/*
 * Copyright (c) 2000, 2017 Oracle and/or its affiliates. All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v. 2.0, which is available at
 * http://www.eclipse.org/legal/epl-2.0.
 *
 * This Source Code may also be made available under the following Secondary
 * Licenses when the conditions for such availability set forth in the
 * Eclipse Public License v. 2.0 are satisfied: GNU General Public License,
 * version 2 with the GNU Classpath Exception, which is available at
 * https://www.gnu.org/software/classpath/license.html.
 *
 * SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
 */

/*
 * @(#)FileTransactionLogWriter.java	1.3 06/29/07
 */

package com.sun.messaging.jmq.io.txnlog.file;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.util.Date;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.zip.Adler32;
import java.util.zip.Checksum;

import com.sun.messaging.jmq.util.MQThread;
import com.sun.messaging.jmq.io.txnlog.CheckPointListener;
import com.sun.messaging.jmq.io.txnlog.TransactionLogRecord;
import com.sun.messaging.jmq.io.txnlog.TransactionLogType;
import com.sun.messaging.jmq.io.txnlog.TransactionLogWriter;

/**
 * This class is used to write FileTransactionLogRecord to the transaction log file.
 * <p>
 * Each transaction is written as a transaction log record. Each record written is synced to the disk. Broker does not
 * need to sync its message stores until a check point request (CheckPointListener is called).
 * <p>
 * <XXX: chiaming (06/30/2006) add comments to describe file/header layout here.
 */
public class FileTransactionLogWriter implements TransactionLogWriter, Runnable {

    // file header constants - version
    public static final short FILE_VERSION = 1;

    /**
     * File header size - 48 bytes.
     */
    public static final int FILE_HEADER_SIZE = 48;
    // file header magic number - constant
    public static final int FILE_MAGIC_NUMBER = 0x5555AAAA;
    // file header seserve field
    public static final short FILE_RESERVED_SHORT = 0;

    // file header status position. If file header is changed,
    // this and check point position values MUST be updated.
    public static final int FILE_STATUS_POSITION = 6;

    // File check point position.
    public static final int FILE_CHECK_POINT_POSITION = 8;

    // File check sum position
    public static final int FILE_CHECK_SUM_POSITION = 32;

    /**
     * record header size - 48 bytes
     */
    public static final int RECORD_HEADER_SIZE = 48;

    public static final int RECORD_MAGIC_NUMBER = 0xAAAA5555;
    public static final int RECORD_TYPE = -1;
    public static final long RECORD_TIME_STAMP = 0;
    public static final int RECORD_BODY_SIZE = 0;
    public static final long RECORD_CHECK_SUM = 0;
    public static final int RECORD_HEADER_RESERVE = 0;

    // transaction log file created for writing -- init
    public static final short FILE_STATUS_CREATE_NORMAL = 0;

    // normal/clean shutdown status - close() called
    public static final short FILE_STATUS_SHUTDOWN_NORMAL = 1;

    // file to be renamed to .bak
    public static final short FILE_STATUS_BACKUP = 2;

    // checkPoint() called
    public static final short FILE_STATUS_CHK_POINT_UPDATED = 3;

    // reset() called
    public static final short FILE_STATUS_RESET = 4;

    public static final long DEFAULT_MAX_SIZE_KB = 10 * 1024L; // 10 M

    public static final String TXNLOG_DEBUG_PROP_NAME = "imq.txnlog.debug";

    public static final String TXNLOG_BACKUP_PROP_NAME = "imq.txnlog.backup";

    private long maxSize = DEFAULT_MAX_SIZE_KB * 1024L; // 10 M

    // when file pointer is > (maxSize - checkPointOffset),
    // this logwriter will reset itself and start from the beginning
    private long cpOffset = 500 * 1024L;
    private long cpSize = maxSize - cpOffset;

    private CheckPointListener callback = null;

    private boolean isListenerCalled = false;

    // The txn file.
    private RandomAccessFile raf = null;

    private File file = null;

    // read/write/sync mode.
    public static final String RWD_MODE = "rwd";

