package net.onrc.onos.core.datastore.ramcloud;

import java.io.File;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;
import java.util.concurrent.ConcurrentHashMap;

import net.onrc.onos.core.datastore.IKVClient;
import net.onrc.onos.core.datastore.IKVTable;
import net.onrc.onos.core.datastore.IKVTable.IKVEntry;
import net.onrc.onos.core.datastore.IKVTableID;
import net.onrc.onos.core.datastore.IMultiEntryOperation;
import net.onrc.onos.core.datastore.IMultiEntryOperation.STATUS;
import net.onrc.onos.core.datastore.ObjectDoesntExistException;
import net.onrc.onos.core.datastore.ObjectExistsException;
import net.onrc.onos.core.datastore.WrongVersionException;
import net.onrc.onos.core.datastore.internal.IModifiableMultiEntryOperation;
import net.onrc.onos.core.datastore.ramcloud.RCTable.Entry;
import net.onrc.onos.core.datastore.utils.ByteArrayUtil;

import org.apache.commons.configuration.Configuration;
import org.apache.commons.configuration.ConfigurationException;
import org.apache.commons.configuration.PropertiesConfiguration;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import edu.stanford.ramcloud.JRamCloud;
import edu.stanford.ramcloud.JRamCloud.MultiReadObject;
import edu.stanford.ramcloud.JRamCloud.MultiWriteObject;
import edu.stanford.ramcloud.JRamCloud.MultiWriteRspObject;
import edu.stanford.ramcloud.JRamCloud.RejectRules;
import edu.stanford.ramcloud.JRamCloud.RejectRulesException;
import edu.stanford.ramcloud.JRamCloud.TableEnumerator2;

/**
 * RAMCloud implementation of datastore IKVClient.
 */
public class RCClient implements IKVClient {

    private static final Logger log = LoggerFactory.getLogger(RCClient.class);

    private static final String DEFAULT_LOCATOR = "zk:localhost:2181";
    private static final String DEFAULT_CLUSTERNAME = "ONOS-RC";

    private static final String DB_CONFIG_FILE = "conf/ramcloud.conf";
    private static final Configuration CONFIG = getConfiguration();
    private static final String CLUSTER_NAME = getClusterName(CONFIG);
    private static final String LOCATOR = getLocator(CONFIG);

    // FIXME These constants should be defined by JRamCloud
    /**
     * Constant defined in RAMCloud's Status.h.
     */
    public static final int STATUS_OK = 0;

    /**
     * Maximum number of Multi-Read operations which can be executed in
     * one RPC call.
     *
     *  There are multiple factors which determines this limit.
     *  - RAMCloud RPC size limit of 8MB.
     *  - JNI implementation store the RPC result on stack.
     *    (Increasing the stack-size limit will help relaxing this limit.)
     */
    public static final int MAX_MULTI_READS = Math.max(1, Integer
            .parseInt(System.getProperty("ramcloud.max_multi_reads", "400")));

    /**
     * Maximum number of Multi-Write operations which can be executed in
     * one RPC call.
     *
     *  There are multiple factors which determines this limit.
     *  - RAMCloud RPC size limit of 8MB.
     *  - JNI implementation store the RPC result on stack.
     *    (Increasing the stack-size limit will help relaxing this limit.)
     */
    public static final int MAX_MULTI_WRITES = Math.max(1, Integer
            .parseInt(System.getProperty("ramcloud.max_multi_writes", "800")));

    private static final ThreadLocal<JRamCloud> TLS_RC_CLIENT = new ThreadLocal<JRamCloud>() {
        @Override
        protected JRamCloud initialValue() {
            return new JRamCloud(LOCATOR, CLUSTER_NAME);
        }
    };

    /**
     * @return JRamCloud instance intended to be used only within the
     * SameThread.
     * @note Do not store the returned instance in a member variable, etc. which
     * may be accessed later by another thread.
     */
    static JRamCloud getJRamCloudClient() {
        return TLS_RC_CLIENT.get();
    }

    // Currently RCClient is state-less
    private static final RCClient THE_INSTANCE = new RCClient();

    /**
     * Default constructor.
     */
    protected RCClient() {
        log.info("locator: {}, cluster name: {}", LOCATOR, CLUSTER_NAME);
    }

