package net.onrc.onos.core.datagrid;

import java.util.Collection;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.Set;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.concurrent.TimeUnit;

import net.onrc.onos.core.util.serializers.KryoFactory;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.esotericsoftware.kryo.Kryo;
import com.esotericsoftware.kryo.io.Input;
import com.esotericsoftware.kryo.io.Output;
import com.hazelcast.core.EntryEvent;
import com.hazelcast.core.EntryListener;
import com.hazelcast.core.HazelcastInstance;
import com.hazelcast.core.IMap;

/**
 * A datagrid event channel that uses Hazelcast as a datagrid.
 *
 * @param <K> The class type of the key.
 * @param <V> The class type of the value.
 */
public class HazelcastEventChannel<K, V> implements IEventChannel<K, V> {
    private static final Logger log =
            LoggerFactory.getLogger(HazelcastEventChannel.class);

    private final HazelcastInstance hazelcastInstance; // The Hazelcast instance
    private final String channelName;        // The event channel name
    private final Class<K> typeK;            // The class type of the key
    private final Class<V> typeV;            // The class type of the value
    private IMap<K, byte[]> channelMap;    // The Hazelcast channel map
    // The channel listeners
    private final CopyOnWriteArrayList<IEventChannelListener<K, V>> listeners =
            new CopyOnWriteArrayList<>();

    // The map entry listener
    private final EntryListener<K, byte[]> mapEntryListener = new MapEntryListener();
    private String mapListenerId;    // The map listener ID

    // TODO: We should use a single global KryoFactory instance
    private final KryoFactory kryoFactory = new KryoFactory();

    // Maximum serialized event size
    private static final int MAX_BUFFER_SIZE = 64 * 1024;

    /**
     * Constructor for a given event channel name.
     *
     * @param newHazelcastInstance the Hazelcast instance to use.
     * @param newChannelName       the event channel name.
     * @param newTypeK             the type of the Key in the Key-Value store.
     * @param newTypeV             the type of the Value in the Key-Value store.
     */
    public HazelcastEventChannel(HazelcastInstance newHazelcastInstance,
                                 String newChannelName, Class<K> newTypeK,
                                 Class<V> newTypeV) {
        hazelcastInstance = newHazelcastInstance;
        channelName = newChannelName;
        typeK = newTypeK;
        typeV = newTypeV;
    }

    /**
     * Verify the key and value types of a channel.
     *
     * @param typeKToVerify the type of the key to verify.
     * @param typeVToVerify the type of the value to verify.
     * @return true if the key and value types of the channel match,
     * otherwise false.
     */
    @Override
    public boolean verifyKeyValueTypes(Class<?> typeKToVerify,
                                       Class<?> typeVToVerify) {
        return (typeK.equals(typeKToVerify)) && (typeV.equals(typeVToVerify));
    }

    /**
     * Cleanup and destroy the channel.
     */
    @Override
    protected void finalize() {
        shutdown();
    }

    /**
     * Startup the channel operation.
     */
    @Override
    public void startup() {
        if (channelMap == null) {
            channelMap = hazelcastInstance.getMap(channelName);
            mapListenerId = channelMap.addEntryListener(mapEntryListener,
                    true);
        }
    }

    /**
     * Shutdown the channel operation.
     */
    @Override
    public void shutdown() {
        if (channelMap != null) {
            channelMap.removeEntryListener(mapListenerId);
            channelMap = null;
            mapListenerId = null;
        }
    }

    /**
     * Add event channel listener.
     *
     * @param listener the listener to add.
     */
    @Override
    public void addListener(IEventChannelListener<K, V> listener) {
        if (listeners.contains(listener)) {
            return;        // Nothing to do: already a listener
        }
        listeners.add(listener);
    }

    /**
     * Remove event channel listener.
     *
     * @param listener the listener to remove.
     */
    @Override
    public void removeListener(IEventChannelListener<K, V> listener) {
        listeners.remove(listener);
    }

