AdvancedCollectionView.cs

// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.

using CommunityToolkit.WinUI.Helpers;
using System;
using System.CodeDom;
using System.Collections;
using System.Collections.Specialized;
using System.Runtime.CompilerServices;
using NotifyCollectionChangedAction = global::System.Collections.Specialized.NotifyCollectionChangedAction;

namespace CommunityToolkit.WinUI.Collections;

/// <summary>
/// A collection view implementation that supports filtering, sorting and incremental loading
/// </summary>
#if NET8_0_OR_GREATER
[System.Diagnostics.CodeAnalysis.RequiresUnreferencedCode("Item sorting uses reflection to get property types and may not be AOT compatible.")]
#endif
public partial class AdvancedCollectionView : IAdvancedCollectionView, INotifyPropertyChanged, ISupportIncrementalLoading, IComparer<object>
{
    private readonly List<object> _view;

    private readonly ObservableCollection<SortDescription> _sortDescriptions;

    private readonly Dictionary<string, PropertyInfo> _sortProperties;

    private readonly bool _liveShapingEnabled;

    private readonly HashSet<string> _observedFilterProperties = new HashSet<string>();

    private IList _source;

    private Predicate<object> _filter;
    private int _deferCounter;

    private WeakEventListener<AdvancedCollectionView, object, NotifyCollectionChangedEventArgs> _sourceWeakEventListener;

    /// <summary>
    /// Initializes a new instance of the <see cref="AdvancedCollectionView"/> class.
    /// </summary>
    public AdvancedCollectionView()
        : this(new List<object>(0))
    {
    }

    /// <summary>
    /// Initializes a new instance of the <see cref="AdvancedCollectionView"/> class.
    /// </summary>
    /// <param name="source">source IEnumerable</param>
    /// <param name="isLiveShaping">Denotes whether or not this ACV should re-filter/re-sort if a PropertyChanged is raised for an observed property.</param>
#pragma warning disable CS8767
#pragma warning disable CS8769
#pragma warning disable CS8622
#pragma warning disable CS8600
#pragma warning disable CS8601
#pragma warning disable CS8604
#pragma warning disable CS8603 // Possible null reference return.
#pragma warning disable CS8618 // Non-nullable field must contain a non-null value when exiting constructor. Consider declaring as nullable.
    public AdvancedCollectionView(IList source, bool isLiveShaping = false)
    {
        _liveShapingEnabled = isLiveShaping;
        _view = new List<object>();
        _sortDescriptions = new ObservableCollection<SortDescription>();
        _sortDescriptions.CollectionChanged += SortDescriptions_CollectionChanged;
        _sortProperties = new Dictionary<string, PropertyInfo>();
        Source = source;
    }

    /// <summary>
    /// Gets or sets the source
    /// </summary>
    public IList Source
    {
        get
        {
            return _source;
        }

        set
        {
            // ReSharper disable once PossibleUnintendedReferenceComparison
            if (_source == value)
            {
                return;
            }

            if (_source != null)
            {
                DetachPropertyChangedHandler(_source);
            }

            _source = value;
            AttachPropertyChangedHandler(_source);

            _sourceWeakEventListener?.Detach();

            if (_source is INotifyCollectionChanged sourceNcc)
            {
                _sourceWeakEventListener =
                    new WeakEventListener<AdvancedCollectionView, object, NotifyCollectionChangedEventArgs>(this)
                    {
                        // Call the actual collection changed event
                        OnEventAction = (source, changed, arg3) => SourceNcc_CollectionChanged(source, arg3),

                        // The source doesn't exist anymore
                        OnDetachAction = (listener) => sourceNcc.CollectionChanged -= _sourceWeakEventListener!.OnEvent
                    };
                sourceNcc.CollectionChanged += _sourceWeakEventListener.OnEvent;
            }

            HandleSourceChanged();
            OnPropertyChanged();
        }
    }

    /// <summary>
    /// Manually refresh the view
    /// </summary>
    public void Refresh()
    {
        HandleSourceChanged();
    }

    /// <inheritdoc/>
    public void RefreshFilter()
    {
        HandleFilterChanged();
    }

    /// <inheritdoc/>
    public void RefreshSorting()
    {
        HandleSortChanged();
    }

    /// <inheritdoc />
    public IEnumerator<object> GetEnumerator() => _view.GetEnumerator();

