feat: implement IProtocolHandler

Kiseki.Launcher.Windows/ProtocolHandler.cs

@@ -1,15 +1,48 @@
+using System.Windows;
+
+using Microsoft.Win32;
+
 namespace Kiseki.Launcher.Windows
 {
     public class ProtocolHandler : IProtocolHandler
     {
-        public void Register()
+        public void Register(string handler)
         {
-            throw new NotImplementedException();
+            string arguments = $"\"{handler}\" \"%1\"";
+
+            RegistryKey uri = Registry.CurrentUser.CreateSubKey(@"Software\Classes\kiseki");
+            RegistryKey icon = uri.CreateSubKey("DefaultIcon");
+            RegistryKey command = uri.CreateSubKey(@"shell\open\command");
+
+            if (uri.GetValue("") is null)
+            {
+                uri.SetValue("", "URL: Kiseki Protocol");
+                uri.SetValue("URL Protocol", "");
+            }
+
+            if ((string?)command.GetValue("") != arguments)
+            {
+                command.SetValue("", arguments);
+            }
+
+            uri.Close();
+            icon.Close();
+            command.Close();
         }
 
         public void Unregister()
         {
-            throw new NotImplementedException();
+            try
+            {
+                Registry.CurrentUser.DeleteSubKeyTree(@"Software\Classes\kiseki");
+            }
+            catch (Exception)
+            {
+                // Key doesn't exist (and why are we here?)
+#if DEBUG
+                throw;
+#endif
+            }
         }
     }
 }

Kiseki.Launcher/Interfaces.cs

@@ -2,7 +2,7 @@ namespace Kiseki.Launcher
 {
     interface IProtocolHandler
     {
-        void Register();
+        void Register(string handler);
         void Unregister();
     }