HungerGames/src/main/java/com/alttd/hunger_games/services/Round.java

package com.alttd.hunger_games.services;

import com.alttd.hunger_games.data_objects.ROUND_STATE;

import java.util.ArrayList;
import java.util.List;
import java.util.Optional;

public class Round {

    private static Round instance = null;
    private final List<RoundListener> listeners = new ArrayList<>();
    private ROUND_STATE roundState = null;

    private Round() {

    }

    public static Round createSingletonInstance() throws IllegalStateException {
        if (instance != null) {
            throw new IllegalStateException("Round is already initialized.");
        }
        instance = new Round();
        return instance;
    }

    public ROUND_STATE register(RoundListener listener) {
        listeners.add(listener);
        return roundState;
    }

    public void unregister(RoundListener listener) {
        listeners.remove(listener);
    }

    public void reset() {
        listeners.forEach(RoundListener::roundReset);
    }

    public void start() {
        roundState = ROUND_STATE.PLAYER_REGISTRATION;
        listeners.forEach(roundListener -> roundListener.stateChange(roundState));
    }

    public void nextStage() {
        Optional<ROUND_STATE> optionalNextRoundState = roundState.next();
        if (optionalNextRoundState.isEmpty()) {
            roundState = null;
            reset();
            return;
        }
        roundState = optionalNextRoundState.get();
        listeners.forEach(roundListener -> roundListener.stateChange(roundState));
    }

}