rubyでmethodの前後に文字列を差し込む

method_rewriter.rb

# bundle exec ruby-rewrite -l method_rewriter.rb -m app.rb

class MethodRewriter < Parser::TreeRewriter
  def on_def(node)
    padding = ' ' * (node.location.column + 2)
    insert_start(node: node, args: node.children[1].location.expression, code: node.children[2], padding: padding)

    insert_after(node.children.last.location.expression, "\n#{padding}#{puts_end}")
    super
  end

  private

  def insert_start(node:, args:, code:, padding:)
    return unless code

    method_name = node.children.first.to_s
    insert_after end_definition(node, args), "\n#{padding}#{puts_start(method_name)}"
  end

  def end_definition(node, args)
    args || node.location.name
  end

  def puts_start(method_name)
    "# $action_counter.audit('helper:#{method_name}') do"
  end

  def puts_end
    '# end # action counter'
  end
end