Another Screensaver with WPF

using System;
using System.Diagnostics;
using System.IO;
using System.Linq;
using System.Windows;
using System.Windows.Forms;
using System.Windows.Input;
using RZWScreenSaver.Properties;
using Application=System.Windows.Application;
using KeyEventArgs=System.Windows.Input.KeyEventArgs;
using KeyEventHandler=System.Windows.Input.KeyEventHandler;
using MessageBox=System.Windows.MessageBox;
using MouseEventArgs=System.Windows.Input.MouseEventArgs;

namespace RZWScreenSaver {
    /// <summary>
    /// Interaction logic for ScreenSaver.xaml
    /// </summary>
    partial class ScreenSaver{
        const int MouseMoveAllowedThreshold = 5;
        System.Drawing.Point lastMousePosition;
        #region ctors
        public ScreenSaver() {
            InitializeComponent();
        }
        internal ScreenSaver(IPictureSource source, Rect displayArea) : base(source, displayArea){
            InitializeComponent();
        }
        #endregion

        internal event KeyEventHandler HandleKey;
        internal void RefreshShowTitle(){
            slide.ShowTitle = Settings.Default.ShowTitle;
        }
        protected override void OnActivated(EventArgs e) {
            lastMousePosition = System.Windows.Forms.Cursor.Position;
            base.OnActivated(e);
        }
        protected override void OnMouseMove(MouseEventArgs e) {
            base.OnMouseMove(e);
            if (!userInteractionMode){
                var current = System.Windows.Forms.Cursor.Position;
                var distant = Math.Abs(current.X - lastMousePosition.X) + Math.Abs(current.Y - lastMousePosition.Y);
                if (distant > MouseMoveAllowedThreshold)
                    Close();
            }
        }
        #region Keyboard handle
        static readonly Key[] SetChangingKeys = new[]{Key.D1, Key.D2, Key.D3, Key.D4};
        protected override void OnKeyUp(KeyEventArgs e) {
            if (isKeyExpected()){
                e.Handled = true;
                return;
            }
            if (HandleKey != null){
                HandleKey(this, e);
                if (e.Handled)
                    return;
            }
            e.Handled = true;
            if (SetChangingKeys.Contains(e.Key)){
                var setIndex = Array.IndexOf(SetChangingKeys, e.Key);
                if (setIndex != Settings.Default.PictureSetSelected){
                    pictureSource.SwitchToSet(setIndex);
                    Settings.Default.PictureSetSelected = setIndex;
                    Settings.Default.Save();
                }
                return;
            }
            switch(e.Key){
            case Key.F2:
                Settings.Default.ShowTitle = !Settings.Default.ShowTitle;
                Settings.Default.Save();
                notifyAllScreenSavers(saver => saver.RefreshShowTitle());
                return;
            case Key.Scroll:
                Debug.WriteLine("Scroll Lock with State = " + e.KeyStates.ToString());
                if (e.KeyStates == KeyStates.Toggled)
                    pictureSource.Stop();
                else
                    pictureSource.Start();
                return;
            case Key.F9:
                deleteOrMoveCurrentFile();
                return;
            case Key.F12:
                using(new UserInteractionScope(this)){
                    var configDialog = new ConfigDialog {Owner=this};
                    var result = configDialog.ShowDialog();
                    if (result != null && result.Value)
                        pictureSource.SwitchToSet(Settings.Default.PictureSetSelected);
                }
                return;
            }
            Debug.Write("Exit with key: ");
            Debug.WriteLine(e.Key.ToString());
            Application.Current.Shutdown();
        }
        void expectKeySoon(){
            expectedKey = true;
            expectedKeyTime = DateTime.Now;
            Debug.WriteLine("Expect key @ " + expectedKeyTime);
        }
        bool isKeyExpected(){
            var result = expectedKey && (DateTime.Now - expectedKeyTime).Milliseconds < 500;
            expectedKey = false;
            if (result)
                Debug.WriteLine("Key is expected!");
            return result;
        }
        bool expectedKey;
        DateTime expectedKeyTime;
        #endregion

        #region User Interaction
        bool userInteractionMode;
        void beginUserInteraction(){
            userInteractionMode = true;
        }
        void endUserInteraction(){
            userInteractionMode = false;
        }
        class UserInteractionScope : IDisposable{
            public UserInteractionScope(ScreenSaver parent){
                caller = parent;
                caller.pictureSource.Pause();
                notifyAllScreenSavers(saver => saver.beginUserInteraction());
                System.Windows.Forms.Cursor.Show();
            }
            public void Dispose(){
                notifyAllScreenSavers(saver => saver.endUserInteraction());
                System.Windows.Forms.Cursor.Hide();
                caller.pictureSource.Resume();
                caller.Focus();
                caller.expectKeySoon();
            }
            readonly ScreenSaver caller;
        }
        #endregion

        void deleteOrMoveCurrentFile(){
            using (new UserInteractionScope(this)){
                var targetFile = pictureSource.CurrentPictureFile;
                var dialog = new DeleteDialog(pictureSource.CurrentPicture, targetFile);
                var dialogResult = dialog.ShowDialog();
                if (dialogResult.HasValue && dialogResult.Value){
                    if (dialog.MoveFileNeeded){
                        var moveDialog = new Microsoft.Win32.SaveFileDialog{
                                                                    InitialDirectory = Path.GetDirectoryName(targetFile),
                                                                    Title = "Select the target folder",
                                                                    FileName = targetFile,
                                                                };
                        if ((bool)moveDialog.ShowDialog() && !pictureSource.MoveCurrentPictureTo(moveDialog.FileName)){
                            MessageBox.Show(this, "Path too long or No permission on the target folder.",
                                            "Move failed", MessageBoxButton.OK);
                        }
                    }else if (!pictureSource.DeleteCurrentPicture())
                        MessageBox.Show(this,
                                        "This picture cannot be deleted (locked?)\nHowever, it's removed from picture list temporarily",
                                        "File Deletion Failed", MessageBoxButton.OK, MessageBoxImage.Information);
                }
            }
        }
        static void notifyAllScreenSavers(Action<ScreenSaver> saverHandler){
            var saverList = from Window w in Application.Current.Windows where w is ScreenSaver select w;
            foreach (ScreenSaver saver in saverList){
                saverHandler(saver);
            }
        }
    }
}