module Mutant
  # Generator for mutations
  class Mutator
    # Abstract base class for node mutators
    class Node < self
      include AbstractType, NodeHelpers, Unparser::Constants

      # Return identity of node
      #
      # @param [Parser::AST::Node] node
      #
      # @return [String]
      #
      # @api private
      #
      def self.identity(node)
        Unparser.unparse(node)
      end

      # Define named child
      #
      # @param [Symbol] name
      # @param [Fixnum] index
      #
      # @return [undefined]
      #
      # @api private
      #
      def self.define_named_child(name, index)
        define_method("#{name}") do
          children.at(index)
        end

        define_method("emit_#{name}_mutations") do
          mutate_child(index)
        end

        define_method("emit_#{name}") do |node|
          emit_child_update(index, node)
        end
      end
      private_class_method :define_named_child

      # Define remaining children
      #
      # @param [Array<Symbol>] names
      #
      # @return [undefined]
      #
      # @api private
      #
      def self.define_remaining_children(names)
        define_method(:remaining_children_with_index) do
          children.each_with_index.drop(names.length)
        end

        define_method(:remaining_children) do
          children.drop(names.length)
        end
      end
      private_class_method :define_remaining_children

      # Create name helpers
      #
      # @return [undefined]
      #
      # @api private
      #
      def self.children(*names)
        names.each_with_index do |name, index|
          define_named_child(name, index)
        end
        define_remaining_children(names)
      end
      private_class_method :children

    private

      # Return mutated node
      #
      # @return [Parser::AST::Node]
      #
      # @api private
      #
      alias_method :node, :input

      # Return duplicated node
      #
      # @return [Parser::AST::Node]
      #
      # @api private
      #
      alias_method :dup_node, :dup_input

      # Emit children mutations
      #
      # @return [undefined]
      #
      # @api private
      #
      def emit_children_mutations
        Mutator::Util::Array.each(children, self) do |children|
          emit_self(*children)
        end
      end

      # Return children
      #
      # @return [Array<Parser::AST::Node>]
      #
      # @api private
      #
      def children
        node.children
      end

      # Dispatch on child index
      #
      # @param [Fixnum] index
      #
      # @return [undefined]
      #
      # @api private
      #
      def mutate_child(index, mutator = Mutator)
        children = node.children
        child = children[index]
        mutator.each(child, self) do |mutation|
          emit_child_update(index, mutation)
        end
      end

      # Emit delete child mutation
      #
      # @param [Fixnum] index
      #
      # @return [undefined]
      #
      # @api private
      #
      def delete_child(index)
        dup_children = children.dup
        dup_children.delete_at(index)
        emit_self(*dup_children)
      end

      # Emit updated child
      #
      # @param [Fixnum] index
      # @param [Object] update
      #
      # @return [undefined]
      #
      # @api private
      #
      def emit_child_update(index, update)
        new_children = children.dup
        new_children[index]=update
        emit_self(*new_children)
      end

      # Emit a new AST node with same class as wrapped node
      #
      # @param [Array<Parser::AST::Node>] children
      #
      # @return [undefined]
      #
      # @api private
      #
      def emit_self(*children)
        emit(new_self(*children))
      end

      # Emit a new AST node with NilLiteral class
      #
      # @return [undefined]
      #
      # @api private
      #
      def emit_nil
        emit(N_NIL)
      end

      # Return new self typed child
      #
      # @return [Parser::AST::Node]
      #
      # @api private
      #
      def new_self(*children)
        Parser::AST::Node.new(node.type, children)
      end

      # Emit values
      #
      # @param [Array<Object>] values
      #
      # @return [undefined]
      #
      # @api private
      #
      def emit_values(values)
        values.each do |value|
          emit_self(value)
        end
      end

    end # Node
  end # Mutator
end # Mutant