/**
 * DataCleaner (community edition)
 * Copyright (C) 2014 Neopost - Customer Information Management
 *
 * This copyrighted material is made available to anyone wishing to use, modify,
 * copy, or redistribute it subject to the terms and conditions of the GNU
 * Lesser General Public License, as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License
 * for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this distribution; if not, write to:
 * Free Software Foundation, Inc.
 * 51 Franklin Street, Fifth Floor
 * Boston, MA  02110-1301  USA
 */
package org.datacleaner.job.concurrent;

import java.util.concurrent.atomic.AtomicInteger;

import org.datacleaner.job.tasks.Task;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Task listener that will wait (join) for a set of tasks to complete before
 * invoking onComplete(...) on a nested task listener.
 */
public final class JoinTaskListener implements TaskListener {

    private static final Logger logger = LoggerFactory.getLogger(JoinTaskListener.class);

    private final AtomicInteger _countDown;
    private final TaskListener _nestedTaskListener;
    private volatile Throwable _error;

    public JoinTaskListener(final int tasksToWaitFor, final TaskListener... nestedTaskListeners) {
        this(tasksToWaitFor, new CompositeTaskListener(nestedTaskListeners));
    }

    public JoinTaskListener(final int tasksToWaitFor, final TaskListener nestedTaskListener) {
        _nestedTaskListener = nestedTaskListener;

        if (tasksToWaitFor == 0) {
            logger.warn(
                    "Was asked to join execution after 0 tasks, this might be a bug. Continuing with immediate completion.");
            // immediate completion
            _countDown = new AtomicInteger(1);
            onComplete(null);
        } else {
            _countDown = new AtomicInteger(tasksToWaitFor);
        }
    }

    @Override
    public String toString() {
        return "Join[countDown=" + _countDown.get() + "]";
    }

    @Override
    public void onBegin(final Task task) {
    }

    @Override
    public void onComplete(final Task task) {
        final int count = _countDown.decrementAndGet();
        logger.debug("onComplete(), count = {}", count);
        invokeNested(count, task);
    }

    @Override
    public void onError(final Task task, final Throwable throwable) {
        _error = throwable;
        final int count = _countDown.decrementAndGet();
        logger.debug("onComplete(), count = {}", count);
        invokeNested(count, task);
    }

    private void invokeNested(final int count, final Task task) {
        if (count == 0) {
            if (_error == null) {
                logger.debug("Calling onComplete(...) on nested TaskListener ()");
                _nestedTaskListener.onComplete(task);
            } else {
                logger.debug("Calling onError(...) on nested TaskListener ()");
                _nestedTaskListener.onError(task, _error);
            }
        }
    }
}