GSS2Rework/GSS2.UI.Core/SectionPanel.cs

using System.Collections;
using System.Collections.Specialized;
using System.Diagnostics;

using Avalonia;
using Avalonia.Animation;
using Avalonia.Controls;
using Avalonia.Controls.Templates;
using Avalonia.Layout;
using Avalonia.Media;
using Avalonia.Styling;
using Avalonia.Threading;

using GSS2.Core.Extensions;

namespace GSS2.UI.Core;

public class SectionPanel : Panel
{
    public static readonly StyledProperty<int> CurrentIndexProperty = AvaloniaProperty.Register<SectionPanel, int>(
        name: nameof(CurrentIndex),
        defaultValue: 0,
        coerce: (obj, value) =>
        {
            if (obj is not SectionPanel sectionPanel)
                return value;
            if (sectionPanel.Cyclic)
                return value;
            if (sectionPanel.Children.Count() == 0)
                return 0;
            return Math.Clamp(value, 0, sectionPanel.Children.Count() - 1);
        });
    public int CurrentIndex
    {
        get => GetValue(CurrentIndexProperty);
        set => SetValue(CurrentIndexProperty, value);
    }
    public static readonly StyledProperty<bool> EnableAnimationProperty = AvaloniaProperty.Register<SectionPanel, bool>(nameof(EnableAnimation), true);
    public bool EnableAnimation
    {
        get => GetValue(EnableAnimationProperty);
        set => SetValue(EnableAnimationProperty, value);
    }
    public static readonly StyledProperty<double> AnimationSpeedProperty = AvaloniaProperty.Register<SectionPanel, double>(nameof(AnimationSpeed), 500);
    public double AnimationSpeed
    {
        get => GetValue(AnimationSpeedProperty);
        set => SetValue(AnimationSpeedProperty, value);
    }
    public static readonly StyledProperty<Orientation> OrientationProperty = AvaloniaProperty.Register<SectionPanel, Orientation>(nameof(Orientation), Orientation.Vertical);
    public Orientation Orientation
    {
        get => GetValue(OrientationProperty);
        set => SetValue(OrientationProperty, value);
    }
    public static readonly StyledProperty<bool> CyclicProperty = AvaloniaProperty.Register<SectionPanel, bool>(nameof(Cyclic), false);
    public bool Cyclic
    {
        get => GetValue(CyclicProperty);
        set => SetValue(CyclicProperty, value);
    }
    public static readonly StyledProperty<bool> CanScrollForwardProperty = AvaloniaProperty.Register<SectionPanel, bool>(nameof(CanScrollForward), false, defaultBindingMode: Avalonia.Data.BindingMode.OneWayToSource);
    public bool CanScrollForward
    {
        get => GetValue(CanScrollForwardProperty);
        set => SetValue(CanScrollForwardProperty, value);
    }
    public static readonly StyledProperty<bool> CanScrollBackwardProperty = AvaloniaProperty.Register<SectionPanel, bool>(nameof(CanScrollBackward), false, defaultBindingMode: Avalonia.Data.BindingMode.OneWayToSource);
    public bool CanScrollBackward
    {
        get => GetValue(CanScrollBackwardProperty);
        set => SetValue(CanScrollBackwardProperty, value);
    }
    public static readonly StyledProperty<IEnumerable?> ChildrenSourceProperty = AvaloniaProperty.Register<SectionPanel, IEnumerable?>(nameof(ChildrenSource), null, defaultBindingMode: Avalonia.Data.BindingMode.OneWay);
    public IEnumerable? ChildrenSource
    {
        get => GetValue(ChildrenSourceProperty);
        set => SetValue(ChildrenSourceProperty, value);
    }
    public static readonly StyledProperty<IDataTemplate?> ChildrenTemplateProperty = AvaloniaProperty.Register<SectionPanel, IDataTemplate?>(nameof(ChildrenTemplate), null);
    public IDataTemplate? ChildrenTemplate
    {
        get => GetValue(ChildrenTemplateProperty);
        set => SetValue(ChildrenTemplateProperty, value);
    }
    public static readonly StyledProperty<bool> IsScrollingProperty = AvaloniaProperty.Register<SectionPanel, bool>(nameof(IsScrolling), false, defaultBindingMode: Avalonia.Data.BindingMode.OneWayToSource);
    public bool IsScrolling
    {
        get => GetValue(IsScrollingProperty);
        set => SetValue(IsScrollingProperty, value);
    }


    private readonly Dictionary<Control, int> _childIndices = new Dictionary<Control, int>();
    private bool _initialized = false;
    private int _previousIndex = 0;