    /**
     * Gets a DataStoreClient implemented on RAMCloud.
     *
     * @return RCClient
     */
    public static RCClient getClient() {
        return THE_INSTANCE;
    }

    /**
     * Gets the {@link Configuration} instance.
     *
     * @return Configuration
     */
    private static final Configuration getConfiguration() {
        final File configFile = new File(
                System.getProperty("ramcloud.config.path",
                                    DB_CONFIG_FILE));
        return getConfiguration(configFile);
    }

    /**
     * Gets the {@link Configuration} instance from properties file.
     *
     * @param configFile properties file
     * @return Configuration
     */
    private static final Configuration getConfiguration(final File configFile) {
        if (configFile == null) {
            throw new IllegalArgumentException("Need to specify a configuration file or storage directory");
        }

        if (!configFile.isFile()) {
            throw new IllegalArgumentException("Location of configuration must be a file");
        }

        try {
            PropertiesConfiguration conf = new PropertiesConfiguration();
            // stop parsing commas in property value
            conf.setDelimiterParsingDisabled(true);
            conf.load(configFile);
            return conf;
        } catch (ConfigurationException e) {
            throw new IllegalArgumentException("Could not load configuration at: " + configFile, e);
        }
    }

    /**
     * Gets the RAMCloud external storage locator from configuration file.
     *
     * @param configuration input
     * @return RAMCloud external storage locator string
     */
    private static String getLocator(final Configuration configuration) {

        final String locator = configuration.getString("ramcloud.locator");
        if (locator != null) {
            return locator;
        }

        // TODO Stop reading obsolete coordinatorIp, etc. once we're ready.
        final String coordinatorIp = configuration.getString("ramcloud.coordinatorIp");
        if (coordinatorIp == null) {
            return DEFAULT_LOCATOR;
        }

        final String coordinatorPort = configuration.getString("ramcloud.coordinatorPort");
        if (coordinatorPort == null) {
            return DEFAULT_LOCATOR;
        }

        final String coordinatorURL = coordinatorIp + "," + coordinatorPort;
        return coordinatorURL;
    }

    /**
     * Gets the RAMCloud clusterName from configuration file.
     *
     * @param configuration input
     * @return RAMCloud clusterName
     */
    private static String getClusterName(final Configuration configuration) {
        return configuration.getString("ramcloud.clusterName",
                                       DEFAULT_CLUSTERNAME);
    }

    @Override
    public IMultiEntryOperation createOp(IKVTableID tableId, byte[] key, byte[] value) {
        return RCMultiEntryOperation.create(tableId, key, value);
    }

    /**
     * @param tableId RCTableID instance
     */
    @Override
    public long create(IKVTableID tableId, byte[] key, byte[] value)
            throws ObjectExistsException {

        RCTableID rcTableId = (RCTableID) tableId;
        JRamCloud rcClient = RCClient.getJRamCloudClient();

        RejectRules rules = new RejectRules();
        rules.rejectIfExists();

        try {
            return rcClient.write(rcTableId.getTableID(), key, value, rules);
        } catch (JRamCloud.ObjectExistsException e) {
            throw new ObjectExistsException(rcTableId, key, e);
        } catch (JRamCloud.RejectRulesException e) {
            log.error("Unexpected RejectRulesException", e);
            return JRamCloud.VERSION_NONEXISTENT;
        }
    }

    @Override
    public IMultiEntryOperation forceCreateOp(IKVTableID tableId, byte[] key, byte[] value) {
        return RCMultiEntryOperation.forceCreate(tableId, key, value);
    }

    @Override
    public long forceCreate(IKVTableID tableId, byte[] key, byte[] value) {
        RCTableID rcTableId = (RCTableID) tableId;
        JRamCloud rcClient = RCClient.getJRamCloudClient();

        long updatedVersion = rcClient.write(rcTableId.getTableID(), key, value);
        return updatedVersion;
    }

    @Override
    public IMultiEntryOperation readOp(IKVTableID tableId, byte[] key) {
        return RCMultiEntryOperation.read(tableId, key);
    }

    @Override
    public IKVEntry read(IKVTableID tableId, byte[] key)
            throws ObjectDoesntExistException {

        RCTableID rcTableId = (RCTableID) tableId;
        JRamCloud rcClient = RCClient.getJRamCloudClient();

