1,3, -3);
      $date->date_format(1);
      print "\$date = $date, \$rest = $rest.\n";
      __END__

    This program calculates "January 3rd of the given year minus 3 work days":

      > perl test.pl 2001
      $date = 28-Dec-2000, $rest = 0.
      > perl test.pl 2002
      $date = 28-Dec-2001, $rest = -0.5.

    Note that December 31st is a "half" holiday in 2001 for the calendar profile used in this example.

    You can easily verify the results above with the help of the "calendar.cgi" CGI script or the "linearcal.pl" script from the "examples" subdirectory in the Date::Calc distribution.

    BEWARE that this method may currently return unexpected (i.e., contradicting the above documentation) or plain wrong results when going back in time (this is a bug!).

    However, it works correctly and as documented above when going forward in time.

•   "$flag = $calendar->is_full(YEAR,MONTH,DAY|DATE);"

    This method returns "true" ("1") if the bit corresponding to the given date is set in the bit vector representing "full" holidays, and "false" ("0") otherwise.

    I.e., the method returns "true" if the given date is a (full) holiday (according to the calendar profile associated with the given calendar object).

    The corresponding Date::Calendar::Year object is created first and stored in the calendar object's cache if necessary (if it's not already there).

    Note that you can get a reference to this bit vector (in order to use this bit vector in bit vector operations) as follows:

      $vec_full = $calendar->year($year)->vec_full();

    The number of bits in this bit vector is the same as the number of days in the given year "$year", which you can retrieve through either ""$days = $vec_full->Size();"" or ""$days = $year->val_days();"".

    See Date::Calendar::Year(3) and Bit::Vector(3) for more details.

•   "$flag = $calendar->is_half(YEAR,MONTH,DAY|DATE);"

    This method returns "true" ("1") if the bit corresponding to the given date is set in the bit vector representing "half" holidays, and "false" ("0") otherwise.

    I.e., the method returns "true" if the given date is a half holiday (according to the calendar profile associated with the given calendar object).

    Note that if a date is a "full" holiday, the "half" bit is never set, even if you try to do so in your calendar profile, on purpose or by accident.

    The corresponding Date::Calendar::Year object is created first and stored in the calendar object's cache if necessary (if it's not already there).

    Note that you can get a reference to this bit vector (in order to use this bit vector in bit vector operations) as follows:

      $vec_half = $calendar->year($year)->vec_half();

    The number of bits in this bit vector is the same as the number of days in the given year "$year", which you can retrieve through either ""$days = $vec_half->Size();"" or ""$days = $year->val_days();"".

    See Date::Calendar::Year(3) and Bit::Vector(3) for more details.

•   "$flag = $calendar->is_work(YEAR,MONTH,DAY|DATE);"

    This method returns "true" ("1") if the bit corresponding to the given date is set in the bit vector used to perform all sorts of calculations, and "false" ("0") otherwise.

    The corresponding Date::Calendar::Year object is created first and stored in the calendar object's cache if necessary (if it's not already there).

    BEWARE that the "work" in this method's name does NOT come from "work days"!

    It comes from the fact that the corresponding bit vector can be used for any "work" that you need to do. In other words, it's a "work space".

    Therefore, this bit vector might contain about everything you could imagine - including a bit pattern which marks all "work days" with set bits, if it so happens!

    But you better don't rely on it, unless you put the bit pattern there yourself in the first place.

    Note that you can get a reference to this bit vector (in order to fill it with any bit pattern you like) as follows:

      $vec_work = $calendar->year($year)->vec_work();

    The number of bits in this bit vector is the same as the number of days in the given year "$year", which you can retrieve through either ""$days = $vec_work->Size();"" or ""$days = $year->val_days();"".

    See Date::Calendar::Year(3) and Bit::Vector(3) for more details.

SEE ALSO
Date::Calendar::Year(3), Date::Calendar::Profiles(3), Date::Calc::Object(3), Date::Calc(3), Date::Calc::Util(3), Bit::Vector(3).

LIMITATIONS
The calendar profiles included in Date::Calendar::Profiles(3) usually do not take historical irregularities into account (even though some do in order to show how this can be done), they only provide means for calculating regularly recurring events (the profiles should therefore not be relied upon for historical faithfulness).

KNOWN BUGS
The method "add_delta_workdays()" is known to produce results which are sometimes off by one working day when a negative offset is used. As a workaround, try to add one working day first and then subtract one working day more than initially intended. See also the file "examples/bug.pl" for how to do this.

VERSION
This man page documents "Date::Calendar" version 6.3.

AUTHOR
  Steffen Beyer
  mailto:STBEY@cpan.org
  http://www.engelschall.com/u/sb/download/

COPYRIGHT
Copyright (c) 2000 - 2009 by Steffen Beyer. All rights reserved.

LICENSE
This package is free software; you can use, modify and redistribute it under the same terms as Perl itself, i.e., at your option, under the terms either of the "Artistic License" or the "GNU General Public License".

The C library at the core of the module "Date::Calc::XS" can, at your discretion, also be used, modified and redistributed under the terms of the "GNU Library General Public License".

Please refer to the files "Artistic.txt", "GNU_GPL.txt" and "GNU_LGPL.txt" in the "license" subdirectory of this distribution for any details!

DISCLAIMER
This package is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

See the "GNU General Public License" for more details.