module Mutant
  class CLI
    # A classifier for input strings
    class Classifier < Matcher
      include AbstractType, Adamantium::Flat, Equalizer.new(:identification)

      SCOPE_NAME_PATTERN  = /[A-Za-z][A-Za-z_0-9]*/.freeze
      METHOD_NAME_PATTERN = /[_A-Za-z][A-Za-z0-9_]*[!?=]?/.freeze
      SCOPE_PATTERN       = /(?:::)?#{SCOPE_NAME_PATTERN}(?:::#{SCOPE_NAME_PATTERN})*/.freeze

      SINGLETON_PATTERN   = %r(\A(#{SCOPE_PATTERN})\z).freeze

      REGISTRY = []

      # Register classifier
      #
      # @return [undefined]
      #
      # @api private
      #
      def self.register
        REGISTRY << self
      end
      private_class_method :register

      # Return constant
      #
      # @param [String] location
      #
      # @return [Class|Module]
      #
      # @api private
      #
      def self.constant_lookup(location)
        location.gsub(%r(\A::), '').split('::').inject(::Object) do |parent, name|
          parent.const_get(name)
        end
      end

      # Return matchers for input
      #
      # @param [String] input
      #
      # @return [Classifier]
      #   if a classifier handles the input
      #
      # @return [nil]
      #   otherwise
      #
      # @api private
      #
      def self.build(input)
        classifiers = REGISTRY.map do |descendant|
          descendant.run(input)
        end.compact

        raise if classifiers.length > 1

        classifiers.first
      end

      # Run classifier
      #
      # @return [Classifier]
      #   if input is handled by classifier
      #
      # @return [nil]
      #   otherwise
      #
      # @api private
      #
      def self.run(input)
        match = self::REGEXP.match(input)
        return unless match

        new(match)
      end

      # No protected_class_method in ruby :(
      class << self; protected :run; end

      # Enumerate subjects
      #
      # @return [self]
      #   if block given
      #
      # @return [Enumerator<Subject>]
      #   otherwise
      #
      # @api private
      #
      def each(&block)
        return to_enum unless block_given?
        matcher.each(&block)
        self
      end

      # Return identification
      #
      # @return [String]
      #
      # @api private
      #
      def identification
        match.to_s
      end
      memoize :identification

    private

      # Initialize object
      #
      # @param [MatchData] match
      #
      # @return [undefined]
      #
      # @api private
      #
      def initialize(match)
        @match = match
      end

      # Return match
      #
      # @return [MatchData]
      #
      # @api private
      #
      attr_reader :match

      # Return matcher
      #
      # @return [Matcher]
      #
      # @api private
      #
      abstract_method :matcher

    end # Classifier
  end # CLI
end # Mutant