# frozen_string_literal: true
module JapaneseCalendar
  module Era
    # Returns the Japanese era name (nengo) since 1 January 1873 (Meiji 6).
    #
    #   heisei = Time.new(1989, 1, 8)  # => 1989-01-08 00:00:00 +0900
    #   heisei.era_name                # => "平成"
    #   heisei.era_name(:romaji)       # => "Heisei"
    #
    #   showa = Time.new(1926, 12, 25) # => 1926-12-25 00:00:00 +0900
    #   showa.era_name                 # => "昭和"
    #   showa.era_name(:romaji)        # => "Showa"
    #
    #   taisho = Time.new(1912, 7, 30) # => 1912-07-30 00:00:00 +0900
    #   taisho.era_name                # => "大正"
    #   taisho.era_name(:romaji)       # => "Taisho"
    #
    #   meiji = Time.new(1873, 1, 1)   # => 1873-01-01 00:00:00 +0900
    #   meiji.era_name                 # => "明治"
    #   meiji.era_name(:romaji)        # => "Meiji"
    #
    # Raises an error when the Japanese era name cannot be found.
    #
    #   Time.new(1872, 12, 31).era_name # => RuntimeError
    def era_name(character = :kanji)
      unless %i(kanji romaji).include?(character)
        raise ArgumentError, "invalid character"
      end

      current_era.send("#{character}_name")
    end

    # Returns the Japanese year since 1 January 1873 (Meiji 6).
    #
    #   Time.new(2016, 12, 11).era_year # => 28
    #   Time.new(1989,  1,  7).era_year # => 64
    #   Time.new(1926, 12, 24).era_year # => 15
    #   Time.new(1912,  7, 29).era_year # => 45
    #
    # Raises an error when the Japanese year cannot be found.
    #
    #   Time.new(1872, 12, 31).era_year # => RuntimeError
    def era_year
      year - current_era.beginning_of_period.year + 1
    end

    # Formats time according to the directives in the given format string.
    #
    #   date_of_birth = Time.new(1978, 7, 19)
    #
    #   date_of_birth.strftime("%JN")  # => "昭和"
    #   date_of_birth.strftime("%JR")  # => "Showa"
    #   date_of_birth.strftime("%^JR") # => "SHOWA"
    #   date_of_birth.strftime("%Jr")  # => "S"
    #   date_of_birth.strftime("%Jy")  # => "53"
    #
    #   date_of_birth.strftime("%JN%-Jy年")  # => "昭和53年"
    #
    # Raises an error when the Japanese year cannot be found.
    #
    #   Time.new(1872, 12, 31).strftime("%JN%-Jy年") # => RuntimeError
    def strftime(format)
      string = format.dup
      string.gsub!(/%JN/,   era_name)
      string.gsub!(/%JR/,   era_name(:romaji))
      string.gsub!(/%\^JR/, era_name(:romaji).upcase)
      string.gsub!(/%Jr/,   era_name(:romaji)[0])
      string.gsub!(/%Jy/,   "%02d" % era_year)
      string.gsub!(/%-Jy/,  "%d"   % era_year)
      string.gsub!(/%_Jy/,  "%2d"  % era_year)
      deprecated_japanese_calendar_era_name_strftime(string)
      deprecated_japanese_calendar_era_year_strftime(string)
      super(string)
    end

    private

      Period = Struct.new(:beginning_of_period, :kanji_name, :romaji_name)

      PERIODS = [
        Period.new(Date.new(2019,  5,  1), "令和", "Reiwa").freeze,
        Period.new(Date.new(1989,  1,  8), "平成", "Heisei").freeze,
        Period.new(Date.new(1926, 12, 25), "昭和", "Showa" ).freeze,
        Period.new(Date.new(1912,  7, 30), "大正", "Taisho").freeze,
        Period.new(Date.new(1868,  1, 25), "明治", "Meiji" ).freeze
      ].freeze

      MEIJI_6 = Date.new(1873, 1, 1)

      def current_era
        error_proc = proc { raise "#{self.class.name.downcase} out of range" }
        error_proc.call if self.to_date < MEIJI_6
        PERIODS.find(error_proc) do |period|
          period.beginning_of_period <= self.to_date
        end
      end

      def deprecated_japanese_calendar_era_name_strftime(string)
        if string =~ /%K/
          warn "%K is deprecated. Please use %JN instead."
          string.gsub!(/%K/, era_name)
        end
        if string =~ /%O/
          warn "%O is deprecated. Please use %JR instead."
          string.gsub!(/%O/, era_name(:romaji))
        end
        if string =~ /%\^O/
          warn "%^O is deprecated. Please use %^JR instead."
          string.gsub!(/%\^O/, era_name(:romaji).upcase)
        end
        if string =~ /%o/
          warn "%o is deprecated. Please use %Jr instead."
          string.gsub!(/%o/, era_name(:romaji)[0])
        end
      end

      def deprecated_japanese_calendar_era_year_strftime(string)
        if string =~ /%J/
          warn "%J is deprecated. Please use %Jy instead."
          string.gsub!(/%J/, "%02d" % era_year)
        end
        if string =~ /%-J/
          warn "%-J is deprecated. Please use %-Jy instead."
          string.gsub!(/%-J/, "%d" % era_year)
        end
        if string =~ /%_J/
          warn "%_J is deprecated. Please use %_Jy instead."
          string.gsub!(/%_J/, "%2d" % era_year)
        end
      end
  end
end