discordid: remove all ID-related casts

In the same vein as mautrix-whatsapp, -slack and others, do not make
assumptions about how the ID is represented in the connector code. Let
the discordid package be entirely responsible.

pkg/discordid/id.go

@@ -21,8 +21,85 @@ import (
 	"maunium.net/go/mautrix/bridgev2/networkid"
 )
 
+func MakeUserID(userID string) networkid.UserID {
+	return networkid.UserID(userID)
+}
+
+func ParseUserID(userID networkid.UserID) string {
+	return string(userID)
+}
+
+func MakeUserLoginID(userID string) networkid.UserLoginID {
+	return networkid.UserLoginID(userID)
+}
+
+func ParseUserLoginID(id networkid.UserLoginID) string {
+	return string(id)
+}
+
+// UserLoginIDToUserID converts a UserLoginID to a UserID. In Discord, both
+// are the same underlying snowflake.
+func UserLoginIDToUserID(id networkid.UserLoginID) networkid.UserID {
+	return networkid.UserID(id)
+}
+
+func MakePortalID(channelID string) networkid.PortalID {
+	return networkid.PortalID(channelID)
+}
+
+func ParsePortalID(portalID networkid.PortalID) string {
+	return string(portalID)
+}
+
+func MakeMessageID(messageID string) networkid.MessageID {
+	return networkid.MessageID(messageID)
+}
+
+func ParseMessageID(messageID networkid.MessageID) string {
+	return string(messageID)
+}
+
+func MakeEmojiID(emojiName string) networkid.EmojiID {
+	return networkid.EmojiID(emojiName)
+}
+
+func ParseEmojiID(emojiID networkid.EmojiID) string {
+	return string(emojiID)
+}
+
+func MakeAvatarID(avatar string) networkid.AvatarID {
+	return networkid.AvatarID(avatar)
+}
+
+// The string prepended to [networkid.PortalKey]s identifying spaces that
+// bridge Discord guilds.
+//
+// Every Discord guild created before August 2017 contained a channel
+// having _the same ID as the guild itself_. This channel also functioned as
+// the "default channel" in that incoming members would view this channel by
+// default. It was also impossible to delete.
+//
+// After this date, these "default channels" became deletable, and fresh guilds
+// were no longer created with a channel that exactly corresponded to the guild
+// ID.
+//
+// To accommodate Discord guilds created before this API change that have also
+// never deleted the default channel, we need a way to distinguish between the
+// guild and the default channel, as we wouldn't be able to bridge the guild
+// as a space otherwise.
+//
+// "*" was chosen as the asterisk character is used to filter by guilds in
+// the quick switcher (in Discord's first-party clients).
+//
+// For more information, see: https://discord.com/developers/docs/change-log#breaking-change-default-channels:~:text=New%20guilds%20will%20no%20longer.
+const GuildPortalKeySigil = "*"
+
+func MakeGuildPortalID(guildID string) networkid.PortalID {
+	return networkid.PortalID(GuildPortalKeySigil + guildID)
+}
+
 func MakePortalKey(ch *discordgo.Channel, userLoginID networkid.UserLoginID, wantReceiver bool) (key networkid.PortalKey) {
-	key.ID = networkid.PortalID(ch.ID)
+	key.ID = MakePortalID(ch.ID)
 	if wantReceiver {
 		key.Receiver = userLoginID
 	}
@@ -30,6 +107,6 @@ func MakePortalKey(ch *discordgo.Channel, userLoginID networkid.UserLoginID, wan
 }
 
 func MakePortalKeyWithID(channelID string) (key networkid.PortalKey) {
-	key.ID = networkid.PortalID(channelID)
+	key.ID = MakePortalID(channelID)
 	return
 }