Identifies whether this calendar is month or week based.

@spec calendar_year(Calendar.year(), Calendar.month(), Calendar.day()) ::
  Calendar.year()

Returns the calendar year as displayed on rendered calendars.

Defines the CLDR calendar type for this calendar.

This type is used in support of Calendrical. localize/3.

@spec cyclic_year(Calendar.year(), Calendar.month(), Calendar.day()) ::
  Calendar.year()

Returns the cyclic year as displayed on rendered calendars.

@spec date_from_iso_days(integer()) :: {year(), month(), day()}

Returns a Saudi sighting-based Islamic {year, month, day} for the given ISO day number.

Arguments

• iso_days is an integer count of days since the proleptic ISO epoch.

Returns

• A three-tuple {year, month, day} in the Saudi sighting-based Islamic calendar.

• Raises Calendrical.UnsupportedDateRangeError if iso_days falls outside the range of the underlying JPL ephemeris.

Examples

iex> Calendrical.Islamic.Rgsa.date_from_iso_days(739_252)
{1445, 6, 20}

@spec date_to_iso_days(year(), month(), day()) :: integer()

Returns the number of ISO days for the given Saudi sighting-based Islamic year, month, and day.

Arguments

• year is any Hijri year as an integer.

• month is a Hijri month in the range 1..12.

• day is a Hijri day-of-month in the range 1..30.

Returns

• An integer count of days since the proleptic ISO epoch.

• Raises Calendrical.UnsupportedDateRangeError if the date falls outside the range of the underlying JPL ephemeris.

Examples

iex> Calendrical.Islamic.Rgsa.date_to_iso_days(1446, 1, 1)
739439

@spec day_of_era(Calendar.year(), Calendar.month(), Calendar.day()) ::
  {day :: Calendar.day(), era :: Calendar.era()}

Calculates the day and era from the given year, month, and day.

By default we consider on two eras: before the epoch and on-or-after the epoch.

@spec day_of_year(Calendar.year(), Calendar.month(), Calendar.day()) :: Calendar.day()

Calculates the day of the year from the given year, month, and day.

@spec days_in_month(Calendar.month()) ::
  Calendar.month()
  | {:ambiguous, Range.t() | [pos_integer()]}
  | {:error, :undefined}

Returns how many days there are in the given month.

Must be implemented in derived calendars because we cannot know what the calendar format is.

@spec days_in_month(Calendar.year(), Calendar.month()) :: Calendar.month()

@spec days_in_month(year(), month()) :: 29..30

Returns the number of days in the given Hijri year and month (29 or 30, determined by predicted crescent visibility at Mecca).

Arguments

• year is any Hijri year as an integer.

• month is a Hijri month in the range 1..12.

Returns

• The number of days in the month (29 or 30).

Examples

iex> Calendrical.Islamic.Rgsa.days_in_month(1446, 1)
30

iex> Calendrical.Islamic.Rgsa.days_in_month(1446, 4)
29

Returns the number days in a a week.

@spec days_in_year(year()) :: 354..355

Returns the number of days in the given Hijri year.

Arguments

• year is any Hijri year as an integer.

Returns

• 354 for an ordinary year or 355 for a leap year.

Examples

iex> Calendrical.Islamic.Rgsa.days_in_year(1446)
354

@spec extended_year(Calendar.year(), Calendar.month(), Calendar.day()) ::
  Calendar.year()

Returns the extended year as displayed on rendered calendars.

@spec iso_week_of_year(Calendar.year(), Calendar.month(), Calendar.day()) ::
  {:error, :not_defined}

Calculates the ISO week of the year from the given year, month, and day.

By default this function always returns {:error, :not_defined}.

@spec leap_year?(year()) :: boolean()

Returns whether the given Hijri year is a 355-day year (the sighting-based analogue of a "leap year").

Year length varies between 354 and 355 days depending on predicted crescent sightings at Mecca, so this is computed by comparing the starts of two successive years.

Arguments

• year is any Hijri year as an integer.

Returns

• true if the year contains 355 days; otherwise false.

