Implemented layer LED assignment

Added a centralised ProfileEditorSurface for communication between VMs
Prefixed Surface, Device and Led with Artemis to differentiate them better

src/Artemis.UI/Screens/Module/ProfileEditor/ProfileTree/ProfileTreeViewModel.cs

@@ -0,0 +1,157 @@
+using System;
+using System.Linq;
+using System.Windows;
+using Artemis.Core.Models.Profile;
+using Artemis.UI.Screens.Module.ProfileEditor.ProfileTree.TreeItem;
+using Artemis.UI.Services.Interfaces;
+using GongSolutions.Wpf.DragDrop;
+
+namespace Artemis.UI.Screens.Module.ProfileEditor.ProfileTree
+{
+    public class ProfileTreeViewModel : ProfileEditorPanelViewModel, IDropTarget
+    {
+        private readonly IProfileEditorService _profileEditorService;
+        private TreeItemViewModel _selectedTreeItem;
+
+        public ProfileTreeViewModel(IProfileEditorService profileEditorService)
+        {
+            _profileEditorService = profileEditorService;
+
+            CreateRootFolderViewModel();
+            _profileEditorService.SelectedProfileChanged += OnSelectedProfileChanged;
+            _profileEditorService.SelectedProfileElementChanged += OnSelectedElementChanged;
+        }
+
+        public FolderViewModel RootFolder { get; set; }
+
+        public TreeItemViewModel SelectedTreeItem
+        {
+            get => _selectedTreeItem;
+            set
+            {
+                _selectedTreeItem = value;
+                _profileEditorService.ChangeSelectedProfileElement(value?.ProfileElement);
+            }
+        }
+
+        public void DragOver(IDropInfo dropInfo)
+        {
+            var dragDropType = GetDragDropType(dropInfo);
+
+            switch (dragDropType)
+            {
+                case DragDropType.Add:
+                    dropInfo.DropTargetAdorner = DropTargetAdorners.Highlight;
+                    dropInfo.Effects = DragDropEffects.Move;
+                    break;
+                case DragDropType.InsertBefore:
+                case DragDropType.InsertAfter:
+                    dropInfo.DropTargetAdorner = DropTargetAdorners.Insert;
+                    dropInfo.Effects = DragDropEffects.Move;
+                    break;
+            }
+        }
+
+        public void Drop(IDropInfo dropInfo)
+        {
+            var source = (TreeItemViewModel) dropInfo.Data;
+            var target = (TreeItemViewModel) dropInfo.TargetItem;
+
+            var dragDropType = GetDragDropType(dropInfo);
+            switch (dragDropType)
+            {
+                case DragDropType.Add:
+                    source.Parent.RemoveExistingElement(source);
+                    target.AddExistingElement(source);
+                    break;
+                case DragDropType.InsertBefore:
+                    target.SetElementInFront(source);
+                    break;
+                case DragDropType.InsertAfter:
+                    target.SetElementBehind(source);
+                    break;
+            }
+
+            _profileEditorService.UpdateSelectedProfile();
+        }
+
+        // ReSharper disable once UnusedMember.Global - Called from view
+        public void AddFolder()
+        {
+            RootFolder?.AddFolder();
+        }
+
+        // ReSharper disable once UnusedMember.Global - Called from view
+        public void AddLayer()
+        {
+            RootFolder?.AddLayer();
+        }
+
+        private void CreateRootFolderViewModel()
+        {
+            var firstChild = _profileEditorService.SelectedProfile?.Children?.FirstOrDefault();
+            if (!(firstChild is Folder folder))
+            {
+                RootFolder = null;
+                return;
+            }
+
+            RootFolder = new FolderViewModel(null, folder, _profileEditorService);
+        }
+
+        private static DragDropType GetDragDropType(IDropInfo dropInfo)
+        {
+            var source = (TreeItemViewModel) dropInfo.Data;
+            var target = (TreeItemViewModel) dropInfo.TargetItem;
+            if (source == target)
+                return DragDropType.None;
+
+            var parent = target;
+            while (parent != null)
+            {
+                if (parent == source)
+                    return DragDropType.None;
+                parent = parent.Parent;
+            }
+
+            switch (dropInfo.InsertPosition)
+            {
+                case RelativeInsertPosition.AfterTargetItem | RelativeInsertPosition.TargetItemCenter:
+                case RelativeInsertPosition.BeforeTargetItem | RelativeInsertPosition.TargetItemCenter:
+                    return target.SupportsChildren ? DragDropType.Add : DragDropType.None;
+                case RelativeInsertPosition.BeforeTargetItem:
+                    return DragDropType.InsertBefore;
+                case RelativeInsertPosition.AfterTargetItem:
+                    return DragDropType.InsertAfter;
+                default:
+                    return DragDropType.None;
+            }
+        }
+
+        #region Event handlers
+
+        private void OnSelectedElementChanged(object sender, EventArgs e)
+        {
+            var vms = RootFolder.GetAllChildren();
+
+            // Don't set it using the setter or that will trigger the event again
+            _selectedTreeItem = vms.FirstOrDefault(vm => vm.ProfileElement == _profileEditorService.SelectedProfileElement);
+            NotifyOfPropertyChange(() => SelectedTreeItem);
+        }
+
+        private void OnSelectedProfileChanged(object sender, EventArgs e)
+        {
+            CreateRootFolderViewModel();
+        }
+
+        #endregion
+    }
+
+    public enum DragDropType
+    {
+        None,
+        Add,
+        InsertBefore,
+        InsertAfter
+    }
+}