    /**
     * "rws" file mode -- for testing use only
     */
    private static final String RWS_MODE = "rws";

    /**
     * read-write mode -- call FileChannel.force() to sync every transaction.
     **/
    public static final String RW_MODE = "rw";

    private String fileMode = RWD_MODE;

    /**
     * This is used only if "useFileChannelSync" flag is true.
     */
    private FileChannel fchannel = null;

    /**
     * This is set to true only when RW_MODE is used.
     */
    private boolean useFileChannelSync = false;

    // check point position, 0 means this log is synced with message store.
    private long checkPointPosition = FILE_HEADER_SIZE;

    private boolean debug = false;

    // sync object for operations to txn file.
    private Object txnLogSyncObj = new Object();

    // to calculate checksum for each record written to txn log.
    private Checksum checksumEngine = new Adler32();

    /**
     * flag to indicate if playback of this file is required.
     */
    private boolean playBackRequired = false;

    /**
     * flag to indicate if file id corrupted. This flag is set to true if
     * <code>FileTransactionLogWriter#readFileHeader</code>detects that the header cannot be validated. Broker MUST call
     * <code>FileTransactionLogWriter#reset</code> to reset the log file.
     */
    private boolean isFileCorrupted = false;

    // check point sequence number. This number is put in the file header
    // and each log record. The value in the file header indicates the last
    // check point sequence number. Each log record from the last check point
    // to the next one contains the same check point sequence number.
    // the number is increased by one for each check point synced.
    private long checkpointSequence = 0;

    // This number is increased by 1 for each record added
    // to the log file. This number is reset to 0 when a check
    // point is called.
    private long entrySequence = 0;

    // last entry written to the log file
    private TransactionLogRecord lastEntry = null;

    // back up txn log file name extension.
    public static final String TXNLOG_BACKUP_EXT = ".1";

    // flag to determine if we want to do txnlog file backup. default to false
    // some systems do not support the OP.
    // Set imq.txnlog.backup to true to turn it on
    private boolean doFileBackup = false;

    private boolean doAsyncWrites = false;

    private boolean closed;

    private MQThread asyncWriteThread = null;

    private boolean synch = true;

    // the following three variables are used to debug the average number of records in a compound record
    private int sampleNum;

    private int sampleCount = 1000;

    private int[] numrecordsArray = new int[sampleCount];

    // a version number passed in by the application that will be stored in the header when the file is first created
    private long currentAppCookie = 0;

    // the version number read from the file when the file already exists.
    private long existingAppCookie = 0;

    // a collection holding log records due for processing
    private List<TransactionLogRecord> transactionLogRecordList = new LinkedList<TransactionLogRecord>();

    // a mutex controlling access to the transactionLogRecordList
    private Object recordListMutex = new Object();

    public FileTransactionLogWriter(File parent, String fileName, long size) throws IOException {
        init(parent, fileName, size);
    }

    public FileTransactionLogWriter(String fileName) throws IOException {
        init(null, fileName, DEFAULT_MAX_SIZE_KB * 1024L);
    }

    /**
     * Constructor.
     *
     */
    public FileTransactionLogWriter(File parent, String fileName, long size, String mode, long applicationCookie) throws IOException {
        this(parent, fileName, size, mode, true, false, applicationCookie);
    }

    /**
     * Constructor.
     *
     */
    public FileTransactionLogWriter(File parent, String fileName, long size, String mode, boolean sync, boolean groupCommit, long applicationCookie)
            throws IOException {

        if (RW_MODE.equals(mode)) {
            this.useFileChannelSync = true;
            fileMode = RW_MODE;
        } else if (RWS_MODE.equals(mode)) {
            fileMode = RWS_MODE;
        } else if (RWD_MODE.equals(mode) == false) {
            throw new java.lang.IllegalArgumentException("This file mode is not supported: " + mode);
        }
        this.currentAppCookie = applicationCookie;
        this.synch = sync;
        this.doAsyncWrites = groupCommit;
        init(parent, fileName, size);
    }

    private void init(File parent, String child, long size) throws IOException {

        this.debug = Boolean.getBoolean(TXNLOG_DEBUG_PROP_NAME);

        this.doFileBackup = Boolean.getBoolean(TXNLOG_BACKUP_PROP_NAME);

        file = new File(parent, child);

        setMaximumSize(size);

        if (raf != null) {
            raf.close();
        }

        if (doAsyncWrites) {
            log("starting asyncwrite");
            asyncWriteThread = new MQThread(this, child + "AsyncWrite");
            asyncWriteThread.setPriority(Thread.NORM_PRIORITY - 1);
            asyncWriteThread.start();
        }