    /// <inheritdoc />
    IEnumerator IEnumerable.GetEnumerator() => _view.GetEnumerator();

    /// <inheritdoc />
    public void Add(object item)
    {
        if (IsReadOnly)
        {
            throw new NotSupportedException("Collection is read-only.");
        }

        _source.Add(item);
    }

    /// <inheritdoc />
    public void Clear()
    {
        if (IsReadOnly)
        {
            throw new NotSupportedException("Collection is read-only.");
        }

        _source.Clear();
    }

    /// <inheritdoc />
    public bool Contains(object item) => _view.Contains(item);

    /// <inheritdoc />
    public void CopyTo(object[] array, int arrayIndex) => _view.CopyTo(array, arrayIndex);

    /// <inheritdoc />
    public bool Remove(object item)
    {
        if (IsReadOnly)
        {
            throw new NotSupportedException("Collection is read-only.");
        }

        _source.Remove(item);
        return true;
    }

    /// <inheritdoc />
    public int Count => _view.Count;

    /// <inheritdoc />
    public bool IsReadOnly => _source == null || _source.IsReadOnly;

    /// <inheritdoc />
    public int IndexOf(object item) => _view.IndexOf(item);

    /// <inheritdoc />
    public void Insert(int index, object item)
    {
        if (IsReadOnly)
        {
            throw new NotSupportedException("Collection is read-only.");
        }

        _source.Insert(index, item);
    }

    /// <summary>
    /// Removes the <see cref="T:System.Collections.Generic.IList`1"/> item at the specified index.
    /// </summary>
    /// <param name="index">The zero-based index of the item to remove.</param><exception cref="T:System.ArgumentOutOfRangeException"><paramref name="index"/> is not a valid index in the <see cref="T:System.Collections.Generic.IList`1"/>.</exception><exception cref="T:System.NotSupportedException">The <see cref="T:System.Collections.Generic.IList`1"/> is read-only.</exception>
    public void RemoveAt(int index) => Remove(_view[index]);

    /// <summary>
    /// Gets or sets the element at the specified index.
    /// </summary>
    /// <returns>
    /// The element at the specified index.
    /// </returns>
    /// <param name="index">The zero-based index of the element to get or set.</param><exception cref="T:System.ArgumentOutOfRangeException"><paramref name="index"/> is not a valid index in the <see cref="T:System.Collections.Generic.IList`1"/>.</exception><exception cref="T:System.NotSupportedException">The property is set and the <see cref="T:System.Collections.Generic.IList`1"/> is read-only.</exception>
    public object this[int index]
    {
        get { return _view[index]; }
        set { _view[index] = value; }
    }

    /// <summary>
    /// Occurs when the vector changes.
    /// </summary>
    public event Windows.Foundation.Collections.VectorChangedEventHandler<object> VectorChanged;

    /// <summary>
    /// Move current index to item
    /// </summary>
    /// <param name="item">item</param>
    /// <returns>success of operation</returns>
    public bool MoveCurrentTo(object item) => item == CurrentItem || MoveCurrentToIndex(IndexOf(item));

    /// <summary>
    /// Moves selected item to position
    /// </summary>
    /// <param name="index">index</param>
    /// <returns>success of operation</returns>
    public bool MoveCurrentToPosition(int index) => MoveCurrentToIndex(index);

    /// <summary>
    /// Move current item to first item
    /// </summary>
    /// <returns>success of operation</returns>
    public bool MoveCurrentToFirst() => MoveCurrentToIndex(0);

    /// <summary>
    /// Move current item to last item
    /// </summary>
    /// <returns>success of operation</returns>
    public bool MoveCurrentToLast() => MoveCurrentToIndex(_view.Count - 1);

    /// <summary>
    /// Move current item to next item
    /// </summary>
    /// <returns>success of operation</returns>
    public bool MoveCurrentToNext() => MoveCurrentToIndex(CurrentPosition + 1);

    /// <summary>
    /// Move current item to previous item
    /// </summary>
    /// <returns>success of operation</returns>
    public bool MoveCurrentToPrevious() => MoveCurrentToIndex(CurrentPosition - 1);

    /// <summary>
    /// Load more items from the source
    /// </summary>
    /// <param name="count">number of items to load</param>
    /// <returns>Async operation of LoadMoreItemsResult</returns>
    /// <exception cref="NotImplementedException">Not implemented yet...</exception>
    public IAsyncOperation<LoadMoreItemsResult> LoadMoreItemsAsync(uint count)
    {
        var sil = _source as ISupportIncrementalLoading;
        return sil?.LoadMoreItemsAsync(count);
    }

