Generic event args types to handle common functionality

Author: DennisDyallo

Yubico.Core/src/Yubico/Core/Devices/DeviceEventArgs.cs

@@ -13,30 +13,63 @@
 // limitations under the License.
 
 using System;
-using System.Collections.Generic;
-using System.Text;
 
 namespace Yubico.Core.Devices
 {
     /// <summary>
-    /// Event arguments given whenever a device is added or removed from the system.
+    /// Defines the contract for device-related event arguments in a generic context.
+    /// This interface allows for type-safe access to device information in event handling
+    /// scenarios, supporting various device types that implement the IDevice interface.
+    /// It provides a flexible foundation for device event systems, enabling specific
+    /// device type information to be preserved and accessed in event handlers.
     /// </summary>
-    public class DeviceEventArgs : EventArgs
+    /// <remarks>
+    /// While this interface does not inherit from <see cref="System.EventArgs"/>, it retains the "Args" suffix
+    /// in its name. This naming convention is deliberately chosen to maintain consistency with standard
+    /// event argument naming patterns in C#, particularly for improved readability when used in delegate
+    /// and event handler signatures. The familiar "Args" suffix clearly indicates the interface's role
+    /// in event-related contexts, despite not directly extending EventArgs.
+    /// </remarks>
+    /// <typeparam name="TDevice">The specific type of <see cref="IDevice"/> this event argument represents.
+    /// This type parameter is covariant, allowing for more specific device types to be used
+    /// where a more general device type is expected.</typeparam>
+    #pragma warning disable CA1711 // Identifiers should not have incorrect suffix
+    public interface IDeviceEventArgs<out TDevice> where TDevice : IDevice
+    #pragma warning restore CA1711 // Identifiers should not have incorrect suffix
     {
         /// <summary>
-        /// The device that originated the event.
+        /// Gets the specific type of <see cref="IDevice"/> that originated the event.
+        /// This property will always be populated, regardless of whether this is an arrival event or a removal event.
+        /// If the device was removed, not all members will be available on the object. An exception will be thrown if
+        /// you try to use the device in a way that requires it to be present.
         /// </summary>
-        public IDevice? BaseDevice { get; set; }
+        /// <remarks>
+        /// This property provides access to the specific <c>TDevice</c> instance associated with the current event.
+        /// </remarks>
+        /// <value>
+        /// An instance of <c>TDevice</c> that triggered this event. This value is set when 
+        /// the event args are created and remains constant for the lifetime of the event 
+        /// args instance.
+        /// </value>
+        TDevice Device { get; }
+    }
+
+    /// <summary>
+    /// Event arguments given whenever a device is added or removed from the system, providing strongly-typed access to the device that triggered the event.
+    /// </summary>
+    /// <typeparam name="TDevice">The type of device associated with this event, which must implement <see cref="IDevice"/>.</typeparam>
+    public abstract class DeviceEventArgs<TDevice> : EventArgs, IDeviceEventArgs<TDevice>
+        where TDevice : IDevice
+    {
+        /// <inheritdoc />
+        public TDevice Device { get; }
 
         /// <summary>
-        /// Constructs a new instance of the <see cref="DeviceEventArgs"/> class.
+        /// Constructs a new instance of the <see cref="DeviceEventArgs{TDevice}"/> class.
         /// </summary>
-        /// <param name="device">
-        /// The device that is originating this event.
-        /// </param>
-        public DeviceEventArgs(IDevice? device)
+        protected DeviceEventArgs(TDevice device)
         {
-            BaseDevice = device;
+            Device = device;
         }
     }
 }

Yubico.Core/src/Yubico/Core/Devices/Hid/HidDeviceEventArgs.cs

@@ -17,27 +17,17 @@ namespace Yubico.Core.Devices.Hid
     /// <summary>
     /// Event arguments given whenever a HID device is added or removed from the system.
     /// </summary>
-    public class HidDeviceEventArgs : DeviceEventArgs
+    public class HidDeviceEventArgs : DeviceEventArgs<IHidDevice>
     {
-        /// <summary>
-        /// The HID device that originated the event.
-        /// </summary>
-        /// <remarks>
-        /// This property will always be populated, regardless of whether this is an arrival event or a removal event.
-        /// If the device was removed, not all members will be available on the object. An exception will be thrown if
-        /// you try to use the device in a way that requires it to be present.
-        /// </remarks>
-        public IHidDevice? Device { get; set; }
 
         /// <summary>
         /// Constructs a new instance of the <see cref="HidDeviceEventArgs"/> class.
         /// </summary>
         /// <param name="device">
         /// The HID device that is originating this event.
         /// </param>
-        public HidDeviceEventArgs(IHidDevice? device) : base(device)
+        public HidDeviceEventArgs(IHidDevice device) : base(device)
         {
-            Device = device;
         }
     }
 }

