class GraphQL::Language::StaticVisitor

def self.make_visit_methods(ast_node_class)
  node_method = ast_node_class.visit_method
  children_of_type = ast_node_class.children_of_type
  child_visit_method = :"#{node_method}_children"
  class_eval(<<-RUBY, __FILE__, __LINE__ + 1)
    # The default implementation for visiting an AST node.
    # It doesn't _do_ anything, but it continues to visiting the node's children.
    # To customize this hook, override one of its make_visit_methods (or the base method?)
    # in your subclasses.
    #
    # @param node [GraphQL::Language::Nodes::AbstractNode] the node being visited
    # @param parent [GraphQL::Language::Nodes::AbstractNode, nil] the previously-visited node, or `nil` if this is the root node.
    # @return [void]
    def #{node_method}(node, parent)
      #{
        if method_defined?(child_visit_method)
          "#{child_visit_method}(node)"
        elsif children_of_type
          children_of_type.map do |child_accessor, child_class|
            "node.#{child_accessor}.each do |child_node|
              #{child_class.visit_method}(child_node, node)
            end"
          end.join("\n")
        else
          ""
        end
      }
    end
  RUBY
end

def initialize(document)
  @document = document
end

def on_argument_children(new_node)
  new_node.children.each do |value_node|
    case value_node
    when Language::Nodes::VariableIdentifier
      on_variable_identifier(value_node, new_node)
    when Language::Nodes::InputObject
      on_input_object(value_node, new_node)
    when Language::Nodes::Enum
      on_enum(value_node, new_node)
    when Language::Nodes::NullValue
      on_null_value(value_node, new_node)
    else
      raise ArgumentError, "Invariant: unexpected argument value node #{value_node.class} (#{value_node.inspect})"
    end
  end
end

def on_document_children(document_node)
  document_node.children.each do |child_node|
    visit_method = child_node.visit_method
    public_send(visit_method, child_node, document_node)
  end
end

def on_field_children(new_node)
  new_node.arguments.each do |arg_node| # rubocop:disable Development/ContextIsPassedCop
    on_argument(arg_node, new_node)
  end
  visit_directives(new_node)
  visit_selections(new_node)
end

def on_fragment_definition_children(new_node)
  visit_directives(new_node)
  visit_selections(new_node)
end

def on_operation_definition_children(new_node)
  new_node.variables.each do |arg_node|
    on_variable_definition(arg_node, new_node)
  end
  visit_directives(new_node)
  visit_selections(new_node)
end

def visit
  # `@document` may be any kind of node:
  visit_method = @document.visit_method
  result = public_send(visit_method, @document, nil)
  @result = if result.is_a?(Array)
    result.first
  else
    # The node wasn't modified
    @document
  end
end

def visit_directives(new_node)
  new_node.directives.each do |dir_node|
    on_directive(dir_node, new_node)
  end
end

def visit_selections(new_node)
  new_node.selections.each do |selection|
    case selection
    when GraphQL::Language::Nodes::Field
      on_field(selection, new_node)
    when GraphQL::Language::Nodes::InlineFragment
      on_inline_fragment(selection, new_node)
    when GraphQL::Language::Nodes::FragmentSpread
      on_fragment_spread(selection, new_node)
    else
      raise ArgumentError, "Invariant: unexpected field selection #{selection.class} (#{selection.inspect})"
    end
  end
end