Added initial Uno Platform frontend project.

FrontendPlatformUno/FrontendPlatformUno/Services/Caching/IWeatherCache.cs

@@ -0,0 +1,10 @@
+using FrontendPlatformUno.DataContracts;
+using System.Collections.Immutable;
+
+namespace FrontendPlatformUno.Services.Caching
+{
+    public interface IWeatherCache
+    {
+        ValueTask<IImmutableList<WeatherForecast>> GetForecast(CancellationToken token);
+    }
+}

FrontendPlatformUno/FrontendPlatformUno/Services/Caching/WeatherCache.cs

@@ -0,0 +1,80 @@
+using Uno.Extensions.Serialization;
+using Windows.Networking.Connectivity;
+using Windows.Storage;
+
+namespace FrontendPlatformUno.Services.Caching
+{
+    public sealed class WeatherCache : IWeatherCache
+    {
+        private readonly IApiClient _api;
+        private readonly ISerializer _serializer;
+        private readonly ILogger _logger;
+
+        public WeatherCache(IApiClient api, ISerializer serializer, ILogger<WeatherCache> logger)
+        {
+            _api = api;
+            _serializer = serializer;
+            _logger = logger;
+        }
+
+        private bool IsConnected => NetworkInformation.GetInternetConnectionProfile().GetNetworkConnectivityLevel() == NetworkConnectivityLevel.InternetAccess;
+
+        public async ValueTask<IImmutableList<WeatherForecast>> GetForecast(CancellationToken token)
+        {
+            var weatherText = await GetCachedWeather();
+            if (!string.IsNullOrWhiteSpace(weatherText))
+            {
+                return _serializer.FromString<ImmutableArray<WeatherForecast>>(weatherText);
+            }
+
+            if (!IsConnected)
+            {
+                _logger.LogWarning("App is offline and cannot connect to the API.");
+                throw new Exception("No internet connection");
+            }
+
+            var response = await _api.GetWeather(token);
+
+            if (response.IsSuccessStatusCode && response.Content is not null)
+            {
+                var weather = response.Content;
+                await Save(weather, token);
+                return weather;
+            }
+            else if (response.Error is not null)
+            {
+                _logger.LogError(response.Error, "An error occurred while retrieving the latest Forecast.");
+                throw response.Error;
+            }
+            else
+            {
+                return ImmutableArray<WeatherForecast>.Empty;
+            }
+        }
+
+        private async ValueTask<StorageFile> GetFile(CreationCollisionOption option) =>
+            await ApplicationData.Current.TemporaryFolder.CreateFileAsync("weather.json", option);
+
+        private async ValueTask<string?> GetCachedWeather()
+        {
+            var file = await GetFile(CreationCollisionOption.OpenIfExists);
+            var properties = await file.GetBasicPropertiesAsync();
+
+            // Reuse latest cache file if offline
+            // or if the file is less than 5 minutes old
+            if (IsConnected || DateTimeOffset.Now.AddMinutes(-5) > properties.DateModified)
+            {
+                return null;
+            }
+
+            return await File.ReadAllTextAsync(file.Path);
+        }
+
+        private async ValueTask Save(IImmutableList<WeatherForecast> weather, CancellationToken token)
+        {
+            var weatherText = _serializer.ToString(weather);
+            var file = await GetFile(CreationCollisionOption.ReplaceExisting);
+            await File.WriteAllTextAsync(file.Path, weatherText);
+        }
+    }
+}