Allow headerless and different header ROMs

CrossPlatformUI/Services/FileDialogService.cs

@@ -21,7 +21,7 @@ public class FileDialogService(TopLevel? target) : IFileDialogService
     {
         var files = await target!.StorageProvider.OpenFolderPickerAsync(new FolderPickerOpenOptions()
         {
-            Title = "Open Folder",
+            Title = "Select ROM Output Folder",
             AllowMultiple = false
         });
 

CrossPlatformUI/ViewModels/GenerateRomViewModel.cs

@@ -105,7 +105,30 @@ async void GenerateSeed()
                         {
                             basename = filename;
                         }
-                        await files.SaveGeneratedBinaryFile(filename, output.romdata!, Main.OutputFilePath);
+                        bool saved = false;
+                        while (!saved)
+                        {
+                            try
+                            {
+                                await files.SaveGeneratedBinaryFile(filename, output.romdata!, Main.OutputFilePath);
+                                saved = true;
+                            }
+                            catch (Exception e)
+                            {
+                                // DirectoryNotFoundException, UnauthorizedAccessException
+                                // We could check for specific exceptions, but it's
+                                // probably fine to do this for all errors while saving
+                                var newFolder = await RandomizerViewModel.SelectSaveFolder();
+                                if (!string.IsNullOrEmpty(newFolder) && newFolder != Main.OutputFilePath)
+                                {
+                                    Main.OutputFilePath = newFolder;
+                                }
+                                else // user did not pick a new save folder
+                                {
+                                    throw new UserFacingException("Unable to save ROM to folder", e.Message);
+                                }
+                            }
+                        }
 #if DEBUG
                         var debugfile = basename + ".mlb";
                         if (!string.IsNullOrEmpty(output.debuginfo))

CrossPlatformUI/ViewModels/RandomizerViewModel.cs

@@ -7,6 +7,7 @@
 using System.Reactive.Linq;
 using System.Reactive.Subjects;
 using System.Text.Json.Serialization;
+using System.Threading.Tasks;
 using Microsoft.Extensions.DependencyInjection;
 using Avalonia.Controls;
 using ReactiveUI;
@@ -117,9 +118,7 @@ public RandomizerViewModel(MainViewModel main)
 
         SaveFolder = ReactiveCommand.CreateFromTask(async () =>
         {
-            var fileDialog = App.Current?.Services?.GetService<IFileDialogService>()!;
-            var folder = await fileDialog.OpenFolderAsync();
-            Main.OutputFilePath = folder?.Path.LocalPath ?? "";
+            Main.OutputFilePath = await SelectSaveFolder() ?? "";
         });
 
         CheckForUpdates = ReactiveCommand.CreateFromTask(async () =>
@@ -203,6 +202,18 @@ public RandomizerViewModel(MainViewModel main)
         this.WhenActivated(OnActivate);
     }
 
+    public static async Task<string?> SelectSaveFolder()
+    {
+        var fileDialog = App.Current?.Services?.GetService<IFileDialogService>()!;
+        var folder = await fileDialog.OpenFolderAsync();
+        Uri? path = folder?.Path;
+        // both LocalPath and TryGetLocalPath() throw for non-absoloute URIs
+        string? localPath = path?.IsAbsoluteUri == true
+            ? path.LocalPath
+            : path?.OriginalString;
+        return localPath;
+    }
+
     private void OnActivate(CompositeDisposable disposables)
     {
         var loadedFlags = Main.Config.SerializeFlags(); // this serializes the configuration

CrossPlatformUI/ViewModels/RomFileViewModel.cs

@@ -7,6 +7,7 @@
 using Microsoft.Extensions.DependencyInjection;
 using ReactiveUI;
 using SD.Tools.BCLExtensions.CollectionsRelated;
+using Z2Randomizer.RandomizerCore;
 using CrossPlatformUI.Services;
 
 namespace CrossPlatformUI.ViewModels;
@@ -25,6 +26,14 @@ public byte[] RomData
         }
     }
 
+    private string message { get; set; } = "Select your Zelda 2 ROM to get started!";
+    [JsonIgnore]
+    public string Message
+    {
+        get => message;
+        set { message = value; this.RaisePropertyChanged(); }
+    }
+
     [JsonIgnore]
     public IObservable<byte[]> RomDataObservable => this.WhenAnyValue(x => x.RomData);
 
