Inject IMediator and fetch merchant details if missing

Refactor MyAccountContactPageViewModel to use IMediator for fetching merchant details when not present in cache. Add caching with expiration and user feedback on failure. Update tests to mock and inject IMediator. Add necessary usings for MediatR and caching.

Author: StuartFerguson

TransactionProcessor.Mobile.BusinessLogic.Tests/ViewModelTests/MyAccount/MyAccountContactPageViewModelTests.cs

@@ -1,4 +1,5 @@
-using Moq;
+using MediatR;
+using Moq;
 using Shouldly;
 using TransactionProcessor.Mobile.BusinessLogic.Services;
 using TransactionProcessor.Mobile.BusinessLogic.UIServices;
@@ -19,17 +20,21 @@ public class MyAccountContactPageViewModelTests
     private readonly MyAccountContactPageViewModel ViewModel;
 
     private readonly Mock<IDeviceService> DeviceService;
+    private readonly Mock<IMediator> Mediator;
 
     public MyAccountContactPageViewModelTests() {
         this.NavigationService = new Mock<INavigationService>();
         this.ApplicationCache = new Mock<IApplicationCache>();
         this.NavigationParameterService = new Mock<INavigationParameterService>();
         this.DialogService = new Mock<IDialogService>();
         this.DeviceService = new Mock<IDeviceService>();
+        this.Mediator = new Mock<IMediator>();
+
         this.ViewModel = new MyAccountContactPageViewModel(this.NavigationService.Object,
                                                            this.ApplicationCache.Object,
                                                            this.DialogService.Object, this.DeviceService.Object,
-                                                           this.NavigationParameterService.Object);
+                                                           this.NavigationParameterService.Object,
+                                                           this.Mediator.Object);
     }
 
     [Fact]

TransactionProcessor.Mobile.BusinessLogic/ViewModels/MyAccount/MyAccountContactPageViewModel.cs

@@ -1,11 +1,17 @@
-using TransactionProcessor.Mobile.BusinessLogic.Models;
+using MediatR;
+using Microsoft.Extensions.Caching.Memory;
+using Microsoft.Extensions.Primitives;
+using SimpleResults;
+using TransactionProcessor.Mobile.BusinessLogic.Models;
+using TransactionProcessor.Mobile.BusinessLogic.Requests;
 using TransactionProcessor.Mobile.BusinessLogic.Services;
 using TransactionProcessor.Mobile.BusinessLogic.UIServices;
 
 namespace TransactionProcessor.Mobile.BusinessLogic.ViewModels.MyAccount;
 
 public class MyAccountContactPageViewModel : ExtendedBaseViewModel
 {
+    private readonly IMediator Mediator;
     private ContactModel contact;
 
     public ContactModel Contact {
@@ -19,17 +25,43 @@ public MyAccountContactPageViewModel(INavigationService navigationService,
                                          IApplicationCache applicationCache,
                                          IDialogService dialogService,
                                          IDeviceService deviceService,
-                                         INavigationParameterService navigationParameterService) : base(applicationCache, dialogService, navigationService, deviceService, navigationParameterService) {
+                                         INavigationParameterService navigationParameterService,
+                                         IMediator mediator) : base(applicationCache, dialogService, navigationService, deviceService, navigationParameterService) {
+        this.Mediator = mediator;
         this.Title = "My Contacts";
     }
 
 
     #endregion
 
-    public async Task Initialise(CancellationToken none) {
+    public async Task Initialise(CancellationToken cancellationToken) {
         MerchantDetailsModel merchantDetails = this.ApplicationCache.GetMerchantDetails();
 
-        // TODO: handle a null
+        if (merchantDetails == null)
+        {
+            GetMerchantDetailsRequest request = GetMerchantDetailsRequest.Create();
+
+            Result<MerchantDetailsModel> merchantDetailsResult = await this.Mediator.Send(request, cancellationToken);
+            if (merchantDetailsResult.IsFailed)
+            {
+                await this.DialogService.ShowWarningToast("Unable to load merchant details. Please try again later.", cancellationToken: cancellationToken);
+                return;
+            }
+
+            DateTime expirationTime = DateTime.Now.AddMinutes(60);
+            CancellationChangeToken expirationToken = new(new CancellationTokenSource(TimeSpan.FromMinutes(60)).Token);
+            MemoryCacheEntryOptions cacheEntryOptions = new MemoryCacheEntryOptions()
+                // Pin to cache.
+                .SetPriority(CacheItemPriority.NeverRemove)
+                // Set the actual expiration time
+                .SetAbsoluteExpiration(expirationTime)
+                // Force eviction to run
+                .AddExpirationToken(expirationToken);
+
+            this.ApplicationCache.SetMerchantDetails(merchantDetailsResult.Data, cacheEntryOptions);
+            merchantDetails = this.ApplicationCache.GetMerchantDetails();
+        }
+
         this.Contact = merchantDetails.Contact;
     }
 }