Fixes exceptions when using Maybe.Value in ViewModels (#257)

* Fix usage of Maybe in ViewModels

* Fix usage of Maybe in ProjectLookup

Author: SuperJMN

src/Angor/Avalonia/AngorApp/Core/SafeMaybe.cs

@@ -0,0 +1,11 @@
+using CSharpFunctionalExtensions;
+
+namespace AngorApp.Core;
+
+public class SafeMaybe<T>(Maybe<T> maybe)
+{
+    public Maybe<T> Maybe { get; } = maybe;
+    public T? Value => Maybe.GetValueOrDefault();
+    public bool HasValue => Maybe.HasValue;
+    public bool HasNoValue => !Maybe.HasValue;
+}

src/Angor/Avalonia/AngorApp/Core/SafeMaybeExtensions.cs

@@ -0,0 +1,12 @@
+using CSharpFunctionalExtensions;
+
+namespace AngorApp.Core;
+
+public static class SafeMaybeExtensions
+{
+    public static SafeMaybe<T> AsSafeMaybe<T>(this Maybe<T> maybe) =>
+        new SafeMaybe<T>(maybe);
+
+    public static SafeMaybe<T> AsSafeMaybe<T>(this T? obj) where T : class =>
+        obj.AsMaybe().AsSafeMaybe();
+}

src/Angor/Avalonia/AngorApp/Sections/Browse/ProjectLookup/IProjectLookupViewModel.cs

@@ -1,4 +1,5 @@
 using System.Windows.Input;
+using AngorApp.Core;
 using CSharpFunctionalExtensions;
 
 namespace AngorApp.Sections.Browse.ProjectLookup;
@@ -9,7 +10,7 @@ public interface IProjectLookupViewModel
     public IProjectViewModel SelectedProject { get; set; }
     public IObservable<bool> IsBusy { get; }
 
-    ReactiveCommand<string, Maybe<IList<IProjectViewModel>>> Lookup { get; }
-    Maybe<IList<IProjectViewModel>> LookupResults { get; }
+    ReactiveCommand<string, SafeMaybe<IList<IProjectViewModel>>> Lookup { get; }
+    SafeMaybe<IList<IProjectViewModel>> LookupResults { get; }
     public ICommand GoToSelectedProject { get; }
 }

src/Angor/Avalonia/AngorApp/Sections/Browse/ProjectLookup/ProjectLookupViewModel.cs

@@ -3,6 +3,7 @@
 using System.Reactive.Linq;
 using System.Windows.Input;
 using Angor.UI.Model;
+using AngorApp.Core;
 using AngorApp.Services;
 using CSharpFunctionalExtensions;
 using ReactiveUI.SourceGenerators;
@@ -16,7 +17,7 @@ public partial class ProjectLookupViewModel : ReactiveObject, IProjectLookupView
 {
     [ObservableAsProperty] private ICommand? goToSelectedProject;
 
-    [ObservableAsProperty] private Maybe<IList<IProjectViewModel>> lookupResults;
+    [ObservableAsProperty] private SafeMaybe<IList<IProjectViewModel>> lookupResults;
 
     [Reactive] private string? projectId;
     [Reactive] private IProjectViewModel? selectedProject;
@@ -27,7 +28,9 @@ public ProjectLookupViewModel(
         INavigator navigator,
         UIServices uiServices)
     {
-        Lookup = ReactiveCommand.CreateFromTask<string, Maybe<IList<IProjectViewModel>>>(
+        lookupResults = new SafeMaybe<IList<IProjectViewModel>>(Maybe<IList<IProjectViewModel>>.None);
+        
+        Lookup = ReactiveCommand.CreateFromTask<string, SafeMaybe<IList<IProjectViewModel>>>(
             async pid =>
             {
                 var maybeProject = await projectService.FindById(pid);
@@ -37,7 +40,7 @@ public ProjectLookupViewModel(
                 {
                     var vm = new ProjectViewModel(walletProvider, project, navigator, uiServices);
                     return new List<IProjectViewModel> { vm };
-                });
+                }).AsSafeMaybe();
             }
         );
 
@@ -51,12 +54,12 @@ public ProjectLookupViewModel(
             .Do(pid => Log.Debug("Search for ProjectId {ProjectId}", pid))
             .InvokeCommand(Lookup!);
 
-        this.WhenAnyValue(x => x.LookupResults).Values().Do(x => SelectedProject = x.FirstOrDefault()).Subscribe();
+        this.WhenAnyValue(x => x.LookupResults).Select(x => x.Maybe).Values().Do(x => SelectedProject = x.FirstOrDefault()).Subscribe();
 
         goToSelectedProjectHelper = this.WhenAnyValue(x => x.SelectedProject!.GoToDetails).ToProperty(this, x => x.GoToSelectedProject);
     }
 
