AfkKicker.java

MetadataKey<AtomicInteger> AFK_TIME_KEY = MetadataKey.create("afk", AtomicInteger.class);
MetadataKey<Direction> AFK_DIRECTION_KEY = MetadataKey.create("afk-direction", Direction.class);

Scheduler.runTaskRepeatingSync(() -> {
    for (Player player : Bukkit.getOnlinePlayers()) {
        MetadataMap metadata = Metadata.provideForPlayer(player);

        Direction prev = metadata.getOrNull(AFK_DIRECTION_KEY);
        Direction now = Direction.from(player.getLocation());
        
        metadata.put(AFK_DIRECTION_KEY, now);

        // no previous yaw/pitch data for the player
        if (prev == null) {
            continue;
        }

        AtomicInteger counter = metadata.getOrPut(AFK_TIME_KEY, AtomicInteger::new);

        // check if they have moved since last time
        if (!prev.equals(now)) {
            counter.set(0);
            continue;
        }
        
        if (counter.incrementAndGet() >= 300) {
            player.kickPlayer("You have been idle for 5 minutes.");
        }
    }
}, 20L, 20L);