    public SectionPanel()
    : base()
    {
        CurrentIndexProperty.Changed.AddClassHandler<SectionPanel>((panel, ea) =>
        {
            if (panel != this)
                return;
            panel.CanScrollBackward = panel.Cyclic || panel.CurrentIndex != 0;
            panel.CanScrollForward = panel.Cyclic || panel.CurrentIndex != panel.Children.Count() - 1;
            panel.InvalidateArrange();
        });
        ChildrenSourceProperty.Changed.AddClassHandler<SectionPanel>((panel, ea) =>
        {
            if (panel != this)
                return;
            (ea.OldValue as INotifyCollectionChanged)?.CollectionChanged -= panel.OnChildrenSourceCollectionChanged;
            (ea.NewValue as INotifyCollectionChanged)?.CollectionChanged += panel.OnChildrenSourceCollectionChanged;
            panel.Children.Clear();
            if (ea.NewValue is IEnumerable enumerable)
            {
                IEnumerable<Control> controls;
                if (ChildrenTemplate is null)
                    controls = enumerable.OfType<Control>();
                else
                    controls = enumerable.Cast<object?>()
                        .Where(ChildrenTemplate.Match)
                        .Select((vm, i) =>
                        {
                            var control = ChildrenTemplate.Build(i);
                            control?.DataContext = vm;
                            control?.Name = $"Элемент {i}";
                            return control;
                        })
                        .OfType<Control>();

                foreach (var control in controls)
                    panel.Children.Add(control);

                if (_initialized)
                {
                    _childIndices.Clear();
                    foreach (var (i, child) in Children.Enumerate())
                        _childIndices.Add(child, i);
                }
            }
            panel.InvalidateArrange();
        });
        Children.CollectionChanged += (_, ea) =>
        {
            CanScrollForward = (Cyclic && Children.Count() > 1) || CurrentIndex != Children.Count() - 1;
            CanScrollBackward = (Cyclic && Children.Count() > 1) || CurrentIndex != 0;
        };
    }

    protected void OnChildrenSourceCollectionChanged(object? sender, NotifyCollectionChangedEventArgs ea)
    {
        switch (ea.Action)
        {
            case NotifyCollectionChangedAction.Add:
                {
                    if (ea.NewItems is null)
                        return;

                    var index = ea.NewStartingIndex >= 0
                        ? ea.NewStartingIndex
                        : Children.Count;

                    IEnumerable<Control> controls;
                    if (ChildrenTemplate is null)
                        controls = ea.NewItems.OfType<Control>();
                    else
                        controls = ea.NewItems.Cast<object?>()
                        .Where(ChildrenTemplate.Match)
                        .Select((vm, i) =>
                        {
                            var control = ChildrenTemplate.Build(i);
                            control?.DataContext = vm;
                            control?.Name = $"Элемент {i}";
                            return control;
                        })
                        .OfType<Control>();

                    foreach (Control control in controls)
                        Children.Insert(index++, control);

                    break;
                }

            case NotifyCollectionChangedAction.Remove:
                {
                    if (ea.OldItems is null)
                        return;

                    foreach (Control control in ea.OldItems)
                        Children.Remove(control);

                    break;
                }

            case NotifyCollectionChangedAction.Replace:
                {
                    if (ea.OldItems is not null)
                        foreach (Control control in ea.OldItems)
                            Children.Remove(control);

                    if (ea.NewItems is not null)
                    {
                        var index = ea.NewStartingIndex >= 0 ?
                            ea.NewStartingIndex :
                            Children.Count;

                        foreach (Control control in ea.NewItems)
                            Children.Insert(index++, control);
                    }

                    break;
                }

            case NotifyCollectionChangedAction.Move:
                {
                    if (ea.OldItems is not IEnumerable<Control> oldControls || oldControls.Count() == 0)
                        return;

                    var control = oldControls.First();

                    if (ea.OldStartingIndex >= 0)
                        Children.RemoveAt(ea.OldStartingIndex);

                    if (ea.NewStartingIndex >= 0)
                        Children.Insert(ea.NewStartingIndex, control);

                    break;
                }

            case NotifyCollectionChangedAction.Reset:
                {
                    Children.Clear();

                    if (ChildrenSource is null)
                        break;

                    IEnumerable<Control> controls;
                    if (ChildrenTemplate is null)
                        controls = ChildrenSource.OfType<Control>();
                    else
                        controls = ChildrenSource.Cast<object?>()
                            .Where(ChildrenTemplate.Match)
                            .Select((vm, i) =>
                            {
                                var control = ChildrenTemplate.Build(i);
                                control?.DataContext = vm;
                                control?.Name = $"Элемент {i}";
                                return control;
                            })
                            .OfType<Control>();

                    foreach (var control in controls)
                        Children.Add(control);

                    break;
                }
        }

        InvalidateMeasure();
        InvalidateArrange();
    }

    protected override void OnSizeChanged(SizeChangedEventArgs e)
    {
        if (!_initialized ||
            e.PreviousSize.Width == 0 ||
            e.PreviousSize.Height == 0)
        {
            base.OnSizeChanged(e);
            return;
        }

        foreach (var (child, i) in _childIndices)
        {
            var transform = child.RenderTransform as TranslateTransform;
            if (transform is null)
            {
                transform = new TranslateTransform();
                child.RenderTransform = transform;
            }
            if (child.RenderTransformOrigin != RelativePoint.TopLeft)
                child.RenderTransformOrigin = RelativePoint.TopLeft;

