# Copyright (c) 2008-2021 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::Changes5to6 - describes differences between 5.xx and 6.00

=head1 SYNOPSIS

Date::Manip 6.00 represents a complete rethink and rewrite of
Date::Manip.  A great deal of effort was made to make sure that 6.00
is almost backwards compatible with 5.xx whenever feasible, but some
functionality has changed in backwards incompatible ways. Other parts
have been deprecated and will be removed at some point in the future.

This document describes the differences between the 5.xx series and
version 6.00. This page primarily describes technical details, most of
which do not impact how Date::Manip is used in scripts. If you want to
make sure that a script which ran with 5.xx will run with 6.xx, refer
to the Date::Manip::Migration5to6 document.

=head1 OVERVIEW

The Date::Manip 5.xx series of suffered from several weaknesses. These
included:

=over 4

=item B<Poor time zone support>

Time zone support in 5.xx was broken. Determining a time zone, and
understanding daylight saving time changes was incomplete (at best)
and totally inadequate to do true timezone operations.

=item B<Parsing too complicated and unstructured>

The parsing routines had grown very complicated, and overly permissive
over time and were in need of a complete overhaul.

=item B<Lacking OO model>

Date::Manip 5.xx was written as a functional module, not an OO module,
but date handling would lend itself very well to being OO with different
classes to handle dates, deltas, and recurrences.

The OO model allows a lot of information to be stored with each date
(such as time zone information) which is discarded in the functional
interface.

=item B<Too monolithic>

The entire Date::Manip module was contained in one huge file. Breaking
up the module would make it much easier to deal with.

=back

Date::Manip 6.00 is a complete rewrite of Date::Manip to address these
and other issues.

The following sections address how Date::Manip 6.00 differs from previous
releases, and describes changes that might need to be made to your script
in order to upgrade from 5.xx to 6.00.

The most important changes are marked with asterisks.

=head1 GENERAL CHANGES

=over 4

=item B<(*) Requires perl 5.10.0>

Please see the Date::Manip::Problems document for a discussion of
this problem. It's in the KNOWN COMPLAINTS section.

=item B<(*) Breaking into smaller modules>

Date::Manip module has been broken up from one huge module into a
large number of smaller more manageable modules. The main Date::Manip
module is still present, and contains all of the functions from
Date::Manip 5.xx (except that they now call functions from all the
other modules to do the actual work). In general, the Date::Manip
module from 6.00 is backwards compatible.

A number of new modules have been created as well. These can be used
directly, bypassing the main Date::Manip module. These include the
following:

Date::Manip::Base contains many basic date operations which may be
used to do simple date manipulation tasks without all the overhead of
the full Date::Manip module.

Date::Manip::TZ contains time zone operations.

Handling dates, deltas, and recurrences are now done in
Date::Manip::Date, Date::Manip::Delta, and Date::Manip::Recur.

All of these modules are object oriented, and are designed to be used
directly, so if you prefer an OO interface over a functional
interface, use these modules.

=item B<(*) Intermediate data cached>

In order to improve the performance of Date::Manip, many intermediate
values are cached. This does impact the memory footprint of the module,
but it has a huge impact on the performance of the module.

Some types of data depend on the config variables used, and these
are cached separately, and this cache is automatically cleared every
time a config variable is set. As a result, it is best if you set
all config variables at the start, and then leave them alone completely
to get optimal use of cached data.

A side effect of all this is that the Memoize module should not be used
in conjunction with Date::Manip.

In the version 5.xx documentation, it was mentioned that the Memoize
module might be used to improve performance in some cases. This is no
longer the case. It should not be used with Date::Manip, even if you
use the functional interface instead of the OO interface.

=item B<Taint safe>

Date::Manip now contains no tainted data, and should run without problems
with taint checking on provided you do not set additional methods for
determining the system time zone using the curr_zone_methods function.

Ideally, this should never be necessary. If it is necessary, I'd like to
hear about it so that I can add whatever standard methods are needed
to the built in list.

=back

=head1 TIME ZONE SUPPORT

=over 4

=item B<(*) Complete handling of time zones>

The biggest problem with Date::Manip 5.xx was it's inability to
correctly handle time zones and Daylight Saving Time. That is now
fixed. Version 6.00 includes support for every time zone included in
the zoneinfo (aka Olson) database which includes the definitions of
(hopefully) all of the time zones used in the world.

