module Mutant
  class Mutator
    class Node

      # Namespace for send mutators
      class Send < self

        handle(:send)

        children :receiver, :selector

        SELECTOR_REPLACEMENTS = IceNine.deep_freeze(
          reverse_map:  [:map, :each],
          reverse_each: [:each],
          map:          [:each],
          send:         [:public_send],
          gsub:         [:sub],
          eql?:         [:equal?],
          :== =>        [:eql?, :equal?]
        )

        INDEX_REFERENCE      = :[]
        INDEX_ASSIGN         = :[]=
        VARIABLE_ASSIGN      = :'='
        ASSIGNMENT_OPERATORS = [INDEX_ASSIGN, VARIABLE_ASSIGN].to_set.freeze
        ATTRIBUTE_ASSIGNMENT = /\A[a-z\d_]+=\z/.freeze

      private

        # Perform dispatch
        #
        # @return [undefined]
        #
        # @api private
        #
        def dispatch
          emit_singletons
          if selector.equal?(INDEX_ASSIGN)
            run(Index::Assign)
          else
            non_index_dispatch
          end
        end

        # Perform non index dispatch
        #
        # @return [undefined]
        #
        # @api private
        #
        def non_index_dispatch
          case
          when binary_operator?
            run(Binary)
          when attribute_assignment?
            run(AttributeAssignment)
          else
            normal_dispatch
          end
        end

        # Return arguments
        #
        # @return [Enumerable<Parser::AST::Node>]
        #
        # @api private
        #
        alias_method :arguments, :remaining_children

        # Perform normal, non special case dispatch
        #
        # @return [undefined]
        #
        # @api private
        #
        def normal_dispatch
          emit_naked_receiver
          emit_selector_replacement
          emit_argument_propagation
          mutate_receiver
          mutate_arguments
        end

        # Emit selector replacement
        #
        # @return [undefined]
        #
        # @api private
        #
        def emit_selector_replacement
          SELECTOR_REPLACEMENTS.fetch(selector, EMPTY_ARRAY).each do |replacement|
            emit_selector(replacement)
          end
        end

        # Emit naked receiver mutation
        #
        # @return [undefined]
        #
        # @api private
        #
        def emit_naked_receiver
          emit(receiver) if receiver && !NOT_ASSIGNABLE.include?(receiver.type)
        end

        # Test for binary operator
        #
        # @return [Boolean]
        #
        # @api private
        #
        def binary_operator?
          arguments.one? && BINARY_METHOD_OPERATORS.include?(selector)
        end

        # Test for attribute assignment
        #
        # @return [Boolean]
        #
        # @api private
        #
        def attribute_assignment?
          arguments.one? && ATTRIBUTE_ASSIGNMENT =~ selector
        end

        # Mutate arguments
        #
        # @return [undefined]
        #
        # @api private
        #
        def mutate_arguments
          emit_type(receiver, selector)
          remaining_children_with_index.each do |_node, index|
            mutate_child(index)
            delete_child(index)
          end
        end

        # Emit argument propagation
        #
        # @return [undefined]
        #
        # @api private
        #
        def emit_argument_propagation
          node = arguments.first
          emit(node) if arguments.one? && !NOT_STANDALONE.include?(node.type)
        end

        # Emit receiver mutations
        #
        # @return [undefined]
        #
        # @api private
        #
        def mutate_receiver
          return unless receiver
          emit_implicit_self
          emit_receiver_mutations do |node|
            !n_nil?(node)
          end
        end

        # Emit implicit self mutation
        #
        # @return [undefined]
        #
        # @api private
        #
        def emit_implicit_self
          emit_receiver(nil) if n_self?(receiver) && !(
            KEYWORDS.include?(selector)     ||
            OP_ASSIGN.include?(parent_type) ||
            attribute_assignment?
          )
        end

        # Test for assignment
        #
        # @return [Boolean]
        #
        # @api private
        #
        def assignment?
          arguments.one? && (ASSIGNMENT_OPERATORS.include?(selector) || attribute_assignment?)
        end

        # Test if node is part of an mlhs
        #
        # @return [Boolean]
        #
        # @api private
        #
        def mlhs?
          assignment? && !arguments?
        end

        # Test for empty arguments
        #
        # @return [Boolean]
        #
        # @api private
        #
        def arguments?
          arguments.any?
        end

      end # Send
    end # Node
  end # Mutator

end # Mutant