Yubico.Core/src/Yubico/Core/Devices/SmartCard/SmartCardDeviceEventArgs.cs

@@ -17,18 +17,8 @@ namespace Yubico.Core.Devices.SmartCard
     /// <summary>
     /// Event arguments given whenever a smart card device is added or removed from the system.
     /// </summary>
-    public class SmartCardDeviceEventArgs : DeviceEventArgs
+    public class SmartCardDeviceEventArgs : DeviceEventArgs<ISmartCardDevice>
     {
-        /// <summary>
-        /// The smart card device that originated the event.
-        /// </summary>
-        /// <remarks>
-        /// This property will always be populated, regardless of whether this is an arrival event or a removal event.
-        /// If the device was removed, not all members will be available on the object. An exception will be thrown if
-        /// you try to use the device in a way that requires it to be present.
-        /// </remarks>
-        public ISmartCardDevice Device { get; set; }
-
         /// <summary>
         /// Constructs a new instance of the <see cref="SmartCardDeviceEventArgs"/> class.
         /// </summary>
@@ -37,7 +27,6 @@ public class SmartCardDeviceEventArgs : DeviceEventArgs
         /// </param>
         public SmartCardDeviceEventArgs(ISmartCardDevice device) : base(device)
         {
-            Device = device;
         }
     }
 }

Yubico.YubiKey/src/Yubico/YubiKey/YubiKeyDeviceListener.cs

@@ -46,9 +46,7 @@ public class YubiKeyDeviceListener : IDisposable
         /// An instance of a <see cref="YubiKeyDeviceListener"/>.
         /// </summary>
         public static YubiKeyDeviceListener Instance => _lazyInstance ??= new YubiKeyDeviceListener();
-
-        internal static bool IsListenerRunning => !(_lazyInstance is null);
-
+        
         /// <summary>
         /// Disposes and closes the singleton instance of <see cref="YubiKeyDeviceListener"/>.
         /// </summary>
@@ -74,12 +72,17 @@ public class YubiKeyDeviceListener : IDisposable
         /// </remarks>
         public static void StopListening()
         {
-            if (_lazyInstance != null)
+            if (_lazyInstance == null)
             {
-                _lazyInstance.Dispose();
-                _lazyInstance = null;
+                return;
             }
+
+            _lazyInstance.Dispose();
+            _lazyInstance = null;
         }
+        
+        internal static bool IsListenerRunning => !(_lazyInstance is null);
+        internal List<IYubiKeyDevice> GetAll() => _internalCache.Keys.ToList();
 
         private static YubiKeyDeviceListener? _lazyInstance;
 
@@ -94,7 +97,8 @@ public static void StopListening()
         private readonly Task _listenTask;
         private readonly CancellationTokenSource _tokenSource = new CancellationTokenSource();
         private CancellationToken CancellationToken => _tokenSource.Token;
-
+        
+        private bool _isDisposed;
         private bool _isListening;
 
         private YubiKeyDeviceListener()
@@ -109,22 +113,14 @@ private YubiKeyDeviceListener()
             _listenTask = ListenForChanges();
         }
 
-        internal List<IYubiKeyDevice> GetAll() => _internalCache.Keys.ToList();
 
-        private void ArriveHandler(object? sender, DeviceEventArgs e) => ListenerHandler("Arrival", e);
+        private void ArriveHandler(object? _, IDeviceEventArgs<IDevice> e) => ListenerHandler("Arrival", e);
 
-        private void RemoveHandler(object? sender, DeviceEventArgs e) => ListenerHandler("Removal", e);
+        private void RemoveHandler(object? _, IDeviceEventArgs<IDevice> e) => ListenerHandler("Removal", e);
 
-        private void ListenerHandler(string eventType, DeviceEventArgs e)
+        private void ListenerHandler(string eventType, IDeviceEventArgs<IDevice> e)
         {
-            IDevice? device = e.BaseDevice;
-            string deviceType = e is HidDeviceEventArgs ? "HID" : "smart card";
-
-            _log.LogInformation(
-                "{EventType} of {DeviceType} {Device} is triggering update.",
-                eventType,
-                deviceType,
-                device);
+            LogEvent(eventType, e);
             _ = _semaphore.Release();
         }
 
@@ -344,6 +340,23 @@ private void CreateAndMarkNewYubiKey(YubiKeyDevice.YubicoDeviceWithInfo deviceWi
         /// Raises event on device removal.
         /// </summary>
         private void OnDeviceRemoved(YubiKeyDeviceEventArgs e) => Removed?.Invoke(typeof(YubiKeyDevice), e);
+        
+        private void LogEvent(string eventType, IDeviceEventArgs<IDevice> e)
+        {
+            var device = e.Device;
+            string deviceTypeText = device switch
+            {
+                ISmartCardDevice _ => "SMART CARD",
+                IHidDevice _ => "HID",
+                _ => "UNKNOWN"
+            };
+
+            _log.LogInformation(
+                "{EventType} of {DeviceType} {Device} is triggering update.",
+                eventType,
+                deviceTypeText,
+                device);
+        }
 
         private static IEnumerable<IDevice> GetHidFidoDevices()
         {
@@ -384,13 +397,10 @@ private static IEnumerable<IDevice> GetSmartCardDevices()
             return Enumerable.Empty<IDevice>();
         }
 
-        private static void ErrorHandler(Exception exception) =>
-            Log
+        private static void ErrorHandler(Exception exception) => Log
                 .GetLogger(typeof(YubiKeyDeviceListener).FullName!)
                 .LogWarning($"Exception caught: {exception}");
-
-        private bool _isDisposed;
-
+        
         /// <summary>
         /// Disposes the objects.
         /// </summary>