Add DM support

Myriad/Cache/DiscordCacheExtensions.cs

@@ -55,16 +55,5 @@ namespace Myriad.Cache
             foreach (var mention in evt.Mentions) 
                 await cache.SaveUser(mention);
         }
-
-        public static async ValueTask<User?> GetOrFetchUser(this IDiscordCache cache, DiscordApiClient rest, ulong userId)
-        {
-            if (cache.TryGetUser(userId, out var cacheUser))
-                return cacheUser;
-
-            var restUser = await rest.GetUser(userId);
-            if (restUser != null)
-                await cache.SaveUser(restUser);
-            return restUser;
-        }
     }
 }

Myriad/Cache/IDiscordCache.cs

@@ -19,6 +19,7 @@ namespace Myriad.Cache
 
         public bool TryGetGuild(ulong guildId, out Guild guild);
         public bool TryGetChannel(ulong channelId, out Channel channel);
+        public bool TryGetDmChannel(ulong userId, out Channel channel);
         public bool TryGetUser(ulong userId, out User user);
         public bool TryGetRole(ulong roleId, out Role role);
 

Myriad/Cache/MemoryDiscordCache.cs

@@ -10,19 +10,12 @@ namespace Myriad.Cache
 {
     public class MemoryDiscordCache: IDiscordCache
     {
-        private readonly ConcurrentDictionary<ulong, Channel> _channels;
-        private readonly ConcurrentDictionary<ulong, CachedGuild> _guilds;
-        private readonly ConcurrentDictionary<ulong, Role> _roles;
-        private readonly ConcurrentDictionary<ulong, User> _users;
-
-        public MemoryDiscordCache()
-        {
-            _guilds = new ConcurrentDictionary<ulong, CachedGuild>();
-            _channels = new ConcurrentDictionary<ulong, Channel>();
-            _users = new ConcurrentDictionary<ulong, User>();
-            _roles = new ConcurrentDictionary<ulong, Role>();
-        }
-
+        private readonly ConcurrentDictionary<ulong, Channel> _channels = new();
+        private readonly ConcurrentDictionary<ulong, ulong> _dmChannels = new();
+        private readonly ConcurrentDictionary<ulong, CachedGuild> _guilds = new();
+        private readonly ConcurrentDictionary<ulong, Role> _roles = new();
+        private readonly ConcurrentDictionary<ulong, User> _users = new();
+        
         public ValueTask SaveGuild(Guild guild)
         {
             SaveGuildRaw(guild);
@@ -35,14 +28,21 @@ namespace Myriad.Cache
             return default;
         }
 
-        public ValueTask SaveChannel(Channel channel)
+        public async ValueTask SaveChannel(Channel channel)
         {
             _channels[channel.Id] = channel;
 
             if (channel.GuildId != null && _guilds.TryGetValue(channel.GuildId.Value, out var guild))
                 guild.Channels.TryAdd(channel.Id, true);
 
-            return default;
+            if (channel.Recipients != null)
+            {
+                foreach (var recipient in channel.Recipients)
+                {
+                    _dmChannels[recipient.Id] = channel.Id;
+                    await SaveUser(recipient);
+                }
+            }
         }
 
         public ValueTask SaveUser(User user)
@@ -125,6 +125,14 @@ namespace Myriad.Cache
         public bool TryGetChannel(ulong channelId, out Channel channel) => 
             _channels.TryGetValue(channelId, out channel!);
 
+        public bool TryGetDmChannel(ulong userId, out Channel channel)
+        {
+            channel = default!;
+            if (!_dmChannels.TryGetValue(userId, out var channelId))
+                return false;
+            return TryGetChannel(channelId, out channel);
+        } 
+
         public bool TryGetUser(ulong userId, out User user) =>
             _users.TryGetValue(userId, out user!);
 

Myriad/Extensions/CacheExtensions.cs

@@ -1,6 +1,8 @@
 using System.Collections.Generic;
+using System.Threading.Tasks;
 
 using Myriad.Cache;
+using Myriad.Rest;
 using Myriad.Types;
 
 namespace Myriad.Extensions
@@ -41,5 +43,26 @@ namespace Myriad.Extensions
                 throw new KeyNotFoundException($"User {roleId} not found in cache");
             return role;
         }
+        
+        public static async ValueTask<User?> GetOrFetchUser(this IDiscordCache cache, DiscordApiClient rest, ulong userId)
+        {
+            if (cache.TryGetUser(userId, out var cacheUser))
+                return cacheUser;
+
+            var restUser = await rest.GetUser(userId);
+            if (restUser != null)
+                await cache.SaveUser(restUser);
+            return restUser;
+        }
+        
+        public static async Task<Channel> GetOrCreateDmChannel(this IDiscordCache cache, DiscordApiClient rest, ulong recipientId)
+        {
+            if (cache.TryGetDmChannel(recipientId, out var cacheChannel))
+                return cacheChannel;
+
+            var restChannel = await rest.CreateDm(recipientId);
+            await cache.SaveChannel(restChannel);
+            return restChannel;
+        }
     }
 }

Myriad/Rest/DiscordApiClient.cs

@@ -120,6 +120,9 @@ namespace Myriad.Rest
             _client.PostMultipart<Message>($"/webhooks/{webhookId}/{webhookToken}?wait=true",
                 ("ExecuteWebhook", webhookId), request, files)!;
 
+        public Task<Channel> CreateDm(ulong recipientId) =>
+            _client.Post<Channel>($"/users/@me/channels", ("CreateDM", default), new CreateDmRequest(recipientId))!;
+
         private static string EncodeEmoji(Emoji emoji) =>
             WebUtility.UrlEncode(emoji.Name) ?? emoji.Id?.ToString() ??
             throw new ArgumentException("Could not encode emoji");

Myriad/Rest/Types/Requests/CreateDmRequest.cs

@@ -0,0 +1,4 @@
+namespace Myriad.Rest.Types.Requests
+{
+    public record CreateDmRequest(ulong RecipientId);
+}

Myriad/Types/Channel.cs

@@ -22,6 +22,7 @@
         public bool? Nsfw { get; init; }
         public ulong? ParentId { get; init; }
         public Overwrite[]? PermissionOverwrites { get; init; }
+        public User[]? Recipients { get; init; }
 
         public record Overwrite
         {