# holiday.rb: Written by Tadayoshi Funaba 1998-2000
# $Id: holiday.rb,v 1.11 2000-07-16 10:23:53+09 tadf Exp $

class Date

  def fixed?
    return false unless jd >= 2432753	# 1948-07-20/PooD
    *x = mon, mday
    (x == [ 1,  1]) or			# --01-01
    (x == [ 1, 15] and			# --01-15 (1948-07-20/1999-12-31)
     jd <= 2451544) or
    (x == [ 2, 11] and			# --02-11 (1966-12-09/PooD)
     jd >= 2439469) or
    (x == [ 4, 29]) or			# --04-29
    (x == [ 5,  3]) or			# --05-03
    (x == [ 5,  5]) or			# --05-05
    (x == [ 7, 20] and			# --07-20 (1996-01-01/PooD)
     jd >= 2450084) or
    (x == [ 9, 15] and			# --09-15 (1966-06-25/PooD)
     jd >= 2439302) or
    (x == [10, 10] and			# --10-10 (1966-06-25/1999-12-31)
     jd >= 2439302 and
     jd <= 2451544) or
    (x == [11,  3]) or			# --11-03
    (x == [11, 23]) or			# --11-23
    (x == [12, 23] and			# --12-23 (1989-02-17/PooD)
     jd >= 2447575)
  end

  def float?
    (mon ==  1 and nth_kday?(2, 1) and	# 2nd Mon, Jan (2000-01-01/PooD)
     jd >= 2451545) or
    (mon == 10 and nth_kday?(2, 1) and	# 2nd Mon, Oct (2000-01-01/PooD)
     jd >= 2451545)
  end

  class << self

    def deq(a, b, y)
      (a + 0.242194 * (y - 1980) - ((y - b) / 4).to_i).to_i
    end

    private :deq

    def veq(y, sg=ITALY)
      case y
      when 1851..1899; a = 19.8277; b = 1983.0
      when 1900..1979; a = 20.8357; b = 1983.0
      when 1980..2099; a = 20.8431; b = 1980.0
      when 2100..2150; a = 21.8510; b = 1980.0
      end
      jd = civil_to_jd(y, 3, deq(a, b, y), sg)
      unless (2397124..2506696) === jd	# 1851-01-01/2150-12-31
	raise ArgumentError, 'domain error'
      end
      return new1(jd, sg)
    end

    def aeq(y, sg=ITALY)
      case y
      when 1851..1899; a = 22.2588; b = 1983.0
      when 1900..1979; a = 23.2588; b = 1983.0
      when 1980..2099; a = 23.2488; b = 1980.0
      when 2100..2150; a = 24.2488; b = 1980.0
      end
      jd = civil_to_jd(y, 9, deq(a, b, y), sg)
      unless (2397124..2506696) === jd	# 1851-01-01/2150-12-31
	raise ArgumentError, 'domain error'
      end
      return new1(jd, sg)
    end

  end

  def veq?
    return false unless jd >= 2432753	# 1948-07-20/PooD
    self === type.veq(year, sg)
  end

  def aeq?
    return false unless jd >= 2432753	# 1948-07-20/PooD
    self === type.aeq(year, sg)
  end

  def nhol2? () fixed? or float? or veq? or aeq? end

  def sun? () wday == 0 end

  protected :sun?

  def nhol32?
    jd >= 2441785 and			# 1973-04-12/PooD
      (self - 1).sun? and (self - 1).nhol2?
  end

  def nhol33?
    jd >= 2446427 and			# 1985-12-27/PooD
      not sun? and not nhol32? and
      (self - 1).nhol2? and (self + 1).nhol2?
  end

  def nholx?
    jd == 2447582 or			# 1989-02-24
    jd == 2448208 or			# 1990-11-12
    jd == 2449148			# 1993-06-09
  end

  def nhol? () nhol2? or nhol32? or nhol33? or nholx? end

  class << self

    def nth_kday(n, k, y, m, sg=ITALY)
      jd = nil
      if n > 0
	1.upto 31 do |d|
	  break if jd = exist?(y, m, d, sg)
	end
	jd -= 1
      else
	31.downto 1 do |d|
	  break if jd = exist?(y, m, d, sg)
	end
	jd += 7
      end
      jd = (jd - (((jd - k) + 1) % 7)) + 7 * n
      return new1(jd, sg)
    end

  end

  def nth_kday? (n, k)
    k == wday and self === type.nth_kday(n, k, year, mon, sg)
  end

  class << self

    def julian_easter(y, sg=ITALY)
      a = y % 4
      b = y % 7
      c = y % 19
      d = (19 * c + 15) % 30
      e = (2 * a + 4 * b - d + 34) % 7
      f, g = (d + e + 114).divmod(31)
      jd = civil_to_jd(y, f, g + 1, JULIAN)
      return new1(jd, sg)
    end

    def gregorian_easter(y, sg=ITALY)
      a = y % 19
      b, c = y.divmod(100)
      d, e = b.divmod(4)
      f = ((b + 8) / 25).to_i
      g = ((b - f + 1) / 3).to_i
      h = (19 * a + b - d - g + 15) % 30
      i, k = c.divmod(4)
      l = (32 + 2 * e + 2 * i - h - k) % 7
      m = ((a + 11 * h + 22 * l) / 451).to_i
      n, p = (h + l - 7 * m + 114).divmod(31)
      jd = civil_to_jd(y, n, p + 1, GREGORIAN)
      return new1(jd, sg)
    end

    alias_method :easter, :gregorian_easter

  end

  def easter?
    self ===
      (if os?
	 type.julian_easter(year, sg)
       else
	 type.gregorian_easter(year, sg)
       end)
  end

end