@@ -59,31 +68,36 @@ private async Task OpenFileInternal(CancellationToken token)
         if (fileprops.Size <= 1024 * 1024 * 1)
         {
             await using var readStream = await file.OpenReadAsync();
-            var tmp = new byte[(uint)fileprops.Size];
-            var read = await readStream.ReadAsync(tmp, token);
-            // TODO: Better validation
-            if (read == 1024 * 256 + 0x10)
+            byte[] fileData = new byte[(uint)fileprops.Size];
+            var read = await readStream.ReadAsync(fileData, token);
+            try
             {
-                RomData = tmp;
-                if (OperatingSystem.IsBrowser())
-                {
-                    // Manually save the state 
-                    await App.PersistState();
-                }
-                else
+                ROM.ValidateVanillaRom(ref fileData);
+            }
+            catch (UserFacingException e)
+            {
+                Message = e.Message;
+                return;
+            }
+            RomData = fileData;
+            if (OperatingSystem.IsBrowser())
+            {
+                // Manually save the state 
+                await App.PersistState();
+            }
+            else
+            {
+                // This part crashes if run in the browser build
+                if ((Main.OutputFilePath ?? "") == "")
                 {
-                    // This part crashes if run in the browser build
-                    if ((Main.OutputFilePath ?? "") == "")
-                    {
-                        Main.OutputFilePath = new Uri(file.Path, ".").LocalPath;
-                    }
+                    Main.OutputFilePath = new Uri(file.Path, ".").LocalPath;
                 }
-                HostScreen.Router.NavigateBack.Execute();
             }
+            HostScreen.Router.NavigateBack.Execute();
         }
         else
         {
-            throw new Exception("File exceeded 1MB limit.");
+            Message = "File exceeded 1MB limit. Please provide an unmodified Zelda 2 ROM (US release) with or without header.";
         }
     }
 

CrossPlatformUI/Views/RomFileView.axaml

@@ -9,7 +9,7 @@
     <Grid RowDefinitions="*, Auto">
         <StackPanel HorizontalAlignment="Center"
                     VerticalAlignment="Center">
-            <TextBlock Text="Select your Zelda 2 ROM to get started!" />
+            <TextBlock Text="{Binding Message}" />
             <Button Command="{Binding OpenFileCommand}">Choose ROM</Button>
         </StackPanel>
         <StackPanel Grid.Row="1" HorizontalAlignment="Right">

RandomizerCore/Hyrule.cs

@@ -265,13 +265,7 @@ public async Task<RandomizerResult> Randomize(byte[] vanillaRomData, RandomizerC
             reachableAreas = new HashSet<string>();
             //areasByLocation = new SortedDictionary<string, List<Location>>();
 
-            byte[] correctVanillaHash = [0x76, 0x4D, 0x36, 0xFA, 0x8A, 0x24, 0x50, 0x83, 0x4D, 0xA5, 0xE8, 0x19, 0x42, 0x81, 0x03, 0x5A];
-            var vanillaRomHash = MD5Hash.ComputeHash(vanillaRomData);
-            if (!correctVanillaHash.SequenceEqual(vanillaRomHash))
-            {
-                throw new UserFacingException("Vanilla ROM checksum failure", "Please provide an unmodified Zelda 2 ROM (US release).");
-            }
-
+            ROM.ValidateVanillaRom(ref vanillaRomData);
             // Make a copy of the vanilla data to prevent seed bleed
             ROMData = new ROM(vanillaRomData.ToArray(), true);
 

RandomizerCore/ROM.cs

@@ -2649,4 +2649,36 @@ public void UpdateItem(Collectable item, Room room)
         logger.Warn($"Could not write Collectable {item} to Item room {room.GetDebuggerDisplay()} in palace {room.PalaceNumber}");
         //throw new Exception("Could not write Collectable to Item room in palace " + PalaceNumber);
     }
+
+    /// Validates the ROM. Tries to fix headerless or bad header ROMs.
+    public static void ValidateVanillaRom(ref byte[] vanillaRomData)
+    {
+        int correctVanillaLengthWithHeader = 1024 * 256 + 0x10;
+        byte[] iNesHeader = [0x4e, 0x45, 0x53, 0x1a, 0x08, 0x10, 0x12, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00]; // (gets overriden with ROM expansion)
+        byte[] correctVanillaHash = [0x76, 0x4D, 0x36, 0xFA, 0x8A, 0x24, 0x50, 0x83, 0x4D, 0xA5, 0xE8, 0x19, 0x42, 0x81, 0x03, 0x5A];
+
+        if (vanillaRomData.Length != correctVanillaLengthWithHeader)
+        {
+            if (vanillaRomData.Length == correctVanillaLengthWithHeader - 0x10)
+            {
+                vanillaRomData = [.. iNesHeader, .. vanillaRomData];
+            }
+            else
+            {
+                throw new UserFacingException("Invalid ROM size", "Please provide an unmodified Zelda 2 ROM (US release) with or without header.");
+            }
+        }
+        else
+        {
+            for (int i = 0; i < 0x10; i++)
+            {
+                vanillaRomData[i] = iNesHeader[i];
+            }
+        }
+        var vanillaRomHash = MD5Hash.ComputeHash(vanillaRomData);
+        if (!correctVanillaHash.SequenceEqual(vanillaRomHash))
+        {
+            throw new UserFacingException("Vanilla ROM checksum failure", "Please provide an unmodified Zelda 2 ROM (US release).");
+        }
+    }
 }