Implement Drag-n'-Drop support

src/Lumper.UI/App.axaml.cs

@@ -1,5 +1,6 @@
 using Avalonia;
 using Avalonia.Controls.ApplicationLifetimes;
+using Avalonia.Input;
 using Avalonia.Markup.Xaml;
 using Lumper.UI.ViewModels;
 using Lumper.UI.Views;
@@ -17,10 +18,12 @@ public override void OnFrameworkInitializationCompleted()
     {
         if (ApplicationLifetime is IClassicDesktopStyleApplicationLifetime
             desktop)
+        {
             desktop.MainWindow = new MainWindow
             {
                 DataContext = new MainWindowViewModel()
             };
+        }
 
         base.OnFrameworkInitializationCompleted();
     }

src/Lumper.UI/ViewModels/MainWindowViewModel.IO.cs

@@ -163,7 +163,7 @@ private async Task LoadBsp(IStorageFile file)
         if(!file.TryGetUri(out var path))
         {
            throw new Exception("Failed to get file path");
-            
+
         }
         LoadBsp(path.AbsolutePath);
     }

src/Lumper.UI/ViewModels/MainWindowViewModel.cs

@@ -1,6 +1,10 @@
 using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.Linq;
 using Avalonia;
 using Avalonia.Controls.ApplicationLifetimes;
+using Avalonia.Input;
 using Lumper.UI.ViewModels.Bsp;
 using ReactiveUI;
 
@@ -27,6 +31,11 @@ public MainWindowViewModel()
         SearchInit();
         TabsInit();
         IOInit();
+
+        if (desktop.Args?.Length > 0)
+        {
+            LoadBsp(desktop.Args[0]);
+        }
     }
 
     public IClassicDesktopStyleApplicationLifetime Desktop
@@ -45,4 +54,48 @@ public BspNodeBase? SelectedNode
         get => _selectedNode;
         set => this.RaiseAndSetIfChanged(ref _selectedNode, value);
     }
+
+    internal static void DragOver(object? sender, DragEventArgs e)
+    {
+        e.DragEffects = DragDropEffects.Link;
+
+        var names = e.Data.GetFileNames() ?? new List<string>();
+
+        if (!e.Data.Contains(DataFormats.FileNames) || !names.FirstOrDefault("").ToLower().EndsWith(".bsp"))
+            e.DragEffects = DragDropEffects.None;
+    }
+
+    internal void Drop(object? sender, DragEventArgs e)
+    {
+        if (!e.Data.Contains(DataFormats.FileNames))
+            return;
+
+        var names = e.Data.GetFileNames() ?? new List<string>();
+        foreach (string target in names)
+        {
+            if (!target.ToLower().EndsWith(".bsp"))
+                continue;
+
+            if (BspModel == null)
+            {
+                // if nothing is open, open it.
+                LoadBsp(target);
+            }
+            else
+            {
+                // Otherwise, open a brand new Lumper instance with it.
+                string? executableFileName = Process.GetCurrentProcess().MainModule?.FileName;
+                if (executableFileName == null)
+                    return;
+
+                ProcessStartInfo startInfo = new()
+                {
+                    ArgumentList = { $"{target}" },
+                    FileName = executableFileName,
+                };
+
+                Process.Start(startInfo);
+            }
+        }
+    }
 }

src/Lumper.UI/Views/MainWindow.axaml

@@ -14,6 +14,7 @@
         TransparencyLevelHint="AcrylicBlur"
         ExtendClientAreaToDecorationsHint="True"
         WindowStartupLocation="CenterScreen"
+        DragDrop.AllowDrop="True"
         Background="Transparent">
 
     <Design.DataContext>

src/Lumper.UI/Views/MainWindow.axaml.cs

@@ -1,12 +1,28 @@
 using System;
 using System.ComponentModel;
 using Avalonia.Controls;
+using Avalonia.Input;
 using Lumper.UI.ViewModels;
 
 namespace Lumper.UI.Views;
 
 public partial class MainWindow : Window
 {
+    // Quietly shadow DataContext to add initializer
+    public new object? DataContext
+    {
+        init // DataContext is never overwritten-- It's ok to not defensively remove the Drop handler, and do DragOver here.
+        {
+            var dc = value as MainWindowViewModel; // It must be (as of 3/16/23)
+            AddHandler(DragDrop.DropEvent, dc!.Drop);
+            AddHandler(DragDrop.DragOverEvent, MainWindowViewModel.DragOver);
+
+            base.DataContext = value;
+        }
+
+        get => base.DataContext;
+    }
+
     public MainWindow()
     {
         InitializeComponent();