// Copyright (c) 2012, 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.

/// Generic utility functions. Stuff that should possibly be in core.
library;

import 'dart:async';
import 'dart:convert';
import 'dart:io';
import 'dart:math' as math;
import 'dart:typed_data';

import 'package:args/args.dart';
import 'package:convert/convert.dart';
import 'package:crypto/crypto.dart' as crypto;
import 'package:pub_semver/pub_semver.dart';
import 'package:stack_trace/stack_trace.dart';
import 'package:yaml/yaml.dart';

import 'exceptions.dart';
import 'io.dart';
import 'log.dart' as log;
import 'pubspec_parse.dart';

/// A regular expression matching a Dart identifier.
///
/// This also matches a package name, since they must be Dart identifiers.
final identifierRegExp = RegExp(r'[a-zA-Z_]\w*');

/// Like [identifierRegExp], but anchored so that it only matches strings that
/// are *just* Dart identifiers.
final onlyIdentifierRegExp = RegExp('^${identifierRegExp.pattern}\$');

/// Dart reserved words, from the Dart spec.
const reservedWords = <String>{
  'abstract',
  'as',
  'assert',
  // 'async', // Reserved, but allowed because package:async already exists.
  'await',
  // 'base', // Reserved, but allowed because package:base already exists.
  'break',
  'case',
  'catch',
  'class',
  'const',
  'continue',
  'covariant',
  'default',
  'deferred',
  'do',
  // 'dynamic', // Reserved, but allowed because package:dynamic already exists.
  'else',
  'enum',
  'export',
  'extends',
  // 'extension', // Reserved, but allowed because package:extension already exists.
  'external',
  // 'factory', // Reserved, but allowed because package:factory already exists.
  'false',
  'final',
  'finally',
  'for',
  // 'get', // Reserved, but allowed because package:get already exists.
  'hide',
  'if',
  'implements',
  'import',
  'in',
  'inline',
  'interface',
  'is',
  'late',
  'library',
  'mixin',
  'new',
  'null',
  'of',
  'on',
  'operator',
  'part',
  'required',
  'rethrow',
  'return',
  'sealed',
  'set',
  // 'show', // Reserved, but allowed because package:show already exists.
  // 'static', // Reserved, but allowed because package:static already exists.
  'super',
  'switch',
  // 'sync', // Reserved, but allowed because package:sync already exists.
  'this',
  'throw',
  'true',
  'try',
  'type',
  // 'typedef', // Reserved, but allowed because package:typedef already exists.
  'var',
  'void',
  // 'when', // Reserved, but allowed because package:when already exists.
  'while',
  'with',
  'yield',
};

const workspacesDocUrl = 'https://dart.dev/go/pub-workspaces';

/// An cryptographically secure instance of [math.Random].
final random = math.Random.secure();

/// The maximum line length for output.
///
/// If pub isn't attached to a terminal, uses an infinite line length and does
/// not wrap text.
final int? _lineLength = () {
  try {
    return stdout.terminalColumns;
  } on StdoutException {
    return null;
  }
}();

/// Runs [callback] in an error zone and pipes any unhandled error to the
/// returned [Future].
///
/// If the returned [Future] produces an error, its stack trace will always be a
/// [Chain]. By default, this chain will contain only the local stack trace, but
/// if [captureStackChains] is passed, it will contain the full stack chain for
/// the error.
Future<T> captureErrors<T>(
  Future<T> Function() callback, {
  bool captureStackChains = false,
}) {
  var completer = Completer<T>();
  void wrappedCallback() {
    Future.sync(callback)
        .then(completer.complete)
        .catchError((Object e, StackTrace? stackTrace) {
      // [stackTrace] can be null if we're running without [captureStackChains],
      // since dart:io will often throw errors without stack traces.
      if (stackTrace != null) {
        stackTrace = Chain.forTrace(stackTrace);
      } else {
        stackTrace = Chain([]);
      }
      if (!completer.isCompleted) {
        completer.completeError(e, stackTrace);
      }
    });
  }

  if (captureStackChains) {
    Chain.capture(
      wrappedCallback,
      onError: (error, stackTrace) {
        if (!completer.isCompleted) completer.completeError(error, stackTrace);
      },
    );
  } else {
    runZonedGuarded(wrappedCallback, (e, stackTrace) {
      stackTrace = Chain([Trace.from(stackTrace)]);

      if (!completer.isCompleted) completer.completeError(e, stackTrace);
    });
  }

  return completer.future;
}

/// Like [Future.wait], but prints all errors from the futures as they occur and
/// only returns once all Futures have completed, successfully or not.
///
/// This will wrap the first error thrown in a [SilentException] and rethrow it.
Future<List<T>> waitAndPrintErrors<T>(Iterable<Future<T>> futures) {
  return Future.wait(
    futures.map((future) {
      return future.catchError((Object error, StackTrace? stackTrace) {
        log.exception(error, stackTrace);
        // ignore: only_throw_errors
        throw error;
      });
    }),
  ).catchError((Object error, StackTrace? stackTrace) {
    throw SilentException(error, stackTrace);
  });
}

