module Calrom
  class DateRange < Range
    def each_month
      return to_enum(:each_month) unless block_given?

      if first.year == last.year && first.month == last.month
        # a single month or it's part
        yield self
        return
      end

      (Month.new(first.year, first.month) .. Month.new(last.year, last.month))
        .each_with_index do |m,i|
        if i == 0 && first.day > 1
          # first month, incomplete
          yield self.class.new(first, m.last)
        elsif m.first.year == last.year && m.first.month == last.month && last != m.last
          # last month, incomplete
          yield self.class.new(m.first, last)
        else
          yield m
        end
      end
    end

    def spans_multiple_months?
      first.month != last.month ||
        first.year != last.year
    end
  end

  class Year < DateRange
    def initialize(year)
      super Date.new(year, 1, 1), Date.new(year, 12, 31)
    end

    def to_s
      first.year.to_s
    end

    def each_month
      return to_enum(:each_month) unless block_given?

      1.upto(12) {|month| yield Month.new(first.year, month) }
    end
  end

  class ThreeMonths < DateRange
    def initialize(year, month)
      super first_day_of_last_month(year, month), last_day_of_next_month(year, month)
    end

    private

    def first_day_of_last_month(year, month)
      Date.new(year, month, 1).prev_month
    end

    def last_day_of_next_month(year, month)
      n = Date.new(year, month).next_month

      Date.new(n.year, n.month, -1)
    end
  end

  class Month < DateRange
    def initialize(year, month)
      @year = year
      @month = month

      super Date.new(year, month, 1), Date.new(year, month, -1)
    end

    def to_s
      first.strftime '%B %Y'
    end

    def each_month
      return to_enum(:each_month) unless block_given?

      yield self
    end

    def succ
      n = Date.new(@year, @month, 1).next_month
      self.class.new(n.year, n.month)
    end

    def <=>(other)
      years_cmp = year <=> other.year

      if years_cmp != 0
        years_cmp
      else
        month <=> other.month
      end
    end

    protected

    attr_reader :year, :month
  end

  class Day < DateRange
    def initialize(date)
      super date, date
    end

    def to_s
      first.to_s
    end

    def each_month
      yield self
    end
  end
end