module Mutant
  class Matcher
    # Matcher for subjects that are a specific method
    class Method < self
      include Adamantium::Flat, Concord::Public.new(:scope, :method)

      # Methods within rbx kernel directory are precompiled and their source
      # cannot be accessed via reading source location
      BLACKLIST = /\Akernel\//.freeze

      # Enumerate matches
      #
      # @return [Enumerable]
      #   returns enumerable when no block given
      #
      # @return [self]
      #   returns self when block given
      #
      # @api private
      #
      def each(&block)
        return to_enum unless block_given?

        return self if skip?

        util = subject
        yield util if util

        self
      end

    private

      # Test if method is skipped
      #
      # @return [true]
      #   true and print warning if location must be filtered
      #
      # @return [false]
      #   otherwise
      #
      # @api private
      #
      def skip?
        location = source_location
        if location.nil? or BLACKLIST.match(location.first)
          $stderr.puts "#{method.inspect} does not have valid source location so mutant is unable to emit matcher"
          return true
        end

        false
      end

      # Return method name
      #
      # @return [String]
      #
      # @api private
      #
      def method_name
        method.name
      end

      # Return context
      #
      # @return [Context::Scope]
      #
      # @api private
      #
      def context
        Context::Scope.new(scope, source_path)
      end

      # Return full ast
      #
      # @return [Parser::AST::Node]
      #
      # @api private
      #
      def ast
        Parser::CurrentRuby.parse(File.read(source_path))
      end

      # Return path to source
      #
      # @return [String]
      #
      # @api private
      #
      def source_path
        source_location.first
      end

      # Return source file line
      #
      # @return [Integer]
      #
      # @api private
      #
      def source_line
        source_location.last
      end

      # Return source location
      #
      # @return [Array]
      #
      # @api private
      #
      def source_location
        method.source_location
      end

      # Return subject
      #
      # @return [Subject]
      #   returns subject if there is a matched node
      #
      # @return [nil]
      #   otherwise
      #
      # @api private
      #
      def subject
        node = matched_node
        return unless node
        self.class::SUBJECT_CLASS.new(context, node)
      end
      memoize :subject

      class Finder
        def self.run(root, &predicate)
          new(root, predicate).match
        end

        private_class_method :new

        attr_reader :match

      private

        def initialize(root, predicate)
          @root, @predicate = root, predicate
          test(root)
        end

        def test(node)
          if @predicate.call(node)
            @match = node 
          end

          node.children.each do |child|
            test(child) if child.kind_of?(Parser::AST::Node)
          end
        end
      end

      # Return matched node
      #
      # @return [Parser::AST::Node]
      #   if node could be found
      #
      # @return [nil]
      #   otherwise
      #
      # @api private
      #
      def matched_node
        Finder.run(ast) do |node|
          match?(node)
        end
      end

    end # Method
  end # Matcher
end # Mutant