-    public ReactiveCommand<string, Maybe<IList<IProjectViewModel>>> Lookup { get; }
+    public ReactiveCommand<string, SafeMaybe<IList<IProjectViewModel>>> Lookup { get; }
 
     public IObservable<bool> IsBusy { get; }
 }

src/Angor/Avalonia/AngorApp/Sections/Browse/ProjectLookup/ProjectLookupViewModelDesign.cs

@@ -1,6 +1,7 @@
 using System.Linq;
 using System.Reactive.Linq;
 using System.Windows.Input;
+using AngorApp.Core;
 using CSharpFunctionalExtensions;
 using ReactiveUI.SourceGenerators;
 
@@ -10,21 +11,21 @@ public partial class ProjectLookupViewModelDesign : ReactiveObject, IProjectLook
 {
     private bool hasResults;
 
-    [Reactive] private Maybe<IList<IProjectViewModel>> lookupResults;
+    [Reactive] private SafeMaybe<IList<IProjectViewModel>> lookupResults;
 
     public bool HasResults
     {
         get => hasResults;
         set
         {
-            var asMaybe = SampleData.GetProjects().Select(project => (IProjectViewModel)new ProjectViewModelDesign(project)).ToList().AsMaybe<IList<IProjectViewModel>>();
-            LookupResults = hasResults ? asMaybe : Maybe<IList<IProjectViewModel>>.None;
+            var asMaybe = SampleData.GetProjects().Select(project => (IProjectViewModel)new ProjectViewModelDesign(project)).ToList().AsSafeMaybe<IList<IProjectViewModel>>();
+            LookupResults = hasResults ? asMaybe : new SafeMaybe<IList<IProjectViewModel>>(Maybe<IList<IProjectViewModel>>.None);
             hasResults = value;
         }
     }
 
     public IObservable<bool> IsBusy { get; set; } = Observable.Return(false);
-    public ReactiveCommand<string, Maybe<IList<IProjectViewModel>>> Lookup { get; }
+    public ReactiveCommand<string, SafeMaybe<IList<IProjectViewModel>>> Lookup { get; }
     public ICommand GoToSelectedProject { get; }
 
     public string? ProjectId { get; set; }

src/Angor/Avalonia/AngorApp/Sections/Wallet/CreateAndRecover/Steps/SeedWordsGeneration/GeneratedWords.axaml

@@ -2,7 +2,6 @@
              xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
              xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
              xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
-             xmlns:generic="clr-namespace:System.Collections.Generic;assembly=System.Collections"
              xmlns:f="clr-namespace:Zafiro.Avalonia.Misc;assembly=Zafiro.Avalonia"
              xmlns:converters="clr-namespace:Zafiro.Avalonia.Converters;assembly=Zafiro.Avalonia"
              xmlns:seedWordsGeneration="clr-namespace:AngorApp.Sections.Wallet.CreateAndRecover.Steps.SeedWordsGeneration"

src/Angor/Avalonia/AngorApp/Sections/Wallet/CreateAndRecover/Steps/SeedWordsGeneration/ISeedWordsViewModel.cs

@@ -1,12 +1,12 @@
 using Angor.UI.Model;
-using CSharpFunctionalExtensions;
+using AngorApp.Core;
 using Zafiro.Avalonia.Controls.Wizards.Builder;
 
 namespace AngorApp.Sections.Wallet.CreateAndRecover.Steps.SeedWordsGeneration;
 
 public interface ISeedWordsViewModel : IStep
 {
-    Maybe<SeedWords> Words { get; }
-    ReactiveCommand<Unit, Maybe<SeedWords>> GenerateWords { get; }
+    SafeMaybe<SeedWords> Words { get; }
+    ReactiveCommand<Unit, SafeMaybe<SeedWords>> GenerateWords { get; }
     bool AreWordsWrittenDown { get; set; }
 }

src/Angor/Avalonia/AngorApp/Sections/Wallet/CreateAndRecover/Steps/SeedWordsGeneration/SeedWordsViewModel.cs

@@ -1,34 +1,44 @@
 using System.Reactive.Linq;
 using System.Threading.Tasks;
 using Angor.UI.Model;
-using AngorApp.Sections.Browse;
+using AngorApp.Core;
 using AngorApp.Services;
 using CSharpFunctionalExtensions;
-using CSharpFunctionalExtensions.ValueTasks;
 using ReactiveUI.SourceGenerators;
 using ReactiveUI.Validation.Helpers;
 using Zafiro.Avalonia.Dialogs;
-using Zafiro.CSharpFunctionalExtensions;
+using SampleData = AngorApp.Sections.Browse.SampleData;
 
 namespace AngorApp.Sections.Wallet.CreateAndRecover.Steps.SeedWordsGeneration;
 
