/*
 * Copyright 2014-present Open Networking Laboratory
 *
 * Licensed 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.onlab.util;

import com.esotericsoftware.kryo.Kryo;
import com.esotericsoftware.kryo.Registration;
import com.esotericsoftware.kryo.Serializer;
import com.esotericsoftware.kryo.io.ByteBufferInput;
import com.esotericsoftware.kryo.io.ByteBufferOutput;
import com.esotericsoftware.kryo.io.Input;
import com.esotericsoftware.kryo.io.Output;
import com.esotericsoftware.kryo.pool.KryoCallback;
import com.esotericsoftware.kryo.pool.KryoFactory;
import com.esotericsoftware.kryo.pool.KryoPool;
import com.google.common.base.MoreObjects;
import com.google.common.collect.ImmutableList;
import org.apache.commons.lang3.tuple.Pair;
import org.objenesis.strategy.StdInstantiatorStrategy;
import org.slf4j.Logger;

import java.io.InputStream;
import java.io.OutputStream;
import java.nio.ByteBuffer;
import java.util.ArrayList;
import java.util.List;
import java.util.Objects;

import static com.google.common.base.Preconditions.checkNotNull;
import static org.slf4j.LoggerFactory.getLogger;

/**
 * Pool of Kryo instances, with classes pre-registered.
 */
//@ThreadSafe
public final class KryoNamespace implements KryoFactory, KryoPool {

    /**
     * Default buffer size used for serialization.
     *
     * @see #serialize(Object)
     */
    public static final int DEFAULT_BUFFER_SIZE = 4096;
    public static final int MAX_BUFFER_SIZE = 100 * 1000 * 1000;

    /**
     * ID to use if this KryoNamespace does not define registration id.
     */
    public static final int FLOATING_ID = -1;

    /**
     * Smallest ID free to use for user defined registrations.
     */
    public static final int INITIAL_ID = 16;

    private static final String NO_NAME = "(no name)";

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


    private final KryoPool pool = new KryoPool.Builder(this)
                                        .softReferences()
                                        .build();

    private final ImmutableList<RegistrationBlock> registeredBlocks;

    private final boolean registrationRequired;
    private final String friendlyName;

    /**
     * KryoNamespace builder.
     */
    //@NotThreadSafe
    public static final class Builder {

        private int blockHeadId = INITIAL_ID;
        private List<Pair<Class<?>, Serializer<?>>> types = new ArrayList<>();
        private List<RegistrationBlock> blocks = new ArrayList<>();
        private boolean registrationRequired = true;

        /**
         * Builds a {@link KryoNamespace} instance.
         *
         * @return KryoNamespace
         */
        public KryoNamespace build() {
            return build(NO_NAME);
        }

        /**
         * Builds a {@link KryoNamespace} instance.
         *
         * @param friendlyName friendly name for the namespace
         * @return KryoNamespace
         */
        public KryoNamespace build(String friendlyName) {
            if (!types.isEmpty()) {
                blocks.add(new RegistrationBlock(this.blockHeadId, types));
            }
            return new KryoNamespace(blocks, registrationRequired, friendlyName).populate(1);
        }

        /**
         * Sets the next Kryo registration Id for following register entries.
         *
         * @param id Kryo registration Id
         * @return this
         *
         * @see Kryo#register(Class, Serializer, int)
         */
        public Builder nextId(final int id) {
            if (!types.isEmpty()) {
                if (id != FLOATING_ID && id < blockHeadId + types.size()) {

                    if (log.isWarnEnabled()) {
                        log.warn("requested nextId {} could potentially overlap " +
                                 "with existing registrations {}+{} ",
                                 id, blockHeadId, types.size(), new RuntimeException());
                    }
                }
                blocks.add(new RegistrationBlock(this.blockHeadId, types));
                types = new ArrayList<>();
            }
            this.blockHeadId = id;
            return this;
        }

        /**
         * Registers classes to be serialized using Kryo default serializer.
         *
         * @param expectedTypes list of classes
         * @return this
         */
        public Builder register(final Class<?>... expectedTypes) {
            for (Class<?> clazz : expectedTypes) {
                types.add(Pair.of(clazz, null));
            }
            return this;
        }

        /**
         * Registers a class and it's serializer.
         *
         * @param classes list of classes to register
         * @param serializer serializer to use for the class
         * @return this
         */
        public Builder register(Serializer<?> serializer, final Class<?>... classes) {
            for (Class<?> clazz : classes) {
                types.add(Pair.of(clazz, serializer));
            }
            return this;
        }

        private Builder register(RegistrationBlock block) {
            if (block.begin() != FLOATING_ID) {
                // flush pending types
                nextId(block.begin());
                blocks.add(block);
                nextId(block.begin() + block.types().size());
            } else {
                // flush pending types
                final int addedBlockBegin = blockHeadId + types.size();
                nextId(addedBlockBegin);
                blocks.add(new RegistrationBlock(addedBlockBegin, block.types()));
                nextId(addedBlockBegin + block.types().size());
            }
            return this;
        }

