class Cucumber::CucumberExpressions::TreeRegexp

def initialize(regexp)
  @regexp = regexp.is_a?(Regexp) ? regexp : Regexp.new(regexp)
  @stack = [GroupBuilder.new]
  group_start_stack = []
  last = nil
  escaping = false
  @non_capturing_maybe = false
  @name_capturing_maybe = false
  char_class = false
  @regexp.source.each_char.with_index do |c, n|
    if c == '[' && !escaping
      char_class = true
    elsif c == ']' && !escaping
      char_class = false
    elsif c == '(' && !escaping && !char_class
      @stack.push(GroupBuilder.new)
      group_start_stack.push(n + 1)
      @non_capturing_maybe = false
    elsif c == ')' && !escaping && !char_class
      gb = @stack.pop
      group_start = group_start_stack.pop
      if gb.capturing?
        gb.source = @regexp.source[group_start...n]
        @stack.last.add(gb)
      else
        gb.move_children_to(@stack.last)
      end
      end_group
    elsif c == '?' && last == '('
      @non_capturing_maybe = true
    elsif (c == '<') && @non_capturing_maybe
      @name_capturing_maybe = true
    elsif (c == ':' || c == '!' || c == '=') && last == '?' && @non_capturing_maybe
      end_non_capturing_group
    elsif (c == '=' || c == '!') && last == '<' && @name_capturing_maybe
      end_non_capturing_group
    elsif @name_capturing_maybe
      raise CucumberExpressionError.new("Named capture groups are not supported. See https://github.com/cucumber/cucumber/issues/329")
    end
    escaping = c == '\\' && !escaping
    last = c
  end
  @group_builder = @stack.pop
end