/// Returns a [StreamTransformer] that will call [onDone] when the stream
/// completes.
///
/// The stream will be passed through unchanged.
StreamTransformer<T, T> onDoneTransformer<T>(void Function() onDone) {
  return StreamTransformer<T, T>.fromHandlers(
    handleDone: (sink) {
      onDone();
      sink.close();
    },
  );
}

/// Pads [source] to [length] by adding [char]s at the beginning.
///
/// If [char] is `null`, it defaults to a space.
String _padLeft(String source, int length, [String char = ' ']) {
  if (source.length >= length) return source;

  return char * (length - source.length) + source;
}

/// Returns a labelled sentence fragment starting with [name] listing the
/// elements [iter].
///
/// If [iter] does not have one item, name will be pluralized by adding "s" or
/// using [plural], if given.
String namedSequence(String name, Iterable iter, [String? plural]) {
  if (iter.length == 1) return '$name ${iter.single}';

  plural ??= '${name}s';
  return '$plural ${toSentence(iter)}';
}

/// Returns a sentence fragment listing the elements of [iter].
///
/// This converts each element of [iter] to a string and separates them with
/// commas and/or [conjunction] (`"and"` by default) where appropriate.
String toSentence(Iterable iter, {String conjunction = 'and'}) {
  if (iter.length == 1) return iter.first.toString();
  return '${iter.take(iter.length - 1).join(', ')} $conjunction ${iter.last}';
}

/// Returns [name] if [number] is 1, or the plural of [name] otherwise.
///
/// By default, this just adds "s" to the end of [name] to get the plural. If
/// [plural] is passed, that's used instead.
String pluralize(String name, int number, {String? plural}) {
  if (number == 1) return name;
  return plural ?? '${name}s';
}

/// Returns [text] with the first letter capitalized.
String capitalize(String text) =>
    text.substring(0, 1).toUpperCase() + text.substring(1);

/// Returns whether [host] is a host for a localhost or loopback URL.
///
/// Unlike [InternetAddress.isLoopback], this hostnames from URLs as well as
/// from [InternetAddress]es, including "localhost".
bool isLoopback(String host) {
  if (host == 'localhost') return true;

  // IPv6 hosts in URLs are surrounded by square brackets.
  if (host.startsWith('[') && host.endsWith(']')) {
    host = host.substring(1, host.length - 1);
  }

  return InternetAddress.tryParse(host)?.isLoopback ?? false;
}

/// Returns a list containing the sorted elements of [iter].
List<T> ordered<T extends Comparable<T>>(Iterable<T> iter) {
  var list = iter.toList();
  list.sort();
  return list;
}

/// Given a list of filenames, returns a set of patterns that can be used to
/// filter for those filenames.
///
/// For a given path, that path ends with some string in the returned set if
/// and only if that path's basename is in [files].
Set<String> createFileFilter(Iterable<String> files) {
  return files.expand<String>((file) {
    var result = ['/$file'];
    if (Platform.isWindows) result.add('\\$file');
    return result;
  }).toSet();
}

/// Given a of unwanted directory names, returns a set of patterns that can
/// be used to filter for those directory names.
///
/// For a given path, that path contains some string in the returned set if
/// and only if one of that path's components is in [dirs].
Set<String> createDirectoryFilter(Iterable<String> dirs) {
  return dirs.expand<String>((dir) {
    var result = ['/$dir/'];
    if (Platform.isWindows) {
      result
        ..add('/$dir\\')
        ..add('\\$dir/')
        ..add('\\$dir\\');
    }
    return result;
  }).toSet();
}

/// Returns the maximum value in [iter] by [compare].
///
/// [compare] defaults to [Comparable.compare].
T maxAll<T extends Comparable>(
  Iterable<T> iter, [
  int Function(T, T) compare = Comparable.compare,
]) =>
    iter.reduce((max, element) => compare(element, max) > 0 ? element : max);

