bitwarden-mobile/src/Core/Utilities/ObservableRangeCollection.cs

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Collections.Specialized;
using System.ComponentModel;

#nullable enable

namespace Bit.Core.Utilities
{
    // TODO: Review this from time to time in case this gets added to MAUI or some toolkit, for now the api/feature
    // has been rejected: https://github.com/CommunityToolkit/dotnet/issues/256

    /// <summary>
    /// Represents a dynamic data collection that provides notifications when items get added, removed, or when the whole list is refreshed.
    /// </summary>
    /// <typeparam name="T"></typeparam>
    public class ObservableRangeCollection<T> : ObservableCollection<T>
    {
        /// <summary>
        /// Initializes a new instance of the System.Collections.ObjectModel.ObservableCollection(Of T) class.
        /// </summary>
        public ObservableRangeCollection()
            : base()
        {
        }

        /// <summary>
        /// Initializes a new instance of the System.Collections.ObjectModel.ObservableCollection(Of T) class that contains elements copied from the specified collection.
        /// </summary>
        /// <param name="collection">collection: The collection from which the elements are copied.</param>
        /// <exception cref="System.ArgumentNullException">The collection parameter cannot be null.</exception>
        public ObservableRangeCollection(IEnumerable<T> collection)
            : base(collection)
        {
        }

        /// <summary>
        /// Adds the elements of the specified collection to the end of the ObservableCollection(Of T).
        /// </summary>
        public void AddRange(IEnumerable<T> collection, NotifyCollectionChangedAction notificationMode = NotifyCollectionChangedAction.Add)
        {
            if (notificationMode != NotifyCollectionChangedAction.Add && notificationMode != NotifyCollectionChangedAction.Reset)
                throw new ArgumentException("Mode must be either Add or Reset for AddRange.", nameof(notificationMode));
            if (collection == null)
                throw new ArgumentNullException(nameof(collection));

            CheckReentrancy();

            var startIndex = Count;

            var itemsAdded = AddArrangeCore(collection);

            if (!itemsAdded)
                return;

            if (notificationMode == NotifyCollectionChangedAction.Reset)
            {
                RaiseChangeNotificationEvents(action: NotifyCollectionChangedAction.Reset);
                return;
            }

            var changedItems = collection is List<T>
                ? (List<T>)collection
                : new List<T>(collection);

            RaiseChangeNotificationEvents(
                action: NotifyCollectionChangedAction.Add,
                changedItems: changedItems,
                startingIndex: startIndex);
        }

        /// <summary>
        /// Removes the first occurence of each item in the specified collection from ObservableCollection(Of T). NOTE: with notificationMode = Remove, removed items starting index is not set because items are not guaranteed to be consecutive.
        /// </summary>
        public void RemoveRange(IEnumerable<T> collection, NotifyCollectionChangedAction notificationMode = NotifyCollectionChangedAction.Reset)
        {
            if (notificationMode != NotifyCollectionChangedAction.Remove && notificationMode != NotifyCollectionChangedAction.Reset)
                throw new ArgumentException("Mode must be either Remove or Reset for RemoveRange.", nameof(notificationMode));
            if (collection == null)
                throw new ArgumentNullException(nameof(collection));

            CheckReentrancy();

            if (notificationMode == NotifyCollectionChangedAction.Reset)
            {
                var raiseEvents = false;
                foreach (var item in collection)
                {
                    Items.Remove(item);
                    raiseEvents = true;
                }

                if (raiseEvents)
                    RaiseChangeNotificationEvents(action: NotifyCollectionChangedAction.Reset);

                return;
            }

            var changedItems = new List<T>(collection);
            for (var i = 0; i < changedItems.Count; i++)
            {
                if (!Items.Remove(changedItems[i]))
                {
                    changedItems.RemoveAt(i); // Can't use a foreach because changedItems is intended to be (carefully) modified
                    i--;
                }
            }

            if (changedItems.Count == 0)
                return;

            RaiseChangeNotificationEvents(
                action: NotifyCollectionChangedAction.Remove,
                changedItems: changedItems);
        }

        /// <summary>
        /// Clears the current collection and replaces it with the specified item.
        /// </summary>
        public void Replace(T item) => ReplaceRange(new T[] { item });

        /// <summary>
        /// Clears the current collection and replaces it with the specified collection.
        /// </summary>
        public void ReplaceRange(IEnumerable<T> collection)
        {
            if (collection == null)
                throw new ArgumentNullException(nameof(collection));

            CheckReentrancy();

            var previouslyEmpty = Items.Count == 0;

            Items.Clear();

            AddArrangeCore(collection);

            var currentlyEmpty = Items.Count == 0;

            if (previouslyEmpty && currentlyEmpty)
                return;

            RaiseChangeNotificationEvents(action: NotifyCollectionChangedAction.Reset);
        }

        bool AddArrangeCore(IEnumerable<T> collection)
        {
            var itemAdded = false;
            foreach (var item in collection)
            {
                Items.Add(item);
                itemAdded = true;
            }
            return itemAdded;
        }

        void RaiseChangeNotificationEvents(NotifyCollectionChangedAction action, List<T>? changedItems = null, int startingIndex = -1)
        {
            OnPropertyChanged(new PropertyChangedEventArgs(nameof(Count)));
            OnPropertyChanged(new PropertyChangedEventArgs("Item[]"));

            if (changedItems == null)
                OnCollectionChanged(new NotifyCollectionChangedEventArgs(action));
            else
                OnCollectionChanged(new NotifyCollectionChangedEventArgs(action, changedItems: changedItems, startingIndex: startingIndex));
        }
    }
}