ShrlAlgoToolkit/WPFluent/Controls/Scroll/DynamicScrollViewer.cs

using System.Windows.Controls;

// ReSharper disable once CheckNamespace
namespace WPFluent.Controls;

/// <summary>
/// HCWhite <see cref="ScrollViewer"/> with events depending on actions taken by the user.
/// </summary>
[DefaultEvent("ScrollChangedEvent")]
public class DynamicScrollViewer : PassiveScrollViewer
{
    /// <summary>
    /// Identifies the <see cref="IsScrollingHorizontally"/> dependency property.
    /// </summary>
    public static readonly DependencyProperty IsScrollingHorizontallyProperty = DependencyProperty.Register(
        nameof(IsScrollingHorizontally),
        typeof(bool),
        typeof(DynamicScrollViewer),
        new PropertyMetadata(false, OnIsScrollingHorizontallyChanged));

    /// <summary>
    /// Identifies the <see cref="IsScrollingVertically"/> dependency property.
    /// </summary>
    public static readonly DependencyProperty IsScrollingVerticallyProperty = DependencyProperty.Register(
        nameof(IsScrollingVertically),
        typeof(bool),
        typeof(DynamicScrollViewer),
        new PropertyMetadata(false, OnIsScrollingVerticallyChanged));

    /// <summary>
    /// Identifies the <see cref="MinimalChange"/> dependency property.
    /// </summary>
    public static readonly DependencyProperty MinimalChangeProperty = DependencyProperty.Register(
        nameof(MinimalChange),
        typeof(double),
        typeof(DynamicScrollViewer),
        new PropertyMetadata(40d, OnMinimalChangeChanged));

    /// <summary>
    /// Identifies the <see cref="Timeout"/> dependency property.
    /// </summary>
    public static readonly DependencyProperty TimeoutProperty = DependencyProperty.Register(
        nameof(Timeout),
        typeof(int),
        typeof(DynamicScrollViewer),
        new PropertyMetadata(1200, OnTimeoutChanged));

    private readonly EventIdentifier _horizontalIdentifier = new();

    private double _minimalChange = 40d;

    private bool _scrollingHorizontally = false;

    // Due to the large number of triggered events, we limit the complex logic of DependencyProperty
    private bool _scrollingVertically = false;

    private int _timeout = 1200;
    private readonly EventIdentifier _verticalIdentifier = new();

    private static void OnIsScrollingHorizontallyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        if(d is not DynamicScrollViewer scroll)
        {
            return;
        }

        scroll._scrollingHorizontally = scroll.IsScrollingHorizontally;
    }

    private static void OnIsScrollingVerticallyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        if(d is not DynamicScrollViewer scroll)
        {
            return;
        }

        scroll._scrollingVertically = scroll.IsScrollingVertically;
    }

    private static void OnMinimalChangeChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        if(d is not DynamicScrollViewer scroll)
        {
            return;
        }

        scroll._minimalChange = scroll.MinimalChange;
    }

    private static void OnTimeoutChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        if(d is not DynamicScrollViewer scroll)
        {
            return;
        }

        scroll._timeout = scroll.Timeout;
    }

    private async void UpdateHorizontalScrollingState()
    {
        // TODO: Optimize
        // My main assumption here is that each scroll causes a new "event / thread" to be assigned.
        // If more than Timeout has passed since the last event, there is no interaction.
        // We pass this value to the ScrollBar and link it to IsMouseOver.
        // This way we have a dynamic scrollbar that responds to scroll / mouse over.
        long currentEvent = _horizontalIdentifier.GetNext();

        if(!_scrollingHorizontally)
        {
            SetCurrentValue(IsScrollingHorizontallyProperty, true);
        }

        await Task.Delay(Timeout < 10000 ? Timeout : 1000);

        if(_horizontalIdentifier.IsEqual(currentEvent) && _scrollingHorizontally)
        {
            SetCurrentValue(IsScrollingHorizontallyProperty, false);
        }
    }

    private async void UpdateVerticalScrollingState()
    {
        // TODO: Optimize
        // My main assumption here is that each scroll causes a new "event / thread" to be assigned.
        // If more than Timeout has passed since the last event, there is no interaction.
        // We pass this value to the ScrollBar and link it to IsMouseOver.
        // This way we have a dynamic scrollbar that responds to scroll / mouse over.
        long currentEvent = _verticalIdentifier.GetNext();

        if(!_scrollingVertically)
        {
            SetCurrentValue(IsScrollingVerticallyProperty, true);
        }

        if(_timeout > -1)
        {
            await Task.Delay(_timeout < 10000 ? _timeout : 1000);
        }

        if(_verticalIdentifier.IsEqual(currentEvent) && _scrollingVertically)
        {
            SetCurrentValue(IsScrollingVerticallyProperty, false);
        }
    }

    /// <summary>
    /// OnScrollChanged is an override called whenever scrolling state changes on this <see
    /// cref="DynamicScrollViewer"/>.
    /// </summary>
    /// <remarks>
    /// OnScrollChanged fires the ScrollChangedEvent. Overriders of this method should call base.OnScrollChanged(args)
    /// if they want the event to be fired.
    /// </remarks>
    /// <param name="e">ScrollChangedEventArgs containing information about the change in scrolling state.</param>
    protected override void OnScrollChanged(ScrollChangedEventArgs e)
    {
        base.OnScrollChanged(e);

        if(e.HorizontalChange > _minimalChange || e.HorizontalChange < -_minimalChange)
        {
            UpdateHorizontalScrollingState();
        }

        if(e.VerticalChange > _minimalChange || e.VerticalChange < -_minimalChange)
        {
            UpdateVerticalScrollingState();
        }
    }

    /// <summary>
    /// Gets or sets a value indicating whether the user was scrolling horizontally for the last few seconds.
    /// </summary>
    public bool IsScrollingHorizontally
    {
        get => (bool)GetValue(IsScrollingHorizontallyProperty);
        set => SetValue(IsScrollingHorizontallyProperty, value);
    }

    /// <summary>
    /// Gets or sets a value indicating whether the user was scrolling vertically for the last few seconds.
    /// </summary>
    public bool IsScrollingVertically
    {
        get => (bool)GetValue(IsScrollingVerticallyProperty);
        set => SetValue(IsScrollingVerticallyProperty, value);
    }

    /// <summary>
    /// Gets or sets the value required for the scroll to show automatically.
    /// </summary>
    public double MinimalChange
    {
        get => (double)GetValue(MinimalChangeProperty);
        set => SetValue(MinimalChangeProperty, value);
    }

    /// <summary>
    /// Gets or sets time after which the scroll is to be hidden.
    /// </summary>
    public int Timeout { get => (int)GetValue(TimeoutProperty); set => SetValue(TimeoutProperty, value); }
}