=item B<Individual time zones will no longer be added>

Prior to 5.55, time zones were added upon request. Since 6.00 now
supports a full set of standard time zones, I will no longer add in
individual time zones (Date::Manip::TZ includes functionality for
adding them yourself if they are needed).  With Date::Manip now having
full time zone support, I'm not interested in supporting my own
time zone database.

However, I am interested in adding sets of time zones from various
"standards".

Date::Manip 6.00 includes time zones from the following standards:

   Olson zoneinfo database
   all Microsoft Windows time zones
   zones listed in RFC-822

If there are additional standards that include additional time zones
not included here, please point me to them so they can be added.
This could include published lists of time zone names supported on
some operating system which have different names than the zoneinfo
list.

=item B<Nonstandard time zone abbreviations removed>

Some of the individual standards that were added in the 5.xx series
are not included in any of the standards listed above.

As of 6.00, only time zones from standards will be included in the
distribution (others can be added by users using the functions
described in Date::Manip::TZ to add aliases for existing time zones).

The following time zones were in Date::Manip 5.xx but not in 6.00.

   IDLW    -1200    International Date Line West
   NT      -1100    Nome
   SAT     -0400    Chile
   CLDT    -0300    Chile Daylight
   AT      -0200    Azores
   MEWT    +0100    Middle European Winter
   MEZ     +0100    Middle European
   FWT     +0100    French Winter
   GB      +0100    GMT with daylight saving
   SWT     +0100    Swedish Winter
   MESZ    +0200    Middle European Summer
   FST     +0200    French Summer
   METDST  +0200    An alias for MEST used by HP-UX
   EETDST  +0300    An alias for eest used by HP-UX
   EETEDT  +0300    Eastern Europe, USSR Zone 1
   BT      +0300    Baghdad, USSR Zone 2
   IT      +0330    Iran
   ZP4     +0400    USSR Zone 3
   ZP5     +0500    USSR Zone 4
   IST     +0530    Indian Standard
   ZP6     +0600    USSR Zone 5
   AWST    +0800    Australian Western Standard
   ROK     +0900    Republic of Korea
   AEST    +1000    Australian Eastern Standard
   ACDT    +1030    Australian Central Daylight
   CADT    +1030    Central Australian Daylight
   AEDT    +1100    Australian Eastern Daylight
   EADT    +1100    Eastern Australian Daylight
   NZT     +1200    New Zealand
   IDLE    +1200    International Date Line East

=item B<A lot of support modules and files>

Date::Manip now includes a large number of files and modules that
are used to support time zones.

A series of modules are included which are auto-generated from the
zoneinfo database.  The Date::Manip::Zones, Date::Manip::TZ::*, and
Date::Manip::Offset::* modules are all automatically generated and are
not intended to be used directly. Instead, the Date::Manip::TZ module
is used to access the data stored there.

A separate time zone module (Date::Manip::TZ::*) is included for every
single time zone. There is also a module (Date::Manip::Offset::*) for
every different offset. All told, there are almost 1000 modules.
These are included to make time zone handling more efficient. Rather
than calculating everything on the fly, information about each
time zone and offset are included here which greatly speeds up the
handling of time zones. These modules are only loaded as needed
(i.e. only the modules related to the specific time zones you refer to
are ever loaded), so there is no performance penalty to having them.

Also included in the distribution are a script (tzdata) and additional
module (Date::Manip::TZdata). These are used to automatically
generate the time zone modules, and are of no use to anyone other
than the maintainer of Date::Manip. They are included solely for the
sake of completeness. If someone wanted to fork Date::Manip, all
the tools necessary to do so are included in the distribution.

=item B<(*) Meaning of $::TZ and $ENV{TZ}>

In Date::Manip 5.x, you could specify what time zone you wanted to work
in using either the $::TZ or $ENV{TZ} variables.

Date::Manip 6.00 makes use of two different time zones: the actual
local time zone the computer is running in (and which is used by the
system clock), and a time zone that you want to work in. Typically,
these are the same, but they do not have to be.

As of Date::Manip 6.00, the $::TZ and $ENV{TZ} variables are used only
to specify the actual local time zone.

In order to specify an alternate time zone to work in, use the
SetDate or ForceDate config variables.

=back

=head1 CONFIG FILES AND VARIABLES

=over 4

=item B<(*) Date_Init handling of config variables>

The handling of config variables has changed slightly.

