module Quantify
  module Unit
    class CompoundBaseUnit

      # Container class for compound unit base units. Each instance is represented
      # by a unit and an index, i.e. a unit raised to some power. If no index is
      # present, 1 is assumed.
      #
      # Instances of this class can be used to initialize base units, and are the
      # structures which hold base units within compound units
      #

      attr_accessor :unit, :index

      def initialize(unit,index=1)
        @unit = Unit.match(unit) || raise(InvalidUnitError, "Base unit not known: #{unit}")
        raise InvalidUnitError, "Base unit cannot be compound unit" if @unit.is_a? Compound
        @index = index
      end

      def dimensions
        @unit.dimensions ** @index
      end

      # Only refers to the unit index, rather than the dimensions configuration
      # of the actual unit
      #
      def is_dimensionless?
        @index == 0
      end

      # Absolute index as names always contain 'per' before denominator units
      def name
        @unit.name.to_power(@index.abs)
      end

      def pluralized_name
        @unit.pluralized_name.to_power(@index.abs)
      end

      def symbol
        @unit.symbol.to_s + ( @index.nil? or @index == 1 ? "" : "^#{@index}" )
      end

      def label
        @unit.label + (@index == 1 ? "" : "^#{@index}")
      end

      # Reciprocalized version of label, i.e. sign changed. This is used to make
      # a denominator unit renderable in cases where there are no numerator units,
      # i.e. where no '/' appears in the label
      #
      def reciprocalized_label
        @unit.label + (@index == -1 ? "" : "^#{@index * -1}")
      end

      def factor
        @unit.factor ** @index
      end

      def is_numerator?
        @index > 0
      end

      def is_denominator?
        @index < 0
      end

      def is_si_unit?
        @unit.is_si_unit?
      end

      def is_non_si_unit?
        @unit.is_non_si_unit?
      end

      # Physical quantity represented by self. This refers only to the unit, rather
      # than the unit together with the index. Is used to match base units with
      # similar units of same physical quantity
      #
      def measures
        @unit.dimensions.physical_quantity
      end

      def initialize_copy(source)
        instance_variable_set("@unit", unit.clone)
      end
    end
  end
end