    /// <summary>
    /// Gets the groups in collection
    /// </summary>
    public IObservableVector<object> CollectionGroups => null;

    /// <summary>
    /// Gets or sets the current item
    /// </summary>
    public object CurrentItem
    {

        get { return CurrentPosition > -1 && CurrentPosition < _view.Count ? _view[CurrentPosition] : null; }
#pragma warning restore CS8603 // Possible null reference return.
        set { MoveCurrentTo(value); }
    }

    /// <summary>
    /// Gets the position of current item
    /// </summary>
    public int CurrentPosition { get; private set; }

    /// <summary>
    /// Gets a value indicating whether the source has more items
    /// </summary>
    public bool HasMoreItems => (_source as ISupportIncrementalLoading)?.HasMoreItems ?? false;

    /// <summary>
    /// Gets a value indicating whether the current item is after the last visible item
    /// </summary>
    public bool IsCurrentAfterLast => CurrentPosition >= _view.Count;

    /// <summary>
    /// Gets a value indicating whether the current item is before the first visible item
    /// </summary>
    public bool IsCurrentBeforeFirst => CurrentPosition < 0;

    /// <summary>
    /// Current item changed event handler
    /// </summary>
    public event EventHandler<object> CurrentChanged;

    /// <summary>
    /// Current item changing event handler
    /// </summary>
    public event CurrentChangingEventHandler CurrentChanging;

    /// <summary>
    /// Gets a value indicating whether this CollectionView can filter its items
    /// </summary>
    public bool CanFilter => true;

    /// <summary>
    /// Gets or sets the predicate used to filter the visible items
    /// </summary>
    public Predicate<object> Filter
    {
        get
        {
            return _filter;
        }

        set
        {
            if (_filter == value)
            {
                return;
            }

            _filter = value;
            HandleFilterChanged();
        }
    }

    /// <summary>
    /// Gets a value indicating whether this CollectionView can sort its items
    /// </summary>
    public bool CanSort => true;

    /// <summary>
    /// Gets SortDescriptions to sort the visible items
    /// </summary>
    public IList<SortDescription> SortDescriptions => _sortDescriptions;

    /*
    /// <summary>
    /// Gets a value indicating whether this CollectionView can group its items
    /// </summary>
    public bool CanGroup => false;

    /// <summary>
    /// Gets GroupDescriptions to group the visible items
    /// </summary>
    public IList<object> GroupDescriptions => null;
    */

    /// <summary>
    /// Gets the source collection
    /// </summary>
    public IEnumerable SourceCollection => _source;

    /// <summary>
    /// IComparer implementation
    /// </summary>
    /// <param name="x">Object A</param>
    /// <param name="y">Object B</param>
    /// <returns>Comparison value</returns>
#pragma warning disable CA1033 // Interface methods should be callable by child types
    int IComparer<object>.Compare(object x, object y)
#pragma warning restore CA1033 // Interface methods should be callable by child types
    {
        if (!_sortProperties.Any())
        {
            var listType = _source?.GetType();
            Type type;

            if (listType == typeof(IncrementalLoadingCollection))
            {
                type = listType.GetGenericArguments()[1];
            }
            else if (listType != null && listType.IsGenericType)
            {
                type = listType.GetGenericArguments()[0];
            }
            else
            {
                type = x.GetType();
            }

            foreach (var sd in _sortDescriptions)
            {
                if (!string.IsNullOrEmpty(sd.PropertyName))
                {
                    _sortProperties[sd.PropertyName] = type.GetProperty(sd.PropertyName);
                }
            }
        }

        foreach (var sd in _sortDescriptions)
        {
            object cx, cy;

            if (string.IsNullOrEmpty(sd.PropertyName))
            {
                cx = x;
                cy = y;
            }
            else
            {
                var pi = _sortProperties[sd.PropertyName];

                cx = pi.GetValue(x!);
                cy = pi.GetValue(y!);
            }

            var cmp = sd.Comparer.Compare(cx, cy);

            if (cmp != 0)
            {
                return sd.Direction == SortDirection.Ascending ? +cmp : -cmp;
            }
        }

        return 0;
    }

    /// <summary>
    /// Occurs when a property value changes.
    /// </summary>
    public event PropertyChangedEventHandler? PropertyChanged;

