lib/src/shelf_unmodifiable_map.dart

// Copyright (c) 2014, 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 'dart:collection';

import 'package:http_parser/http_parser.dart';

/// A simple wrapper over [UnmodifiableMapView] which avoids re-wrapping itself.
class ShelfUnmodifiableMap extends UnmodifiableMapView<String, Object> {
  /// `true` if the key values are already lowercase.
  final bool _ignoreKeyCase;

  /// If [source] is a [ShelfUnmodifiableMap] with matching [ignoreKeyCase],
  /// then [source] is returned.
  ///
  /// If [source] is `null` it is treated like an empty map.
  ///
  /// If [ignoreKeyCase] is `true`, the keys will have case-insensitive access.
  ///
  /// [source] is copied to a new [Map] to ensure changes to the parameter value
  /// after constructions are not reflected.
  factory ShelfUnmodifiableMap(
    Map<String, Object>? source, {
    bool ignoreKeyCase = false,
  }) {
    if (source is ShelfUnmodifiableMap &&
        //        !ignoreKeyCase: no transformation of the input is required
        // source._ignoreKeyCase: the input cannot be transformed any more
        (!ignoreKeyCase || source._ignoreKeyCase)) {
      return source;
    }

    if (source == null || source.isEmpty) {
      return const _EmptyShelfUnmodifiableMap();
    }

    if (ignoreKeyCase) {
      source = CaseInsensitiveMap<Object>.from(source);
    } else {
      source = Map<String, Object>.from(source);
    }

    return ShelfUnmodifiableMap._(source, ignoreKeyCase);
  }

  /// Returns an empty [ShelfUnmodifiableMap].
  const factory ShelfUnmodifiableMap.empty() = _EmptyShelfUnmodifiableMap;

  ShelfUnmodifiableMap._(Map<String, Object> source, this._ignoreKeyCase)
      : super(source);
}

/// A const implementation of an empty [ShelfUnmodifiableMap].
class _EmptyShelfUnmodifiableMap extends MapView<String, Object>
    implements ShelfUnmodifiableMap {
  @override
  bool get _ignoreKeyCase => true;

  const _EmptyShelfUnmodifiableMap() : super(const <String, Object>{});

  // Override modifier methods that care about the type of key they use so that
  // when V is Null, they throw UnsupportedErrors instead of type errors.
  @override
  void operator []=(String key, Object value) => super[key] = const Object();

  @override
  void addAll(Map<String, Object> other) => super.addAll({});

  @override
  Object putIfAbsent(String key, Object Function() ifAbsent) =>
      super.putIfAbsent(key, () => const Object());

  @override
  // TODO: https://github.com/dart-lang/sdk/issues/44264
  Object remove(Object? key) => super.remove(key)!;
}