fix: Drastically simplifies regions (#1400)

### Summary
- [X] Gets rid of the Dtos
- [X] Simplifies the json serializer registration
- [X] Adds a custom `RegionByName` JsonConverter that can look up other regions that have already been registered.


### BREAKING CHANGE
1. **Child regions must appear after their parents in the JSON file**
2. In the regions json file, _"Parent"_ can no longer be just a string. It must be an object that includes the map.
      - ```json
        "Parent": { "Name": "Britain", "Map": "Felucca" }
        ```

Projects/Server/Json/Converters/RegionByNameConverter.cs

@@ -0,0 +1,85 @@
+/*************************************************************************
+ * ModernUO                                                              *
+ * Copyright 2019-2023 - ModernUO Development Team                       *
+ * Email: hi@modernuo.com                                                *
+ * File: RegionByNameConverter.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;
+
+public class RegionByNameConverter : JsonConverter<Region>
+{
+    public override Region Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+    {
+        string name = null;
+        Map map = null;
+
+        if (reader.TokenType != JsonTokenType.StartObject)
+        {
+            throw new JsonException("Invalid json for RegionByName");
+        }
+
+        while (true)
+        {
+            reader.Read();
+            if (reader.TokenType == JsonTokenType.EndObject)
+            {
+                break;
+            }
+
+            if (reader.TokenType != JsonTokenType.PropertyName)
+            {
+                throw new JsonException("Invalid json for RegionByName");
+            }
+
+            string property = reader.GetString()?.ToLower();
+
+            if (property != "name" && property != "map")
+            {
+                continue;
+            }
+
+            reader.Read();
+            if (reader.TokenType != JsonTokenType.String)
+            {
+                throw new JsonException($"Value for {property} must be a string");
+            }
+
+            if (property == "name")
+            {
+                name = reader.GetString();
+            }
+            else
+            {
+                map = Map.Parse(reader.GetString());
+            }
+        }
+
+        if (name == null || map == null)
+        {
+            throw new JsonException("Invalid json for RegionByName");
+        }
+
+        return Region.Find(name, map);
+    }
+
+    public override void Write(Utf8JsonWriter writer, Region value, JsonSerializerOptions options)
+    {
+        writer.WriteStartObject();
+        writer.WriteString("Name", value.Name);
+        writer.WriteString("Map", value.Map.Name);
+        writer.WriteEndObject();
+    }
+}

Projects/Server/Json/Converters/RegionByNameConverterFactory.cs

@@ -0,0 +1,28 @@
+/*************************************************************************
+ * ModernUO                                                              *
+ * Copyright 2019-2023 - ModernUO Development Team                       *
+ * Email: hi@modernuo.com                                                *
+ * File: RegionByNameConverterFactory.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;
+
+public class RegionByNameConverterFactory : JsonConverterFactory
+{
+    public override bool CanConvert(Type typeToConvert) => typeToConvert == typeof(Region);
+
+    public override JsonConverter CreateConverter(Type typeToConvert, JsonSerializerOptions options) =>
+        new RegionByNameConverter();
+}

Projects/Server/Regions/Region.cs

@@ -1,5 +1,8 @@
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
+using System.Text.Json.Serialization;
+using Server.Json;
 using Server.Logging;
 using Server.Network;
 using Server.Targeting;
@@ -136,6 +139,7 @@ public class Region : IComparable<Region>
     {
     }
 
+    [JsonConstructor] // Don't include parent, since it is special
     public Region(string name, Map map, int priority, params Rectangle3D[] area) : this(name, map, null, area) =>
         Priority = priority;
 
@@ -173,10 +177,10 @@ public class Region : IComparable<Region>
     }
 
     // Used during deserialization only
-    public Expansion MinExpansion { get; set; }
+    public Expansion MinExpansion { get; set; } = Expansion.None;
 
     // Used during deserialization only
-    public Expansion MaxExpansion { get; set; }
+    public Expansion MaxExpansion { get; set; } = Expansion.EJ;
 
     public static List<Region> Regions { get; } = new();
 
