# Copyright (c) 1995-2021 Sullivan Beck. All rights reserved.
# This program is free software; you can redistribute it and/or modify it
# under the same terms as Perl itself.

=pod

=head1 NAME

Date::Manip::Base - Base methods for date manipulation

=head1 SYNOPSIS

   use Date::Manip::Base;
   $dmb = new Date::Manip::Base;

=head1 DESCRIPTION

The Date::Manip package of modules consists of several modules for
doing high level date operations with full error checking and a lot of
flexibility.

The high level operations, though intended to be used in most
situations, have a lot of overhead associated with them. As such, a
number of the most useful low level routines (which the high level
routines use to do much of the real work) are included in this module
and are available directly to users.

These low level routines are powerful enough that they can be used
independent of the high level routines and perform useful (though much
simpler) operations. They are also significantly faster than the high
level routines.

These routines do little error checking on input. Invalid data will
result in meaningless results.  If you need error checking, you must
call the higher level Date::Manip routines instead of these.

These routines also ignore all effects of time zones and daylight
saving time. One way to think of these routines is working with times
and dates in the GMT time zone.

=head1 BASE METHODS

This class inherits several base methods from the L<Date::Manip::Obj>
class. Please refer to the documentation for that class for a
description of those methods.

=over 4

=item B<err>

=item B<new>

=item B<new_config>

Please refer to the L<Date::Manip::Obj> documentation for these methods.

=item B<config>

   $dmb->config($var1,$val1,$var2,$val2,...);

This will set the value of any configuration variable. Please refer to the
L<Date::Manip::Config> manual for a list of all configuration variables and their
description.

=back

=head1 DATE METHODS

In all of the following method descriptions, the following variables
are used:

=over 4

=item B<$date>

This is a list reference containing a full date and time:

   [$y, $m, $d, $h, $mn, $s]

=item B<$ymd>

A list reference containing only the date portion:

   [$y, $m, $d]

=item B<$hms>

A list reference containing only the time portion:

   [$h, $mn, $s]

=item B<$delta>

A list containing a full delta (an amount of time elapsed, or a duration):

   [$dy, $dm, $dw, $dd, $dh, $dmn, $ds]

=item B<$time>

A list reference containing the hour/minute/second portion of a delta:

   [$dh, $dmn, $ds]

=item B<$offset>

A list containing a time zone expressed as an offset:

   [ $offh, $offm, $offs ]

Although this module does not make use of timezone information, a few of
the functions perform operations on time zone offsets, primarily because
these operations are needed in the higher level modules.

=back

The elements C<($y, $m, $d, $h, $mn, $s)> are all numeric. In most of
the routines described below, no error checking is done on the input.
C<$y> should be between 1 and 9999, C<$m> between 1 and 12, C<$d>
between 1 and 31, C<$h> should be between 0 and 23, C<$mn> and C<$s>
between 0 and 59.

C<$hms> can be between 00:00:00 and 24:00:00, but an C<$offset> must be
between -23:59:59 and +23:59:59.

Years are not translated to 4 digit years, so passing in a year of
"04" will be equivalent to "0004", NOT "2004".

The elements C<($dy, $dm, $dw, $dd, $dh, $dmn, $ds)> are all numeric,
but can be positive or negative. They represent an elapsed amount
of time measured in years, months, weeks, etc.

Since no error checking is done, passing in C<($y,$m,$d) = (2004,2,31)>
will NOT trigger an error, even though February does not have 31 days.
Instead, some meaningless result will be returned.

=over 4

=item B<calc_date_date>

=item B<calc_date_days>

=item B<calc_date_delta>

=item B<calc_date_time>

=item B<calc_time_time>

These are all routines for doing simple date and time calculations.
As mentioned above, they ignore all affects of time zones and daylight
saving time.

The following methods are available:

   $time = $dmb->calc_date_date($date1,$date2);

This take two dates and determine the amount of time between them.

   $date = $dmb->calc_date_days($date,$n [,$subtract]);
   $ymd  = $dmb->calc_date_days($ymd,$n [,$subtract]);

This returns a date C<$n> days later (if C<$nE<gt>0>) or earlier (if
C<$nE<lt>0>) than the date passed in. If C<$subtract> is passed in,
the sign of C<$n> is reversed.

   $date = $dmb->calc_date_delta($date,$delta [,$subtract]);

This take a date and add the given delta to it (or subtract the delta
if C<$subtract> is non-zero).

   $date = $dmb->calc_date_time($date,$time [,$subtract]);

This take a date and add the given time to it (or subtract the time
if C<$subtract> is non-zero).

   $time = $dmb->calc_time_time(@time1,@time2 [,$subtract]);

This take two times and add them together (or subtract the second from
the first if C<$subtract> is non-zero).