/// Returns the element of [values] for which [orderBy] returns the smallest
/// value.
///
/// Returns the first such value in case of ties.
///
/// Starts all the [orderBy] invocations in parallel.
Future<S?> minByAsync<S, T>(
  Iterable<S> values,
  Future<T> Function(S) orderBy,
) async {
  int? minIndex;
  T? minOrderBy;
  var valuesList = values.toList();
  final orderByResults = await Future.wait(values.map(orderBy));
  for (var i = 0; i < orderByResults.length; i++) {
    final elementOrderBy = orderByResults[i];
    if (minOrderBy == null ||
        (elementOrderBy as Comparable).compareTo(minOrderBy) < 0) {
      minIndex = i;
      minOrderBy = elementOrderBy;
    }
  }
  if (minIndex == null) {
    return null; // when [values] is empty!
  }
  return valuesList[minIndex];
}

/// Like [List.sublist], but for any iterable.
Iterable<T> slice<T>(Iterable<T> values, int start, int end) {
  if (end <= start) {
    throw RangeError.range(
      end,
      start + 1,
      null,
      'end',
      'must be greater than start',
    );
  }
  return values.skip(start).take(end - start);
}

/// Like [Iterable.fold], but for an asynchronous [combine] function.
Future<S> foldAsync<S, T>(
  Iterable<T> values,
  S initialValue,
  Future<S> Function(S previous, T element) combine,
) =>
    values.fold(
      Future.value(initialValue),
      (previousFuture, element) =>
          previousFuture.then((previous) => combine(previous, element)),
    );

/// Replace each instance of [matcher] in [source] with the return value of
/// [fn].
String replace(String source, Pattern matcher, String Function(Match) fn) {
  var buffer = StringBuffer();
  var start = 0;
  for (var match in matcher.allMatches(source)) {
    buffer.write(source.substring(start, match.start));
    start = match.end;
    buffer.write(fn(match));
  }
  buffer.write(source.substring(start));
  return buffer.toString();
}

/// Returns the hex-encoded sha1 hash of [source].
String sha1(String source) =>
    crypto.sha1.convert(utf8.encode(source)).toString();

String hexEncode(List<int> bytes) => hex.encode(bytes);

Uint8List hexDecode(String string) => hex.decode(string) as Uint8List;

/// A regular expression matching a trailing CR character.
final _trailingCR = RegExp(r'\r$');

// TODO(nweiz): Use `text.split(new RegExp("\r\n?|\n\r?"))` when issue 9360 is
// fixed.
/// Splits [text] on its line breaks in a Windows-line-break-friendly way.
List<String> splitLines(String text) =>
    text.split('\n').map((line) => line.replaceFirst(_trailingCR, '')).toList();

/// Like [String.split], but only splits on the first occurrence of the pattern.
///
/// This always returns an array of two elements or fewer.
List<String> split1(String toSplit, String pattern) {
  if (toSplit.isEmpty) return <String>[];

  var index = toSplit.indexOf(pattern);
  if (index == -1) return [toSplit];
  return [
    toSplit.substring(0, index),
    toSplit.substring(index + pattern.length),
  ];
}

/// Convert a URL query string (or `application/x-www-form-urlencoded` body)
/// into a [Map] from parameter names to values.
Map<String, String> queryToMap(String queryList) {
  var map = <String, String>{};
  for (var pair in queryList.split('&')) {
    var split = split1(pair, '=');
    if (split.isEmpty) continue;
    var key = _urlDecode(split[0]);
    var value = split.length > 1 ? _urlDecode(split[1]) : '';
    map[key] = value;
  }
  return map;
}

/// Returns a human-friendly representation of [duration].
String niceDuration(Duration duration) {
  var hasMinutes = duration.inMinutes > 0;
  var result = hasMinutes ? '${duration.inMinutes}:' : '';

  var s = duration.inSeconds % 60;
  var ms = duration.inMilliseconds % 1000;

  // If we're using verbose logging, be more verbose but more accurate when
  // reporting timing information.
  var msString = log.verbosity.isLevelVisible(log.Level.fine)
      ? _padLeft(ms.toString(), 3, '0')
      : (ms ~/ 100).toString();

  return "$result${hasMinutes ? _padLeft(s.toString(), 2, '0') : s}"
      '.${msString}s';
}