        RejectRules rules = new RejectRules();
        rules.rejectIfDoesntExists();
        try {
            JRamCloud.Object rcObj = rcClient.read(rcTableId.getTableID(), key, rules);
            return new Entry(rcObj.key, rcObj.value, rcObj.version);
        } catch (JRamCloud.ObjectDoesntExistException e) {
            throw new ObjectDoesntExistException(rcTableId, key, e);
        } catch (JRamCloud.RejectRulesException e) {
            log.error("Unexpected RejectRulesException", e);
            return null;
        }
    }

    @Override
    public IMultiEntryOperation updateOp(IKVTableID tableId, byte[] key, byte[] value, long version) {
        return RCMultiEntryOperation.update(tableId, key, value, version);
    }

    @Override
    public long update(IKVTableID tableId, byte[] key, byte[] value,
                       long version) throws ObjectDoesntExistException,
            WrongVersionException {

        RCTableID rcTableId = (RCTableID) tableId;
        JRamCloud rcClient = RCClient.getJRamCloudClient();

        RejectRules rules = new RejectRules();
        rules.rejectIfDoesntExists();
        rules.rejectIfNeVersion(version);

        try {
            return rcClient.write(rcTableId.getTableID(), key, value, rules);
        } catch (JRamCloud.ObjectDoesntExistException e) {
            throw new ObjectDoesntExistException(rcTableId, key, e);
        } catch (JRamCloud.WrongVersionException e) {
            throw new WrongVersionException(rcTableId, key, version, e);
        } catch (JRamCloud.RejectRulesException e) {
            log.error("Unexpected RejectRulesException", e);
            return JRamCloud.VERSION_NONEXISTENT;
        }
    }


    @Override
    public long update(IKVTableID tableId, byte[] key, byte[] value)
            throws ObjectDoesntExistException {

        RCTableID rcTableId = (RCTableID) tableId;
        JRamCloud rcClient = RCClient.getJRamCloudClient();

        RejectRules rules = new RejectRules();
        rules.rejectIfDoesntExists();

        try {
            return rcClient.write(rcTableId.getTableID(), key, value, rules);
        } catch (JRamCloud.ObjectDoesntExistException e) {
            throw new ObjectDoesntExistException(rcTableId, key, e);
        } catch (JRamCloud.RejectRulesException e) {
            log.error("Unexpected RejectRulesException", e);
            return JRamCloud.VERSION_NONEXISTENT;
        }
    }

    @Override
    public IMultiEntryOperation deleteOp(IKVTableID tableId, byte[] key, byte[] value, long version) {
        return RCMultiEntryOperation.delete(tableId, key, value, version);
    }

    @Override
    public long delete(IKVTableID tableId, byte[] key, long version)
            throws ObjectDoesntExistException, WrongVersionException {

        RCTableID rcTableId = (RCTableID) tableId;
        JRamCloud rcClient = RCClient.getJRamCloudClient();

        RejectRules rules = new RejectRules();
        rules.rejectIfDoesntExists();
        rules.rejectIfNeVersion(version);

        try {
            return rcClient.remove(rcTableId.getTableID(), key, rules);
        } catch (JRamCloud.ObjectDoesntExistException e) {
            throw new ObjectDoesntExistException(rcTableId, key, e);
        } catch (JRamCloud.WrongVersionException e) {
            throw new WrongVersionException(rcTableId, key, version, e);
        } catch (JRamCloud.RejectRulesException e) {
            log.error("Unexpected RejectRulesException", e);
            return JRamCloud.VERSION_NONEXISTENT;
        }
    }

    @Override
    public IMultiEntryOperation forceDeleteOp(IKVTableID tableId, byte[] key) {
        return RCMultiEntryOperation.forceDelete(tableId, key);
    }

    @Override
    public long forceDelete(IKVTableID tableId, byte[] key) {
        RCTableID rcTableId = (RCTableID) tableId;
        JRamCloud rcClient = RCClient.getJRamCloudClient();
        final long removedVersion = rcClient.remove(rcTableId.getTableID(), key);
        return removedVersion;
    }

    @Override
    public Iterable<IKVEntry> getAllEntries(IKVTableID tableId) {
        return new RCTableEntryIterable((RCTableID) tableId);
    }

    static class RCTableEntryIterable implements Iterable<IKVEntry> {
        private final RCTableID tableId;

        public RCTableEntryIterable(final RCTableID tableId) {
            this.tableId = tableId;
        }

