/*
 * 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.cassandra.utils;


import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.lang.management.ManagementFactory;
import java.nio.file.FileStore;
import java.nio.file.Path;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

import javax.management.MBeanServer;

import com.sun.management.HotSpotDiagnosticMXBean;

import org.apache.commons.lang3.ArrayUtils;
import org.apache.commons.lang3.text.StrBuilder;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import org.apache.cassandra.config.DatabaseDescriptor;
import org.apache.cassandra.io.util.File;
import org.apache.cassandra.io.util.PathUtils;

import static org.apache.cassandra.config.CassandraRelevantEnv.JAVA_HOME;
import static org.apache.cassandra.utils.Clock.Global.currentTimeMillis;

/**
 * Utility to log heap histogram.
 *
 */
public final class HeapUtils
{
    private static final Logger logger = LoggerFactory.getLogger(HeapUtils.class);

    private static final Lock DUMP_LOCK = new ReentrantLock();

    /**
     * Generates a HEAP histogram in the log file.
     */
    public static void logHeapHistogram()
    {
        try
        {
            logger.info("Trying to log the heap histogram using jcmd");

            Long processId = getProcessId();
            if (processId == null)
            {
                logger.error("The process ID could not be retrieved. Skipping heap histogram generation.");
                return;
            }

            String jcmdPath = getJcmdPath();

            // The jcmd file could not be found. In this case let's default to jcmd in the hope that it is in the path.
            String jcmdCommand = jcmdPath == null ? "jcmd" : jcmdPath;

            String[] histoCommands = new String[] {jcmdCommand,
                    processId.toString(),
                    "GC.class_histogram"};

            logProcessOutput(Runtime.getRuntime().exec(histoCommands));
        }
        catch (Throwable e)
        {
            logger.error("The heap histogram could not be generated due to the following error: ", e);
        }
    }

    /**
     * @return full path to the created heap dump file
     */
    public static String maybeCreateHeapDump()
    {
        // Make sure that only one heap dump can be in progress across all threads, and abort for
        // threads that cannot immediately acquire the lock, allowing them to fail normally.
        if (DUMP_LOCK.tryLock())
        {
            try
            {
                if (DatabaseDescriptor.getDumpHeapOnUncaughtException())
                {
                    MBeanServer server = ManagementFactory.getPlatformMBeanServer();

                    Path absoluteBasePath = DatabaseDescriptor.getHeapDumpPath();
                    // We should never reach this point with this value null as we initialize the bool only after confirming
                    // the -XX param / .yaml conf is present on initial init and the JMX entry point, but still worth checking.
                    if (absoluteBasePath == null)
                    {
                        DatabaseDescriptor.setDumpHeapOnUncaughtException(false);
                        throw new RuntimeException("Cannot create heap dump unless -XX:HeapDumpPath or cassandra.yaml:heap_dump_path is specified.");
                    }

                    long maxMemoryBytes = Runtime.getRuntime().maxMemory();
                    long freeSpaceBytes = PathUtils.tryGetSpace(absoluteBasePath, FileStore::getUnallocatedSpace);

                    // Abort if there isn't enough room on the target disk to dump the entire heap and then copy it.
                    if (freeSpaceBytes < 2 * maxMemoryBytes)
                        throw new RuntimeException("Cannot allocated space for a heap dump snapshot. There are only " + freeSpaceBytes + " bytes free at " + absoluteBasePath + '.');

                    HotSpotDiagnosticMXBean mxBean = ManagementFactory.newPlatformMXBeanProxy(server, "com.sun.management:type=HotSpotDiagnostic", HotSpotDiagnosticMXBean.class);
                    String filename = String.format("pid%s-epoch%s.hprof", HeapUtils.getProcessId().toString(), currentTimeMillis());
                    String fullPath = File.getPath(absoluteBasePath.toString(), filename).toString();

                    logger.info("Writing heap dump to {} on partition w/ {} free bytes...", absoluteBasePath, freeSpaceBytes);
                    mxBean.dumpHeap(fullPath, false);
                    logger.info("Heap dump written to {}", fullPath);

                    // Disable further heap dump creations until explicitly re-enabled.
                    DatabaseDescriptor.setDumpHeapOnUncaughtException(false);

                    return fullPath;
                }
            }
            catch (Throwable e)
            {
                logger.warn("Unable to create heap dump.", e);
            }
            finally
            {
                DUMP_LOCK.unlock();
            }
        }
        else
        {
            logger.debug("Heap dump creation is already in progress. Request aborted.");
        }

        return null;
    }

    /**
     * Retrieve the path to the JCMD executable.
     * @return the path to the JCMD executable or null if it cannot be found.
     */
    private static String getJcmdPath()
    {
        // Searching in the JAVA_HOME is safer than searching into System.getProperty("java.home") as the Oracle
        // JVM might use the JRE which do not contains jmap.
        String javaHome = JAVA_HOME.getString();
        if (javaHome == null)
            return null;
        File javaBinDirectory = new File(javaHome, "bin");
        File[] files = javaBinDirectory.tryList((dir, name) -> name.startsWith("jcmd"));
        return ArrayUtils.isEmpty(files) ? null : files[0].path();
    }

    /**
     * Logs the output of the specified process.
     *
     * @param p the process
     * @throws IOException if an I/O problem occurs
     */
    private static void logProcessOutput(Process p) throws IOException
    {
        try (BufferedReader input = new BufferedReader(new InputStreamReader(p.getInputStream())))
        {
            StrBuilder builder = new StrBuilder();
            String line;
            while ((line = input.readLine()) != null)
            {
                builder.appendln(line);
            }
            logger.info(builder.toString());
        }
    }

    /**
     * Retrieves the process ID or <code>null</code> if the process ID cannot be retrieved.
     * @return the process ID or <code>null</code> if the process ID cannot be retrieved.
     */
    private static Long getProcessId()
    {
        long pid = NativeLibrary.getProcessID();
        if (pid >= 0)
            return pid;

        return getProcessIdFromJvmName();
    }

    /**
     * Retrieves the process ID from the JVM name.
     * @return the process ID or <code>null</code> if the process ID cannot be retrieved.
     */
    private static Long getProcessIdFromJvmName()
    {
        // the JVM name in Oracle JVMs is: '<pid>@<hostname>' but this might not be the case on all JVMs
        String jvmName = ManagementFactory.getRuntimeMXBean().getName();
        try
        {
            return Long.valueOf(jvmName.split("@")[0]);
        }
        catch (NumberFormatException e)
        {
            // ignore
        }
        return null;
    }

    /**
     * The class must not be instantiated.
     */
    private HeapUtils()
    {
    }
}