=item B<check>

=item B<check_time>

   $valid = $dmb->check($date);
   $valid = $dmb->check_time($hms);

This tests a list of values to see if they form a valid date or time
ignoring all time zone affects. The date/time would be valid in GMT,
but perhaps not in all time zones.

1 is returned if the the fields are valid, 0 otherwise.

C<$hms> is in the range 00:00:00 to 24:00:00.

=item B<cmp>

   $flag = $dmb->cmp($date1,$date2);

Returns -1, 0, or 1 if date1 is before, the same as, or after date2.

=item B<day_of_week>

   $day = $dmb->day_of_week($date);
   $day = $dmb->day_of_week($ymd);

Returns the day of the week (1 for Monday, 7 for Sunday).

=item B<day_of_year>

   $day = $dmb->day_of_year($ymd);
   $day = $dmb->day_of_year($date);

In the first case, returns the day of the year (1 to 366) for C<($y,
$m, $d)>.  In the second case, it returns a fractional day (1.0 <=
C<$day> < 367.0).  For example, day 1.5 falls on Jan 1, at noon.  The
somewhat non-intuitive answer (1.5 instead of 0.5) is to make the two
forms return numerically equivalent answers for times of 00:00:00
. You can look at the integer part of the number as being the day of
the year, and the fractional part of the number as the fraction of the
day that has passed at the given time.

The inverse operations can also be done:

   $ymd   = $dmb->day_of_year($y,$day);
   $date  = $dmb->day_of_year($y,$day);

If C<$day> is an integer, the year, month, and day is returned. If C<$day>
is a floating point number, it returns the year, month, day, hour,
minutes, and decimal seconds.

C<$day> must be greater than or equal to 1 and less than 366 on non-leap years
or 367 on leap years.

=item B<days_in_month>

   $days = $dmb->days_in_month($y,$m);

Returns the number of days in the month.

   @days = $dmb->days_in_month($y,0);

Returns a list of 12 elements with the days in each month of the year.

=item B<days_in_year>

   $days = $dmb->days_in_year($y);

Returns the number of days in the year (365 or 366)

=item B<days_since_1BC>

   $days = $dmb->days_since_1BC($date);
   $days = $dmb->days_since_1BC($ymd);

Returns the number of days since Dec 31, 1BC. Since the calendar has
changed a number of times, the number returned is based on the current
calendar projected backwards in time, and in no way reflects a true
number of days since then. As such, the result is largely meaningless,
except when called twice as a means of determining the number of days
separating two dates.

The inverse operation is also available:

   $ymd = $dmb->days_since_1BC($days);

Returns the date C<$days> since Dec 31, 1BC. So day 1 is Jan 1, 0001.

=item B<leapyear>

   $flag = $dmb->leapyear($y);

Returns 1 if the argument is a leap year.

=item B<nth_day_of_week>

   $ymd = $dmb->nth_day_of_week($y,$n,$dow);

Returns the C<$n>th occurrence of C<$dow> (1 for Monday, 7 for Sunday) in the
year.  C<$n> must be between 1 and 53 or -1 through -53.

   $ymd = $dmb->nth_day_of_week($y,$n,$dow,$m);

Returns the C<$n>th occurrence of C<$dow> in the given month.  C<$n>
must be between 1 and 5 or it can be -1 through -5.

In all cases, nothing is returned if C<$n> is beyond the last actual
result (i.e. the 5th Sunday in a month with only four Sundays).

=item B<secs_since_1970>

   $secs = $dmb->secs_since_1970($date);

Returns the number of seconds since Jan 1, 1970 00:00:00 (negative if date is
earlier).

   $date = $dmb->secs_since_1970($secs);

Translates number of seconds into a date.

=item B<split>

=item B<join>

The split and join functions are used to take a string containing a common
type of time data and split it into a list of fields. The join function takes
the list and forms it into a string.

The general format for these is:

  $obj    = $dmb->split($type,$string,\%opts);
  $string = $dmb->join($type,$obj,\%opts);

An older format is also supported:

  $obj    = $dmb->split($type,$string,[$no_normalize]);
  $string = $dmb->join($type,$obj,[$no_normalize]);

but this is deprecated and will be removed in Date::Manip 7.00.  These
are equivalent to:

  $obj    = $dmb->split($type,$string,{ 'nonorm' => $no_normalize });
  $string = $dmb->join($type,$obj,{ 'nonorm' => $no_normalize });

The value of C<$type> determines what type of join/split operation occurs.

Rudimentary error checking is performed with both of these functions
and undef is returned in the case of any error. No error checking is done
on the specific values.

