/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 org.apache.logging.log4j.core.config;

import java.util.Objects;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

import org.apache.logging.log4j.Level;
import org.apache.logging.log4j.Marker;
import org.apache.logging.log4j.core.LogEvent;
import org.apache.logging.log4j.message.Message;
import org.apache.logging.log4j.util.Supplier;

ReliabilityStrategy that counts the number of threads that have started to log an event but have not completed yet,
and waits for these threads to finish before allowing the appenders to be stopped.
/**
 * ReliabilityStrategy that counts the number of threads that have started to log an event but have not completed yet,
 * and waits for these threads to finish before allowing the appenders to be stopped.
 */
public class AwaitCompletionReliabilityStrategy implements ReliabilityStrategy {
    private static final int MAX_RETRIES = 3;
    private final AtomicInteger counter = new AtomicInteger();
    private final AtomicBoolean shutdown = new AtomicBoolean(false);
    private final Lock shutdownLock = new ReentrantLock();
    private final Condition noLogEvents = shutdownLock.newCondition(); // should only be used when shutdown == true
    private final LoggerConfig loggerConfig;

    public AwaitCompletionReliabilityStrategy(final LoggerConfig loggerConfig) {
        this.loggerConfig = Objects.requireNonNull(loggerConfig, "loggerConfig is null");
    }

    /*
     * (non-Javadoc)
     *
     * @see org.apache.logging.log4j.core.config.ReliabilityStrategy#log(org.apache.logging.log4j.util.Supplier,
     * java.lang.String, java.lang.String, org.apache.logging.log4j.Marker, org.apache.logging.log4j.Level,
     * org.apache.logging.log4j.message.Message, java.lang.Throwable)
     */
    @Override
    public void log(final Supplier<LoggerConfig> reconfigured, final String loggerName, final String fqcn,
            final Marker marker, final Level level, final Message data, final Throwable t) {

        final LoggerConfig config = getActiveLoggerConfig(reconfigured);
        try {
            config.log(loggerName, fqcn, marker, level, data, t);
        } finally {
            config.getReliabilityStrategy().afterLogEvent();
        }
    }

    /*
     * (non-Javadoc)
     *
     * @see org.apache.logging.log4j.core.config.ReliabilityStrategy#log(org.apache.logging.log4j.util.Supplier,
     * org.apache.logging.log4j.core.LogEvent)
     */
    @Override
    public void log(final Supplier<LoggerConfig> reconfigured, final LogEvent event) {
        final LoggerConfig config = getActiveLoggerConfig(reconfigured);
        try {
            config.log(event);
        } finally {
            config.getReliabilityStrategy().afterLogEvent();
        }
    }

    /*
     * (non-Javadoc)
     *
     * @see
     * org.apache.logging.log4j.core.config.ReliabilityStrategy#beforeLogEvent(org.apache.logging.log4j.core.config.
     * LoggerConfig, org.apache.logging.log4j.util.Supplier)
     */
    @Override
    public LoggerConfig getActiveLoggerConfig(final Supplier<LoggerConfig> next) {
        LoggerConfig result = this.loggerConfig;
        if (!beforeLogEvent()) {
            result = next.get();
            return result == this.loggerConfig ? result : result.getReliabilityStrategy().getActiveLoggerConfig(next);
        }
        return result;
    }

    private boolean beforeLogEvent() {
        return counter.incrementAndGet() > 0;
    }

    @Override
    public void afterLogEvent() {
        if (counter.decrementAndGet() == 0 && shutdown.get()) {
            signalCompletionIfShutdown();
        }
    }

    private void signalCompletionIfShutdown() {
        final Lock lock = shutdownLock;
        lock.lock();
        try {
            noLogEvents.signalAll();
        } finally {
            lock.unlock();
        }
    }

    /*
     * (non-Javadoc)
     *
     * @see org.apache.logging.log4j.core.config.ReliabilityStrategy#beforeStopAppenders()
     */
    @Override
    public void beforeStopAppenders() {
        waitForCompletion();
    }

    
Waits for all log events to complete before returning.
/**
     * Waits for all log events to complete before returning.
     */
    private void waitForCompletion() {
        shutdownLock.lock();
        try {
            if (shutdown.compareAndSet(false, true)) {
                int retries = 0;
                // repeat while counter is non-zero
                while (!counter.compareAndSet(0, Integer.MIN_VALUE)) {

                    // counter was non-zero
                    if (counter.get() < 0) { // this should not happen
                        return; // but if it does, we are already done
                    }
                    // counter greater than zero, wait for afterLogEvent to decrease count
                    try {
                        noLogEvents.await(retries + 1, TimeUnit.SECONDS);
                    } catch (final InterruptedException ie) {
                        if (++retries > MAX_RETRIES) {
                            break;
                        }
                    }
                }
            }
        } finally {
            shutdownLock.unlock();
        }
    }

    /*
     * (non-Javadoc)
     *
     * @see
     * org.apache.logging.log4j.core.config.ReliabilityStrategy#beforeStopConfiguration(org.apache.logging.log4j.core
     * .config.Configuration)
     */
    @Override
    public void beforeStopConfiguration(final Configuration configuration) {
        // no action
    }

}