        /**
         * The default file mode is RWD_MODE ("rwd"). If this class is instantiated with a file mode, the file mode is set to
         * the specified mode ("rw", "rws", "rwd" only).
         */
        log("Using file mode: " + fileMode);
        raf = new RandomAccessFile(file, fileMode);

        /**
         * If "rw" mode is specified, useFileChannelSync flag is set to true.
         */
        if (this.useFileChannelSync) {
            log("File Channel Sync flag is on ...");
            fchannel = raf.getChannel();
        }

        if (raf.length() > 0) {

            if (debug) {
                log("file exists: " + file.getAbsolutePath() + ", file size: " + raf.length());
            }

            readFileHeader();

            if (this.playBackRequired == false) {
                writeFileHeader(FILE_STATUS_CHK_POINT_UPDATED, FILE_HEADER_SIZE);
            }

        } else {

            // do create header for now.
            existingAppCookie = currentAppCookie;
            initNewFile();
        }
    }

    private void initNewFile() throws IOException {

        // always rewind.
        raf.seek(0);

        raf.setLength((int) maxSize);

        // allocate size for perf. reason.
        // raf.write( new byte [(int)maxSize] );
        doWrite(new byte[(int) maxSize]);

        // init check point sequence
        this.checkpointSequence = 0;
        // init entry sequence
        this.entrySequence = 0;

        // write file header.
        // fileStatus=CREATE_NORMAL, cpPosition=0
        writeFileHeader(FILE_STATUS_CREATE_NORMAL, FILE_HEADER_SIZE);

        if (debug) {
            log("file created: " + file.getAbsolutePath() + ", size: " + raf.length());
        }
    }

    /**
     * Read and validate file header.
     *
     * @throws IOException
     */
    private void readFileHeader() throws IOException {

        raf.seek(0);

        byte[] bytes = new byte[FILE_HEADER_SIZE];

        int size = raf.read(bytes);

        // 1. check header size
        if (size != FILE_HEADER_SIZE) {
            // set flag
            this.isFileCorrupted = true;

            throw new FileCorruptedException("File Header size mismatch. Expected:  " + FILE_HEADER_SIZE + ", read: " + size);
        }

        ByteBuffer buf = ByteBuffer.wrap(bytes);

        int magic = buf.getInt();
        short fversion = buf.getShort();
        short shutdownState = buf.getShort();
        long cpPosition = buf.getLong();
        long timestamp = buf.getLong();

        long cpseq = buf.getLong(); // cp seq

        long chksum = buf.getLong();

        long fileCookie = buf.getLong();

        long calculated = calculateCheckSum(bytes, 0, FILE_CHECK_SUM_POSITION);

        if (debug) {
            log("read file header, magic=" + magic + ", fversion=" + fversion + ", status=" + shutdownState + ", cpPosition=" + cpPosition + ", timestamp="
                    + timestamp + ", cpSequence=" + cpseq + ", chksum=" + chksum);
        }

        // 2. validate check sum
        if (chksum != calculated) {

            // set flag
            this.isFileCorrupted = true;

            throw new FileCorruptedException("File Header checksum mismatch. Expected: " + chksum + ", calculated: " + calculated);
        }

        // 3. validate magic number/version
        if ((magic != FILE_MAGIC_NUMBER) || fversion != FILE_VERSION) {

            // set flag
            this.isFileCorrupted = true;

            throw new FileCorruptedException("File Magic number/version mismatch: " + magic + ":" + fversion);
        }

        // 4. check if playback is required.
        if (shutdownState != FILE_STATUS_SHUTDOWN_NORMAL) {
            // we need to playback. set flag to true
            this.playBackRequired = true;

