// Copyright 2018 The Fuchsia Authors. 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:async';
import 'dart:collection';

import '../change.dart';
import '../leaf_value.dart';
import '../value_observer.dart';
import 'converted_change.dart';
import 'converter.dart';
import 'key_value_storage.dart';

/// Sledge Value to store Set.
class SetValue<E> extends SetBase<E> implements LeafValue {
  // Stores elements of [this]. Each element is stored both in a key and in a
  // value. It's done to provide an appropriate [lookup] method.
  final KeyValueStorage<E, E> _map;
  final MapToKVListConverter<E, bool> _converter;
  final StreamController<SetChange<E>> _changeController =
      new StreamController<SetChange<E>>.broadcast();

  // TODO: consider Converter as a provider of [equals] and [hashCode] methods.
  /// Creates a SetValue with provided [equals] as equality.
  /// It should be coherent with encoding of [E] done by Converter.
  SetValue({bool equals(E entry1, E entry2), int hashCode(E entry)})
      : _map = new KeyValueStorage<E, E>(equals: equals, hashCode: hashCode),
        _converter = new MapToKVListConverter<E, bool>();

  @override
  Change getChange() => _converter.serialize(_removeValue(_map.getChange()));

  @override
  void completeTransaction() {
    _map.completeTransaction();
  }

  @override
  void applyChange(Change input) {
    final change = _copyKeyToValue(_converter.deserialize(input));
    _map.applyChange(change);
    _changeController.add(new SetChange<E>(change));
  }

  @override
  void rollbackChange() {
    _map.rollbackChange();
  }

  @override
  set observer(ValueObserver observer) {
    _map.observer = observer;
  }

  /// Returns true if [value] is in the set.
  @override
  bool contains(Object value) => _map.containsKey(value);

  /// Adds [value] to the set.
  /// Returns true if [value] was not yet in the set. Otherwise returns
  /// false and the set is not changed.
  @override
  bool add(Object value) {
    final result = !contains(value);
    _map[value] = value;
    return result;
  }

  @override
  Set<E> toSet() => _map.keys.toSet();

  @override
  E lookup(Object object) {
    return _map[object];
  }

  @override
  int get length => _map.length;

  /// Removes [value] from the set. Returns true if [value] was in the set.
  /// Returns false otherwise. The method has no effect if [value] was not in
  /// the set.
  @override
  bool remove(Object value) {
    final result = (_map.remove(value) != null);
    return result;
  }

  @override
  Iterator<E> get iterator => toSet().iterator;

  @override
  Stream<SetChange<E>> get onChange => _changeController.stream;

  ConvertedChange<E, bool> _removeValue(ConvertedChange<E, E> change) {
    return new ConvertedChange<E, bool>(
        new Map<E, bool>.fromIterable(change.changedEntries.keys,
            value: (item) => true),
        change.deletedKeys);
  }

  ConvertedChange<E, E> _copyKeyToValue(ConvertedChange<E, bool> change) {
    return new ConvertedChange<E, E>(
        new Map<E, E>.fromIterable(change.changedEntries.keys),
        change.deletedKeys);
  }
}