        @Override
        public Iterator<IKVEntry> iterator() {
            return new RCClient.RCTableIterator(tableId);
        }
    }

    public static class RCTableIterator implements Iterator<IKVEntry> {
        private final RCTableID tableId;
        protected final TableEnumerator2 enumerator;
        private JRamCloud.Object last;

        public RCTableIterator(final RCTableID tableId) {
            this.tableId = tableId;
            this.enumerator = getJRamCloudClient().new TableEnumerator2(tableId.getTableID());
            this.last = null;
        }

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

        @Override
        public RCTable.Entry next() {
            last = enumerator.next();
            return new RCTable.Entry(last.key, last.value, last.version);
        }

        @Override
        public void remove() {
            if (last != null) {
                getJRamCloudClient();
                JRamCloud rcClient = RCClient.getJRamCloudClient();

                RejectRules rules = new RejectRules();
                rules.rejectIfNeVersion(last.version);
                try {
                    rcClient.remove(tableId.getTableID(), last.key, rules);
                } catch (RejectRulesException e) {
                    log.trace("remove failed", e);
                }
                last = null;
            }
        }
    }

    @Override
    public boolean multiRead(final Collection<IMultiEntryOperation> ops) {

        if (ops.size() <= MAX_MULTI_READS && ops instanceof ArrayList) {
            @SuppressWarnings({ "unchecked", "rawtypes" })
            final ArrayList<RCMultiEntryOperation> arrays = (ArrayList) ops;
            return multiReadInternal(arrays);
        }

        boolean failExists = false;

        ArrayList<RCMultiEntryOperation> req = new ArrayList<>();
        Iterator<IMultiEntryOperation> it = ops.iterator();
        while (it.hasNext()) {

            req.add((RCMultiEntryOperation) it.next());

            if (req.size() >= MAX_MULTI_READS) {
                // dispatch multiRead
                failExists |= multiReadInternal(req);
                req.clear();
            }
        }

        if (!req.isEmpty()) {
            // dispatch multiRead
            failExists |= multiReadInternal(req);
            req.clear();
        }

        return failExists;
    }

    @Override
    public boolean multiWrite(final List<IMultiEntryOperation> ops) {

        if (ops.size() <= MAX_MULTI_WRITES && ops instanceof ArrayList) {
            @SuppressWarnings({ "unchecked", "rawtypes" })
            final ArrayList<RCMultiEntryOperation> arrays = (ArrayList) ops;
            return multiWriteInternal(arrays);
        }

        boolean failExists = false;

        ArrayList<RCMultiEntryOperation> req = new ArrayList<>();
        Iterator<IMultiEntryOperation> it = ops.iterator();
        while (it.hasNext()) {

            req.add((RCMultiEntryOperation) it.next());

            if (req.size() >= MAX_MULTI_WRITES) {
                // dispatch multiWrite
                failExists |= multiWriteInternal(req);
                req.clear();
            }
        }

        if (!req.isEmpty()) {
            // dispatch multiWrite
            failExists |= multiWriteInternal(req);
            req.clear();
        }

        return failExists;
    }

    @Override
    public boolean multiDelete(final Collection<IMultiEntryOperation> ops) {

        // TODO implement multiRemove JNI, etc. if we need performance

        boolean failExists = false;
        JRamCloud rcClient = getJRamCloudClient();

        for (IMultiEntryOperation iop : ops) {
            RCMultiEntryOperation op = (RCMultiEntryOperation) iop;
            switch (op.getOperation()) {
                case DELETE:
                    RejectRules rules = new RejectRules();
                    rules.rejectIfDoesntExists();
                    rules.rejectIfNeVersion(op.getVersion());

                    try {
                        final long removedVersion = rcClient.remove(op.tableId.getTableID(), op.entry.getKey(), rules);
                        op.entry.setVersion(removedVersion);
                        op.status = STATUS.SUCCESS;
                    } catch (JRamCloud.ObjectDoesntExistException | JRamCloud.WrongVersionException e) {
                        log.error("Failed to remove key:" + ByteArrayUtil.toHexStringBuilder(op.entry.getKey(), "") + " from tableID:" + op.tableId, e);
                        failExists = true;
                        op.status = STATUS.FAILED;
                    } catch (JRamCloud.RejectRulesException e) {
                        log.error("Failed to remove key:" + ByteArrayUtil.toHexStringBuilder(op.entry.getKey(), "") + " from tableID:" + op.tableId, e);
                        failExists = true;
                        op.status = STATUS.FAILED;
                    }
                    break;