        }
        if (debug) {
            log("playbackRequired=" + playBackRequired);
        }

        // set chk position position.
        this.checkPointPosition = cpPosition;
        // set check point sequence
        this.checkpointSequence = cpseq;

        // move to the end of file header.
        raf.seek(FILE_HEADER_SIZE);
        // fchannel.position(FILE_HEADER_SIZE);

        // check application cookie matches
        this.existingAppCookie = fileCookie;
        if (this.existingAppCookie != currentAppCookie) {
            log("application cookies do not match! Existing file has version=" + this.existingAppCookie + " Current version of software="
                    + this.currentAppCookie);
        }

    }

    /**
     * Write file header into ByteBuffer.
     *
     * This file has a 48 byte fixed header as specified below.
     */
    private void writeFileHeader(short fileStatus, long cpPosition) throws IOException {

        // increase check point sequence. this value is used so that all entries in each
        // check point contains the same (and unique) checkPointSequence number.
        //
        if (checkpointSequence > Long.MAX_VALUE - 1) {
            // reset
            checkpointSequence = 0;
        } else {
            checkpointSequence++;
        }

        // reset entry seq number when check point seq is increased
        entrySequence = 0;

        // rewind.
        raf.seek(0);

        byte[] bytes = new byte[FILE_HEADER_SIZE];

        ByteBuffer buf = ByteBuffer.wrap(bytes);

        // 1. Magic number
        buf.putInt(FILE_MAGIC_NUMBER); // 0-3
        // 2. version
        buf.putShort(FILE_VERSION); // 4-5
        // 3. status.
        buf.putShort(fileStatus);// 6-7
        // 4. check point position
        buf.putLong(cpPosition);// 8-15
        // 5. timestamp
        long timestamp = System.currentTimeMillis();
        buf.putLong(timestamp); // 16-23
        // 6. check point sequence number
        buf.putLong(checkpointSequence); // 24-31

        long chksum = this.calculateCheckSum(bytes, 0, FILE_CHECK_SUM_POSITION);

        // 6. check sum
        buf.putLong(chksum); // 32-39
        // 7. reserve
        buf.putLong(existingAppCookie); // 40-47

        // raf.write(bytes);
        doWrite(bytes);

        if (debug) {
            log("write file header. magic=" + FILE_MAGIC_NUMBER + ", fversion=" + FILE_VERSION + ", status=" + fileStatus + ", cpPosition=" + cpPosition
                    + ", timestamp=" + timestamp + ", cpSequence=" + checkpointSequence + ", chksum=" + chksum);
        }
    }

    /**
     * sets the point where a checkpoint automatically occurs XXX: should we remove this?
     */
    @Override
    public void setCheckpointSize(long bytes) {
        this.cpSize = bytes;
    }

    /**
     * sets the maximum size of all State logs. When the maximum is hit, the log is checkpointed and renamed as a back up
     * file.
     */
    @Override
    public void setMaximumSize(long bytes) {
        this.maxSize = bytes;
        this.cpSize = maxSize - this.cpOffset;
        if (this.cpSize < (FILE_HEADER_SIZE + RECORD_HEADER_SIZE)) {
            this.cpSize = FILE_HEADER_SIZE + RECORD_HEADER_SIZE;
        }
    }

    /**
     * Set check point offset. When the file pointer position reached to (maxSize-offset), a check point is triggerred.
     */
    @Override
    public void setCheckPointOffset(long offset) {
        this.cpOffset = offset;
        this.cpSize = maxSize - offset;
        if (this.cpSize < (FILE_HEADER_SIZE + RECORD_HEADER_SIZE)) {
            this.cpSize = FILE_HEADER_SIZE + RECORD_HEADER_SIZE;
        }
    }

