add guild scoping [#11]

command.go

@@ -30,6 +30,15 @@ type Command interface {
 	Run(ctx *Ctx) (err error)
 }
 
+// GuildScopedCommand can be implemented by your
+// commands to scope them to specific guilds.
+//
+// The command then will be only registered on
+// the guild returned by the Guild method.
+type GuildScopedCommand interface {
+	Guild() string
+}
+
 func toApplicationCommand(c Command) *discordgo.ApplicationCommand {
 	switch cm := c.(type) {
 	case UserCommand:

ken.go

@@ -269,11 +269,16 @@ func (k *Ken) onReady(s *discordgo.Session, e *discordgo.Ready) {
 	)
 
 	for name, cmd := range k.cmds {
+		guildId := ""
+		if gsc, ok := cmd.(GuildScopedCommand); ok {
+			guildId = gsc.Guild()
+		}
+
 		if _, ok := k.idcache[name]; ok {
 			acmd := toApplicationCommand(cmd)
 			update = append(update, acmd)
 		} else {
-			ccmd, err = s.ApplicationCommandCreate(e.User.ID, "", toApplicationCommand(cmd))
+			ccmd, err = s.ApplicationCommandCreate(e.User.ID, guildId, toApplicationCommand(cmd))
 			if err != nil {
 				k.opt.OnSystemError("command registration", err)
 			} else {