class Propane

  class Rule

    # @return [Array<Token, RuleSet>]
    #   Rule components.
    attr_reader :components

    # @return [Hash]
    #   Field aliases.
    attr_reader :aliases

    # @return [String]
    #   User code associated with the rule.
    attr_reader :code

    # @return [Integer]
    #   Rule ID.
    attr_accessor :id

    # @return [String, nil]
    #   Parser type name.
    attr_accessor :ptypename

    # @return [Integer]
    #   Line number where the rule was defined in the input grammar.
    attr_reader :line_number

    # @return [String]
    #   Rule name.
    attr_reader :name

    # @return [RuleSet]
    #   The RuleSet that this Rule is a part of.
    attr_accessor :rule_set

    # @return [Array<Integer>]
    #   Map this rule's components to their positions in the parent RuleSet's
    #   node field pointer array. This is used for tree construction.
    attr_accessor :rule_set_node_field_index_map

    # Construct a Rule.
    #
    # @param name [String]
    #   Rule name.
    # @param components [Array<String>]
    #   Rule components.
    # @param code [String]
    #   User code associated with the rule.
    # @param ptypename [String, nil]
    #   Parser type name.
    # @param line_number [Integer]
    #   Line number where the rule was defined in the input grammar.
    def initialize(name, components, code, ptypename, line_number)
      @name = name
      @aliases = {}
      @components = components.each_with_index.map do |component, i|
        if component =~ /(\S+):(\S+)/
          c, aliasname = $1, $2
          if @aliases[aliasname]
            raise Error.new("Error: duplicate field alias `#{aliasname}` for rule #{name} defined on line #{line_number}")
          end
          @aliases[aliasname] = i
          c
        else
          component
        end
      end
      @rule_set_node_field_index_map = components.map {0}
      @code = code
      @ptypename = ptypename
      @line_number = line_number
    end

    # Return whether the Rule is empty.
    #
    # A Rule is empty if it has no components.
    #
    # @return [Boolean]
    #   Whether the Rule is empty.
    def empty?
      @components.empty?
    end

    # Return whether this is an optional Rule.
    #
    # @return [Boolean]
    #   Whether this is an optional Rule.
    def optional?
      @name.end_with?("?")
    end

    # Represent the Rule as a String.
    #
    # @return [String]
    #   Rule represented as a String.
    def to_s
      "#{@name} -> #{@components.map(&:name).join(" ")}"
    end

    # Check whether the rule set node field index map is just a 1:1 mapping.
    #
    # @return [Boolean]
    #   Boolean indicating whether the rule set node field index map is just a
    #   1:1 mapping.
    def flat_rule_set_node_field_index_map?
      @rule_set_node_field_index_map.each_with_index.all? do |v, i|
        v == i
      end
    end

  end

end