    /**
     * registeres the checkpoint CB. The callback is triggered when checkpoint is called whether because the system hit a
     * size limit or the application explicitly called checkpoint();
     *
     * @see checkpoint();
     */
    @Override
    public void setCheckPointListener(CheckPointListener cb) {
        this.callback = cb;
    }

    public void writeAsyncRecord(TransactionLogRecord entry) throws IOException {

        // add record to list
        synchronized (recordListMutex) {
            // log("adding record");
            transactionLogRecordList.add(entry);
            // log("notifying recordListMutex");
            recordListMutex.notifyAll();
        }

        // now wait for record to be processed by logger thread
        synchronized (entry) {
            try {
                while (!entry.isWritten()) {
                    // log("waiting for record to be written");
                    entry.wait();
                    // log("woken up from waiting for record to be written");
                }
                // log("record now written");
            } catch (InterruptedException e) {
            }
        }

    }

    private void processTransactionLogRecordList() {
        TransactionLogRecord[] records = null;
        synchronized (recordListMutex) {
            while (transactionLogRecordList.size() == 0 && !closed) {
                try {
                    // log("waiting for transactionLogRecordList to be >0 ");
                    recordListMutex.wait(1000);
                    // log("waking up from recordListMutex.wait()");
                } catch (InterruptedException e) {
                }
            }
            records = new TransactionLogRecord[transactionLogRecordList.size()];
            records = transactionLogRecordList.toArray(records);
            transactionLogRecordList.clear();
        }
        // log("processing " + records.length + " records");

        // there should be something in the list now.

        if (debug) {
            numrecordsArray[sampleNum] = records.length;
            sampleNum++;
            int totalCount = 0;
            if (sampleNum == sampleCount) {
                sampleNum = 0;
                for (int i = 0; i < sampleCount; i++) {
                    totalCount += numrecordsArray[i];
                    System.out.print(numrecordsArray[i] + ",");
                }
                float averageCount = ((float) totalCount) / sampleCount;
                log(" average records in compound txn record = " + averageCount);

            }
        }

        if (records.length == 1) {
            // log("transactionLogRecordList ==1 ");
            // only a single record so just save it normally
            TransactionLogRecord entry = records[0];

            try {
                writeRecord(entry);
            } catch (IOException e) {
                entry.setException(e);

            }

            // wake up waiting thread
            // log("synchronized (entry) ");
            synchronized (entry) {
                // log("notifying entry ");
                entry.setWritten(true);
                entry.notifyAll();
            }

            return;
        }

        try {
            writeCompoundRecord(records);
        } catch (IOException ioe) {
            for (int i = 0; i < records.length; i++) {
                TransactionLogRecord e = records[i];
                e.setException(ioe);
            }
        }

        for (int i = 0; i < records.length; i++) {
            TransactionLogRecord e = records[i];
            // log("synchronized (entry) ");
            synchronized (e) {
                // log("notifying entry ");
                e.setWritten(true);
                e.notifyAll();
            }
        }

    }

    @Override
    public void run() {

        log("run called ");
        while (!closed) {
            try {
                processTransactionLogRecordList();
            } catch (Exception e) {
            }
        }
        log("run ending ");
    }

    void writeCompoundRecord(TransactionLogRecord[] records) throws IOException {
        synchronized (txnLogSyncObj) {
            if (closed) {
                // don't write record if txnLog has been closed
                return;
            }

            int numRecords = records.length;
            // log("writeCompoundRecord list size = "+records.length);

            TransactionLogRecord entry = new FileTransactionLogRecord();
            entry.setType(TransactionLogType.COMPOUND_TRANSACTION);

            // get bytes

            // calculate compoundBody size;
            int compoundBodySize = 4;
            for (int i = 0; i < numRecords; i++) {
                compoundBodySize += 8;
                compoundBodySize += records[i].getBody().length;
            }

            byte[] compoundBody = new byte[compoundBodySize];
            ByteBuffer subBuf = ByteBuffer.wrap(compoundBody);

            subBuf.putInt(numRecords);
            for (int i = 0; i < numRecords; i++) {
                subBuf.putInt(records[i].getType());
                subBuf.putInt(records[i].getBody().length);
                subBuf.put(records[i].getBody());
            }

            entry.setBody(compoundBody);

            // write entry, we need to sync from this point
            // First come first serve
            entry.setCheckPointSequence(checkpointSequence);

