Port the DM stuff

Myriad/Extensions/CacheExtensions.cs

@@ -55,6 +55,17 @@ namespace Myriad.Extensions
             return restUser;
         }
         
+        public static async ValueTask<Channel?> GetOrFetchChannel(this IDiscordCache cache, DiscordApiClient rest, ulong channelId)
+        {
+            if (cache.TryGetChannel(channelId, out var cacheChannel))
+                return cacheChannel;
+
+            var restChannel = await rest.GetChannel(channelId);
+            if (restChannel != null)
+                await cache.SaveChannel(restChannel);
+            return restChannel;
+        }
+
         public static async Task<Channel> GetOrCreateDmChannel(this IDiscordCache cache, DiscordApiClient rest, ulong recipientId)
         {
             if (cache.TryGetDmChannel(recipientId, out var cacheChannel))

Myriad/Gateway/Events/MessageUpdateEvent.cs

@@ -1,7 +1,10 @@
-namespace Myriad.Gateway
+using Myriad.Utils;
+
+namespace Myriad.Gateway
 {
     public record MessageUpdateEvent(ulong Id, ulong ChannelId): IGatewayEvent
     {
+        public Optional<string?> Content { get; init; }
         // TODO: lots of partials
     }
 }

Myriad/Serialization/JsonSerializerOptionsExtensions.cs

@@ -13,6 +13,7 @@ namespace Myriad.Serialization
 
             opts.Converters.Add(new PermissionSetJsonConverter());
             opts.Converters.Add(new ShardInfoJsonConverter());
+            opts.Converters.Add(new OptionalConverterFactory());
 
             return opts;
         }

Myriad/Serialization/OptionalConverter.cs

@@ -7,28 +7,33 @@ using Myriad.Utils;
 
 namespace Myriad.Serialization
 {
-    public class OptionalConverter: JsonConverter<IOptional>
+    public class OptionalConverterFactory: JsonConverterFactory
     {
-        public override IOptional? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+        public class Inner<T>: JsonConverter<Optional<T>>
+        {
+            public override Optional<T> Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+            {
+                var inner = JsonSerializer.Deserialize<T>(ref reader, options);
+                return new(inner!);
+            }
+
+            public override void Write(Utf8JsonWriter writer, Optional<T> value, JsonSerializerOptions options)
+            {
+                JsonSerializer.Serialize(writer, value.HasValue ? value.GetValue() : default, typeof(T), options);
+            }
+        }
+        
+        public override JsonConverter? CreateConverter(Type typeToConvert, JsonSerializerOptions options)
         {
             var innerType = typeToConvert.GetGenericArguments()[0];
-            var inner = JsonSerializer.Deserialize(ref reader, innerType, options);
-
-            // TODO: rewrite to JsonConverterFactory to cut down on reflection
-            return (IOptional?) Activator.CreateInstance(
-                typeof(Optional<>).MakeGenericType(innerType),
+            return (JsonConverter?) Activator.CreateInstance(
+                typeof(Inner<>).MakeGenericType(innerType),
                 BindingFlags.Instance | BindingFlags.Public,
                 null,
-                new[] {inner}, 
+                null,
                 null);
         }
 
-        public override void Write(Utf8JsonWriter writer, IOptional value, JsonSerializerOptions options)
-        {
-            var innerType = value.GetType().GetGenericArguments()[0];
-            JsonSerializer.Serialize(writer, value.GetValue(), innerType, options);
-        }
-
         public override bool CanConvert(Type typeToConvert)
         {
             if (!typeToConvert.IsGenericType)

Myriad/Types/Message.cs

@@ -1,6 +1,9 @@
 using System;
 using System.Collections.Generic;
 using System.Net.Mail;
+using System.Text.Json.Serialization;
+
+using Myriad.Utils;
 
 namespace Myriad.Types
 {
@@ -59,8 +62,8 @@ namespace Myriad.Types
         public Reference? MessageReference { get; set; }
         public MessageFlags Flags { get; init; }
         
-        // todo: null vs. absence
-        public Message? ReferencedMessage { get; init; }
+        [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingDefault)]
+        public Optional<Message?> ReferencedMessage { get; init; }
 
         public record Reference(ulong? GuildId, ulong? ChannelId, ulong? MessageId);
 

Myriad/Utils/Optional.cs

@@ -1,16 +1,10 @@
-using System.Text.Json.Serialization;
-
-using Myriad.Serialization;
-
-namespace Myriad.Utils
+namespace Myriad.Utils
 {
     public interface IOptional
     {
-        bool HasValue { get; }
         object? GetValue();
     }
     
-    [JsonConverter(typeof(OptionalConverter))]
     public readonly struct Optional<T>: IOptional
     {
         public Optional(T value)