require 'time_crisis/tzinfo/time_or_datetime'

module TimeCrisis
  module TZInfo
    # Represents an offset defined in a Timezone data file.
    class TimezoneTransitionInfo #:nodoc:
      # The offset this transition changes to (a TimezoneOffsetInfo instance).
      attr_reader :offset

      # The offset this transition changes from (a TimezoneOffsetInfo instance).
      attr_reader :previous_offset

      # The numerator of the DateTime if the transition time is defined as a
      # DateTime, otherwise the transition time as a timestamp.
      attr_reader :numerator_or_time
      protected :numerator_or_time

      # Either the denominotor of the DateTime if the transition time is defined
      # as a DateTime, otherwise nil.
      attr_reader :denominator
      protected :denominator

      # Creates a new TimezoneTransitionInfo with the given offset,
      # previous_offset (both TimezoneOffsetInfo instances) and UTC time.
      # if denominator is nil, numerator_or_time is treated as a number of
      # seconds since the epoch. If denominator is specified numerator_or_time
      # and denominator are used to create a DateTime as follows:
      #
      #  DateTime.new!(Rational.send(:new!, numerator_or_time, denominator), 0, Date::ITALY)
      #
      # For performance reasons, the numerator and denominator must be specified
      # in their lowest form.
      def initialize(offset, previous_offset, numerator_or_time, denominator = nil)
        @offset = offset
        @previous_offset = previous_offset
        @numerator_or_time = numerator_or_time
        @denominator = denominator

        @at = nil
        @local_end = nil
        @local_start = nil
      end

      # A TimeOrDateTime instance representing the UTC time when this transition
      # occurs.
      def at
        unless @at
          unless @denominator
            @at = TimeOrDateTime.new(@numerator_or_time)
          else
            r = RubyCoreSupport.rational_new!(@numerator_or_time, @denominator)
            dt = RubyCoreSupport.datetime_new!(r, 0, (::Date::ITALY rescue 2299161))
            @at = TimeOrDateTime.new(dt)
          end
        end

        @at
      end

      # A TimeOrDateTime instance representing the local time when this transition
      # causes the previous observance to end (calculated from at using
      # previous_offset).
      def local_end
        @local_end = at.add_with_convert(@previous_offset.utc_total_offset) unless @local_end
        @local_end
      end

      # A TimeOrDateTime instance representing the local time when this transition
      # causes the next observance to start (calculated from at using offset).
      def local_start
        @local_start = at.add_with_convert(@offset.utc_total_offset) unless @local_start
        @local_start
      end

      # Returns true if this TimezoneTransitionInfo is equal to the given
      # TimezoneTransitionInfo. Two TimezoneTransitionInfo instances are
      # considered to be equal by == if offset, previous_offset and at are all
      # equal.
      def ==(tti)
        tti.respond_to?(:offset) && tti.respond_to?(:previous_offset) && tti.respond_to?(:at) &&
                offset == tti.offset && previous_offset == tti.previous_offset && at == tti.at
      end

      # Returns true if this TimezoneTransitionInfo is equal to the given
      # TimezoneTransitionInfo. Two TimezoneTransitionInfo instances are
      # considered to be equal by eql? if offset, previous_offset,
      # numerator_or_time and denominator are all equal. This is stronger than ==,
      # which just requires the at times to be equal regardless of how they were
      # originally specified.
      def eql?(tti)
        tti.respond_to?(:offset) && tti.respond_to?(:previous_offset) &&
                tti.respond_to?(:numerator_or_time) && tti.respond_to?(:denominator) &&
                offset == tti.offset && previous_offset == tti.previous_offset &&
                numerator_or_time == tti.numerator_or_time && denominator == tti.denominator
      end

      # Returns a hash of this TimezoneTransitionInfo instance.
      def hash
        @offset.hash ^ @previous_offset.hash ^ @numerator_or_time.hash ^ @denominator.hash
      end

      # Returns internal object state as a programmer-readable string.
      def inspect
        "#<#{self.class}: #{at.inspect},#{@offset.inspect}>"
      end
    end
  end

end