            // set timestamp
            entry.setTimestamp(System.currentTimeMillis());

            // set entry sequence. increase 1 after addition.
            entry.setSequence(entrySequence++);

            // 1. calculate record size
            int size = RECORD_HEADER_SIZE + entry.getBody().length;

            // 2. allocate byte buffer
            byte[] bytes = new byte[size];
            ByteBuffer buf = ByteBuffer.wrap(bytes);

            // 3. write record header
            writeRecordHeader(buf, entry);

            // 4. write body
            buf.put(entry.getBody());

            // write (and sync) bytes to disk
            // raf.write(bytes);
            doWrite(bytes);

            // check if we need to notify CP listener.
            if (raf.getFilePointer() > cpSize) {

                // we only call the listener once
                if (this.isListenerCalled == false) {

                    if (debug) {
                        log("calling check point listener, fpointer: " + raf.getFilePointer());
                    }

                    callback.checkpoint();

                    // set flag to true so that we only call the listener once.
                    this.isListenerCalled = true;
                }
            }

            // last record added to the log file
            this.lastEntry = entry;
            // log("wroteCompoundRecord list ");
        }
    }

    /*
     * public void write(TransactionLogRecord entry) throws IOException {
     *
     * synchronized (txnLogSyncObj) {
     *
     * if (isFileCorrupted) { throw new IllegalStateException("File is corrupted. You must reset the log file to
     * continue."); }
     *
     * if (playBackRequired) { throw new IllegalStateException("File not synced. You must call Iterator to play back log
     * file."); }
     *
     * if (callback == null) { throw new IllegalStateException("Check point listener not set. You must set a
     * CheckPointListener before writing TransactionLogRecords."); } // write entry, we need to sync from this point //
     * First come first serve entry.setCheckPointSequence(checkpointSequence);
     *
     * //set timestamp entry.setTimestamp (System.currentTimeMillis ());
     *
     * //set entry sequence. increase 1 after addition. entry.setSequence (entrySequence++); // 1. calculate record size int
     * size = RECORD_HEADER_SIZE + entry.getBody().length; // 2. allocate byte buffer byte[] bytes = new byte[size];
     * ByteBuffer buf = ByteBuffer.wrap(bytes); // 3. write record header writeRecordHeader(buf, entry); // 4. write body
     * buf.put(entry.getBody()); // write (and sync) bytes to disk //raf.write(bytes); doWrite (bytes);
     *
     * //check if we need to notify CP listener. if (raf.getFilePointer() > cpSize) {
     *
     * //we only call the listener once if ( this.isListenerCalled == false) {
     *
     * if (debug) { log ("calling check point listener, fpointer: " + raf.getFilePointer ()); }
     *
     * callback.checkpoint();
     *
     * //set flag to true so that we only call the listener once. this.isListenerCalled = true; } }
     *
     * //last record added to the log file this.lastEntry = entry; } }
     *
     */
    @Override
    public void write(TransactionLogRecord entry) throws IOException {
        if (doAsyncWrites) {
            writeAsyncRecord(entry);
        } else {
            writeRecord(entry);
        }
    }

    public void writeRecord(TransactionLogRecord entry) throws IOException {

        synchronized (txnLogSyncObj) {
            if (closed) {
                // don't attempt to write record if txnLog has been closed
                return;
            }
            if (isFileCorrupted) {
                throw new IllegalStateException("File is corrupted. You must reset the log file to continue.");
            }

            if (playBackRequired) {
                throw new IllegalStateException("File not synced.  You must call Iterator to play back log file.");
            }

            if (callback == null) {
                throw new IllegalStateException("Check point listener not set. You must set a CheckPointListener before writing TransactionLogRecords.");
            }

            // write entry, we need to sync from this point
            // First come first serve
            entry.setCheckPointSequence(checkpointSequence);

            // set timestamp
            entry.setTimestamp(System.currentTimeMillis());

            // set entry sequence. increase 1 after addition.
            entry.setSequence(entrySequence++);

            // 1. calculate record size
            int size = RECORD_HEADER_SIZE + entry.getBody().length;