                case FORCE_DELETE:
                    final long removedVersion = rcClient.remove(op.tableId.getTableID(), op.entry.getKey());
                    if (removedVersion != VERSION_NONEXISTENT) {
                        op.entry.setVersion(removedVersion);
                        op.status = STATUS.SUCCESS;
                    } else {
                        log.error("Failed to remove key:{} from tableID:{}", ByteArrayUtil.toHexStringBuilder(op.entry.getKey(), ""), op.tableId);
                        failExists = true;
                        op.status = STATUS.FAILED;
                    }
                    break;

                default:
                    log.error("Invalid operation {} specified on multiDelete", op.getOperation());
                    failExists = true;
                    op.status = STATUS.FAILED;
                    break;
            }
        }
        return failExists;
    }

    private boolean multiReadInternal(final ArrayList<RCMultiEntryOperation> ops) {
        boolean failExists = false;
        JRamCloud rcClient = RCClient.getJRamCloudClient();

        final int reqs = ops.size();

        MultiReadObject multiReadObjects = new MultiReadObject(reqs);

        // setup multi-read operation objects
        for (int i = 0; i < reqs; ++i) {
            IMultiEntryOperation op = ops.get(i);
            multiReadObjects.setObject(i, ((RCTableID) op.getTableId()).getTableID(), op.getKey());
        }

        // execute
        JRamCloud.Object[] results = rcClient.multiRead(multiReadObjects.tableId, multiReadObjects.key, multiReadObjects.keyLength, reqs);
        if (results.length != reqs) {
            log.error("multiRead returned unexpected number of results. (requested:{}, returned:{})", reqs, results.length);
            failExists = true;
        }

        for (int i = 0; i < results.length; ++i) {
            IModifiableMultiEntryOperation op = ops.get(i);
            if (results[i] == null) {
                // Logging as error gets too noisy when doing speculative read.
                log.trace("MultiRead error {}, {}", op.getTableId(), op);
                failExists = true;
                op.setStatus(STATUS.FAILED);
                continue;
            }
            assert (Arrays.equals(results[i].key, op.getKey()));

            op.setValue(results[i].value, results[i].version);
            if (results[i].version == JRamCloud.VERSION_NONEXISTENT) {
                failExists = true;
                op.setStatus(STATUS.FAILED);
            } else {
                op.setStatus(STATUS.SUCCESS);
            }
        }

        return failExists;
    }

    private boolean multiWriteInternal(final ArrayList<RCMultiEntryOperation> ops) {
        boolean failExists = false;
        JRamCloud rcClient = RCClient.getJRamCloudClient();

        final int reqs = ops.size();

        MultiWriteObject multiWriteObjects = new MultiWriteObject(reqs);

        for (int i = 0; i < reqs; ++i) {

            IModifiableMultiEntryOperation op = ops.get(i);
            RejectRules rules = new RejectRules();

            switch (op.getOperation()) {
                case CREATE:
                    rules.rejectIfExists();
                    break;
                case FORCE_CREATE:
                    // no reject rule
                    break;
                case UPDATE:
                    rules.rejectIfDoesntExists();
                    rules.rejectIfNeVersion(op.getVersion());
                    break;

                default:
                    log.error("Invalid operation {} specified on multiWriteInternal", op.getOperation());
                    failExists = true;
                    op.setStatus(STATUS.FAILED);
                    return failExists;
            }
            multiWriteObjects.setObject(i, ((RCTableID) op.getTableId()).getTableID(), op.getKey(), op.getValue(), rules);
        }

