/*
 * Copyright (c) 2013 Cisco Systems, Inc. and others.  All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v1.0 which accompanies this distribution,
 * and is available at http://www.eclipse.org/legal/epl-v10.html
 */
package org.opendaylight.controller.config.manager.impl.osgi;

import com.google.common.util.concurrent.ThreadFactoryBuilder;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.concurrent.ThreadFactory;
import org.osgi.framework.Bundle;
import org.osgi.framework.BundleContext;
import org.osgi.framework.BundleEvent;
import org.osgi.util.tracker.BundleTracker;
import org.osgi.util.tracker.BundleTrackerCustomizer;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Extensible bundle tracker. Takes several BundleTrackerCustomizers and
 * propagates bundle events to all of them.
 *
 * <p>
 * Primary customizer may return tracking object, which will be passed to it
 * during invocation of
 * {@link BundleTrackerCustomizer#removedBundle(Bundle, BundleEvent, Object)}
 *
 * <p>
 * This extender modifies behavior to not leak platform thread in
 * {@link BundleTrackerCustomizer#addingBundle(Bundle, BundleEvent)} but deliver
 * this event from its own single threaded executor.
 *
 * <p>
 * If bundle is removed before event for adding bundle was executed, that event
 * is cancelled. If addingBundle event is currently in progress or was already
 * executed, platform thread is block until addingBundle finishes so bundle
 * could be removed correctly in platform thread.
 *
 * <p>
 * Method
 * {@link BundleTrackerCustomizer#removedBundle(Bundle, BundleEvent, Object)} is
 * never invoked on registered trackers.
 *
 * @param <T> value
 */
public final class ExtensibleBundleTracker<T> extends BundleTracker<Future<T>> {
    private static final ThreadFactory THREAD_FACTORY = new ThreadFactoryBuilder()
            .setNameFormat("config-bundle-tracker-%d").build();
    private final ExecutorService eventExecutor;
    private final BundleTrackerCustomizer<T> primaryTracker;
    private final BundleTrackerCustomizer<?>[] additionalTrackers;

    private static final Logger LOG = LoggerFactory.getLogger(ExtensibleBundleTracker.class);

    public ExtensibleBundleTracker(final BundleContext context,
            final BundleTrackerCustomizer<T> primaryBundleTrackerCustomizer,
            final BundleTrackerCustomizer<?>... additionalBundleTrackerCustomizers) {
        this(context, Bundle.ACTIVE, primaryBundleTrackerCustomizer, additionalBundleTrackerCustomizers);
    }

    public ExtensibleBundleTracker(final BundleContext context, final int bundleState,
            final BundleTrackerCustomizer<T> primaryBundleTrackerCustomizer,
            final BundleTrackerCustomizer<?>... additionalBundleTrackerCustomizers) {
        super(context, bundleState, null);
        this.primaryTracker = primaryBundleTrackerCustomizer;
        this.additionalTrackers = additionalBundleTrackerCustomizers;
        eventExecutor = Executors.newSingleThreadExecutor(THREAD_FACTORY);
        LOG.trace("Registered as extender with context {} and bundle state {}", context, bundleState);
    }

    @Override
    public Future<T> addingBundle(final Bundle bundle, final BundleEvent event) {
        LOG.trace("Submiting AddingBundle for bundle {} and event {} to be processed asynchronously", bundle, event);
        return eventExecutor.submit(() -> {
            T primaryTrackerRetVal = primaryTracker.addingBundle(bundle, event);

            forEachAdditionalBundle(tracker -> tracker.addingBundle(bundle, event));
            LOG.trace("AddingBundle for {} and event {} finished successfully", bundle, event);
            return primaryTrackerRetVal;
        });
    }

    @Override
    public void modifiedBundle(final Bundle bundle, final BundleEvent event, final Future<T> object) {
        // Intentionally NOOP
    }

    @Override
    public void removedBundle(final Bundle bundle, final BundleEvent event, final Future<T> object) {
        if (!object.isDone() && object.cancel(false)) {
            // We canceled adding event before it was processed
            // so it is safe to return
            LOG.trace("Adding Bundle event for {} was cancelled. No additional work required.", bundle);
            return;
        }
        try {
            LOG.trace("Invoking removedBundle event for {}", bundle);
            primaryTracker.removedBundle(bundle, event, object.get());
            forEachAdditionalBundle(tracker -> tracker.removedBundle(bundle, event, null));
            LOG.trace("Removed bundle event for {} finished successfully.", bundle);
        } catch (final ExecutionException | InterruptedException e) {
            LOG.error("Failed to remove bundle {}", bundle, e);
        }
    }

    private void forEachAdditionalBundle(final BundleStrategy lambda) {
        for (BundleTrackerCustomizer<?> trac : additionalTrackers) {
            lambda.execute(trac);
        }
    }

    private interface BundleStrategy {
        void execute(BundleTrackerCustomizer<?> tracker);
    }
}