module RDF; class Literal
  ##
  # An integer literal.
  #
  # @example Arithmetic with integer literals
  #   RDF::Literal(40) + 2                    #=> RDF::Literal(42)
  #   RDF::Literal(45) - 3                    #=> RDF::Literal(42)
  #   RDF::Literal(6) * 7                     #=> RDF::Literal(42)
  #   RDF::Literal(84) / 2                    #=> RDF::Literal(42)
  #
  # @see   http://www.w3.org/TR/xmlschema11-2/#integer
  # @see   http://www.w3.org/TR/2004/REC-xmlschema-2-20041028/#integer
  # @since 0.2.1
  class Integer < Decimal
    DATATYPE = RDF::XSD.integer
    GRAMMAR  = /^[\+\-]?\d+$/.freeze

    ##
    # @param  [Integer, #to_i] value
    # @option options [String] :lexical (nil)
    def initialize(value, options = {})
      @datatype = RDF::URI(options[:datatype] || self.class.const_get(:DATATYPE))
      @string   = options[:lexical] if options.has_key?(:lexical)
      @string   ||= value if value.is_a?(String)
      @object   = case
        when value.is_a?(::String)    then Integer(value) rescue nil
        when value.is_a?(::Integer)   then value
        when value.respond_to?(:to_i) then value.to_i
        else Integer(value.to_s) rescue nil
      end
    end

    ##
    # Converts this literal into its canonical lexical representation.
    #
    # @return [RDF::Literal] `self`
    # @see    http://www.w3.org/TR/xmlschema11-2/#integer
    def canonicalize!
      @string = @object.to_s if @object
      self
    end

    ##
    # Returns the predecessor value of `self`.
    #
    # @return [RDF::Literal]
    # @since  0.2.3
    def pred
      RDF::Literal(to_i.pred)
    end

    ##
    # Returns the successor value of `self`.
    #
    # @return [RDF::Literal]
    # @since  0.2.3
    def succ
      RDF::Literal(to_i.succ)
    end
    alias_method :next, :succ

    ##
    # Returns `true` if the value is even.
    #
    # @return [Boolean]
    # @since  0.2.3
    def even?
      to_i.even?
    end

    ##
    # Returns `true` if the value is odd.
    #
    # @return [Boolean]
    # @since  0.2.3
    def odd?
      to_i.odd?
    end

    ##
    # Returns the absolute value of `self`.
    #
    # @return [RDF::Literal]
    # @since  0.2.3
    def abs
      (n = to_i) && n > 0 ? self : self.class.new(n.abs)
    end

    ##
    # Returns `self`.
    #
    # @return [RDF::Literal]
    def round
      self
    end

    ##
    # Returns `true` if the value is zero.
    #
    # @return [Boolean]
    # @since  0.2.3
    def zero?
      to_i.zero?
    end

    ##
    # Returns `self` if the value is not zero, `nil` otherwise.
    #
    # @return [Boolean]
    # @since  0.2.3
    def nonzero?
      to_i.nonzero? ? self : nil
    end

    ##
    # Returns the value as a string.
    #
    # @return [String]
    def to_s
      @string || @object.to_s
    end

    ##
    # Returns the value as an `OpenSSL::BN` instance.
    #
    # @return [OpenSSL::BN]
    # @see    http://ruby-doc.org/stdlib/libdoc/openssl/rdoc/classes/OpenSSL/BN.html
    # @since  0.2.4
    def to_bn
      require 'openssl' unless defined?(OpenSSL::BN)
      OpenSSL::BN.new(to_s)
    end
  end # Integer
end; end # RDF::Literal