/// Decodes a URL-encoded string.
///
/// Unlike [Uri.decodeComponent], this includes replacing `+` with ` `.
String _urlDecode(String encoded) =>
    Uri.decodeComponent(encoded.replaceAll('+', ' '));

enum ForceColorOption {
  always,
  never,
  auto,
}

/// Change to decide if ANSI colors should be output regardless of terminalD.
ForceColorOption forceColors = ForceColorOption.auto;

/// Whether ansi codes such as color escapes are safe to use.
///
/// On a terminal we can use ansi codes also on Windows.
///
/// Tests should make sure to run the subprocess with or without an attached
/// terminal to decide if colors will be provided.
bool get canUseAnsiCodes {
  switch (forceColors) {
    case ForceColorOption.always:
      return true;
    case ForceColorOption.never:
      return false;
    case ForceColorOption.auto:
      return (!Platform.environment.containsKey('NO_COLOR')) &&
          terminalOutputForStdout &&
          stdout.supportsAnsiEscapes;
  }
}

/// Gets an ANSI escape if those are supported by stdout (or nothing).
String getAnsi(String ansiCode) => canUseAnsiCodes ? ansiCode : '';

/// Gets a emoji special character as unicode, or the [alternative] if unicode
/// characters are not supported by stdout.
String emoji(String unicode, String alternative) =>
    canUseUnicode ? unicode : alternative;

// Assume unicode emojis are supported when not on Windows.
// If we are on Windows, unicode emojis are supported in Windows Terminal,
// which sets the WT_SESSION environment variable. See:
// https://github.com/microsoft/terminal/blob/master/doc/user-docs/index.md#tips-and-tricks
bool get canUseUnicode =>
    // The tests support unicode also on windows.
    runningFromTest ||
    // When not outputting to terminal we can also use unicode.
    !terminalOutputForStdout ||
    !Platform.isWindows ||
    Platform.environment.containsKey('WT_SESSION');

/// Prepends each line in [text] with [prefix].
///
/// If [firstPrefix] is passed, the first line is prefixed with that instead.
String prefixLines(String text, {String prefix = '| ', String? firstPrefix}) {
  var lines = text.split('\n');
  if (firstPrefix == null) {
    return lines.map((line) => '$prefix$line').join('\n');
  }

  var firstLine = '$firstPrefix${lines.first}';
  lines = lines.skip(1).map((line) => '$prefix$line').toList();
  lines.insert(0, firstLine);
  return lines.join('\n');
}

/// The subset of strings that don't need quoting in YAML.
///
/// This pattern does not strictly follow the plain scalar grammar of YAML,
/// which means some strings may be unnecessarily quoted, but it's much simpler.
final _unquotableYamlString = RegExp(r'^[a-zA-Z_-][a-zA-Z_0-9-]*$');

/// Converts [data], which is a parsed YAML object, to a pretty-printed string,
/// using indentation for maps.
String yamlToString(Object? data) {
  var buffer = StringBuffer();

  void stringify(bool isMapValue, String indent, Object? data) {
    // TODO(nweiz): Serialize using the YAML library once it supports
    // serialization.

    // Use indentation for (non-empty) maps.
    if (data is Map && data.isNotEmpty) {
      if (isMapValue) {
        buffer.writeln();
        indent += '  ';
      }

      // Sort the keys. This minimizes deltas in diffs.
      var keys = data.keys.toList();
      keys.sort((a, b) => a.toString().compareTo(b.toString()));

      var first = true;
      for (var key in keys) {
        if (!first) buffer.writeln();
        first = false;

        var keyString = key;
        if (key is! String || !_unquotableYamlString.hasMatch(key)) {
          keyString = jsonEncode(key);
        }

        buffer.write('$indent$keyString:');
        stringify(true, indent, data[key]);
      }

      return;
    }

    // Everything else we just stringify using JSON to handle escapes in
    // strings and number formatting.
    var string = data;

    // Don't quote plain strings if not needed.
    if (data is! String || !_unquotableYamlString.hasMatch(data)) {
      string = jsonEncode(data);
    }

    if (isMapValue) {
      buffer.write(' $string');
    } else {
      buffer.write('$indent$string');
    }
  }

  stringify(false, '', data);
  return buffer.toString();
}

/// Throw a [ApplicationException] with [message].
Never fail(String message, [Object? innerError, StackTrace? innerTrace]) {
  if (innerError != null) {
    throw WrappedException(message, innerError, innerTrace);
  } else {
    throw ApplicationException(message);
  }
}