Previously, variables passed in to Date_Init overrode values from
config files. This has changed slightly. Options to Date_Init are
now parsed in the order they are listed, so the following:

   Date_Init("DateFormat=Other","ConfigFile=DateManip.cnf")

would first set the DateFormat variable, and then it would read
the config file "DateManip.cnf". If that config file included
a DateFormat definition, it would override the one passed in to
Date_Init.

The proper way to override config files is to pass the config files
in first, followed by any script-specific overrides. In other
words:

   Date_Init("ConfigFile=DateManip.cnf","DateFormat=Other")

=item B<Date_Init doesn't return the config variables>

In Date::Manip::5.xx, Date_Init could return the list of all
config variables. This functionality is no longer supported.
Date_Init is used strictly to set config variables.

=item B<(*) Config file options>

Date::Manip 5.xx had the concept of a global and personal config
file. In addition, the personal config file could be looked for
in a path of directories. All this was specified using the
config variables:

   GlobalCnf
   IgnoreGlobalCnf
   PersonalCnf
   PersonalCnfPath
   PathSep

All of these have been removed. Instead, the single config variable:

   ConfigFile

will be used to specify config files (with no distinction between a
global and personal config file). Also, no path searching is
done. Each must be specified by a complete path. Finally, any number
of config files can be used. So the following is valid:

   Date_Init("ConfigFile=./Manip.cnf","ConfigFile=/tmp/Manip.cnf")

=item B<Other config variables removed>

The following config variables have been removed.

   TodayIsMidnight  Use DefaultTime instead.

   ConvTZ           Use SetDate or ForceDate instead.

   Internal         Use Printable instead.

   DeltaSigns       Use the Date::Manip::Delta::printf
                    method to print deltas

   UpdateCurrTZ     With real time zone handling in
                    place, this is no longer necessary

   IntCharSet      This has been replaced with better support for
                   international character sets. The Encoding config
                   variable may be used instead.

=item B<Other config variables deprecated>

The following config variables are deprecated and will be removed
in some future version:

   TZ              Use SetDate or ForceDate instead.

=item B<Holidays>

Previously, holidays could be defined as a "Date + Delta" or "Date -
Delta" string. These predate recurrences, and introduce some complexity
into the handling of holidays. Since recurrences are a much better
way to define holidays, the "Date + Delta" and "Date - Delta" strings
are no longer supported.

=item B<TZ replaced (and enhanced)>

The SetDate and ForceDate variables (which include the functionality
of the deprecated TZ variable) are much improved as described in the
Date::Manip::Config documentation.

Since it is now handles time change correctly (allowing time changes
to occur in the alternate time zone), parsed results may be different
than in 5.x (but since 5.x didn't have proper time zone handling, this
is a good thing).

=back

=head1 DATE PARSING AND OPERATIONS

=over 4

=item B<(*) today, tomorrow, yesterday>

The words "today", "tomorrow", and "yesterday" in 5.xx referred to the
time now, 24 hours in the future, and 24 hours in the past respectively.

As of 6.00, these are treated strictly as date strings, so they are
the current day, the day before, or the day after at the time 00:00:00.

The string "now" still refers to the current date and time.

=item B<ISO 8601 formats>

A couple of the date formats from Date::Manip 5.xx conflicted with ISO
8601 formats in the spec. These are documented in the
Date::Manip::Date documentation.

Dates are now parsed according to the spec (though a couple extensions
have been made, which are also documented in the Date::Manip::Date
documentation).

There is one change with respect to Date::Manip 5.xx that results from
a possible misinterpretation of the standard. In Date::Manip, there is
a small amount of ambiguity in how the Www-D date formats are
understood.

The date:

   1996-w02-3

might be interpreted in two different ways. It could be interpreted as
Wednesday (day 3) of the 2nd week of 1996, or as the 3rd day of the
2nd week of 1996 (which would be Tuesday if the week begins on
Sunday). Since the specification only works with weeks which begin on
day 1, the two are always equivalent in the specification, and the
language of the specification doesn't clearly indicate one
interpretation over the other.

Since Date::Manip supports the concept of weeks starting on days other
than day 1 (Monday), the two interpretations are not equivalent.

In Date::Manip 5.xx, the date was interpreted as Wednesday of the 2nd
week, but I now believe that the other interpretation (3rd day of the
week) is the interpretation intended by the specification. In addition,
if this interpretation is used, it is easy to get the other interpretation.

