Calendrical.Calendar.Shifted (Calendrical v2.2.0)

Makes a calendar whose year begins elsewhere in a base calendar's year: a fiscal year beginning in July, a year counted from Lady Day as the Old Style did, or any year begun on a day of a calendar of months.

A date of the calendar is a counted month and a day of it, so dates order by time. A year that begins on the first day of a base month has the base's months counted from that month; a year that begins within a base month has a short month 1, from the day it begins on to the end of that base month, and a short last month, the days of that base month before it, so a year begun on 25 March has thirteen months, of which month 1 is 25 to 31 March and month 13 is 1 to 24 March.

The kernel falls out of the base: a date is the base's date relabelled, a month's length is the base month's, and shift/6 is the base's arithmetic on the base date, relabelled.

Options

:base is the calendar of months the year is cut from, a calendar with as many months in every year. The default is Calendrical.Gregorian.
:year_begins is {month, day} of the base calendar the year begins on. The default is {1, 1}.
:year_number is the base year the year takes its number from: :beginning, the one it begins in, :ending, the one it ends in, or :majority, the one most of it falls in, which is the default.
:written_year is the year a date is written with: :base, the base calendar's year the day falls in, as a fiscal date is written with the Gregorian year, which is the default, or :label, the calendar's own year, as the Old Style wrote its dates.
:weeks is the rule the calendar's own weeks follow: a keyword list with :first_day, 1 for Monday to 7 for Sunday, and :min_days_in_first_week, or :from_first_day for weeks counted from the first day of the year. The default is Monday and 1.
:cldr_calendar_type, :era_calendar_type and :years_in_cycle are facts for Calendrical.info/0, each defaulting to the base calendar's, and :parsing_calendar names the calendar a written date is parsed in, the calendar itself by default.

Examples

defmodule FiscalFromJuly do
  use Calendrical.Calendar.Shifted, year_begins: {7, 1}, year_number: :ending
end

defmodule LadyDay do
  use Calendrical.Calendar.Shifted,
    base: Calendrical.Julian,
    year_begins: {3, 25},
    year_number: :beginning,
    written_year: :label
end