        /**
         * Registers all the class registered to given KryoNamespace.
         *
         * @param ns KryoNamespace
         * @return this
         */
        public Builder register(final KryoNamespace ns) {

            if (blocks.containsAll(ns.registeredBlocks)) {
                // Everything was already registered.
                log.debug("Ignoring {}, already registered.", ns);
                return this;
            }
            for (RegistrationBlock block : ns.registeredBlocks) {
                this.register(block);
            }
            return this;
        }

        /**
         * Sets the registrationRequired flag.
         *
         * @param registrationRequired Kryo's registrationRequired flag
         * @return this
         *
         * @see Kryo#setRegistrationRequired(boolean)
         */
        public Builder setRegistrationRequired(boolean registrationRequired) {
            this.registrationRequired = registrationRequired;
            return this;
        }
    }

    /**
     * Creates a new {@link KryoNamespace} builder.
     *
     * @return builder
     */
    public static Builder newBuilder() {
        return new Builder();
    }

    /**
     * Creates a Kryo instance pool.
     *
     * @param registeredTypes types to register
     * @param registrationRequired
     * @param friendlyName friendly name for the namespace
     */
    private KryoNamespace(final List<RegistrationBlock> registeredTypes,
                          boolean registrationRequired,
                          String friendlyName) {
        this.registeredBlocks = ImmutableList.copyOf(registeredTypes);
        this.registrationRequired = registrationRequired;
        this.friendlyName =  checkNotNull(friendlyName);
    }

    /**
     * Populates the Kryo pool.
     *
     * @param instances to add to the pool
     * @return this
     */
    public KryoNamespace populate(int instances) {

        for (int i = 0; i < instances; ++i) {
            release(create());
        }
        return this;
    }

    /**
     * Serializes given object to byte array using Kryo instance in pool.
     * <p>
     * Note: Serialized bytes must be smaller than {@link #MAX_BUFFER_SIZE}.
     *
     * @param obj Object to serialize
     * @return serialized bytes
     */
    public byte[] serialize(final Object obj) {
        return serialize(obj, DEFAULT_BUFFER_SIZE);
    }

    /**
     * Serializes given object to byte array using Kryo instance in pool.
     *
     * @param obj Object to serialize
     * @param bufferSize maximum size of serialized bytes
     * @return serialized bytes
     */
    public byte[] serialize(final Object obj, final int bufferSize) {
        Output out = new Output(bufferSize, MAX_BUFFER_SIZE);
        return pool.run(kryo -> {
            kryo.writeClassAndObject(out, obj);
            out.flush();
            return out.toBytes();
        });
    }

    /**
     * Serializes given object to byte buffer using Kryo instance in pool.
     *
     * @param obj Object to serialize
     * @param buffer to write to
     */
    public void serialize(final Object obj, final ByteBuffer buffer) {
        ByteBufferOutput out = new ByteBufferOutput(buffer);
        Kryo kryo = borrow();
        try {
            kryo.writeClassAndObject(out, obj);
            out.flush();
        } finally {
            release(kryo);
        }
    }

    /**
     * Serializes given object to OutputStream using Kryo instance in pool.
     *
     * @param obj Object to serialize
     * @param stream to write to
     */
    public void serialize(final Object obj, final OutputStream stream) {
        serialize(obj, stream, DEFAULT_BUFFER_SIZE);
    }

    /**
     * Serializes given object to OutputStream using Kryo instance in pool.
     *
     * @param obj Object to serialize
     * @param stream to write to
     * @param bufferSize size of the buffer in front of the stream
     */
    public void serialize(final Object obj, final OutputStream stream, final int bufferSize) {
        ByteBufferOutput out = new ByteBufferOutput(stream, bufferSize);
        Kryo kryo = borrow();
        try {
            kryo.writeClassAndObject(out, obj);
            out.flush();
        } finally {
            release(kryo);
        }
    }

    /**
     * Deserializes given byte array to Object using Kryo instance in pool.
     *
     * @param bytes serialized bytes
     * @param <T> deserialized Object type
     * @return deserialized Object
     */
    public <T> T deserialize(final byte[] bytes) {
        Input in = new Input(bytes);
        Kryo kryo = borrow();
        try {
            @SuppressWarnings("unchecked")
            T obj = (T) kryo.readClassAndObject(in);
            return obj;
        } finally {
            release(kryo);
        }
    }

    /**
     * Deserializes given byte buffer to Object using Kryo instance in pool.
     *
     * @param buffer input with serialized bytes
     * @param <T> deserialized Object type
     * @return deserialized Object
     */
    public <T> T deserialize(final ByteBuffer buffer) {
        ByteBufferInput in = new ByteBufferInput(buffer);
        Kryo kryo = borrow();
        try {
            @SuppressWarnings("unchecked")
            T obj = (T) kryo.readClassAndObject(in);
            return obj;
        } finally {
            release(kryo);
        }
    }

