Implement desktop sync protocol handling

WirelessTextSyncer.Windows/Models/SyncAction.cs

@@ -1,5 +1,8 @@
 namespace WirelessTextSyncer.Windows.Models;
 
+using System.Text.Json.Serialization;
+
+[JsonConverter(typeof(SyncActionJsonConverter))]
 public enum SyncAction
 {
     InsertText,

WirelessTextSyncer.Windows/Models/SyncActionJsonConverter.cs

@@ -0,0 +1,41 @@
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace WirelessTextSyncer.Windows.Models;
+
+public sealed class SyncActionJsonConverter : JsonConverter<SyncAction>
+{
+    public override SyncAction Read(
+        ref Utf8JsonReader reader,
+        Type typeToConvert,
+        JsonSerializerOptions options)
+    {
+        var value = reader.GetString();
+
+        return value switch
+        {
+            "insertText" => SyncAction.InsertText,
+            "backspace" => SyncAction.Backspace,
+            "enter" => SyncAction.Enter,
+            "ping" => SyncAction.Ping,
+            _ => throw new JsonException($"Unsupported sync action: {value}")
+        };
+    }
+
+    public override void Write(
+        Utf8JsonWriter writer,
+        SyncAction value,
+        JsonSerializerOptions options)
+    {
+        var action = value switch
+        {
+            SyncAction.InsertText => "insertText",
+            SyncAction.Backspace => "backspace",
+            SyncAction.Enter => "enter",
+            SyncAction.Ping => "ping",
+            _ => throw new JsonException($"Unsupported sync action: {value}")
+        };
+
+        writer.WriteStringValue(action);
+    }
+}