Class: Holidays::DateCalculator::HijriDate

Inherits:
Object
  • Object
show all
Defined in:
lib/holidays/date_calculator/hijri_date.rb

Overview

Arithmetic ("tabular", a.k.a. Kuwaiti) Islamic calendar.

Months alternate 30 and 29 days; leap years add a day to the twelfth month on a fixed 11-of-30 cycle. This is a purely arithmetic calendar, so it can land a day (occasionally two) either side of a locally proclaimed date. Callers that need the proclaimed date layer their own override table on top of this (see Holidays::Definition::CustomMethods::TR).

Constant Summary collapse

EPOCH_JDN =

Julian day number of 1 Muharram 1 AH minus one day, chosen so that to_jd's month/day terms are added directly. Corresponds to the civil epoch (Friday, 16 July 622 CE proleptic Julian).

1948439

Instance Method Summary collapse

Instance Method Details

#gregorian_year_occurrence(gregorian_year, hijri_month, hijri_day) ⇒ Object

Given a Gregorian year and a fixed Hijri month/day, return the occurrence that falls within that Gregorian year, or nil if none does.

A fixed Hijri date drifts ~11 days earlier each Gregorian year, so roughly once every 33 years it falls twice in the same Gregorian year (once in early January, once in late December). Only the earlier occurrence is returned.



30
31
32
33
34
35
36
37
38
39
 
# File 'lib/holidays/date_calculator/hijri_date.rb', line 30

def gregorian_year_occurrence(gregorian_year, hijri_month, hijri_day)
  candidate_hijri_year = gregorian_year - 579

  (candidate_hijri_year - 1..candidate_hijri_year + 1).each do |hijri_year|
    date = to_gregorian(hijri_year, hijri_month, hijri_day)
    return date if date.year == gregorian_year
  end

  nil
end

#to_gregorian(hijri_year, hijri_month, hijri_day) ⇒ Object 



19
20
21
 
# File 'lib/holidays/date_calculator/hijri_date.rb', line 19

def to_gregorian(hijri_year, hijri_month, hijri_day)
  Date.jd(to_jd(hijri_year, hijri_month, hijri_day))
end