/*
 * ============LICENSE_START=======================================================
 * ONAP
 * ================================================================================
 * Copyright (C) 2018-2021 AT&T Intellectual Property. All rights reserved.
 * ================================================================================
 * 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.
 * ============LICENSE_END=========================================================
 */

package org.onap.policy.drools.pooling;

import java.util.List;
import java.util.Properties;
import java.util.UUID;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.CountDownLatch;
import lombok.AccessLevel;
import lombok.Getter;
import org.onap.policy.common.endpoints.event.comm.Topic.CommInfrastructure;
import org.onap.policy.common.endpoints.event.comm.TopicEndpointManager;
import org.onap.policy.common.endpoints.event.comm.TopicSink;
import org.onap.policy.common.endpoints.event.comm.TopicSource;
import org.onap.policy.common.utils.properties.SpecProperties;
import org.onap.policy.common.utils.properties.exception.PropertyException;
import org.onap.policy.drools.controller.DroolsController;
import org.onap.policy.drools.features.DroolsControllerFeatureApi;
import org.onap.policy.drools.features.PolicyControllerFeatureApi;
import org.onap.policy.drools.features.PolicyEngineFeatureApi;
import org.onap.policy.drools.persistence.SystemPersistenceConstants;
import org.onap.policy.drools.system.PolicyController;
import org.onap.policy.drools.system.PolicyControllerConstants;
import org.onap.policy.drools.system.PolicyEngine;
import org.onap.policy.drools.util.FeatureEnabledChecker;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Controller/session pooling. Multiple hosts may be launched, all servicing the same
 * controllers/sessions. When this feature is enabled, the requests are divided across the different
 * hosts, instead of all running on a single, active host.
 *
 * <p>With each controller, there is an
 * associated DMaaP topic that is used for internal communication between the different hosts
 * serving the controller.
 */
public class PoolingFeature implements PolicyEngineFeatureApi, PolicyControllerFeatureApi, DroolsControllerFeatureApi {

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

    /**
     * ID of this host.
     */
    @Getter
    private final String host;

    /**
     * Entire set of feature properties, including those specific to various controllers.
     */
    private Properties featProps = null;

    /**
     * Maps a controller name to its associated manager.
     */
    private final ConcurrentHashMap<String, PoolingManagerImpl> ctlr2pool = new ConcurrentHashMap<>(107);

    /**
     * Decremented each time a manager enters the Active state. Used by junit tests.
     */
    @Getter(AccessLevel.PROTECTED)
    private final CountDownLatch activeLatch = new CountDownLatch(1);

    /**
     * Topic names passed to beforeOffer(), which are saved for when the beforeInsert() is
     * called later. As multiple threads can be active within the methods at the same
     * time, we must keep this in thread local storage.
     */
    private ThreadLocal<String> offerTopics = new ThreadLocal<>();

    /**
     * Constructor.
     */
    public PoolingFeature() {
        super();

        this.host = UUID.randomUUID().toString();
    }

    @Override
    public int getSequenceNumber() {
        return 0;
    }

    @Override
    public boolean beforeStart(PolicyEngine engine) {
        logger.info("initializing {}", PoolingProperties.FEATURE_NAME);
        featProps = getProperties(PoolingProperties.FEATURE_NAME);

        // remove any generic pooling topic - always use controller-specific property
        featProps.remove(PoolingProperties.POOLING_TOPIC);

        initTopicSources(featProps);
        initTopicSinks(featProps);

        return false;
    }

    @Override
    public boolean beforeStart(PolicyController controller) {
        return doManager(controller, mgr -> {
            mgr.beforeStart();
            return false;
        });
    }

    /**
     * Adds the controller and a new pooling manager to {@link #ctlr2pool}.
     *
     * @throws PoolingFeatureRtException if an error occurs
     */
    @Override
    public boolean afterCreate(PolicyController controller) {

        if (featProps == null) {
            logger.error("pooling feature properties have not been loaded");
            throw new PoolingFeatureRtException(new IllegalStateException("missing pooling feature properties"));
        }

        String name = controller.getName();

        var specProps = new SpecProperties(PoolingProperties.PREFIX, name, featProps);

        if (FeatureEnabledChecker.isFeatureEnabled(specProps, PoolingProperties.FEATURE_ENABLED)) {
            try {
                // get & validate the properties
                var props = new PoolingProperties(name, featProps);

                logger.info("pooling enabled for {}", name);
                ctlr2pool.computeIfAbsent(name, xxx -> makeManager(host, controller, props, activeLatch));

            } catch (PropertyException e) {
                logger.error("pooling disabled due to exception for {}", name);
                throw new PoolingFeatureRtException(e);
            }

        } else {
            logger.info("pooling disabled for {}", name);
        }


        return false;
    }

    @Override
    public boolean afterStart(PolicyController controller) {
        return doManager(controller, mgr -> {
            mgr.afterStart();
            return false;
        });
    }

    @Override
    public boolean beforeStop(PolicyController controller) {
        return doManager(controller, mgr -> {
            mgr.beforeStop();
            return false;
        });
    }

    @Override
    public boolean afterStop(PolicyController controller) {
        return doManager(controller, mgr -> {
            mgr.afterStop();
            return false;
        });
    }

