feat: add PATCH request support, expand PATCH /users/@me, serialize enums correctly

Foxnouns.Backend/Utils/PatchRequest.cs

@@ -0,0 +1,35 @@
+using System.Reflection;
+using Newtonsoft.Json;
+using Newtonsoft.Json.Serialization;
+
+namespace Foxnouns.Backend.Utils;
+
+/// <summary>
+/// A base class used for PATCH requests which stores information on whether a key is explicitly set to null or not passed at all.
+/// </summary>
+public abstract class PatchRequest
+{
+    private readonly HashSet<string> _properties = [];
+    public bool HasProperty(string propertyName) => _properties.Contains(propertyName);
+    public void SetHasProperty(string propertyName) => _properties.Add(propertyName);
+}
+
+/// <summary>
+/// A custom contract resolver to reduce the boilerplate needed to use <see cref="PatchRequest" />.
+/// Based on this StackOverflow answer: https://stackoverflow.com/a/58748036
+/// </summary>
+public class PatchRequestContractResolver : DefaultContractResolver
+{
+    protected override JsonProperty CreateProperty(MemberInfo member, MemberSerialization memberSerialization)
+    {
+        var prop = base.CreateProperty(member, memberSerialization);
+
+        prop.SetIsSpecified += (o, _) =>
+        {
+            if (o is not PatchRequest patchRequest) return;
+            patchRequest.SetHasProperty(prop.UnderlyingName!);
+        };
+
+        return prop;
+    }
+}