    /**
     * Add an entry to the channel.
     *
     * @param key   the key of the entry to add.
     * @param value the value of the entry to add.
     */
    @Override
    public void addEntry(K key, V value) {
        byte[] valueBytes = serializeValue(value);
        //
        // Put the entry in the map:
        //  - Key : Type <K>
        //  - Value : Serialized Value (byte[])
        //
        channelMap.putAsync(key, valueBytes);
    }

    /**
     * Add a transient entry to the channel.
     * <p/>
     * The added entry is transient and will automatically timeout after 1ms.
     *
     * @param key   the key of the entry to add.
     * @param value the value of the entry to add.
     */
    @Override
    public void addTransientEntry(K key, V value) {
        byte[] valueBytes = serializeValue(value);
        //
        // Put the entry in the map:
        //  - Key : Type <K>
        //  - Value : Serialized Value (byte[])
        //  - Timeout: 1ms
        //
        channelMap.putAsync(key, valueBytes, 1L, TimeUnit.MILLISECONDS);
    }

    /**
     * Serialize the value.
     *
     * @param value the value to serialize.
     * @return the serialized value.
     */
    private byte[] serializeValue(V value) {
        //
        // Encode the value
        //
        byte[] buffer = new byte[MAX_BUFFER_SIZE];
        Kryo kryo = kryoFactory.newKryo();
        try {
            Output output = new Output(buffer, -1);
            kryo.writeClassAndObject(output, value);
            byte[] valueBytes = output.toBytes();
            return valueBytes;
        } finally {
            kryoFactory.deleteKryo(kryo);
        }
    }

    /**
     * Deserialize the value.
     *
     * @param kryo the Kryo instance to use for the deserialization.
     * @param valueBytes the buffer with the serialized value.
     * @return the deserialized value.
     */
    private V deserializeValue(Kryo kryo, byte[] valueBytes) {
        V value;

        //
        // Decode the value
        //
        Input input = new Input(valueBytes);
        Object objValue = kryo.readClassAndObject(input);
        try {
            value = typeV.cast(objValue);
        } catch (ClassCastException e) {
            log.error("Received notification value cast failed", e);
            return null;
        }

        return value;
    }

    /**
     * Remove an entry from the channel.
     *
     * @param key the key of the entry to remove.
     */
    @Override
    public void removeEntry(K key) {
        //
        // Remove the entry:
        //  - Key : Type <K>
        //  - Value : Serialized Value (byte[])
        //
        channelMap.removeAsync(key);
    }

    /**
     * Update an entry in the channel.
     *
     * @param key   the key of the entry to update.
     * @param value the value of the entry to update.
     */
    @Override
    public void updateEntry(K key, V value) {
        // NOTE: Adding an entry with an existing key automatically updates it
        addEntry(key, value);
    }

    /**
     * Get an entry from the channel.
     *
     * @param key the key of the entry to get.
     * @return the entry if found, otherwise null.
     */
    @Override
    @Deprecated
    public V getEntry(K key) {
        byte[] valueBytes = channelMap.get(key);
        if (valueBytes == null) {
            return null;
        }

        //
        // Decode the value
        //
        Kryo kryo = kryoFactory.newKryo();
        try {
            V value = deserializeValue(kryo, valueBytes);
            return value;
        } finally {
            kryoFactory.deleteKryo(kryo);
        }
    }

    /**
     * Get all entries in the channel.
     *
     * @return all entries that are currently in the channel.
     */
    @Override
    @Deprecated
    public Collection<V> getAllEntries() {
        Collection<V> allEntries = new LinkedList<V>();

        if (channelMap == null) {
            return allEntries;        // Nothing found
        }