        MultiWriteRspObject[] results = rcClient.multiWrite(multiWriteObjects.tableId, multiWriteObjects.key, multiWriteObjects.keyLength, multiWriteObjects.value, multiWriteObjects.valueLength, ops.size(), multiWriteObjects.rules);
        if (results.length != reqs) {
            log.error("multiWrite returned unexpected number of results. (requested:{}, returned:{})", reqs, results.length);
            failExists = true;
        }

        for (int i = 0; i < results.length; ++i) {
            IModifiableMultiEntryOperation op = ops.get(i);

            if (results[i] != null
                    && results[i].getStatus() == RCClient.STATUS_OK) {
                op.setStatus(STATUS.SUCCESS);
                op.setVersion(results[i].getVersion());
            } else {
                op.setStatus(STATUS.FAILED);
                failExists = true;
            }
        }

        return failExists;
    }

    private static final ConcurrentHashMap<String, RCTable> TABLES = new ConcurrentHashMap<>();

    @Override
    public IKVTable getTable(final String tableName) {
        RCTable table = TABLES.get(tableName);
        if (table == null) {
            RCTable newTable = new RCTable(tableName);
            RCTable existingTable = TABLES
                    .putIfAbsent(tableName, newTable);
            if (existingTable != null) {
                return existingTable;
            } else {
                return newTable;
            }
        }
        return table;
    }

    @Override
    public void dropTable(IKVTable table) {
        JRamCloud rcClient = RCClient.getJRamCloudClient();
        rcClient.dropTable(table.getTableId().getTableName());
        TABLES.remove(table.getTableId().getTableName());
    }

    static final long VERSION_NONEXISTENT = JRamCloud.VERSION_NONEXISTENT;

    @Override
    public long getVersionNonexistant() {
        return VERSION_NONEXISTENT;
    }

    @Override
    public void createCounter(final IKVTableID tableId, final byte[] key,
            final long initialValue)
            throws ObjectExistsException {

        ByteBuffer valueBytes = ByteBuffer.allocate(8)
                .order(ByteOrder.LITTLE_ENDIAN).putLong(initialValue);
        valueBytes.flip();
        final long version = create(tableId, key, valueBytes.array());
        if (log.isTraceEnabled()) {
            log.trace("Created counter {}-{}={}@{}",
                    tableId, ByteArrayUtil.toHexStringBuilder(key, ":"),
                    initialValue, version);
        }
    }

    @Override
    public void setCounter(final IKVTableID tableId, final byte[] key,
            final long value) {

        ByteBuffer valueBytes = ByteBuffer.allocate(8)
                .order(ByteOrder.LITTLE_ENDIAN).putLong(value);
        valueBytes.flip();

        final long version = forceCreate(tableId, key, valueBytes.array());
        if (log.isTraceEnabled()) {
            log.trace("set counter {}-{}={}@{}",
                    tableId, ByteArrayUtil.toHexStringBuilder(key, ":"),
                    value, version);
        }
    }

    @Override
    public long incrementCounter(final IKVTableID tableId, final byte[] key,
            final long incrementValue) {

        RCTableID rcTableId = (RCTableID) tableId;
        JRamCloud rcClient = RCClient.getJRamCloudClient();

        try {
            return rcClient.increment(rcTableId.getTableID(), key, incrementValue);
        } catch (JRamCloud.ObjectDoesntExistException e) {
            log.warn("Counter {}-{} was not present",
                    tableId,
                    ByteArrayUtil.toHexStringBuilder(key, ":"));
            try {
                // creating counter initialized to 0
                createCounter(rcTableId, key, 0L);
            } catch (ObjectExistsException e1) {
                // someone concurrently created it
                log.debug("Counter {}-{} seemed to be concurrently created.",
                        tableId,
                        ByteArrayUtil.toHexStringBuilder(key, ":"));
            }
            try {
                return rcClient.increment(rcTableId.getTableID(), key, incrementValue);
            } catch (edu.stanford.ramcloud.JRamCloud.ObjectDoesntExistException e1) {
                log.error("Should never happen");
                throw new IllegalStateException("Created counter disappeared.");
            }
        }
    }

    @Override
    public void destroyCounter(final IKVTableID tableId, final byte[] key) {

        RCTableID rcTableId = (RCTableID) tableId;
        JRamCloud rcClient = RCClient.getJRamCloudClient();

        rcClient.remove(rcTableId.getTableID(), key);
    }

    @Override
    public long getCounter(IKVTableID tableId, byte[] key)
            throws ObjectDoesntExistException {

        IKVEntry entry = read(tableId, key);
        ByteBuffer counter = ByteBuffer.wrap(entry.getValue()).order(ByteOrder.LITTLE_ENDIAN);
        return counter.getLong();
    }
}