If 1996-w02-3 means the 3rd day of the 2nd week, then to get Wednesday
(day 3) of the week, use the following two Date::Manip::Date methods:

   $err   = $date->parse("1996-w02-1");
   $date2 = $date->next(3,1);

The first call gets the 1st day of the 2nd week, and the second call
gets the next Wednesday.

If 1996-w02-3 is interpreted as Wednesday of the 2nd week, then to
get the 3rd day of the week involves significantly more work.

In Date::Manip 6.00, the date will now be parsed as the 3rd day of the
2nd week.

=item B<(*) Parsing is now more rigid>

The philosophy in Date::Manip 5.xx with respect to parsing dates was
"if there's any conceivable way to find a valid date in the string, do
so". As a result, strings which did not look like they could contain a
valid date often would.

This manifested itself it two ways. First, a lot of punctuation was
ignored. For example, the string "01 // 03 -. 75" was the date
1975-01-03.

Second, a lot of word breaks were optional and it was often acceptable
to run strings together. For example, the delta "in5seconds" would
have worked.

With Date::Manip 6.00, parsing now tries to find a valid date in the
string, but uses a more rigidly defined set of allowed formats which
should more closely match how the dates would actually be expressed in
real life.  The punctuation allowed is more rigidly defined, and word
breaks are required. So "01/03/75" will work, but "01//03/75" and
"01/03-75" won't. Also, "in5seconds" will no longer work, though "in 5
seconds" will work.

These changes serve to simplify some of the regular expressions used
in parsing dates, as well as simplifying the parsing routines. They
also help to recognize actually dates as opposed to typos... it was too
easy to pass in garbage and get a date out.

=item B<Support dropped for a few formats>

I've dropped support for a few very uncommon (probably never used)
formats. These include (with Jan 3, 2009 as an example):

   DD/YYmmm      03/09Jan
   DD/YYYYmmm    03/2009Jan
   mmmYYYY/DD    Jan2009/03
   YYYY/DDmmm    2009/03Jan

   mmmYYYY       Jan2009
   YYYYmmm       2009Jan

The last two are no longer supported since they are incomplete.

With the exception of the incomplete forms, these could be added back in
with very little effort. If there is ever a request to do so, I probably
will.

=item B<No longer parses the Apache format>

Date::Manip 5.xx supported the format:

   DD/mmm/YYYY:HH:MN:SS

used in the apache logs. Due to the stricter parsing, this format
is no longer supported directly. However, the parse_format method
may be used to parse the date directly from an apache log line
with no need to extract the date string beforehand.

=item B<Date_PrevWorkDay behavior>

The behavior of Date_PrevWorkDay has changed slightly.

The starting date is checked. If $timecheck was non-zero, the
check failed if the date was not a business date, or if the time was
not during business hours. If $timecheck was zero, the check failed
if the date was not a business date, but the time was ignored.

In 5.xx, if the check failed, and $timecheck was non-zero, day 0
was defined as the start of the next business day, but if $timecheck
was zero, day 0 was defined as the previous business day at the
same time.

In 6.xx, if the check fails, and $timecheck is non-zero, the behavior
is the same as before. If $timecheck is zero, day 0 is defined as the
next business day at the same time.

So day 0 is now always the same, where before, day 0 meant two
different things depending on whether $timecheck was zero or not.

=item B<(*) Default time>

In Date::Manip 5.xx, the default times for dates was handled in an
inconsistent manner.  In the Date::Manip::Date documentation, if you
parse a date from the "Common date formats" section, in Date::Manip
5.xx, if no time was included, it defaulted to "00:00:00". If you
parsed a date from the "Less common formats" section, the default time
was the current time.

So running a program on Jun 5, 2009 at noon that parsed the following
dates gave the following return values:

   Jun 12     =>  Jun 12, 2009 at 00:00:00
   next week  =>  Jun 12, 2009 at 12:00:00

This behavior is changed and now relies on the config variable DefaultTime.
If DefaultTime is "curr", the default time for any date which includes no
information about the time is the current time. Otherwise, the default time
is midnight.