@@ -188,7 +192,9 @@ public class Region : IComparable<Region>
 
     public Map Map { get; }
 
-    public Region Parent { get; }
+    [JsonInclude]
+    [JsonConverter(typeof(RegionByNameConverter))]
+    public Region Parent { get; private set; }
 
     public List<Region> Children { get; } = new();
 

Projects/Server/Regions/RegionJsonDto.cs

@@ -1,67 +0,0 @@
-/*************************************************************************
- * ModernUO                                                              *
- * Copyright 2019-2022 - ModernUO Development Team                       *
- * Email: hi@modernuo.com                                                *
- * File: RegionJsonDto.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.Serialization;
-using Server.Utilities;
-
-namespace Server;
-
-public class RegionJsonDto
-{
-    public Expansion MinExpansion { get; set; } = Expansion.None;
-
-    public Expansion? MaxExpansion { get; set; } = Expansion.EJ;
-
-    [JsonIgnore]
-    public virtual Type RegionType => typeof(Region);
-
-    public Map Map { get; set; }
-    public string? Parent { get; set; }
-    public string Name { get; set; }
-    public int? Priority { get; set; }
-    public Rectangle3D[] Area { get; set; }
-    public Point3D GoLocation { get; set; }
-    public MusicName? Music { get; set; }
-
-    public virtual void FromRegion(Region region)
-    {
-        Map = region.Map;
-        Parent = region.Parent?.Name;
-        Name = region.Name;
-        Priority = region.Priority;
-        Area = region.Area;
-        GoLocation = region.GoLocation;
-        Music = region.Music != MusicName.Invalid && region.Music != region.DefaultMusic ? region.Music : null;
-        MaxExpansion = region.MaxExpansion == Expansion.EJ ? null : region.MaxExpansion;
-        MinExpansion = region.MinExpansion;
-    }
-
-    public Region ToRegion()
-    {
-        var region = Priority != null
-            ? RegionType.CreateInstance<Region>(Name, Map, Region.Find(Parent, Map), Priority, Area)
-            : RegionType.CreateInstance<Region>(Name, Map, Region.Find(Parent, Map), Area);
-
-        HydrateRegion(region);
-        return region;
-    }
-
-    protected virtual void HydrateRegion(Region region)
-    {
-        region.GoLocation = GoLocation;
-        region.Music = Music ?? region.DefaultMusic;
-    }
-}

Projects/Server/Regions/RegionJsonSerializer.cs

@@ -22,7 +22,6 @@ using System.Text.Json.Serialization;
 using System.Text.Json.Serialization.Metadata;
 using Server.Json;
 using Server.Logging;
-using Server.Utilities;
 
 namespace Server;
 
@@ -30,10 +29,7 @@ public static class RegionJsonSerializer
 {
     private static readonly ILogger logger = LogFactory.GetLogger(typeof(RegionJsonSerializer));
 
-    // Note: This is filled during the `Configure` phase by RegisterRegionForSerialization,
-    // so it is not available to a JsonConverter which might be used during earlier phases.
-    private static Dictionary<Type, Type> _regionToDtoLookup = new() { { typeof(Region), typeof(RegionJsonDto) } };
-    private static JsonDerivedType[] _derivedTypes = { new(typeof(RegionJsonDto), nameof(Region)) };
+    private static JsonDerivedType[] _derivedTypes = { new(typeof(Region), nameof(Region)) };
 
     private static JsonSerializerOptions _options = new(JsonConfig.DefaultOptions)
     {
@@ -44,7 +40,7 @@ public static class RegionJsonSerializer
             {
                 static typeInfo =>
                 {
-                    if (typeInfo.Type != typeof(RegionJsonDto))
+                    if (typeInfo.Type != typeof(Region))
                     {
                         return;
                     }
@@ -55,26 +51,39 @@ public static class RegionJsonSerializer
                         typeInfo.PolymorphismOptions.DerivedTypes.Add(_derivedTypes[i]);
                     }
                 },
+                static typeInfo =>
+                {
+                    if (!typeInfo.Type.IsAssignableTo(typeof(Region)))
+                    {
+                        return;
+                    }
+
+                    typeInfo.OnDeserialized = o =>
+                    {
+                        if (o is Region region && Core.Expansion >= region.MinExpansion && Core.Expansion <= region.MaxExpansion)
+                        {
+                            region.Register();
+                        }
+                    };
+                }
             }
         }
     };
 
