module Rails::Generators::Actions

def route_namespace_pattern(namespace)
  namespace.each_with_index.reverse_each.reduce(nil) do |pattern, (name, i)|
    cummulative_margin = "\\#{i + 1}[ ]{2}"
    blank_or_indented_line = "^[ ]*\n|^#{cummulative_margin}.*\n"
    "(?:(?:#{blank_or_indented_line})*?^(#{cummulative_margin})namespace :#{name} do\n#{pattern})?"
  end.then do |pattern|
    /^([ ]*).+\.routes\.draw do[ ]*\n#{pattern}/
  end
end