/// Throw a [DataException] with [message] to indicate that the command has
/// failed because of invalid input data.
///
/// This will report the error and cause pub to exit with [exit_codes.DATA].
Never dataError(String message) => throw DataException(message);

/// Returns a UUID in v4 format as a `String`.
///
/// If [bytes] is provided, it must be length 16 and have values between `0` and
/// `255` inclusive.
///
/// If [bytes] is not provided, it is generated using `Random.secure`.
String createUuid([List<int>? bytes]) {
  var rnd = math.Random.secure();

  // See http://www.cryptosys.net/pki/uuid-rfc4122.html for notes
  bytes ??= List<int>.generate(16, (_) => rnd.nextInt(256));
  bytes[6] = (bytes[6] & 0x0F) | 0x40;
  bytes[8] = (bytes[8] & 0x3f) | 0x80;

  var chars = bytes
      .map((b) => b.toRadixString(16).padLeft(2, '0'))
      .join()
      .toUpperCase();

  return '${chars.substring(0, 8)}-${chars.substring(8, 12)}-'
      '${chars.substring(12, 16)}-${chars.substring(16, 20)}-${chars.substring(20, 32)}';
}

/// Wraps [text] so that it fits within [_lineLength], if there is a line length.
///
/// This preserves existing newlines and doesn't consider terminal color escapes
/// part of a word's length. It only splits words on spaces, not on other sorts
/// of whitespace.
///
/// If [prefix] is passed, it's added at the beginning of any wrapped lines.
String wordWrap(String text, {String prefix = ''}) {
  // If there is no limit, don't wrap.
  final lineLength = _lineLength;
  if (lineLength == null) {
    return text;
  }

  return text.split('\n').map((originalLine) {
    var buffer = StringBuffer();
    var lengthSoFar = 0;
    var firstLine = true;
    for (var word in originalLine.split(' ')) {
      var wordLength = _withoutColors(word).length;
      if (wordLength > lineLength) {
        if (lengthSoFar != 0) buffer.writeln();
        if (!firstLine) buffer.write(prefix);
        buffer.writeln(word);
        firstLine = false;
      } else if (lengthSoFar == 0) {
        if (!firstLine) buffer.write(prefix);
        buffer.write(word);
        lengthSoFar = wordLength + prefix.length;
      } else if (lengthSoFar + 1 + wordLength > lineLength) {
        buffer.writeln();
        buffer.write(prefix);
        buffer.write(word);
        lengthSoFar = wordLength + prefix.length;
        firstLine = false;
      } else {
        buffer.write(' $word');
        lengthSoFar += 1 + wordLength;
      }
    }
    return buffer.toString();
  }).join('\n');
}

/// A regular expression matching terminal color codes.
final _colorCode = RegExp('\u001b\\[[0-9;]+m');

/// Returns [str] without any color codes.
String _withoutColors(String str) => str.replaceAll(_colorCode, '');

/// A regular expression to match the exception prefix that some exceptions'
/// [Object.toString] values contain.
final _exceptionPrefix = RegExp(r'^([A-Z][a-zA-Z]*)?(Exception|Error): ');

/// Get a string description of an exception.
///
/// Many exceptions include the exception class name at the beginning of their
/// [toString], so we remove that if it exists.
String getErrorMessage(Object error) =>
    error.toString().replaceFirst(_exceptionPrefix, '');

/// Returns whether [version1] and [version2] are the same, ignoring the
/// pre-release modifiers on each if they exist.
bool equalsIgnoringPreRelease(Version version1, Version version2) =>
    version1.major == version2.major &&
    version1.minor == version2.minor &&
    version1.patch == version2.patch;

/// Creates a new map from [map] with new keys and values.
///
/// The return values of [key] are used as the keys and the return values of
/// [value] are used as the values for the new map.
Map<K2, V2> mapMap<K1, V1, K2, V2>(
  Map<K1, V1> map, {
  K2 Function(K1, V1)? key,
  V2 Function(K1, V1)? value,
}) {
  key ??= (mapKey, _) => mapKey as K2;
  value ??= (_, mapValue) => mapValue as V2;

  return <K2, V2>{
    for (var entry in map.entries)
      key(entry.key, entry.value): value(entry.key, entry.value),
  };
}

/// Compares two lists. If the lists have equal length this comparison will
/// iterate all elements, thus taking a fixed amount of time making timing
/// attacks harder.
bool fixedTimeBytesEquals(List<int>? a, List<int>? b) {
  if (a == null || b == null) return a == b;
  if (a.length != b.length) return false;
  var e = 0;
  for (var i = 0; i < a.length; i++) {
    e |= a[i] ^ b[i];
  }
  return e == 0;
}

