jkr2255 / prop_logic

  class NotTerm < Term

    def initialize(term)

      @terms = [term].freeze

      @is_nnf = @terms[0].is_a?(Variable)

      @is_reduced = @is_nnf && ! (@terms[0].is_a?(Constant))

    end

    def nnf?

      @is_nnf

    end

    def to_nnf

      term = @terms[0]

      case term

      when NotTerm

        term.terms[0].to_nnf

      when Variable

        self

      when ThenTerm

        (~(term.to_nnf)).to_nnf

      when AndTerm

        all_or(*term.terms.map{|t| (~t).to_nnf})

      when OrTerm

        all_and(*term.terms.map{|t| (~t).to_nnf})

      end

    end

    def reduced?

      @is_reduced

    end

    def reduce

      return self if reduced?

      reduced_term = @terms[0].reduce

      case reduced_term

      when TrueConstant

        False

      when FalseConstant

        True

      else

        (~reduced_term).to_nnf

      end

    end

    def to_cnf

      if reduced?

        self

      else

        super

      end

    end

    def tseitin(pool)

      if nnf?

        self

      elsif @terms[0].is_a?(NotTerm) && @terms[0].terms[0].is_a(Variable)

        @terms[0].terms[0]

      else

        raise 'Non-NNF terms cannot be converted to Tseitin form.' + self.to_s

      end

    end

    alias_method :cnf?, :reduced?

  end

end