Initial commit, basic proxying working

Myriad/Extensions/ChannelExtensions.cs

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+namespace Myriad.Extensions
+{
+    public static class ChannelExtensions
+    {
+        
+    }
+}

Myriad/Extensions/MessageExtensions.cs

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+namespace Myriad.Extensions
+{
+    public class MessageExtensions
+    {
+        
+    }
+}

Myriad/Extensions/PermissionExtensions.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+using Myriad.Gateway;
+using Myriad.Types;
+
+namespace Myriad.Extensions
+{
+    public static class PermissionExtensions
+    {
+        public static PermissionSet EveryonePermissions(this Guild guild) =>
+            guild.Roles.FirstOrDefault(r => r.Id == guild.Id)?.Permissions ?? PermissionSet.Dm;
+        
+        public static PermissionSet PermissionsFor(Guild guild, Channel channel, MessageCreateEvent msg) =>
+            PermissionsFor(guild, channel, msg.Author.Id, msg.Member!.Roles);
+
+        public static PermissionSet PermissionsFor(Guild guild, Channel channel, ulong userId,
+                                                   ICollection<ulong> roleIds)
+        {
+            if (channel.Type == Channel.ChannelType.Dm)
+                return PermissionSet.Dm;
+
+            var perms = GuildPermissions(guild, userId, roleIds);
+            perms = ApplyChannelOverwrites(perms, channel, userId, roleIds);
+
+            if ((perms & PermissionSet.Administrator) == PermissionSet.Administrator)
+                return PermissionSet.All;
+
+            if ((perms & PermissionSet.ViewChannel) == 0)
+                perms &= ~NeedsViewChannel;
+
+            if ((perms & PermissionSet.SendMessages) == 0)
+                perms &= ~NeedsSendMessages;
+
+            return perms;
+        }
+
+        public static bool Has(this PermissionSet value, PermissionSet flag) =>
+            (value & flag) == flag;
+
+        public static PermissionSet GuildPermissions(this Guild guild, ulong userId, ICollection<ulong> roleIds)
+        {
+            if (guild.OwnerId == userId)
+                return PermissionSet.All;
+
+            var perms = PermissionSet.None;
+            foreach (var role in guild.Roles)
+            {
+                if (role.Id == guild.Id || roleIds.Contains(role.Id))
+                    perms |= role.Permissions;
+            }
+
+            if (perms.Has(PermissionSet.Administrator))
+                return PermissionSet.All;
+
+            return perms;
+        }
+
+        public static PermissionSet ApplyChannelOverwrites(PermissionSet perms, Channel channel, ulong userId,
+                                                           ICollection<ulong> roleIds)
+        {
+            if (channel.PermissionOverwrites == null)
+                return perms;
+
+            var everyoneDeny = PermissionSet.None;
+            var everyoneAllow = PermissionSet.None;
+            var roleDeny = PermissionSet.None;
+            var roleAllow = PermissionSet.None;
+            var userDeny = PermissionSet.None;
+            var userAllow = PermissionSet.None;
+
+            foreach (var overwrite in channel.PermissionOverwrites)
+            {
+                switch (overwrite.Type)
+                {
+                    case Channel.OverwriteType.Role when overwrite.Id == channel.GuildId:
+                        everyoneDeny |= overwrite.Deny;
+                        everyoneAllow |= overwrite.Allow;
+                        break;
+                    case Channel.OverwriteType.Role when roleIds.Contains(overwrite.Id):
+                        roleDeny |= overwrite.Deny;
+                        roleAllow |= overwrite.Allow;
+                        break;
+                    case Channel.OverwriteType.Member when overwrite.Id == userId:
+                        userDeny |= overwrite.Deny;
+                        userAllow |= overwrite.Allow;
+                        break;
+                }
+            }
+
+            perms &= ~everyoneDeny;
+            perms |= everyoneAllow;
+            perms &= ~roleDeny;
+            perms |= roleAllow;
+            perms &= ~userDeny;
+            perms |= userAllow;
+            return perms;
+        }
+
+        private const PermissionSet NeedsViewChannel =
+            PermissionSet.SendMessages |
+            PermissionSet.SendTtsMessages |
+            PermissionSet.ManageMessages |
+            PermissionSet.EmbedLinks |
+            PermissionSet.AttachFiles |
+            PermissionSet.ReadMessageHistory |
+            PermissionSet.MentionEveryone |
+            PermissionSet.UseExternalEmojis |
+            PermissionSet.AddReactions |
+            PermissionSet.Connect |
+            PermissionSet.Speak |
+            PermissionSet.MuteMembers |
+            PermissionSet.DeafenMembers |
+            PermissionSet.MoveMembers |
+            PermissionSet.UseVad |
+            PermissionSet.Stream |
+            PermissionSet.PrioritySpeaker;
+
+        private const PermissionSet NeedsSendMessages =
+            PermissionSet.MentionEveryone |
+            PermissionSet.SendTtsMessages |
+            PermissionSet.AttachFiles |
+            PermissionSet.EmbedLinks;
+    }
+}

Myriad/Extensions/UserExtensions.cs

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+using Myriad.Types;
+
+namespace Myriad.Extensions
+{
+    public static class UserExtensions
+    {
+        public static string AvatarUrl(this User user) => 
+            $"https://cdn.discordapp.com/avatars/{user.Id}/{user.Avatar}.png";
+    }
+}