fix(core): Updates expansion and map configurations (fixes map issues) (#570)

- [X] Adds question about expansion at start of server
- [X] Adds question about client version to determine old have and map diffs
- [X] Adds config setting "maps.enablePre6000Trammel"
- [X] Rearranges some of the loading order.
- [X] Added support for deserializing nullable enums from json

TODO:
Expand the nullable enums deserialization factory to work with any type by pulling the factory and creating an instance of the converter.

Projects/Server/Json/Converters/JsonNullableEnumConverter.cs

@@ -0,0 +1,51 @@
+/*************************************************************************
+ * ModernUO                                                              *
+ * Copyright 2019-2021 - ModernUO Development Team                       *
+ * Email: hi@modernuo.com                                                *
+ * File: JsonNullableEnumConverter.cs                                    *
+ *                                                                       *
+ * This program is free software: you can redistribute it and/or modify  *
+ * it under the terms of the GNU General Public License as published by  *
+ * the Free Software Foundation, either version 3 of the License, or     *
+ * (at your option) any later version.                                   *
+ *                                                                       *
+ * You should have received a copy of the GNU General Public License     *
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>. *
+ *************************************************************************/
+
+using System;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace Server.Json.Converters
+{
+    class JsonNullableEnumConverter<T> : JsonConverter<T?> where T : struct, Enum
+    {
+        private readonly JsonConverter<T> _converter;
+
+        public JsonNullableEnumConverter(JsonConverter<T> converter) => _converter = converter;
+
+        public override T? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+        {
+            if (reader.TokenType == JsonTokenType.Null)
+            {
+                reader.Read();
+                return null;
+            }
+
+            return _converter.Read(ref reader, typeof(T), options);
+        }
+
+        public override void Write(Utf8JsonWriter writer, T? value, JsonSerializerOptions options)
+        {
+            if (value == null)
+            {
+                writer.WriteNullValue();
+            }
+            else
+            {
+                _converter.Write(writer, value.Value, options);
+            }
+        }
+    }
+}

Projects/Server/Json/Converters/JsonNullableEnumConverterFactory.cs

@@ -0,0 +1,38 @@
+/*************************************************************************
+ * ModernUO                                                              *
+ * Copyright 2019-2021 - ModernUO Development Team                       *
+ * Email: hi@modernuo.com                                                *
+ * File: JsonNullableEnumConverterFactory.cs                             *
+ *                                                                       *
+ * This program is free software: you can redistribute it and/or modify  *
+ * it under the terms of the GNU General Public License as published by  *
+ * the Free Software Foundation, either version 3 of the License, or     *
+ * (at your option) any later version.                                   *
+ *                                                                       *
+ * You should have received a copy of the GNU General Public License     *
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>. *
+ *************************************************************************/
+
+using System;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace Server.Json.Converters
+{
+    public class JsonNullableEnumConverterFactory : JsonConverterFactory
+    {
+        private readonly JsonStringEnumConverter _stringEnumConverter;
+
+        public JsonNullableEnumConverterFactory(JsonNamingPolicy? namingPolicy = null, bool allowIntegerValues = true) =>
+            _stringEnumConverter = new JsonStringEnumConverter(namingPolicy, allowIntegerValues);
+
+        public override bool CanConvert(Type typeToConvert) => Nullable.GetUnderlyingType(typeToConvert)?.IsEnum == true;
+
+        public override JsonConverter? CreateConverter(Type typeToConvert, JsonSerializerOptions options)
+        {
+            var type = Nullable.GetUnderlyingType(typeToConvert);
+            return (JsonConverter?)Activator.CreateInstance(typeof(JsonNullableEnumConverter<>).MakeGenericType(type!),
+                _stringEnumConverter.CreateConverter(type, options));
+        }
+    }
+}

Projects/Server/Json/JsonConfig.cs

@@ -19,6 +19,7 @@ using System.IO;
 using System.Text.Encodings.Web;
 using System.Text.Json;
 using System.Text.Json.Serialization;
+using Server.Json.Converters;
 using Server.Text;
 
 namespace Server.Json
@@ -39,6 +40,7 @@ namespace Server.Json
                 Encoder = JavaScriptEncoder.UnsafeRelaxedJsonEscaping
             };
 
+            options.Converters.Add(new JsonNullableEnumConverterFactory());
             options.Converters.Add(new JsonStringEnumConverter());
             options.Converters.Add(new MapConverterFactory());
             options.Converters.Add(new Point3DConverterFactory());