    /// <summary>
    /// Property changed event invoker
    /// </summary>
    /// <param name="propertyName">name of the property that changed</param>
    protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null!)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }

    /// <inheritdoc/>
    public void ObserveFilterProperty(string propertyName)
    {
        _observedFilterProperties.Add(propertyName);
    }

    /// <inheritdoc/>
    public void ClearObservedFilterProperties()
    {
        _observedFilterProperties.Clear();
    }

    private void ItemOnPropertyChanged(object item, PropertyChangedEventArgs e)
    {
        if (!_liveShapingEnabled)
        {
            return;
        }

        var filterResult = _filter?.Invoke(item);

        if (filterResult.HasValue && _observedFilterProperties.Contains(e.PropertyName))
        {
            var viewIndex = _view.IndexOf(item);
            if (viewIndex != -1 && !filterResult.Value)
            {
                RemoveFromView(viewIndex, item);
            }
            else if (viewIndex == -1 && filterResult.Value)
            {
                var index = _source.IndexOf(item);
                HandleItemAdded(index, item);
            }
        }

        if ((filterResult ?? true) && SortDescriptions.Any(sd => sd.PropertyName == e.PropertyName))
        {
            var oldIndex = _view.IndexOf(item);

            // Check if item is in view:
            if (oldIndex < 0)
            {
                return;
            }

            _view.RemoveAt(oldIndex);
            var targetIndex = _view.BinarySearch(item, this);
            if (targetIndex < 0)
            {
                targetIndex = ~targetIndex;
            }

            // Only trigger expensive UI updates if the index really changed:
            if (targetIndex != oldIndex)
            {
                OnVectorChanged(new VectorChangedEventArgs(CollectionChange.ItemRemoved, oldIndex, item));

                _view.Insert(targetIndex, item);

                OnVectorChanged(new VectorChangedEventArgs(CollectionChange.ItemInserted, targetIndex, item));
            }
            else
            {
                _view.Insert(targetIndex, item);
            }
        }
        else if (string.IsNullOrEmpty(e.PropertyName))
        {
            HandleSourceChanged();
        }
    }

    private void AttachPropertyChangedHandler(IEnumerable items)
    {
        if (!_liveShapingEnabled || items == null)
        {
            return;
        }

        foreach (var item in items.OfType<INotifyPropertyChanged>())
        {
            item.PropertyChanged += ItemOnPropertyChanged;
        }
    }

    private void DetachPropertyChangedHandler(IEnumerable items)
    {
        if (!_liveShapingEnabled || items == null)
        {
            return;
        }

        foreach (var item in items.OfType<INotifyPropertyChanged>())
        {
            item.PropertyChanged -= ItemOnPropertyChanged;
        }
    }

    private void HandleSortChanged()
    {
        _sortProperties.Clear();
        _view.Sort(this);
        _sortProperties.Clear();
        OnVectorChanged(new VectorChangedEventArgs(CollectionChange.Reset));
    }

    private void HandleFilterChanged()
    {
        if (_filter != null)
        {
            for (var index = 0; index < _view.Count; index++)
            {
                var item = _view.ElementAt(index);
                if (_filter(item))
                {
                    continue;
                }

                RemoveFromView(index, item);
                index--;
            }
        }

        var viewHash = new HashSet<object>(_view);
        var viewIndex = 0;
        for (var index = 0; index < _source.Count; index++)
        {
            var item = _source[index];
            if (viewHash.Contains(item))
            {
                viewIndex++;
                continue;
            }

            if (HandleItemAdded(index, item, viewIndex))
            {
                viewIndex++;
            }
        }
    }

    private void HandleSourceChanged()
    {
        _sortProperties.Clear();
        var currentItem = CurrentItem;
        _view.Clear();
        foreach (var item in Source)
        {
            if (_filter != null && !_filter(item))
            {
                continue;
            }

            if (_sortDescriptions.Any())
            {
                var targetIndex = _view.BinarySearch(item, this);
                if (targetIndex < 0)
                {
                    targetIndex = ~targetIndex;
                }

                _view.Insert(targetIndex, item);
            }
            else
            {
                _view.Add(item);
            }
        }

