module Vedeu

  module Geometry

    # A Dimension is either the height or width of an entity.
    #
    class Dimension

      # @param (see #initialize)
      # @return [Array<Fixnum>]
      def self.pair(attributes = {})
        new(attributes).pair
      end

      # Returns a new instance of Vedeu::Geometry::Dimension.
      #
      # @param attributes [Hash<Symbol => Fixnum, NilClass>]
      # @option attributes d [Fixnum|NilClass]
      #   The starting value (y or x).
      # @option attributes dn [Fixnum|NilClass]
      #   The ending value (yn or xn).
      # @option attributes d_dn [Fixnum|NilClass] A width or a height.
      # @option attributes default [Fixnum|NilClass]
      #   The terminal width or height.
      # @option attributes options [Hash]
      # @return [Vedeu::Geometry::Dimension]
      def initialize(attributes = {})
        defaults.merge!(attributes).each do |key, value|
          instance_variable_set("@#{key}", value)
        end
      end

      # Fetch the starting coordinate.
      #
      # @return [Fixnum]
      def d1
        dimension[0] < 1 ? 1 : dimension[0]
      end

      # Fetch the ending coordinate.
      #
      # @return [Fixnum]
      def d2
        dimension[-1]
      end

      # Fetch the coordinates.
      #
      # @return [Array<Fixnum>]
      def pair
        dimension
      end

      protected

      # @!attribute [r] d
      # @return [Fixnum|NilClass]
      attr_reader :d

      # @!attribute [r] dn
      # @return [Fixnum|NilClass]
      attr_reader :dn

      # @!attribute [r] d_dn
      # @return [Fixnum|NilClass]
      attr_reader :d_dn

      # @!attribute [r] default
      # @return [Fixnum|NilClass]
      attr_reader :default

      # @!attribute [r] maximised
      # @return [Boolean]
      attr_reader :maximised
      alias_method :maximised?, :maximised

      # @!attribute [r] centred
      # @return [Boolean]
      attr_reader :centred
      alias_method :centred?, :centred

      private

      # @return [Array<Fixnum>]
      def dimension
        @dimension = if maximised?
                       [1, default]

                     elsif centred? && length?
                       [centred_d, centred_dn]

                     else
                       [_d, _dn]

                     end
      end

      # @return [Boolean]
      def length?
        default && length
      end

      # @return [Fixnum|NilClass]
      def length
        if d && dn
          (d..dn).size

        elsif d_dn
          d_dn

        elsif default
          default

        end
      end

      # Ascertains the centred starting coordinate.
      #
      # @return [Fixnum]
      def centred_d
        (default / 2) - (length / 2)
      end

      # Ascertains the centred ending coordinate.
      #
      # @return [Fixnum]
      def centred_dn
        (default / 2) + (length / 2)
      end

      # Fetch the starting coordinate, or use 1 when not set.
      #
      # @return [Fixnum]
      def _d
        d || 1
      end

      # Fetch the ending coordinate.
      #
      # 1) if an end value was given, use that.
      # 2) if a start value wasn't given, but a width or height was,
      #    use the width or height
      # 3) if a start value was given and a width or height was given,
      #    add the width or height to the start and minus 1.
      # 4) otherwise, use the terminal default width or height
      #
      # @return [Fixnum]
      def _dn
        if dn
          dn

        elsif d.nil? && d_dn
          d_dn

        elsif d && d_dn
          (d + d_dn) - 1

        else
          default

        end
      end

      # Returns the default options/attributes for this class.
      #
      # @return [Hash<Symbol => NilClass,Boolean>]
      def defaults
        {
          d:         nil,
          dn:        nil,
          d_dn:      nil,
          default:   nil,
          centred:   false,
          maximised: false,
        }
      end

    end # Dimension

  end # Geometry

end # Vedeu