simplified how the download client selection works (#22)

code/Infrastructure/Verticals/DownloadClient/Deluge/DelugeService.cs

@@ -21,6 +21,7 @@ public sealed class DelugeService : IDownloadService
     )
     {
         _logger = logger;
+        config.Value.Validate();
         _client = new (config, httpClientFactory);
         _filenameEvaluator = filenameEvaluator;
     }

code/Infrastructure/Verticals/DownloadClient/DownloadServiceFactory.cs

@@ -3,6 +3,7 @@ using Common.Configuration.DownloadClient;
 using Infrastructure.Verticals.DownloadClient.Deluge;
 using Infrastructure.Verticals.DownloadClient.QBittorrent;
 using Infrastructure.Verticals.DownloadClient.Transmission;
+using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Options;
 
@@ -10,57 +11,25 @@ namespace Infrastructure.Verticals.DownloadClient;
 
 public sealed class DownloadServiceFactory
 {
-    private readonly QBitConfig _qBitConfig;
-    private readonly DelugeConfig _delugeConfig;
-    private readonly TransmissionConfig _transmissionConfig;
     private readonly IServiceProvider _serviceProvider;
+    private readonly Domain.Enums.DownloadClient _downloadClient;
     
-    public DownloadServiceFactory(
-        IOptions<QBitConfig> qBitConfig,
-        IOptions<DelugeConfig> delugeConfig,
-        IOptions<TransmissionConfig> transmissionConfig,
-        IServiceProvider serviceProvider)
+    public DownloadServiceFactory(IServiceProvider serviceProvider, IConfiguration configuration)
     {
-        _qBitConfig = qBitConfig.Value;
-        _delugeConfig = delugeConfig.Value;
-        _transmissionConfig = transmissionConfig.Value;
         _serviceProvider = serviceProvider;
-        
-        _qBitConfig.Validate();
-        _delugeConfig.Validate();
-        _transmissionConfig.Validate();
-
-        int enabledCount = new[] { _qBitConfig.Enabled, _delugeConfig.Enabled, _transmissionConfig.Enabled }
-            .Count(enabled => enabled);
-
-        if (enabledCount > 1)
-        {
-            throw new Exception("only one download client can be enabled");
-        }
-
-        if (enabledCount == 0)
-        {
-            throw new Exception("no download client is enabled");
-        }
+        _downloadClient = (Domain.Enums.DownloadClient)Enum.Parse(
+            typeof(Domain.Enums.DownloadClient),
+            configuration[EnvironmentVariables.DownloadClient] ?? Domain.Enums.DownloadClient.QBittorrent.ToString(),
+            true
+        );
     }
 
-    public IDownloadService CreateDownloadClient()
-    {
-        if (_qBitConfig.Enabled)
+    public IDownloadService CreateDownloadClient() =>
+        _downloadClient switch
         {
-            return _serviceProvider.GetRequiredService<QBitService>();
-        }
-
-        if (_delugeConfig.Enabled)
-        {
-            return _serviceProvider.GetRequiredService<DelugeService>();
-        }
-
-        if (_transmissionConfig.Enabled)
-        {
-            return _serviceProvider.GetRequiredService<TransmissionService>();
-        }
-
-        throw new NotSupportedException();
-    }
+            Domain.Enums.DownloadClient.QBittorrent => _serviceProvider.GetRequiredService<QBitService>(),
+            Domain.Enums.DownloadClient.Deluge => _serviceProvider.GetRequiredService<DelugeService>(),
+            Domain.Enums.DownloadClient.Transmission => _serviceProvider.GetRequiredService<TransmissionService>(),
+            _ => throw new ArgumentOutOfRangeException()
+        };
 }

code/Infrastructure/Verticals/DownloadClient/QBittorrent/QBitService.cs

@@ -22,6 +22,7 @@ public sealed class QBitService : IDownloadService
     {
         _logger = logger;
         _config = config.Value;
+        _config.Validate();
         _client = new(_config.Url);
         _filenameEvaluator = filenameEvaluator;
     }

code/Infrastructure/Verticals/DownloadClient/Transmission/TransmissionService.cs

@@ -25,6 +25,7 @@ public sealed class TransmissionService : IDownloadService
     {
         _logger = logger;
         _config = config.Value;
+        _config.Validate();
         _client = new(
             new Uri(_config.Url, "/transmission/rpc").ToString(),
             login: _config.Username,