        _sortProperties.Clear();
        OnVectorChanged(new VectorChangedEventArgs(CollectionChange.Reset));
        MoveCurrentTo(currentItem);
    }

    private void SourceNcc_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
    {
        // ReSharper disable once SwitchStatementMissingSomeCases
        switch (e.Action)
        {
            case NotifyCollectionChangedAction.Add:
                AttachPropertyChangedHandler(e.NewItems);
                if (_deferCounter <= 0)
                {
                    if (e.NewItems?.Count == 1)
                    {
                        HandleItemAdded(e.NewStartingIndex, e.NewItems[0]);
                    }
                    else
                    {
                        HandleSourceChanged();
                    }
                }

                break;
            case NotifyCollectionChangedAction.Remove:
                DetachPropertyChangedHandler(e.OldItems);
                if (_deferCounter <= 0)
                {
                    if (e.OldItems?.Count == 1)
                    {
                        HandleItemRemoved(e.OldStartingIndex, e.OldItems[0]);
                    }
                    else
                    {
                        HandleSourceChanged();
                    }
                }

                break;
            case NotifyCollectionChangedAction.Move:
            case NotifyCollectionChangedAction.Replace:
            case NotifyCollectionChangedAction.Reset:
                if (_deferCounter <= 0)
                {
                    HandleSourceChanged();
                }

                break;
        }
    }

    private bool HandleItemAdded(int newStartingIndex, object newItem, int? viewIndex = null)
    {
        if (_filter != null && !_filter(newItem))
        {
            return false;
        }

        var newViewIndex = _view.Count;

        if (_sortDescriptions.Any())
        {
            _sortProperties.Clear();
            newViewIndex = _view.BinarySearch(newItem, this);
            if (newViewIndex < 0)
            {
                newViewIndex = ~newViewIndex;
            }
        }
        else if (_filter != null)
        {
            if (_source == null)
            {
                HandleSourceChanged();
                return false;
            }

            if (newStartingIndex == 0 || _view.Count == 0)
            {
                newViewIndex = 0;
            }
            else if (newStartingIndex == _source.Count - 1)
            {
                newViewIndex = _view.Count;
            }
            else if (viewIndex.HasValue)
            {
                newViewIndex = viewIndex.Value;
            }
            else
            {
                for (int i = 0, j = 0; i < _source.Count; i++)
                {
                    if (i == newStartingIndex)
                    {
                        newViewIndex = j;
                        break;
                    }

                    if (_view[j] == _source[i])
                    {
                        j++;
                    }
                }
            }
        }

        _view.Insert(newViewIndex, newItem);
        if (newViewIndex <= CurrentPosition)
        {
            CurrentPosition++;
        }

        var e = new VectorChangedEventArgs(CollectionChange.ItemInserted, newViewIndex, newItem);
        OnVectorChanged(e);
        return true;
    }

    private void HandleItemRemoved(int oldStartingIndex, object oldItem)
    {
        if (_filter != null && !_filter(oldItem))
        {
            return;
        }

        if (oldStartingIndex < 0 || oldStartingIndex >= _view.Count || !Equals(_view[oldStartingIndex], oldItem))
        {
            oldStartingIndex = _view.IndexOf(oldItem);
        }

        if (oldStartingIndex < 0)
        {
            return;
        }

        RemoveFromView(oldStartingIndex, oldItem);
    }

    private void RemoveFromView(int itemIndex, object item)
    {
        _view.RemoveAt(itemIndex);
        if (itemIndex <= CurrentPosition)
        {
            CurrentPosition--;
        }

        var e = new VectorChangedEventArgs(CollectionChange.ItemRemoved, itemIndex, item);
        OnVectorChanged(e);
    }

    private void SortDescriptions_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
    {
        if (_deferCounter > 0)
        {
            return;
        }

        HandleSortChanged();
    }

    private bool MoveCurrentToIndex(int i)
    {
        if (i < -1 || i >= _view.Count)
        {
            return false;
        }

        if (i == CurrentPosition)
        {
            return false;
        }

        var e = new CurrentChangingEventArgs();
        OnCurrentChanging(e);
        if (e.Cancel)
        {
            return false;
        }

        CurrentPosition = i;
        OnCurrentChanged(null!);
        return true;
    }
}

#pragma warning restore CS8767
#pragma warning restore CS8769
#pragma warning restore CS8622
#pragma warning restore CS8601
#pragma warning restore CS8600
#pragma warning restore CS8604
#pragma warning restore CS8618 // Non-nullable field must contain a non-null value when exiting constructor. Consider declaring as nullable.
#pragma warning restore CS8603 // Possible null reference return.