initialize repo

Lib/Civilization.Shared/JsonPolymorphicConverter.cs

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+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace Civilization.Shared;
+
+public class JsonPolymorphicConverter<TBase> : JsonConverter<TBase>
+{
+    private readonly Dictionary<string, Type> _typeMap;
+
+    public JsonPolymorphicConverter()
+    {
+        _typeMap = AppDomain.CurrentDomain.GetAssemblies()
+            .SelectMany(a => a.GetTypes())
+            .Where(t => typeof(TBase).IsAssignableFrom(t) && !t.IsAbstract && !t.IsInterface)
+            .ToDictionary(t => t.Name, t => t);
+    }
+    
+    public override TBase? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+    {
+        using var doc = JsonDocument.ParseValue(ref reader);
+        if (!doc.RootElement.TryGetProperty("type", out var typeProp))
+            throw new JsonException("Missing 'type' field for polymorphic deserialization");
+
+        var typeName = typeProp.GetString();
+        if (typeName is null || !_typeMap.TryGetValue(typeName, out var derivedType))
+            throw new JsonException($"Unknown type discriminator: '{typeName}'");
+
+        var json = doc.RootElement.GetRawText();
+        return (TBase?)JsonSerializer.Deserialize(json, derivedType, options);
+    }
+    
+    public override void Write(Utf8JsonWriter writer, TBase value, JsonSerializerOptions options)
+    {
+        using var jsonDoc = JsonDocument.Parse(JsonSerializer.Serialize(value, value.GetType(), options));
+
+        writer.WriteStartObject();
+        writer.WriteString("type", value.GetType().Name);
+
+        foreach (var prop in jsonDoc.RootElement.EnumerateObject())
+        {
+            prop.WriteTo(writer);
+        }
+
+        writer.WriteEndObject();
+    }
+}