            _ = Orientation switch
            {
                Orientation.Vertical => transform.Y += transform.Y == 0 ? 0 : e.PreviousSize.Height - e.NewSize.Height,
                Orientation.Horizontal => transform.X += transform.X == 0 ? 0 : e.PreviousSize.Width - e.NewSize.Width,
                _ => 0
            };
        }
        base.OnSizeChanged(e);
    }
    protected override Size MeasureOverride(Size availableSize)
    {
        foreach (var child in Children)
            child.Measure(availableSize);
        return availableSize;
    }
    protected override Size ArrangeOverride(Size finalSize)
    {
        if (!_initialized)
        {
            foreach (var (i, child) in Children.Enumerate())
                _childIndices.Add(child, i);
            _initialized = true;
        }

        if (_previousIndex == CurrentIndex)
        {
            foreach (var (child, i) in _childIndices)
            {
                var rect = Orientation switch
                {
                    Orientation.Vertical => new Rect(0, i * finalSize.Height, finalSize.Width, finalSize.Height),
                    Orientation.Horizontal => new Rect(i * finalSize.Width, 0, finalSize.Width, finalSize.Height),
                    _ => default
                };
                child.Arrange(rect);
            }
        }
        else if (Children.Count() > 1)
            Dispatcher.UIThread.Post(async () => _ = ApplyOffset(finalSize, true), DispatcherPriority.Render);

        return finalSize;
    }

    private async Task ApplyOffset(Size size, bool animate)
    {
        int indexShift = CurrentIndex - _previousIndex;

        while (indexShift != 0)
        {
            int indexSingleShift = indexShift / Math.Abs(indexShift);

            var firstIndex = _childIndices.Min(ch => ch.Value);
            var lastIndex = _childIndices.Max(ch => ch.Value);

            if (indexSingleShift == -1 &&
                _previousIndex - 1 < firstIndex)
            {
                var newIndex = firstIndex - 1;
                var (child, _) = _childIndices.MaxBy(ch => ch.Value);
                InstantTransform(child, -Children.Count(), size);

                _childIndices[child] = newIndex;
            }

            if (indexSingleShift == 1 &&
                _previousIndex + 1 > lastIndex)
            {
                var newIndex = lastIndex + 1;
                var (child, _) = _childIndices.MinBy(ch => ch.Value);
                InstantTransform(child, Children.Count(), size);

                _childIndices[child] = newIndex;
            }

            List<Task> animations = new List<Task>();
            double offset = Orientation switch
            {
                Orientation.Vertical => -indexSingleShift * size.Height,
                Orientation.Horizontal => -indexSingleShift * size.Width,
                _ => 0
            };

            foreach (var (i, child) in Children.Enumerate())
                if (!animate || !EnableAnimation)
                    InstantTransform(child, offset);
                else
                    animations.Add(AnimationTransform(child, offset, Math.Abs(indexShift)));

            if (animations.Count() > 0)
                await Task.WhenAll(animations);

            indexShift -= indexSingleShift;
            _previousIndex += indexSingleShift;
        }
    }

    private void InstantTransform(Control control, double offset, Size? size = null)
    {
        var transform = control.RenderTransform as TranslateTransform;
        if (transform is null)
        {
            transform = new TranslateTransform();
            control.RenderTransform = transform;
        }
        if (control.RenderTransformOrigin != RelativePoint.TopLeft)
            control.RenderTransformOrigin = RelativePoint.TopLeft;

        _ = Orientation switch
        {
            Orientation.Vertical => transform.Y += offset * (size is null ? 1 : size.Value.Height),
            Orientation.Horizontal => transform.X += offset * (size is null ? 1 : size.Value.Width),
            _ => throw new UnreachableException(),
        };
    }
    private Task AnimationTransform(Control control, double offset, double speedRatio, Size? size = null)
    {
        var transform = control.RenderTransform as TranslateTransform;
        if (transform is null)
        {
            transform = new TranslateTransform();
            control.RenderTransform = transform;
        }
        if (control.RenderTransformOrigin != RelativePoint.TopLeft)
            control.RenderTransformOrigin = RelativePoint.TopLeft;

        var animation = new Animation
        {
            Duration = TimeSpan.FromMilliseconds(Math.Clamp(AnimationSpeed / speedRatio, 120, 1000)),
            FillMode = FillMode.Forward,
            Children =
                {
                new KeyFrame
                {
                    Cue = new Cue(1),
                    Setters =
                    {
                        Orientation switch
                        {
                            Orientation.Vertical => new Setter(TranslateTransform.YProperty, transform.Y + offset * (size is null ? 1 : size.Value.Height)),
                            Orientation.Horizontal => new Setter(TranslateTransform.XProperty, transform.X + offset * (size is null ? 1 : size.Value.Width)),
                            _ => throw new UnreachableException(),
                        }
                    }
                }
                }
        };

        IsScrolling = true;
        return animation.RunAsync(control).ContinueWith(_ => Dispatcher.UIThread.Invoke(() => IsScrolling = false));
    }
}