        //
        // Get all entries
        //
        Collection<byte[]> values = channelMap.values();
        Kryo kryo = kryoFactory.newKryo();
        try {
            for (byte[] valueBytes : values) {
                //
                // Decode the value
                //
                V value = deserializeValue(kryo, valueBytes);
                allEntries.add(value);
            }
        } finally {
            kryoFactory.deleteKryo(kryo);
        }

        return allEntries;
    }

    /**
     * Remove all entries in the channel.
     */
    @Override
    @Deprecated
    public void removeAllEntries() {
        //
        // Remove all entries
        //
        // NOTE: We remove the entries one-by-one so the per-entry
        // notifications will be delivered.
        //
        // channelMap.clear();
        Set<K> keySet = channelMap.keySet();
        for (K key : keySet) {
            channelMap.removeAsync(key);
        }
    }

    /**
     * Class for receiving event notifications for the channel.
     * <p/>
     * The datagrid map is:
     * - Key: Type K
     * - Value: Serialized V (byte[])
     */
    private class MapEntryListener implements EntryListener<K, byte[]> {
        /**
         * Receive a notification that an entry is added.
         *
         * @param event the notification event for the entry.
         */
        @Override
        public void entryAdded(EntryEvent<K, byte[]> event) {
            //
            // Decode the value
            //
            byte[] valueBytes = event.getValue();
            Kryo kryo = kryoFactory.newKryo();
            try {
                V value = deserializeValue(kryo, valueBytes);

                //
                // Deliver the notification
                //
                final Iterator<IEventChannelListener<K, V>> it = listeners.iterator();
                while (it.hasNext()) {
                    final IEventChannelListener<K, V> listener = it.next();
                    if (it.hasNext()) {
                        // Each listener should get a deep copy of the value
                        // TODO: compare which is faster
                        //        - kryo.copy(value)
                        //        - deserializeValue(kryo, valueBytes)
                        listener.entryAdded(kryo.copy(value));
                    } else {
                        // Last listener can use the value
                        listener.entryAdded(value);
                    }
                }
            } finally {
                kryoFactory.deleteKryo(kryo);
            }
        }

        /**
         * Receive a notification that an entry is removed.
         *
         * @param event the notification event for the entry.
         */
        @Override
        public void entryRemoved(EntryEvent<K, byte[]> event) {
            //
            // Decode the value
            //
            byte[] valueBytes = event.getValue();
            Kryo kryo = kryoFactory.newKryo();
            try {
                V value = deserializeValue(kryo, valueBytes);

                //
                // Deliver the notification
                //
                final Iterator<IEventChannelListener<K, V>> it = listeners.iterator();
                while (it.hasNext()) {
                    final IEventChannelListener<K, V> listener = it.next();
                    if (it.hasNext()) {
                        // Each listener should get a deep copy of the value
                        listener.entryRemoved(kryo.copy(value));
                    } else {
                        // Last listener can use the value
                        listener.entryRemoved(value);
                    }
                }
            } finally {
                kryoFactory.deleteKryo(kryo);
            }
        }

        /**
         * Receive a notification that an entry is updated.
         *
         * @param event the notification event for the entry.
         */
        @Override
        public void entryUpdated(EntryEvent<K, byte[]> event) {
            //
            // Decode the value
            //
            byte[] valueBytes = event.getValue();
            Kryo kryo = kryoFactory.newKryo();
            try {
                V value = deserializeValue(kryo, valueBytes);

                //
                // Deliver the notification
                //
                final Iterator<IEventChannelListener<K, V>> it = listeners.iterator();
                while (it.hasNext()) {
                    final IEventChannelListener<K, V> listener = it.next();
                    if (it.hasNext()) {
                        // Each listener should get a deep copy of the value
                        listener.entryUpdated(kryo.copy(value));
                    } else {
                        // Last listener can use the value
                        listener.entryUpdated(value);
                    }
                }
            } finally {
                kryoFactory.deleteKryo(kryo);
            }
        }

        /**
         * Receive a notification that an entry is evicted.
         *
         * @param event the notification event for the entry.
         */
        @Override
        public void entryEvicted(EntryEvent<K, byte[]> event) {
            // NOTE: We don't use eviction for this map
        }
    }
}