            // 2. allocate byte buffer
            byte[] bytes = new byte[size];
            ByteBuffer buf = ByteBuffer.wrap(bytes);

            // 3. write record header
            writeRecordHeader(buf, entry);

            // 4. write body
            buf.put(entry.getBody());

            // write (and sync) bytes to disk
            // raf.write(bytes);
            doWrite(bytes);

            // check if we need to notify CP listener.
            if (raf.getFilePointer() > cpSize) {

                // we only call the listener once
                if (this.isListenerCalled == false) {

                    if (debug) {
                        log("calling check point listener, fpointer: " + raf.getFilePointer());
                    }

                    callback.checkpoint();

                    // set flag to true so that we only call the listener once.
                    this.isListenerCalled = true;
                }
            }

            // last record added to the log file
            this.lastEntry = entry;
        }
    }

    /**
     * header size - 32 bytes.
     *
     * @param buf
     * @param entry XXX: NEED SEQUENCE NUMBER?
     */
    private void writeRecordHeader(ByteBuffer buf, TransactionLogRecord entry) {

        // 1. record magic number
        buf.putInt(RECORD_MAGIC_NUMBER); // 0-3

        // 2. record type
        buf.putInt(entry.getType());// 4-7

        // 3. body size
        buf.putInt(entry.getBody().length);// 8-11

        // 4. timestamp
        buf.putLong(entry.getTimestamp());// 12-19

        // 5. entry seq
        buf.putLong(entry.getSequence()); // 20-28

        // 6. check point sequence
        buf.putLong(entry.getCheckPointSequence()); // 29-36

        // 7. calculate and write body check sum
        long value = this.calculateCheckSum(entry.getBody());
        buf.putLong(value); // 37-44, check sum

        // 8. header reserve
        buf.putInt(RECORD_HEADER_RESERVE);// 45-48
    }

    /**
     * Writes bytes to the file.
     */
    private void doWrite(byte[] bytes) throws IOException {

        raf.write(bytes);

        if (this.useFileChannelSync && synch) {
            // this.fchannel.force(false);
            raf.getFD().sync();
        }

    }

    long calculateCheckSum(byte[] body) {

        long value = calculateCheckSum(body, 0, body.length);

        return value;
    }

    /**
     * Calculate check sum. A simple perf showed that average time spent here is about 0.001
     * (total-checksum-time/total-time) when writing 2000 records to a synced file (hard drive cache off).
     *
     * @param body
     * @param offset
     * @param length
     * @return
     */
    long calculateCheckSum(byte[] body, int offset, int length) {

        long value = -1;

        synchronized (txnLogSyncObj) {
            checksumEngine.update(body, offset, length);
            value = checksumEngine.getValue();
            checksumEngine.reset();
        }

        return value;
    }

    /**
     *
     * @return the next check point sequence number.
     */
    @Override
    public TransactionLogRecord checkpoint() throws IOException {

        synchronized (this.txnLogSyncObj) {

            long pos = raf.getFilePointer();

            if (pos > cpSize) {
                // rewind -- update file header only.
                writeFileHeader(FILE_STATUS_CHK_POINT_UPDATED, FILE_HEADER_SIZE);
            } else {
                // update file header only
                writeFileHeader(FILE_STATUS_CHK_POINT_UPDATED, pos);
                raf.seek(pos);
            }

            // reset this flag
            this.isListenerCalled = false;

            return this.lastEntry;
        }
    }

    /**
     * iterates from the last checkpoint
     */
    @Override
    public Iterator iterator() throws IOException {

        Iterator it = new FileLogRecordIterator(this);

        return it;
    }

    /**
     * Rewind/Refresh the log file.
     *
     * This method should be called if one of the following conditions occurs.
     * <p>
     * 1. When broker starts up, and detects that playback is required. The broker should call the iterator() method and
     * playback the transaction entries from the iterator API. The broker then calls reset to clear the state of the
     * transaction log file.
     * <p>
     * 2.
     */
    @Override
    public void reset() throws IOException {

        log("Reseting txn log file ...");

        synchronized (this.txnLogSyncObj) {

            if (this.doFileBackup) {
                this.backupLogFile();
            }

            if (this.isFileCorrupted) {
                this.initNewFile();
            } else {
                writeFileHeader(FILE_STATUS_CHK_POINT_UPDATED, FILE_HEADER_SIZE);
            }