    @Override
    public boolean afterShutdown(PolicyController controller) {
        return commonShutdown(controller);
    }

    @Override
    public boolean afterHalt(PolicyController controller) {
        return commonShutdown(controller);
    }

    private boolean commonShutdown(PolicyController controller) {
        deleteManager(controller);
        return false;
    }

    @Override
    public boolean beforeLock(PolicyController controller) {
        return doManager(controller, mgr -> {
            mgr.beforeLock();
            return false;
        });
    }

    @Override
    public boolean afterUnlock(PolicyController controller) {
        return doManager(controller, mgr -> {
            mgr.afterUnlock();
            return false;
        });
    }

    @Override
    public boolean beforeOffer(PolicyController controller, CommInfrastructure protocol, String topic2, String event) {
        /*
         * As this is invoked a lot, we'll directly call the manager's method instead of using the
         * functional interface via doManager().
         */
        PoolingManagerImpl mgr = ctlr2pool.get(controller.getName());
        if (mgr == null) {
            return false;
        }

        if (mgr.beforeOffer(topic2, event)) {
            return true;
        }

        offerTopics.set(topic2);
        return false;
    }

    @Override
    public boolean beforeInsert(DroolsController droolsController, Object fact) {

        String topic = offerTopics.get();
        if (topic == null) {
            logger.warn("missing arguments for feature-pooling-dmaap in beforeInsert");
            return false;
        }

        PolicyController controller;
        try {
            controller = getController(droolsController);

        } catch (IllegalArgumentException | IllegalStateException e) {
            logger.warn("cannot get controller for {} {}", droolsController.getGroupId(),
                    droolsController.getArtifactId(), e);
            return false;
        }


        if (controller == null) {
            logger.warn("cannot determine controller for {} {}", droolsController.getGroupId(),
                    droolsController.getArtifactId());
            return false;
        }

        /*
         * As this is invoked a lot, we'll directly call the manager's method instead of using the
         * functional interface via doManager().
         */
        PoolingManagerImpl mgr = ctlr2pool.get(controller.getName());
        if (mgr == null) {
            return false;
        }

        return mgr.beforeInsert(topic, fact);
    }

    @Override
    public boolean afterOffer(PolicyController controller, CommInfrastructure protocol, String topic, String event,
            boolean success) {

        // clear any stored arguments
        offerTopics.remove();

        return false;
    }

    /**
     * Executes a function using the manager associated with the controller. Catches any exceptions
     * from the function and re-throws it as a runtime exception.
     *
     * @param controller controller
     * @param func function to be executed
     * @return {@code true} if the function handled the request, {@code false} otherwise
     * @throws PoolingFeatureRtException if an error occurs
     */
    private boolean doManager(PolicyController controller, MgrFunc func) {
        PoolingManagerImpl mgr = ctlr2pool.get(controller.getName());
        if (mgr == null) {
            return false;
        }

        try {
            return func.apply(mgr);

        } catch (PoolingFeatureException e) {
            throw new PoolingFeatureRtException(e);
        }
    }

    /**
     * Deletes the manager associated with a controller.
     *
     * @param controller controller
     * @throws PoolingFeatureRtException if an error occurs
     */
    private void deleteManager(PolicyController controller) {

        String name = controller.getName();
        logger.info("remove feature-pool-dmaap manager for {}", name);

        ctlr2pool.remove(name);
    }

    /**
     * Function that operates on a manager.
     */
    @FunctionalInterface
    private static interface MgrFunc {

        /**
         * Apply.
         *
         * @param mgr manager
         * @return {@code true} if the request was handled by the manager, {@code false} otherwise
         * @throws PoolingFeatureException feature exception
         */
        boolean apply(PoolingManagerImpl mgr) throws PoolingFeatureException;
    }

    /*
     * The remaining methods may be overridden by junit tests.
     */

    /**
     * Get properties.
     *
     * @param featName feature name
     * @return the properties for the specified feature
     */
    protected Properties getProperties(String featName) {
        return SystemPersistenceConstants.getManager().getProperties(featName);
    }

    /**
     * Makes a pooling manager for a controller.
     *
     * @param host name/uuid of this host
     * @param controller controller
     * @param props properties to use to configure the manager
     * @param activeLatch decremented when the manager goes Active
     * @return a new pooling manager
     */
    protected PoolingManagerImpl makeManager(String host, PolicyController controller, PoolingProperties props,
            CountDownLatch activeLatch) {
        return new PoolingManagerImpl(host, controller, props, activeLatch);
    }

    /**
     * Gets the policy controller associated with a drools controller.
     *
     * @param droolsController drools controller
     * @return the policy controller associated with a drools controller
     */
    protected PolicyController getController(DroolsController droolsController) {
        return PolicyControllerConstants.getFactory().get(droolsController);
    }

    /**
     * Initializes the topic sources.
     *
     * @param props properties used to configure the topics
     * @return the topic sources
     */
    protected List<TopicSource> initTopicSources(Properties props) {
        return TopicEndpointManager.getManager().addTopicSources(props);
    }

    /**
     * Initializes the topic sinks.
     *
     * @param props properties used to configure the topics
     * @return the topic sinks
     */
    protected List<TopicSink> initTopicSinks(Properties props) {
        return TopicEndpointManager.getManager().addTopicSinks(props);
    }
}