Patterns

• %C

  The number of hundreds of years in the duration. 400 years would return 4. This is similar to centuries.

• %d

  The number of days zero-padded to two digits. 2 days returns 02. 22 days returns 22 and 220 days returns 220.

• %e

  The number of days.

• %F

  Equivalent of %Y-%m-%d

• %H

  The number of hours zero-padded to two digits.

• %I

  Same as %H

• %j

  The duration expressed in whole days. 36 hours returns 1

• %k

  The hours without any padding

• %l

  Same as %k

• %m

  The months, zero-padded to two digits

• %M

  The minutes, zero-padded to two digits

• %n

  A linebreak when formatting and any whitespace when parsing

• %N

  Nanoseconds - see note on precision at end

• %p

  Either a '+' or a '-' indicating the positiveness of the duration

• %P

  A '-' for negative durations and nothing for positive durations.

• %r

  Equivalent of %H:%M:%S

• %R

  Equivalent of %H:%M

• %s

  Returns the value as seconds. 1 day, 5 seconds return 86405

• %S

  Returns the seconds, zero-padded to two digits

• %t

  A tab character when formatting or any whitespace when parsing

• %T

  Equivalent of %P%H:%M:%S

• %u

  Days after weeks are removed. 4 days returns 4, but 22 days returns 1 (22 days is three weeks, 1 day)

• %V

  Duration expressed as weeks. 355 days returns 52.

• %W

  Duration expressed as floating weeks. 10 days, 12 hours returns 1.5 weeks.

• %y

  Years in the century. 145 years returns 45.

• %Y

  Years, zero-padded to four digits

• %%

  A '%' symbol

Precision can be changed for any and all the above values. For all but nanoseconds (%N), the precision is the zero-padding. To change the precision insert a number between the '%' and the letter. For example: 1 year formatted with %6Y would return 000001 rather than the default 0001. Likewise, to remove padding %1Y would just return a 1.

Nanosecond precision is the other way (nanoseconds are fractional and thus should be right padded). 123456789 nanoseconds formatted with %3N would return 123 and formatted as %12N would return 123456789000.

Normalisation

The complexity comes from three places:

• Mixed positive and negative components

  The duration of 1 day, minus 2 hours is easy to normalise in your head to 22 hours. However consider something more complex such as -2 years, +1 month, +22 days, +11 hours, -9 minutes.

  This module works from lowest to highest precision to calculate the duration. So, based on a "base" of 2004-03-28T00:00:00 the following transformations take place:

      2003-01-01T00:00:00 - 2 years   = 2001-01-01T00:00:00 === -2 years
      2001-01-01T00:00:00 + 1 month   = 2001-02-01T00:00:00 === -1 year, 11 months
      2001-02-01T00:00:00 + 22 days   = 2001-02-23T00:00:00 === -1yr, 10mths, 6days
      2001-02-22T00:00:00 + 11 hours  = 2001-02-23T11:00:00 === -1y, 10m, 6d, 13h
      2001-02-22T11:00:00 - 9 minutes = 2001-02-23T10:51:00 === -1y, 10m, 6d, 13h, 9m
      

  See: https://raw.githubusercontent.com/karenetheridge/DateTime-Format-Duration/master/docs/figure1.gif

  Figure 1 illustrates that, with the given base, -2 years, +1 month, +22 days, +11 hours, -9 minutes is normalised to -1 year, 10 months, 6 days, 13 hours and 9 minutes.

• Months of unequal length.

  Unfortunately months can have 28, 29, 30 or 31 days and it can change from year to year. Thus if I wanted to normalise 2 months it could be any of 59 (Feb-Mar), 60 (Feb-Mar in a leap year), 61 (Mar-Apr, Apr-May, May-Jun, Jun-Jul, Aug-Sep, Sep-Oct, Oct-Nov or Nov-Dec) or 62 days (Dec-Jan or Jul-Aug). Because of this the module uses a base datetime for its calculations. If we use the base 2003-01-01T00:00:00 then two months would be 59 days (2003-03-01 - 2003-01-01)

• The order of components

  Components will always be assessed from lowest to highest precision (years, months, days, hours, minutes, seconds, nanoseconds). This can really change things.

  Consider the duration of 1 day, 24 hours. Normally this will normalise to 2 days. However, consider changes to Daylight Savings. On the changes to and from DST days have 25 and 23 hours.

  If we take the base DateTime as midnight on the day DST ends (when there's 25 hours in the day), and add 1 day, 24 hours we end up at midnight 2 days later. So our duration normalises to two days.

  However, if we add 24 hours, 1 day we end up at 11pm on the next day! Why is this? Because midnight + 24 hours = 11pm (there's 25 hours on this day!), then we add 1 day and end up at 11pm on the following day. See: https://raw.githubusercontent.com/karenetheridge/DateTime-Format-Duration/master/docs/figure2.gif

  Figure 2 illustrates the above problem on timelines.

• Leap years and leap seconds

  Leap years and seconds further add to the confusion in normalisation. Leap seconds mean there are minutes that are 61 seconds long, thus 130 seconds can be 2 minutes, 10 seconds or 2 minutes 9 seconds, depending on the base DateTime. Similarly leap years mean a day can have 23, 24 or 25 hours. See: https://raw.githubusercontent.com/karenetheridge/DateTime-Format-Duration/master/docs/figure3.gif

  Figure 3 shows how leaps are calculated on timelines.

Normalising without a base

• Standard Normalisation

  Using standard normalisation without a base, 45 days will stay as 45 days as there is no way to accurately convert to months. However the following assumptions will be made: There are 24 hours in a day and there are 60 seconds in a minute.

• ISO Normalisation

  In ISO8601v2000, Section 5.5.3.2 says that "The values used must not exceed the 'carry-over points' of 12 months, 30 days, 24 hours, 60 minutes and 60 seconds". Thus if you set the normalise option of the constructor, or use set_normalising to 'ISO', months will be normalised to 30 days.

Deltas vs Duration Objects

These extra methods have been left in here firstly for backwards-compatibility but also as an added 'syntactic sugar'. Consider these two equivalent expressions:

    $one = $o->format_duration(
        DateTime::Duration->new(
            years => -2,
            days  => 13,
            hours => -1
        )
    );

    $two = $o->format_duration_from_deltas(
        years => -2,
        days  => 13,
        hours => -1
    );

These both create the same string in $one and $two, but if you don't already have a DateTime::Duration object, the later looks cleaner.