// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

import 'package:string_scanner/string_scanner.dart';

/// An HTTP token.
final token = RegExp(r'[^()<>@,;:"\\/[\]?={} \t\x00-\x1F\x7F]+');

/// Linear whitespace.
final _lws = RegExp(r'(?:\r\n)?[ \t]+');

/// A quoted string.
///
/// [RFC-2616 2.2](https://datatracker.ietf.org/doc/html/rfc2616#section-2.2)
/// defines the `quoted-string` production. This expression is identical to
/// the RFC definition expect that, in this regex, `qdtext` is not allowed to
/// contain `"\"`.
final _quotedString = RegExp(r'"(?:[^"\x00-\x1F\x7F\\]|\\.)*"');

/// A quoted pair.
final _quotedPair = RegExp(r'\\(.)');

/// A character that is *not* a valid HTTP token.
final nonToken = RegExp(r'[()<>@,;:"\\/\[\]?={} \t\x00-\x1F\x7F]');

/// A regular expression matching any number of [_lws] productions in a row.
final whitespace = RegExp('(?:${_lws.pattern})*');

/// Parses a list of elements, as in `1#element` in the HTTP spec.
///
/// [scanner] is used to parse the elements, and [parseElement] is used to parse
/// each one individually. The values returned by [parseElement] are collected
/// in a list and returned.
///
/// Once this is finished, [scanner] will be at the next non-LWS character in
/// the string, or the end of the string.
List<T> parseList<T>(StringScanner scanner, T Function() parseElement) {
  final result = <T>[];

  // Consume initial empty values.
  while (scanner.scan(',')) {
    scanner.scan(whitespace);
  }

  result.add(parseElement());
  scanner.scan(whitespace);

  while (scanner.scan(',')) {
    scanner.scan(whitespace);

    // Empty elements are allowed, but excluded from the results.
    if (scanner.matches(',') || scanner.isDone) continue;

    result.add(parseElement());
    scanner.scan(whitespace);
  }

  return result;
}

/// Parses a double quoted string, and returns its contents.
///
/// If [name] is passed, it's used to describe the expected value if it's not
/// found.
String expectQuotedString(
  StringScanner scanner, {
  String name = 'quoted string',
}) {
  scanner.expect(_quotedString, name: name);
  final string = scanner.lastMatch![0]!;
  return string
      .substring(1, string.length - 1)
      .replaceAllMapped(_quotedPair, (match) => match[1]!);
}