            /**
             * reset check point position.
             */
            this.checkPointPosition = FILE_HEADER_SIZE;

            this.playBackRequired = false;
            this.isFileCorrupted = false;
            this.isListenerCalled = false;

        }
    }

    /**
     * The last entry added to the log file.
     *
     * XXX: only works when the txn log is in writing/inserting mode.
     */
    @Override
    public TransactionLogRecord getLastEntry() {
        synchronized (this.txnLogSyncObj) {
            return this.lastEntry;
        }
    }

    @Override
    public void close(boolean clean) throws IOException {
        if (clean) {
            close();
            return;
        }

        synchronized (this.txnLogSyncObj) {
            // close file.
            raf.close();
            closed = true;
        }
    }

    /**
     * 1. set SHUTDOWN_NORMAL. 2. set cpPosition to current file position.
     */
    @Override
    public void close() throws IOException {
        synchronized (this.txnLogSyncObj) {

            // get current file pointer
            // long pos = raf.getFilePointer();
            raf.getFilePointer();

            // set file status and cpPosition.
            writeFileHeader(FILE_STATUS_SHUTDOWN_NORMAL, FILE_HEADER_SIZE);

            // close file.
            raf.close();

            closed = true;
        }
    }

    /**
     * XXX chiaming; Not required to sync the class since we have a cp sequence.
     */
    @Override
    public TransactionLogRecord newTransactionLogRecord() {
        return new FileTransactionLogRecord();
    }

    RandomAccessFile getRAF() {
        return this.raf;
    }

    long getCPPosition() {
        return this.checkPointPosition;
    }

    public synchronized long getCPSequence() {
        return this.checkpointSequence;
    }

    private void backupLogFile() throws IOException {

        synchronized (this.txnLogSyncObj) {

            /**
             * Get txn log file name
             */
            String txnlogName = file.getCanonicalPath();

            this.deleteBackUpFile(txnlogName);

            // rename the current file
            copyFile(txnlogName);
        }

    }

    /**
     * copy txnlogName contents to txnlogName.1
     *
     */
    private void copyFile(String txnlogName) throws IOException {

        String bname = txnlogName + TXNLOG_BACKUP_EXT;

        File bfile = new File(bname);

        if (bfile.exists()) {
            throw new IOException("Cannot backup txnlog.  You must remove the back up file to continue: " + bname);
        }

        long savedPosition = raf.getFilePointer();

        if (this.useFileChannelSync == false) {
            fchannel = raf.getChannel();
        }

        fchannel.position(0);

        FileChannel fc2 = new FileOutputStream(bfile).getChannel();

        fc2.transferFrom(fchannel, 0, fchannel.size());

        fc2.close();

        if (this.useFileChannelSync == false) {

            fchannel.close();
            raf.close();

            // reopen the file.
            raf = new RandomAccessFile(file, fileMode);

        }

        raf.seek(savedPosition);
    }

    /**
     * delete the old back up file if exists.
     *
     */
    private void deleteBackUpFile(String txnLogName) throws IOException {

        // 1. remove txnLogName.2 file if exists.
        String backupName2 = txnLogName + TXNLOG_BACKUP_EXT;

        File bfile2 = new File(backupName2);

        if (bfile2.exists()) {
            bfile2.delete();
        }

        // 2. move txnLogName.1 to txnLogName.2

        // String backupName1 = txnLogName +".1";
        // File bfile1 = new File (backupName1);
        // if (bfile1.exists ()) {
        // bfile1.renameTo (bfile2);
        // }

    }

    @Override
    public boolean playBackRequired() {
        return this.playBackRequired;
    }

    private void log(String msg) {
        if (debug) {
            System.out.println(new Date() + " " + Thread.currentThread() + ": " + msg);
        }
    }

    public long getExistingAppCookie() {
        return existingAppCookie;
    }

}