/// Call [fn] retrying so long as [retryIf] return `true` for the exception
/// thrown, up-to [maxAttempts] times.
///
/// Defaults to 8 attempts, sleeping as following after 1st, 2nd, 3rd, ...,
/// 7th attempt:
///  1. 400 ms +/- 25%
///  2. 800 ms +/- 25%
///  3. 1600 ms +/- 25%
///  4. 3200 ms +/- 25%
///  5. 6400 ms +/- 25%
///  6. 12800 ms +/- 25%
///  7. 25600 ms +/- 25%
///
/// ```dart
/// final response = await retry(
///   // Make a GET request
///   () => http.get('https://google.com').timeout(Duration(seconds: 5)),
///   // Retry on SocketException or TimeoutException
///   retryIf: (e) => e is SocketException || e is TimeoutException,
/// );
/// print(response.body);
/// ```
///
/// If no [retryIf] function is given this will retry any for any [Exception]
/// thrown. To retry on an [Error], the error must be caught and _rethrown_
/// as an [Exception].
///
/// See https://github.com/google/dart-neats/blob/master/retry/lib/retry.dart
Future<T> retry<T>(
  FutureOr<T> Function() fn, {
  Duration delayFactor = const Duration(milliseconds: 200),
  double randomizationFactor = 0.25,
  Duration maxDelay = const Duration(seconds: 30),
  int maxAttempts = 8,
  FutureOr<bool> Function(Exception)? retryIf,
  FutureOr<void> Function(Exception, int attemptNumber)? onRetry,
}) async {
  var attempt = 0;
  // ignore: literal_only_boolean_expressions
  while (true) {
    attempt++; // first invocation is the first attempt
    try {
      return await fn();
    } on Exception catch (e) {
      if (attempt >= maxAttempts || (retryIf != null && !(await retryIf(e)))) {
        rethrow;
      }

      if (onRetry != null) {
        await onRetry(e, attempt + 1);
      }
    }

    // Sleep for a delay
    final rf = randomizationFactor * (random.nextDouble() * 2 - 1) + 1;
    final exp = math.min(attempt, 31); // prevent overflows.
    final delay = delayFactor * math.pow(2.0, exp) * rf;
    await Future<void>.delayed(delay < maxDelay ? delay : maxDelay);
  }
}

extension RetrieveFlags on ArgResults {
  String optionWithDefault(String name) => option(name)!;
}

/// Limits the range of characters and length.
///
/// Useful for displaying externally provided strings.
///
/// Only allowd printable ASCII, map anything else to whitespace, take at-most
/// 1024 characters.
String sanitizeForTerminal(String input) => String.fromCharCodes(
      input.runes.map((r) => 32 <= r && r <= 127 ? r : 32).take(1024),
    );

extension ExpectField on YamlMap {
  /// Looks up the [key] in this map, and validates that it is of type [T],
  /// returning it if so.
  ///
  /// Throws a [SourceSpanApplicationException] if not present and [T] is not
  /// nullable, or if the value is not of type [T].
  T expectField<T extends Object?>(String key) {
    final value = this[key];
    if (value is T) return value;
    if (value == null) {
      throw SourceSpanApplicationException(
        'Missing the required "$key" field.',
        span,
      );
    } else {
      throw SourceSpanApplicationException(
        '"$key" field must be a $T.',
        nodes[key]?.span,
      );
    }
  }

  String expectPackageNameField() {
    final name = expectField<String>('name');
    if (!packageNameRegExp.hasMatch(name)) {
      throw SourceSpanApplicationException(
        '"name" field must be a valid Dart identifier.',
        nodes['name']?.span,
      );
    } else if (reservedWords.contains(name.toLowerCase())) {
      throw SourceSpanApplicationException(
        '"name" field may not be a Dart reserved word.',
        nodes['name']?.span,
      );
    }
    return name;
  }
}

extension ExpectEntries on YamlList {
  /// Expects each entry in [this] to have a value of type [T],
  /// and returns a `List<T>`.
  ///
  /// Throws a [SourceSpanApplicationException] for the first entry that does
  /// not have a value of type [T].
  List<T> expectElements<T extends Object?>() => [
        for (var node in nodes)
          if (node.value case T value)
            value
          else
            throw SourceSpanApplicationException(
              'Elements must be of type $T.',
              node.span,
            ),
      ];
}