    /**
     * Deserializes given InputStream to an Object using Kryo instance in pool.
     *
     * @param stream input stream
     * @param <T> deserialized Object type
     * @return deserialized Object
     */
    public <T> T deserialize(final InputStream stream) {
        return deserialize(stream, DEFAULT_BUFFER_SIZE);
    }

    /**
     * Deserializes given InputStream to an Object using Kryo instance in pool.
     *
     * @param stream input stream
     * @param <T> deserialized Object type
     * @return deserialized Object
     * @param bufferSize size of the buffer in front of the stream
     */
    public <T> T deserialize(final InputStream stream, final int bufferSize) {
        ByteBufferInput in = new ByteBufferInput(stream, bufferSize);
        Kryo kryo = borrow();
        try {
            @SuppressWarnings("unchecked")
            T obj = (T) kryo.readClassAndObject(in);
            return obj;
        } finally {
            release(kryo);
        }
    }

    private String friendlyName() {
        return friendlyName;
    }

    /**
     * Gets the number of classes registered in this Kryo namespace.
     *
     * @return size of namespace
     */
    public int size() {
        return (int) registeredBlocks.stream()
                .flatMap(block -> block.types().stream())
                .count();
    }

    /**
     * Creates a Kryo instance.
     *
     * @return Kryo instance
     */
    @Override
    public Kryo create() {
        log.trace("Creating Kryo instance for {}", this);
        Kryo kryo = new Kryo();
        kryo.setRegistrationRequired(registrationRequired);

        // TODO rethink whether we want to use StdInstantiatorStrategy
        kryo.setInstantiatorStrategy(
                new Kryo.DefaultInstantiatorStrategy(new StdInstantiatorStrategy()));

        for (RegistrationBlock block : registeredBlocks) {
            int id = block.begin();
            if (id == FLOATING_ID) {
                id = kryo.getNextRegistrationId();
            }
            for (Pair<Class<?>, Serializer<?>> entry : block.types()) {
                register(kryo, entry.getLeft(), entry.getRight(), id++);
            }
        }
        return kryo;
    }

    /**
     * Register {@code type} and {@code serializer} to {@code kryo} instance.
     *
     * @param kryo       Kryo instance
     * @param type       type to register
     * @param serializer Specific serializer to register or null to use default.
     * @param id         type registration id to use
     */
    private void register(Kryo kryo, Class<?> type, Serializer<?> serializer, int id) {
        Registration existing = kryo.getRegistration(id);
        if (existing != null) {
            if (existing.getType() != type) {
                log.error("{}: Failed to register {} as {}, {} was already registered.",
                          friendlyName(), type, id, existing.getType());

                throw new IllegalStateException(String.format(
                          "Failed to register %s as %s, %s was already registered.",
                          type, id, existing.getType()));
            }
            // falling through to register call for now.
            // Consider skipping, if there's reasonable
            // way to compare serializer equivalence.
        }
        Registration r;
        if (serializer == null) {
            r = kryo.register(type, id);
        } else {
            r = kryo.register(type, serializer, id);
        }
        if (r.getId() != id) {
            log.warn("{}: {} already registed as {}. Skipping {}.",
                     friendlyName(), r.getType(), r.getId(), id);
        }
        log.trace("{} registered as {}", r.getType(), r.getId());
    }

    @Override
    public Kryo borrow() {
        return pool.borrow();
    }

    @Override
    public void release(Kryo kryo) {
        pool.release(kryo);
    }

    @Override
    public <T> T run(KryoCallback<T> callback) {
        return pool.run(callback);
    }

    @Override
    public String toString() {
        if (friendlyName != NO_NAME) {
            return MoreObjects.toStringHelper(getClass())
                    .omitNullValues()
                    .add("friendlyName", friendlyName)
                    // omit lengthy detail, when there's a name
                    .toString();
        }
        return MoreObjects.toStringHelper(getClass())
                    .add("registeredBlocks", registeredBlocks)
                    .toString();
    }

    static final class RegistrationBlock {
        private final int begin;
        private final ImmutableList<Pair<Class<?>, Serializer<?>>> types;

        public RegistrationBlock(int begin, List<Pair<Class<?>, Serializer<?>>> types) {
            this.begin = begin;
            this.types = ImmutableList.copyOf(types);
        }

        public int begin() {
            return begin;
        }

        public ImmutableList<Pair<Class<?>, Serializer<?>>> types() {
            return types;
        }

        @Override
        public String toString() {
            return MoreObjects.toStringHelper(getClass())
                    .add("begin", begin)
                    .add("types", types)
                    .toString();
        }

        @Override
        public int hashCode() {
            return types.hashCode();
        }

        // Only the registered types are used for equality.
        @Override
        public boolean equals(Object obj) {
            if (this == obj) {
                return true;
            }

            if (obj instanceof RegistrationBlock) {
                RegistrationBlock that = (RegistrationBlock) obj;
                return Objects.equals(this.types, that.types);
            }
            return false;
        }
    }
}