# `Calendrical.Buddhist` Implementation of the Thai Buddhist (Buddhist Era) calendar. The Buddhist calendar shares its month and day structure with the proleptic Gregorian calendar exactly. The only difference is the *year numbering*: years are counted from the death (*parinirvana*) of Gautama Buddha, traditionally placed at **543 BCE** in the Gregorian calendar. The relation is: buddhist_year = gregorian_year + 543 So 1 BE corresponds to proleptic Gregorian year **−542** (543 BCE in the historical "no year zero" convention) and modern Gregorian 2026 CE corresponds to **2569 BE**. This calendar is the official solar calendar of Thailand, where it is used alongside the Gregorian calendar in everyday life. ## Month and day structure Months and days are identical to `Calendrical.Gregorian`. Leap years follow the proleptic Gregorian rule: > A year is a leap year if it is divisible by 4, except for centurial > years that are not divisible by 400. Day boundaries are at midnight, matching the Thai civil convention. ## Reference - CLDR `:buddhist` calendar type. The CLDR era data places 1 BE (`:be`) at proleptic Gregorian `−542-01-01`. - This module follows Reingold & Dershowitz's *Calendrical Calculations* (4th ed.) practice of treating year-shifted Gregorian variants as a thin wrapper around the Gregorian implementation. # `day` ```elixir @type day() :: 1..31 ``` # `month` ```elixir @type month() :: 1..12 ``` # `year` ```elixir @type year() :: integer() ``` # `buddhist_year` ```elixir @spec buddhist_year(integer()) :: year() ``` Returns the Buddhist year corresponding to the given Gregorian year. # `calendar_base` Identifies whether this calendar is month or week based. # `calendar_year` ```elixir @spec calendar_year(Calendar.year(), Calendar.month(), Calendar.day()) :: Calendar.year() ``` Returns the calendar year as displayed on rendered calendars. # `cldr_calendar_type` Defines the CLDR calendar type for this calendar. This type is used in support of `Calendrical. localize/3`. # `cyclic_year` ```elixir @spec cyclic_year(Calendar.year(), Calendar.month(), Calendar.day()) :: Calendar.year() ``` Returns the cyclic year as displayed on rendered calendars. # `date_from_iso_days` ```elixir @spec date_from_iso_days(integer()) :: {year(), month(), day()} ``` Returns a Buddhist `{year, month, day}` for the given ISO day number. # `date_to_iso_days` ```elixir @spec date_to_iso_days(year(), month(), day()) :: integer() ``` Returns the number of ISO days for the given Buddhist `year`, `month`, and `day`. # `day_of_era` ```elixir @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. # `day_of_year` ```elixir @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`. # `days_in_month` ```elixir @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. # `days_in_month` ```elixir @spec days_in_month(Calendar.year(), Calendar.month()) :: Calendar.month() @spec days_in_month(year(), month()) :: 28..31 ``` Returns the number of days in the given Buddhist `year` and `month`. # `days_in_week` Returns the number days in a a week. # `days_in_year` Returns the number of days in the given Buddhist `year` (365 or 366). # `epoch` # `epoch_day_of_week` # `extended_year` ```elixir @spec extended_year(Calendar.year(), Calendar.month(), Calendar.day()) :: Calendar.year() ``` Returns the extended year as displayed on rendered calendars. # `first_day_of_week` # `gregorian_offset` ```elixir @spec gregorian_offset() :: 543 ``` Returns the offset (in years) between the Buddhist Era and the proleptic Gregorian calendar. `buddhist_year - gregorian_offset()` yields the corresponding Gregorian year. # `gregorian_year` ```elixir @spec gregorian_year(year()) :: integer() ``` Returns the Gregorian year corresponding to the given Buddhist year. # `iso_week_of_year` ```elixir @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}`. # `last_day_of_week` # `leap_year?` ```elixir @spec leap_year?(year()) :: boolean() ``` Returns whether the given Buddhist `year` is a leap year. The underlying calendar is proleptic Gregorian, so the leap-year rule applies to the corresponding Gregorian year. # `month` Returns a `t:Date.Range.t/0` representing a given month of a year. # `month_of_year` ```elixir @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`. # `months_in_leap_year` Returns the number of months in a leap year. # `months_in_ordinary_year` Returns the number of months in a normal year. # `months_in_year` Returns the number of months in a given `year`. # `naive_datetime_from_iso_days` ```elixir @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. # `naive_datetime_to_iso_days` ```elixir @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. # `periods_in_year` 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. # `plus` Adds an `increment` number of `date_part`s to a `year-month-day`. `date_part` can be `:months` only. # `quarter` Returns a `t:Date.Range.t/0` representing a given quarter of a year. # `quarter_of_year` ```elixir @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`. # `related_gregorian_year` ```elixir @spec related_gregorian_year(Calendar.year(), Calendar.month(), Calendar.day()) :: Calendar.year() ``` Returns the related gregorain year as displayed on rendered calendars. # `valid_date?` Determines if the given `year`, `month`, and `day` form a valid Buddhist date. # `week` Returns a `t:Date.Range.t/0` representing a given week of a year. # `week_of_month` ```elixir @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}`. # `week_of_year` ```elixir @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}`. # `weeks_in_year` Returns the number of weeks in a given `year`. # `year` Returns a `t:Date.Range.t/0` representing a given year. # `year_of_era` ```elixir @spec year_of_era(Calendar.year()) :: {year :: Calendar.year(), era :: Calendar.era()} ``` Calculates the year and era from the given `year`. # `year_of_era` ```elixir @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`. --- *Consult [api-reference.md](api-reference.md) for complete listing*