-    public static void Register<TDto, TRegion>()
-        where TDto : RegionJsonDto, new() where TRegion : Region
+    public static void Register<TRegion>() where TRegion : Region
     {
         for (var i = 0; i < _derivedTypes.Length; i++)
         {
-            if (_derivedTypes[i].DerivedType == typeof(TDto))
+            if (_derivedTypes[i].DerivedType == typeof(TRegion))
             {
                 throw new Exception(
-                    $"Type '{typeof(TDto)}' has already been registered for serialization with the region loader."
+                    $"Type '{typeof(TRegion)}' has already been registered for serialization with the region loader."
                 );
             }
         }
 
         Array.Resize(ref _derivedTypes, _derivedTypes.Length + 1);
-        _derivedTypes[^1] = new JsonDerivedType(typeof(TDto), typeof(TRegion).Name);
-        _regionToDtoLookup[typeof(TRegion)] = typeof(TDto);
+        _derivedTypes[^1] = new JsonDerivedType(typeof(TRegion), typeof(TRegion).Name);
     }
 
     internal static void LoadRegions()
@@ -85,19 +94,17 @@ public static class RegionJsonSerializer
 
         var stopwatch = Stopwatch.StartNew();
 
-        var regions = JsonConfig.Deserialize<List<RegionJsonDto>>(path, _options);
+        var regions = JsonConfig.Deserialize<List<Region>>(path, _options);
         if (regions == null)
         {
             throw new JsonException($"Failed to deserialize {path}.");
         }
 
         var count = 0;
-        foreach (var dto in regions)
+        foreach (var region in regions)
         {
-            if (Core.Expansion >= dto.MinExpansion && Core.Expansion <= dto.MaxExpansion)
+            if (Core.Expansion >= region.MinExpansion && Core.Expansion <= region.MaxExpansion)
             {
-                var region = dto.ToRegion();
-                region.Register();
                 count++;
             }
         }
@@ -111,43 +118,4 @@ public static class RegionJsonSerializer
             stopwatch.Elapsed.TotalSeconds
         );
     }
-
-    // Note: This is not thread safe. To make `SerializeRegions` threadsafe, use `[ThreadStatic]` or just create the lists
-    // in the function and take the GC hit.
-    private static List<RegionJsonDto> _regionJsonDtos;
-
-    public static void SerializeRegions(string path, IEnumerable<Region> regions)
-    {
-        _regionJsonDtos ??= new List<RegionJsonDto>();
-        foreach (var region in regions)
-        {
-            if (_regionToDtoLookup.TryGetValue(region.GetType(), out var dtoType))
-            {
-                var dto = dtoType.CreateInstance<RegionJsonDto>();
-                dto.FromRegion(region);
-                _regionJsonDtos.Add(dto);
-            }
-        }
-
-        JsonConfig.Serialize(path, _regionJsonDtos, _options);
-        _regionJsonDtos.Clear();
-    }
-
-    public static string SerializeRegions(IEnumerable<Region> regions)
-    {
-        _regionJsonDtos ??= new List<RegionJsonDto>();
-        foreach (var region in regions)
-        {
-            if (_regionToDtoLookup.TryGetValue(region.GetType(), out var dtoType))
-            {
-                var dto = dtoType.CreateInstance<RegionJsonDto>();
-                dto.FromRegion(region);
-                _regionJsonDtos.Add(dto);
-            }
-        }
-
-        var output = JsonConfig.Serialize(_regionJsonDtos, _options);
-        _regionJsonDtos.Clear();
-        return output;
-    }
 }