Examples

iex> Calendrical.Islamic.Rgsa.leap_year?(1447)
true

iex> Calendrical.Islamic.Rgsa.leap_year?(1446)
false

@spec location() :: Geo.PointZ.t()

Returns the geographic location used to determine crescent visibility for this calendar.

Returns

• A Geo.PointZ.t/0 for Mecca, Saudi Arabia (the al-Masjid al-Ḥarām).

Examples

iex> Calendrical.Islamic.Rgsa.location().coordinates
{39.8262, 21.4225, 277.0}

Returns a Date.Range.t/0 representing a given month of a year.

@spec month_of_year(Calendar.year(), Calendar.month(), Calendar.day()) ::
  Calendar.month() | {Calendar.month(), Calendrical.leap_month?()}

Returns the month of the year from the given year, month, and day.

Returns the number of months in a leap year.

Returns the number of months in a normal year.

Returns the number of months in a year, without a year.

Returns an integer when every year has the same number of months, or {:ambiguous, first..last} for lunisolar calendars whose year length varies (e.g. the Hebrew calendar's 12 or 13 months).

Returns the number of months in a given year.

@spec naive_datetime_from_iso_days(Calendar.iso_days()) ::
  {Calendar.year(), Calendar.month(), Calendar.day(), Calendar.hour(),
   Calendar.minute(), Calendar.second(), Calendar.microsecond()}

Converts the t:Calendar.iso_days format to the datetime format specified by this calendar.

@spec naive_datetime_to_iso_days(
  Calendar.year(),
  Calendar.month(),
  Calendar.day(),
  Calendar.hour(),
  Calendar.minute(),
  Calendar.second(),
  Calendar.microsecond()
) :: Calendar.iso_days()

Returns the t:Calendar.iso_days format of the specified date.

Returns the number of periods in a given year. A period corresponds to a month in month-based calendars and a week in week-based calendars.

Adds an increment number of date_parts to a year-month-day.

date_part can be :years, :months, :weeks or :days.

Returns a Date.Range.t/0 representing a given quarter of a year.

@spec quarter_of_year(Calendar.year(), Calendar.month(), Calendar.day()) ::
  Calendrical.quarter()

Returns the quarter of the year from the given year, month, and day.

@spec related_gregorian_year(Calendar.year(), Calendar.month(), Calendar.day()) ::
  Calendar.year()

Returns the related Gregorian year as displayed on rendered calendars.

Per TR35 this is the Gregorian year in which this calendar's year begins, so it is constant for every date of the calendar year.

@spec valid_date?(year(), month(), day()) :: boolean()

Returns whether the given year, month, and day form a valid Saudi sighting-based Islamic date.

Arguments

• year is any positive Hijri year as an integer.

• month is a Hijri month in the range 1..12.

• day is a Hijri day-of-month in the range 1..30.

Returns

• true if the date is valid; otherwise false.

Examples

iex> Calendrical.Islamic.Rgsa.valid_date?(1446, 1, 30)
true

iex> Calendrical.Islamic.Rgsa.valid_date?(1446, 4, 30)
false

Returns a Date.Range.t/0 representing a given week of a year.

@spec week_of_month(Calendar.year(), Calendar.month(), Calendar.day()) ::
  {pos_integer(), pos_integer()} | {:error, :not_defined}

Calculates the week of the year from the given year, month, and day.

By default this function always returns {:error, :not_defined}.

@spec week_of_year(Calendar.year(), Calendar.month(), Calendar.day()) ::
  {:error, :not_defined}

Calculates the week of the year from the given year, month, and day.

By default this function always returns {:error, :not_defined}.

Returns the number of weeks in a given year.

Returns a Date.Range.t/0 representing a given year.

@spec year_of_era(Calendar.year()) :: {year :: Calendar.year(), era :: Calendar.era()}

Calculates the year and era from the given year.

@spec year_of_era(Calendar.year(), Calendar.month(), Calendar.day()) ::
  {year :: Calendar.year(), era :: Calendar.era()}

Calculates the year and era from the given date.