 public partial class SeedWordsViewModel : ReactiveValidationObject, ISeedWordsViewModel
 {
     public SeedWordsViewModel(UIServices uiServices)
     {
-        GenerateWords = ReactiveCommand.CreateFromTask(() =>
+        // Start without seed words
+        words = new SafeMaybe<SeedWords>(Maybe<SeedWords>.None);
+
+        GenerateWords = ReactiveCommand.CreateFromTask(async () =>
         {
-            return words.Match(
-                async wordList => 
-                {
-                    var dialogResult = await ShowConfirmation(uiServices);
-                    return dialogResult.Match(confirmed => confirmed ? CreateNewWords() : wordList, () => wordList).AsMaybe();
-                },
-                () => Task.FromResult(CreateNewWords().AsMaybe())
-            );
+            if (words.HasValue)
+            {
+                // Existing words? ask for others
+                var dialogResult = await ShowConfirmation(uiServices);
+                var newWords = dialogResult.Match(
+                    confirmed => confirmed ? CreateNewWords() : words.Value,
+                    () => words.Value);
+                return newWords.AsSafeMaybe();
+            }
+            else
+            {
+                // No seedwords? Create them
+                return CreateNewWords().AsSafeMaybe();
+            }
         });
 
-        GenerateWords.Values().Do(_ => AreWordsWrittenDown = false).Subscribe();
+        GenerateWords
+            .Do(_ => AreWordsWrittenDown = false)
+            .Subscribe();
 
         wordsHelper = GenerateWords.ToProperty(this, x => x.Words);
     }
@@ -40,16 +50,20 @@ private static SeedWords CreateNewWords()
 
     private static Task<Maybe<bool>> ShowConfirmation(UIServices uiServices)
     {
-        return uiServices.Dialog.ShowConfirmation("Do you want to generate new seed words?",
+        return uiServices.Dialog.ShowConfirmation(
+            "Do you want to generate new seed words?",
             "You will see a different set of seed words. Make sure not to mix them with the ones you just saw and write down only the new ones.");
     }
 
-    public ReactiveCommand<Unit,Maybe<SeedWords>> GenerateWords { get; }
-    
+    public ReactiveCommand<Unit, SafeMaybe<SeedWords>> GenerateWords { get; }
+
     [Reactive] private bool areWordsWrittenDown;
 
-    [ObservableAsProperty] private Maybe<SeedWords> words;
-    public IObservable<bool> IsValid => this.WhenAnyValue<SeedWordsViewModel, bool, bool, Maybe<SeedWords>>(x => x.AreWordsWrittenDown, x => x.Words, (written, maybeWords) => written && maybeWords.HasValue);
+    [ObservableAsProperty] private SafeMaybe<SeedWords> words;
+
+    public IObservable<bool> IsValid => this.WhenAnyValue(x => x.AreWordsWrittenDown, x => x.Words,
+        (written, safeWords) => written && safeWords.HasValue);
+
     public IObservable<bool> IsBusy => Observable.Return(false);
     public bool AutoAdvance => false;
 

src/Angor/Avalonia/AngorApp/Sections/Wallet/CreateAndRecover/Steps/SeedWordsGeneration/SeedWordsViewModelDesign.cs

@@ -1,8 +1,9 @@
 using System.Reactive.Linq;
 using Angor.UI.Model;
-using AngorApp.Sections.Browse;
+using AngorApp.Core;
 using CSharpFunctionalExtensions;
 using ReactiveUI.SourceGenerators;
+using SampleData = AngorApp.Sections.Browse.SampleData;
 
 namespace AngorApp.Sections.Wallet.CreateAndRecover.Steps.SeedWordsGeneration;
 
@@ -13,7 +14,7 @@ public partial class SeedWordsViewModelDesign : ReactiveObject, ISeedWordsViewMo
     public IObservable<bool> IsBusy { get; } = Observable.Return(false);
     public bool AutoAdvance => false; 
 
-    [Reactive] private Maybe<SeedWords> words = Maybe<SeedWords>.None;
+    [Reactive] private SafeMaybe<SeedWords> words = new(Maybe<SeedWords>.None);
 
     public bool HasWords
     {
@@ -25,11 +26,11 @@ public bool HasWords
 
             if (value)
             {
-                Words = SampleData.Seedwords.AsMaybe();                
+                Words = SampleData.Seedwords.AsSafeMaybe();                
             }
             else
             {
-                Words = Maybe<SeedWords>.None;
+                Words = Maybe<SeedWords>.None.AsSafeMaybe();
             }
 
             hasWords = value;
@@ -38,6 +39,6 @@ public bool HasWords
         }
     }
 
-    public ReactiveCommand<Unit, Maybe<SeedWords>> GenerateWords { get; }
+    public ReactiveCommand<Unit, SafeMaybe<SeedWords>> GenerateWords { get; }
     [Reactive] private bool areWordsWrittenDown;
 }