emby-toolbox/EmbyToolbox/Behaviors/MergeDropTargetBehavior.cs

using System.Windows;
using EmbyToolbox.ViewModels;

namespace EmbyToolbox.Behaviors;

public static class MergeDropTargetBehavior
{
    public static readonly DependencyProperty IsEnabledProperty = DependencyProperty.RegisterAttached(
        "IsEnabled",
        typeof(bool),
        typeof(MergeDropTargetBehavior),
        new PropertyMetadata(false, OnIsEnabledChanged));

    public static void SetIsEnabled(DependencyObject d, bool value) => d.SetValue(IsEnabledProperty, value);
    public static bool GetIsEnabled(DependencyObject d) => (bool)d.GetValue(IsEnabledProperty);

    private static void OnIsEnabledChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        if (d is not FrameworkElement fe)
        {
            return;
        }

        fe.AllowDrop = false;
        fe.PreviewDragOver -= OnPreviewDragOver;
        fe.PreviewDragLeave -= OnPreviewDragLeave;
        fe.PreviewDrop -= OnPreviewDrop;

        if (e.NewValue is true)
        {
            fe.AllowDrop = true;
            fe.PreviewDragOver += OnPreviewDragOver;
            fe.PreviewDragLeave += OnPreviewDragLeave;
            fe.PreviewDrop += OnPreviewDrop;
        }
    }

    private static void OnPreviewDragOver(object sender, DragEventArgs e)
    {
        if (sender is not FrameworkElement fe || fe.DataContext is not MergeViewModel vm)
        {
            return;
        }

        if (vm.IsRunning)
        {
            e.Effects = DragDropEffects.None;
            vm.IsMergeDropHighlight = false;
            return;
        }

        if (e.Data.GetDataPresent(DataFormats.FileDrop))
        {
            e.Effects = DragDropEffects.Copy;
            e.Handled = true;
            vm.IsMergeDropHighlight = true;
        }
        else
        {
            e.Effects = DragDropEffects.None;
            vm.IsMergeDropHighlight = false;
        }
    }

    private static void OnPreviewDragLeave(object sender, DragEventArgs e)
    {
        if (sender is not FrameworkElement fe || fe.DataContext is not MergeViewModel vm)
        {
            return;
        }

        vm.IsMergeDropHighlight = false;
    }

    private static void OnPreviewDrop(object sender, DragEventArgs e)
    {
        if (sender is not FrameworkElement fe || fe.DataContext is not MergeViewModel vm)
        {
            return;
        }

        vm.IsMergeDropHighlight = false;
        if (vm.IsRunning)
        {
            e.Handled = true;
            return;
        }
        if (e.Data.GetData(DataFormats.FileDrop) is not string[] paths || paths.Length == 0)
        {
            e.Handled = true;
            return;
        }

        vm.ApplyDroppedPaths(paths);
        e.Handled = true;
    }
}