#
# $Id: chinesedate.rb,v 1.9 2003/02/28 18:26:11 fukumoto Exp $
#
# ChineseDate
#   KAN, KAN_ON, KAN_YOMI
#   SI, SI_YOMI, SI_ON
#   KANSI
#   year_eto
#   day_eto
#   most_recent_year
#   most_recent_day
#

raise if $KCODE == 'NONE'

module ChineseDate
  KAN = '甲乙丙丁戊己庚辛壬癸' . split(//) . freeze
  KAN_ON = ['こう', 'おつ', 'へい', 'てい', 'ぼ', 
    'き', 'こう', 'しん', 'じん', 'き'] . freeze
  ELEMENTS = ['き', 'ひ', 'つち', 'か', 'みず'] . freeze  # 木火土金水
  E_TO = ['え', 'と'] . freeze
  KAN_YOMI = ELEMENTS.map {|i| E_TO.map{|j| i+'の'+j}}.flatten.freeze
  SI = '子丑寅卯辰巳午未申酉戌亥' . split(//) . freeze
  SI_ON = ['し', 'ちゅう', 'いん', 'ぼう', 'しん', 'し',
    'ご', 'び', 'しん', 'ゆう', 'じゅつ', 'がい'].freeze
  SI_YOMI = ['ね', 'うし', 'とら', 'う', 'たつ', 'み',
    'うま', 'ひつじ', 'さる', 'とり', 'いぬ', 'い'].freeze

  KANSI = (0..59).map{|i| KAN[i%10] + SI[i%12]}.freeze
  KANSI_YOMI = (0..59).map{|i| KAN_YOMI[i%10] + SI_YOMI[i%12]}.freeze
  KANSI_ON = (0..59).map{|i| KAN_ON[i%10] + SI_ON[i%12]}.freeze

  KANSI_TO_INDEX = Hash.new
  60.times do |i| KANSI_TO_INDEX[KANSI[i]] = i end
  KANSI_TO_INDEX.freeze
  YOMI_TO_INDEX = Hash.new
  60.times do |i| YOMI_TO_INDEX[KANSI_YOMI[i]] = i end
  YOMI_TO_INDEX.freeze
  ON_TO_INDICES = Hash.new
  60.times do |i| (ON_TO_INDICES[KANSI_ON[i]] ||= Array.new).push(i) end
  ON_TO_INDICES.freeze

  # gregorian to eto_index modulo 60.
  # Note that the definition of the year is different
  YEAR_OFFSET = 56

  # jd to eto_index modulo 60
  DAY_OFFSET = 49

  class <<self
    def kansi(x)
      KANSI[x % 60]
    end
  
    def kansi_yomi(x)
      KANSI_YOMI[x % 60]
    end
    
    def kansi_on(x)
      KANSI_ON[x % 60]
    end

    def most_recent(str, origin, offset)
      o = origin + offset
      value = (KANSI_TO_INDEX[str] || YOMI_TO_INDEX[str])
      if value
	value = [value]
      elsif ON_TO_INDICES[str]
	value = ON_TO_INDICES[str]
      else
	if (value = KAN.index(str)) or (value = KAN_YOMI.index(str)) or (value = KAN_ON.index(str))
	  return (o - (o % 10) + value + (o % 10 < value ? -10 : 0) - offset)
	elsif (value = SI.index(str)) or (value = SI_YOMI.index(str)) or (value = SI_ON.index(str))
	  return (o - (o % 12) + value + (o % 12 < value ? -12 : 0) - offset)
	else
	  raise ArgumentError
	end
      end

      # p value if $DEBUG
      v = if o % 60 < value[0]
	  then value[-1] - 60
	  else value.reverse.find{ |i| i <= o % 60 }
	  end
      return (o - (o % 60) + v - offset)
    end
  end
  
  def year_eto
    y = year + YEAR_OFFSET
    [SI[y % 12], SI_YOMI[y % 12], 
      ChineseDate::kansi(y), ChineseDate::kansi_yomi(y), ChineseDate::kansi_on(y)]
  end

  def day_eto
    d = jd + DAY_OFFSET
    [ChineseDate::kansi(d), ChineseDate::kansi_yomi(d), ChineseDate::kansi_on(d)]
  end

  def most_recent_year(str)
    self.class.new(ChineseDate::most_recent(str, year, YEAR_OFFSET))
  end

  def most_recent_day(str)
    self.class.jd(ChineseDate::most_recent(str, jd, DAY_OFFSET))
  end
end


if $0 == __FILE__

  require 'date'

  a = Date.today
  a.extend(ChineseDate)
  p a.year_eto

  class Date; include ChineseDate; end
  a = Date.today
  p a.day_eto

end