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

package com.alttd.hunger_games.services;

import com.alttd.hunger_games.config.Config;
import com.alttd.hunger_games.data_objects.GameStage;
import com.alttd.hunger_games.data_objects.ROUND_STATE;
import com.alttd.hunger_games.game.GameStageHandler;

import java.time.Duration;
import java.util.ArrayList;
import java.util.List;
import java.util.Optional;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;

public class Round {

    private static Round instance = null;
    private final List<RoundListener> listeners = new ArrayList<>();
    private ROUND_STATE roundState = ROUND_STATE.PLAYER_REGISTRATION;
    private ScheduledExecutorService scheduledExecutorService = Executors.newSingleThreadScheduledExecutor();

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

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

    public void startRound() {
        if (roundState.equals(ROUND_STATE.PLAYER_REGISTRATION)) {
            throw new IllegalStateException("Round can not be started before player registration.");
        }
        roundState = ROUND_STATE.COUNTDOWN;
        listeners.forEach(roundListener -> roundListener.stateChange(roundState));
        GameStageHandler.handleWarmup();
        Duration warmupDuration = Config.ROUND.COUNTDOWN;
        scheduledExecutorService.schedule(() -> {
            GameStageHandler.handleCountdownEnd();
            nextStage();
            scheduleNextStage(0);
        }, warmupDuration.toSeconds(), TimeUnit.SECONDS);
    }

    private void scheduleNextStage(int index) {
        List<GameStage> gameStageList = Config.ROUND.STAGES;
        if (gameStageList.size() <= index) {
            nextStage();
            return;
        }

        GameStage gameStage = gameStageList.get(index);
        Duration duration = gameStage.getDuration();
        scheduledExecutorService.schedule(() -> {
            GameStageHandler.handleStageChange(gameStage.getWorldBorderSize());
            scheduleNextStage(index + 1);
        }, duration.toSeconds(), TimeUnit.SECONDS);
    }
}