// Copyright (c) 2020, 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';
import 'package:shelf/src/util.dart';

final _emptyHeaders = Headers._empty();

/// Unmodifiable, key-insensitive header map.
class Headers extends UnmodifiableMapView<String, List<String>> {
  Map<String, String> _singleValues;

  factory Headers.from(Map<String, List<String>> values) {
    if (values == null || values.isEmpty) {
      return _emptyHeaders;
    } else if (values is Headers) {
      return values;
    } else {
      return Headers._(values);
    }
  }

  Headers._(Map<String, List<String>> values)
      : super(CaseInsensitiveMap.from(Map.fromEntries(values.entries
            .where((e) => e.value?.isNotEmpty ?? false)
            .map((e) => MapEntry(e.key, List.unmodifiable(e.value))))));

  Headers._empty() : super(const {});
  factory Headers.empty() => _emptyHeaders;

  Map<String, String> get singleValues => _singleValues ??= UnmodifiableMapView(
        CaseInsensitiveMap.from(
            map((key, value) => MapEntry(key, joinHeaderValues(value)))),
      );
}