class Cucumber::CucumberExpressions::CucumberExpressionParser

def parse(expression)
  # text := whitespace | ')' | '}' | .
  parse_text = lambda do |_, tokens, current|
    token = tokens[current]
    case token.type
    when TokenType::WHITE_SPACE, TokenType::TEXT, TokenType::END_PARAMETER, TokenType::END_OPTIONAL
      return [1, [Node.new(NodeType::TEXT, nil, token.text, token.start, token.end)]]
    when TokenType::ALTERNATION
      raise AlternationNotAllowedInOptional.new(expression, token)
    when TokenType::BEGIN_PARAMETER, TokenType::START_OF_LINE, TokenType::END_OF_LINE, TokenType::BEGIN_OPTIONAL
    else
      # If configured correctly this will never happen
      return [0, nil]
    end
    # If configured correctly this will never happen
    return [0, nil]
  end
  # name := whitespace | .
  parse_name = lambda do |_, tokens, current|
    token = tokens[current]
    case token.type
    when TokenType::WHITE_SPACE, TokenType::TEXT
      return [1, [Node.new(NodeType::TEXT, nil, token.text, token.start, token.end)]]
    when TokenType::BEGIN_PARAMETER, TokenType::END_PARAMETER, TokenType::BEGIN_OPTIONAL, TokenType::END_OPTIONAL, TokenType::ALTERNATION
      raise InvalidParameterTypeNameInNode.new(expression, token)
    when TokenType::START_OF_LINE, TokenType::END_OF_LINE
      # If configured correctly this will never happen
      return [0, nil]
    else
      # If configured correctly this will never happen
      return [0, nil]
    end
  end
  # parameter := '{' + name* + '}'
  parse_parameter = parse_between(NodeType::PARAMETER, TokenType::BEGIN_PARAMETER, TokenType::END_PARAMETER, [parse_name])
  # optional := '(' + option* + ')'
  # option := optional | parameter | text
  optional_sub_parsers = []
  parse_optional = parse_between(NodeType::OPTIONAL, TokenType::BEGIN_OPTIONAL, TokenType::END_OPTIONAL, optional_sub_parsers)
  optional_sub_parsers << parse_optional << parse_parameter << parse_text
  # alternation := alternative* + ( '/' + alternative* )+
  parse_alternative_separator = lambda do |_, tokens, current|
    return [0, nil] unless looking_at(tokens, current, TokenType::ALTERNATION)
    token = tokens[current]
    return [1, [Node.new(NodeType::ALTERNATIVE, nil, token.text, token.start, token.end)]]
  end
  alternative_parsers = [
    parse_alternative_separator,
    parse_optional,
    parse_parameter,
    parse_text,
  ]
  # alternation := (?<=left-boundary) + alternative* + ( '/' + alternative* )+ + (?=right-boundary)
  # left-boundary := whitespace | } | ^
  # right-boundary := whitespace | { | $
  # alternative: = optional | parameter | text
  parse_alternation = lambda do |expr, tokens, current|
    previous = current - 1
    return [0, nil] unless looking_at_any(tokens, previous, [TokenType::START_OF_LINE, TokenType::WHITE_SPACE, TokenType::END_PARAMETER])
    consumed, ast = parse_tokens_until(expr, alternative_parsers, tokens, current, [TokenType::WHITE_SPACE, TokenType::END_OF_LINE, TokenType::BEGIN_PARAMETER])
    sub_current = current + consumed
    return [0, nil] unless ast.map { |ast_node| ast_node.type }.include? NodeType::ALTERNATIVE
    start = tokens[current].start
    _end = tokens[sub_current].start
    # Does not consume right hand boundary token
    return [consumed, [Node.new(NodeType::ALTERNATION, split_alternatives(start, _end, ast), nil, start, _end)]]
  end
  #
  # cucumber-expression :=  ( alternation | optional | parameter | text )*
  #
  parse_cucumber_expression = parse_between(
    NodeType::EXPRESSION,
    TokenType::START_OF_LINE,
    TokenType::END_OF_LINE,
    [parse_alternation, parse_optional, parse_parameter, parse_text]
  )
  tokenizer = CucumberExpressionTokenizer.new
  tokens = tokenizer.tokenize(expression)
  _, ast = parse_cucumber_expression.call(expression, tokens, 0)
  ast[0]
end