Implement desktop sync protocol handling

WirelessTextSyncer.Windows/Services/KeyboardInjectionService.cs

@@ -1,7 +1,15 @@
 namespace WirelessTextSyncer.Windows.Services;
 
+using System.Runtime.InteropServices;
+
 public sealed class KeyboardInjectionService : IKeyboardInjectionService
 {
+    private const uint InputKeyboard = 1;
+    private const uint KeyEventFKeyUp = 0x0002;
+    private const uint KeyEventFUnicode = 0x0004;
+    private const ushort VirtualKeyBack = 0x08;
+    private const ushort VirtualKeyReturn = 0x0D;
+
     public void InsertText(string text)
     {
         if (string.IsNullOrEmpty(text))
@@ -9,16 +17,103 @@ public sealed class KeyboardInjectionService : IKeyboardInjectionService
             return;
         }
 
-        SendKeys.SendWait(text);
+        foreach (var character in text)
+        {
+            SendUnicode(character);
+        }
     }
 
     public void Backspace()
     {
-        SendKeys.SendWait("{BACKSPACE}");
+        SendVirtualKey(VirtualKeyBack);
     }
 
     public void Enter()
     {
-        SendKeys.SendWait("{ENTER}");
+        SendVirtualKey(VirtualKeyReturn);
+    }
+
+    private static void SendUnicode(char character)
+    {
+        Send([
+            CreateUnicodeInput(character, 0),
+            CreateUnicodeInput(character, KeyEventFKeyUp)
+        ]);
+    }
+
+    private static void SendVirtualKey(ushort virtualKey)
+    {
+        Send([
+            CreateVirtualKeyInput(virtualKey, 0),
+            CreateVirtualKeyInput(virtualKey, KeyEventFKeyUp)
+        ]);
+    }
+
+    private static void Send(INPUT[] inputs)
+    {
+        var sent = SendInput((uint)inputs.Length, inputs, Marshal.SizeOf<INPUT>());
+        if (sent != inputs.Length)
+        {
+            throw new InvalidOperationException("Windows did not accept all keyboard input events.");
+        }
+    }
+
+    private static INPUT CreateUnicodeInput(char character, uint flags)
+    {
+        return new INPUT
+        {
+            type = InputKeyboard,
+            U = new InputUnion
+            {
+                ki = new KEYBDINPUT
+                {
+                    wScan = character,
+                    dwFlags = KeyEventFUnicode | flags
+                }
+            }
+        };
+    }
+
+    private static INPUT CreateVirtualKeyInput(ushort virtualKey, uint flags)
+    {
+        return new INPUT
+        {
+            type = InputKeyboard,
+            U = new InputUnion
+            {
+                ki = new KEYBDINPUT
+                {
+                    wVk = virtualKey,
+                    dwFlags = flags
+                }
+            }
+        };
+    }
+
+    [DllImport("user32.dll", SetLastError = true)]
+    private static extern uint SendInput(uint numberOfInputs, INPUT[] inputs, int sizeOfInputStructure);
+
+    [StructLayout(LayoutKind.Sequential)]
+    private struct INPUT
+    {
+        public uint type;
+        public InputUnion U;
+    }
+
+    [StructLayout(LayoutKind.Explicit)]
+    private struct InputUnion
+    {
+        [FieldOffset(0)]
+        public KEYBDINPUT ki;
+    }
+
+    [StructLayout(LayoutKind.Sequential)]
+    private struct KEYBDINPUT
+    {
+        public ushort wVk;
+        public ushort wScan;
+        public uint dwFlags;
+        public uint time;
+        public UIntPtr dwExtraInfo;
     }
 }