simple shop command

@Katton.command(name = "shop", permission = "all")
function shopCommand(sender, args) {
    if (args.size() == 0) {
        sender.sendMessage("&eavailable items: " + shopItems.keys())
        return
    }

    val choice = args[0]

    if (!shopItems.containsKey(choice)) {
        sender.sendMessage("&cunknown item '" + choice + "'. Available: " + shopItems.keys())
        return
    }

    val onCooldownUntil = Katton.vars.player(sender.uuid).get("shop_cooldown")
    if (onCooldownUntil != null && onCooldownUntil == true) {
        sender.sendMessage("&cyou're still on cooldown! try again in a moment")
        return
    }

    val material = shopItems.get(choice)
    sender.give(Katton.item(material))
    sender.sendMessage("&ahere's your " + choice + "!")

    Katton.vars.player(sender.uuid).set("shop_cooldown", true)
    Katton.after(3.seconds) {
        sender.sendMessage("&ayou're no longer on cooldown!")
        Katton.vars.player(sender.uuid).set("shop_cooldown", false)
    }
}

/katton run shop
/katton run shop sword
/katton run shop sword (immediately again shows the cooldown message)