=item B<%z format>

In Date::Manip 5.xx, the %z format would give an offset in the form: -0500.
Now it gives it in the form: -05:00:00

=back

=head1 DELTAS

=over 4

=item B<Dropped mixed style delta parsing>

In Date::Manip 5.xx, a parsed delta could be written in the delta style

   1:2:3

or in a language-specific expanded form:

   1 hour 2 minutes 3 seconds

or in a mixed form:

   1 hour 2:3

The mixed form has been dropped since I doubt that it sees much use in
real life, and by dropping the mixed form, the parsing is much
simpler.

=item B<Approximate date/date calculations>

In Date::Manip 5.xx, the approximate delta between the two dates:

   Jan 10 1996 noon
   Jan  7 1998 noon

was +1:11:4:0:0:0:0 (or 1 year, 11 months, 4 weeks).  As of
Date::Manip 6.00, the delta is +2:0:-0:3:0:0:0 (or 2 years minus 3
days). Although this leads to mixed-sign deltas, it is actually
how more people would think about the delta. It has the additional
advantage of being MUCH easier and faster to calculate.

=item B<Approximate relationships in deltas>

When printing parts of deltas in Date::Manip::5.xx, the approximate
relationship of 1 year = 365.25 days was used. This is the correct
value for the Julian calendar, but for the Gregorian calendar, a
better value is 365.2425, and this is used in version 6.00.

=item B<Old style formats>

The formats used in the printf command are slightly different than in the
old Delta_Format command.

The old formats are described in the Date::Manip::DM5 manual, and the
new ones are in the Date::Manip::Delta manual.

The new formats are much more flexible and I encourage you to switch over,
however at this point, the old style formats are officially supported for
the Delta_Format command.

At some point, the old style formats may be deprecated (and removed at
some point beyond that), but for now, they are not.

The old formats are NOT available using the printf method.

=back

=head1 RECURRENCES

=over 4

=item B<The day field meaning changed in a few recurrences>

The value of the day field can refer to several different things
including the day of week number (Monday=1 to Sunday=7), day of month (1-31),
day of year (1-366), etc.

In Date::Manip 5.xx, it could also refer to the nth day of the week
(i.e. 1 being the 1st day of the week, -1 being the last day of the
week).  This meaning is no longer used in 6.xx.

For example, the recurrence:

   1*2:3:4:0:0:0

referred to the 3rd occurrence of the 4th day of the week in February.

The meaning has been changed to refer to the 3rd occurrence of day 4
(Thursday) in February. This is a much more useful type of recurrence.

As a result of this change, the related recurrence:

   1*2:3:-1:0:0:0

is invalid. Negative numbers may be used to refer to the nth day
of the week, but NOT when referring to the day of week numbers.

=item B<Recurrence range now inclusive>

Previously, the list of dates implied by the recurrence were on or
after the start date, but before the end date.

This has been changed so that the dates may be on or before the end
date.

=item B<Dropped support for a couple English recurrences>

Date::Manip 5.xx claimed support for a recurrence:

   every 2nd day in June [1997]

In actuality, this recurrence is not practical to calculate. It
requires a base date which might imply June 1,3,5,... in 1997 but June
2,4,6 in 1998.

In addition, the recurrence does not fit the mold for other
recurrences that are an approximate distance apart. This type of
recurrence has a number of closely spaced events with 11-month gaps
between groups.

I no longer consider this a valid recurrence and support is now
dropped for this string.

I also dropped the following for a similar reason:

   every 6th Tuesday [in 1999]

=item B<Other minor recurrence changes>

Previously, ParseRecur would supply default dates if the start or
end were missing. This is no longer done.

=back

=head1 DATE::MANIP FUNCTIONS

The Date::Manip module contains the same functions that Date::Manip 5.xx had
(though the OO modules do all the work now). In general, the routines behave
the same as before with the following exceptions:

=over 4

=item B<Date_ConvTZ>

Previously, Date_ConvTZ took 1 to 4 arguments and used the local time zone and
the ConvTZ config variable to fill in missing arguments.

Now, the Date_ConvTZ function only supports a 3 argument call:

   $date = Date_ConvTZ($date,$from,$to);

If $from is not given, it defaults to the local time zone. If $to is not given,
it defaults to the local time zone.

The optional 4th argument ($errlevel) is no longer supported. If there is
an error, an empty string is returned.

=item B<DateCalc>

In Date::Manip 5.xx, it was recommended that you pass arguments to
ParseDate or ParseDateDelta. This is not recommended with 6.00 since it
is much more intelligent about handling the arguments, and you'll just
end up parsing the date/delta twice.

=back

=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
