Improve MultiTypeClassConverter to support null types and multi word …

…enum values

src/RxTelegram.Bot/Utils/Converter/MultiTypeClassConverter.cs

@@ -17,6 +17,12 @@ public override object ReadJson(JsonReader reader, Type objectType, object exist
         CheckForValidInterfaces(objectType);
         var distinguishingProperty = GetNameOfDistinguishingProperty(objectType);
         var jsonObject = JObject.Load(reader);
+        if (!jsonObject.HasValues)
+        {
+            return null;
+        }
+        jsonObject[distinguishingProperty] = ToPascalCaseIfNecessary(jsonObject[distinguishingProperty]
+                                                                         ?.ToString());
         var valueToDefineResultType = jsonObject.GetValue(distinguishingProperty) ??
                                       throw new InvalidOperationException("The property is not found");
         var resultTypeEnum = GetEnumOfGenericInterface(objectType);
@@ -40,6 +46,15 @@ public override object ReadJson(JsonReader reader, Type objectType, object exist
         return objectInstance;
     }
 
+    private static JToken ToPascalCaseIfNecessary(string toString)
+    {
+        var words = toString.Split(new[] { '-', '_' }, StringSplitOptions.RemoveEmptyEntries)
+                            .Select(word => word.Substring(0, 1).ToUpper() +
+                                            word.Substring(1).ToLower());
+
+        return string.Concat(words);
+    }
+
     private static Type GetEnumOfGenericInterface(Type objectType)
     {
         var interfaces = objectType.GetInterfaces();

src/UnitTests/JsonConverters/BackgroundTypeConverterTest.cs

@@ -0,0 +1,56 @@
+using System;
+using Newtonsoft.Json;
+using NUnit.Framework;
+using NUnit.Framework.Constraints;
+using RxTelegram.Bot.Interface.ChatBackground;
+using RxTelegram.Bot.Utils.Converter;
+
+namespace RxTelegram.Bot.UnitTests.JsonConverters;
+
+[TestFixture]
+public class BackgroundTypeConverterTest
+{
+    private readonly JsonSerializerSettings _jsonSettings = new()
+                                                            {
+                                                                Converters = { new MultiTypeClassConverter() }
+                                                            };
+
+    [Test]
+    [TestCase("chat_theme", typeof(BackgroundTypeChatTheme))]
+    [TestCase("fill", typeof(BackgroundTypeFill))]
+    [TestCase("pattern", typeof(BackgroundTypePattern))]
+    [TestCase("wallpaper", typeof(BackgroundTypeWallpaper))]
+    public void CanRead(string type, Type expectedType)
+    {
+        var json = $"{{\"type\":\"{type}\"}}";
+        var actual = JsonConvert.DeserializeObject<BackgroundType>(json, _jsonSettings);
+        Assert.That(actual, Is.Not.Null);
+        Assert.That(actual.GetType(), Is.EqualTo(expectedType));
+    }
+
+    [Test]
+    public void CanReadNull()
+    {
+        const string json = "{}";
+        var actual = JsonConvert.DeserializeObject<BackgroundType>(json, _jsonSettings);
+        Assert.That(actual, Is.Null);
+    }
+
+    [Test]
+    [TestCase(typeof(BackgroundFillFreeformGradient), 0)]
+    [TestCase(typeof(BackgroundFillGradient), 1)]
+    [TestCase(typeof(BackgroundFillSolid), 2)]
+    public void CanWrite(Type type, int expectedType)
+    {
+        var instance = Activator.CreateInstance(type);
+        var json = JsonConvert.SerializeObject(instance, _jsonSettings);
+        Assert.That(json, new StartsWithConstraint($"{{\"Type\":{expectedType}"));
+    }
+
+    [Test]
+    public void CanWriteNull()
+    {
+        var json = JsonConvert.SerializeObject(null, _jsonSettings);
+        Assert.That(json, Is.EqualTo("null"));
+    }
+}