=over 8

=item B<$type = 'date'>

   $date = $dmb->split("date",$string);
   $string = $dmb->join("date",$date);

This splits a string containing a date or creates one from a list reference.
The string split must be of one of the forms:

   YYYYMMDDHH:MN:SS
   YYYYMMDDHHMNSS
   YYYY-MM-DD-HH:MN:SS

The string formed by join is one of the above, depending on the value of
the Printable config variable. The default format is YYYYMMDDHH:MN:SS,
but if Printable is set to 1, YYYYMMDDHHMNSS is produced, and if Printable
is set to 2, the YYYY-MM-DD-HH:MN:SS form is produced.

=item B<$type = 'hms'>

   $hms = $dmb->split("hms",$string);
   $string = $dmb->join("hms",$hms);

This works with the hours, minutes, and seconds portion of a date.

When splitting a string, the string can be of any of the forms:

   H
   H:MN
   H:MN:SS
   HH
   HHMN
   HHMNSS

Here, H is a 1 or 2 digit representation of the hours but HH (and all
other fields) are two digit representations.

The string formed by the join function will always be of the form HH:MN:SS.

The time must be between 00:00:00 and 24:00:00.

=item B<$type = 'offset'>

   $offset = $dmb->split("offset",$string);
   $string = $dmb->join("offset",$offset);

An offset string should have a sign (though it is optional if it is
positive) and is any of the forms:

   +H
   +H:MN
   +H:MN:SS
   +HH
   +HHMN
   +HHMNSS

Here, H is a 1 or 2 digit representation of the hours. All other fields are
two digit representations.

The string formed by the join function will always be of the form
+HH:MN:SS.

The offset must be between -23:59:59 and +23:59:59 .

=item B<$type = 'time'>

   $time = $dmb->split("time",$string,\%opts]);
   $string = $dmb->join("time",$time,\%opts);

The only option supported is:

   'nonorm'   0/1

This works with an amount of time in hours, minutes, and seconds. The
string is of the format:

   +H:MN:S

where all signs are optional. The returned value (whether a list reference
from the split function, or a string from the join function) will have
all fields normalized unless C<no_norm> is true.

=item B<$type = 'delta'>

   $delta = $dmb->split("delta",$string,\%opts);
   $string = $dmb->join("delta",$delta,\%opts);

Options recognized are:

  mode     : standard/business
  nonorm   : 0/1
  type     : exact/semi/approx/estimated

A second format is also supported, but is deprecated and will be removed in
Date::Manip 7.0.

   $delta = $dmb->split("business",$string,\%opts);
   $string = $dmb->join("business",$delta,\%opts);

These are equivalent to using 'delta' with an option of C<'mode' => 'business'>.

These split a string containing a delta, or create a string
containing one using the rules described in the L<Date::Manip::Delta>
documentation.

The string that can be split is of the form:

  Y:M:W:D:H:MN:S

Any field may have a sign, but they are optional.

Fields may be omitted entirely. For example:

  D:H:MN:S
  D:::S

are both valid.

The string or list output is normalized unless the B<nonorm> option is passed in.

The type of the delta (which determines how it will be normalized) will be
automatically determined if not specified.  The type will default to the
value given in the table below based on the FIRST condition that is true.

   default_type  condition

   estimated     any field is a non-integer
   approx        any of the approximate fields are non-zero
   semi          any of the semi-exact fields are non-zero
   exact         only the exact fields are non-zero

=back

=item B<week1_day1>

   $ymd = $dmb->week1_day1($y);

This returns the date of the 1st day of the 1st week in the given year.
Note that this uses the ISO 8601 definition of week, so the year returned
may be the year before the one passed in.

This uses the FirstDay and Jan1Week1 config variables to evaluate the
results.

=item B<weeks_in_year>

   $w = $dmb->weeks_in_year($y);

This returns the number of ISO 8601 weeks in the year. It will always be
52 or 53.

=item B<week_of_year>

   ($y,$w) = $dmb->week_of_year($date);
   ($y,$w) = $dmb->week_of_year($ymd);

This returns the week number (1-53) of the given date and the year
that it falls in. Since the ISO 8601 definition of a week is used, the
year returned is not necessarily the one passed in (it may differ for
the first or last week of the year).

The inverse operation is also available:

   $ymd = $dmb->week_of_year($y,$w);

which returns the first day of the given week.

This uses the FirstDay and Jan1Week1 config variables to evaluate the
results.

=back

=head1 KNOWN BUGS

None known.

=head1 BUGS AND QUESTIONS

Please refer to the L<Date::Manip::Problems> documentation for
information on submitting bug reports or questions to the author.

=head1 SEE ALSO

L<Date::Manip>        - main module documentation

=head1 LICENSE

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

=head1 AUTHOR

Sullivan Beck (sbeck@cpan.org)

=cut