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/*
 * Copyright 2017 The RoboZonky Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.github.triceo.robozonky.app;

import java.util.Optional;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.atomic.AtomicReference;
import java.util.function.Consumer;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Makes sure that when Ctrl+C is pressed in daemon-mode, the app cleanly shuts down.
 */
public class ShutdownEnabler implements ShutdownHook.Handler {

    public static final AtomicReference DAEMON_ALLOWED_TO_TERMINATE =
            new AtomicReference<>(new CountDownLatch(1));
    private static final Logger LOGGER = LoggerFactory.getLogger(ShutdownEnabler.class);

    @Override
    public Optional> get() {
        return Optional.of((returnCode -> {
            /*
             * when the code gets here during shutdown, control is handed over to the daemon, which is already
             * waiting to acquire; application will relinquish control and the JVM will shut down.
             */
            final CountDownLatch daemonAllowedToTerminate =
                    ShutdownEnabler.DAEMON_ALLOWED_TO_TERMINATE.getAndUpdate(l -> new CountDownLatch(1));
            ShutdownEnabler.LOGGER.debug("Running with {}.", daemonAllowedToTerminate);
            daemonAllowedToTerminate.countDown();
        }));
    }
}