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

namespace Futonizer.Services;

/// <summary>
/// Scrolls a list/grid by an amount proportional to the mouse wheel delta
/// instead of relying on WPF's default per-event line scrolling. Mouse
/// "smooth scroll" utilities send many finer-grained wheel events per
/// physical notch to animate motion; WPF's default handling treats each
/// event as a full notch regardless of its magnitude, which multiplies the
/// effective scroll speed far beyond what the user intended.
/// </summary>
public static class SmoothScrollHelper
{
    private const double PixelsPerStandardNotch = 48.0;

    public static void HandlePreviewMouseWheel(object sender, MouseWheelEventArgs e)
    {
        if (sender is not DependencyObject start) return;
        var scrollViewer = FindVisualChild<ScrollViewer>(start);
        if (scrollViewer == null) return;

        double offsetDelta = -(e.Delta / 120.0) * PixelsPerStandardNotch;
        scrollViewer.ScrollToVerticalOffset(scrollViewer.VerticalOffset + offsetDelta);
        e.Handled = true;
    }

    private static T? FindVisualChild<T>(DependencyObject parent) where T : DependencyObject
    {
        int count = VisualTreeHelper.GetChildrenCount(parent);
        for (int i = 0; i < count; i++)
        {
            var child = VisualTreeHelper.GetChild(parent, i);
            if (child is T typed) return typed;

            var descendant = FindVisualChild<T>(child);
            if (descendant != null) return descendant;
        }
        return null;
    }
}