using System.Windows.Controls;
using System.Windows.Input;

namespace WPFluent.Controls;

/// <summary>
/// A custom ScrollViewer that allows certain mouse events to bubble through when it's inactive.
/// </summary>
public class PassiveScrollViewer : ScrollViewer
{
    /// <summary>
    /// Identifies the <see cref="IsScrollSpillEnabled"/> dependency property.
    /// </summary>
    public static readonly DependencyProperty IsScrollSpillEnabledProperty = DependencyProperty.Register(
        nameof(IsScrollSpillEnabled),
        typeof(bool),
        typeof(PassiveScrollViewer),
        new PropertyMetadata(true));

    private bool HasReachedEndOfScrolling(MouseWheelEventArgs e)
    {
        var isScrollingUp = e.Delta > 0;
        var isScrollingDown = e.Delta < 0;
        var isTopOfViewport = VerticalOffset == 0;
        var isBottomOfViewport = VerticalOffset >= ScrollableHeight;

        return isScrollingUp && isTopOfViewport || isScrollingDown && isBottomOfViewport;
    }

    private bool IsContentSmallerThanViewport => ScrollableHeight <= 0;

    private bool IsVerticalScrollingDisabled => VerticalScrollBarVisibility == ScrollBarVisibility.Disabled;

    protected override void OnMouseWheel(MouseWheelEventArgs e)
    {
        if(IsVerticalScrollingDisabled ||
            IsContentSmallerThanViewport ||
            IsScrollSpillEnabled &&
            HasReachedEndOfScrolling(e))
        {
            return;
        }

        base.OnMouseWheel(e);
    }

    /// <summary>
    /// Gets or sets a value indicating whether blocked inner scrolling should be propagated forward.
    /// </summary>
    public bool IsScrollSpillEnabled
    {
        get { return (bool)GetValue(IsScrollSpillEnabledProperty); }
        set { SetValue(IsScrollSpillEnabledProperty, value); }
    }
}