/*
 * Copyright 2015 Terracotta, Inc., a Software AG company.
 *
 * 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.terracotta.offheapstore.storage;

import java.nio.ByteBuffer;
import java.util.Collection;
import java.util.concurrent.locks.Lock;

import org.terracotta.offheapstore.paging.OffHeapStorageArea;
import org.terracotta.offheapstore.paging.PageSource;
import org.terracotta.offheapstore.storage.portability.Portability;
import org.terracotta.offheapstore.storage.portability.WriteContext;
import org.terracotta.offheapstore.util.DebuggingUtils;
import org.terracotta.offheapstore.util.Factory;

import static java.util.Collections.emptyList;
import static java.util.Collections.singleton;
import static org.terracotta.offheapstore.util.ByteBufferUtils.totalLength;

A generic ByteBuffer based key/value store.
 This storage engine implementation uses Portability instances to convert key/value instances in to ByteBuffers. The content of these ByteBuffers are then stored in slices of a single large data area. 
Author:
Chris Dennis
Type parameters:
<K> – key type handled by this engine
<V> – value type handled by this engine/**
 * A generic ByteBuffer based key/value store.
 * <p>
 * This storage engine implementation uses {@link Portability} instances to
 * convert key/value instances in to ByteBuffers.  The content of these
 * ByteBuffers are then stored in slices of a single large data area.
 *
 * @param <K> key type handled by this engine
 * @param <V> value type handled by this engine
 *
 * @author Chris Dennis
 */
public class OffHeapBufferStorageEngine<K, V> extends PortabilityBasedStorageEngine<K, V> implements OffHeapStorageArea.Owner {

  private static final int KEY_HASH_OFFSET = 0;
  private static final int KEY_LENGTH_OFFSET = 4;
  private static final int VALUE_LENGTH_OFFSET = 8;
  private static final int DATA_OFFSET = 12;
  private static final int HEADER_SIZE = DATA_OFFSET;

  /*
   * Future design ideas:
   *
   * We might want to look in to supporting shrinking of the data areas, in case
   * our storage demands change (e.g. due to a change in key distribution, or
   * change in value types).
   */

  public static <K, V> Factory<OffHeapBufferStorageEngine<K, V>> createFactory(final PointerSize width, final PageSource source, final int pageSize, final Portability<? super K> keyPortability, final Portability<? super V> valuePortability, final boolean thief, final boolean victim) {
    return () -> new OffHeapBufferStorageEngine<>(width, source, pageSize, keyPortability, valuePortability, thief, victim);
  }

  public static <K, V> Factory<OffHeapBufferStorageEngine<K, V>> createFactory(final PointerSize width, final PageSource source, final int pageSize, final Portability<? super K> keyPortability, final Portability<? super V> valuePortability, final boolean thief, final boolean victim, final float compressThreshold) {
    return () -> new OffHeapBufferStorageEngine<>(width, source, pageSize, keyPortability, valuePortability, thief, victim, compressThreshold);
  }

  public static <K, V> Factory<OffHeapBufferStorageEngine<K, V>> createFactory(final PointerSize width, final PageSource source, final int initialPageSize, final int maximalPageSize, final Portability<? super K> keyPortability, final Portability<? super V> valuePortability, final boolean thief, final boolean victim) {
    return () -> new OffHeapBufferStorageEngine<>(width, source, initialPageSize, maximalPageSize, keyPortability, valuePortability, thief, victim);
  }

  public static <K, V> Factory<OffHeapBufferStorageEngine<K, V>> createFactory(final PointerSize width, final PageSource source, final int initialPageSize, final int maximalPageSize, final Portability<? super K> keyPortability, final Portability<? super V> valuePortability, final boolean thief, final boolean victim, final float compressThreshold) {
    return () -> new OffHeapBufferStorageEngine<>(width, source, initialPageSize, maximalPageSize, keyPortability, valuePortability, thief, victim, compressThreshold);
  }

  protected final OffHeapStorageArea storageArea;

  protected volatile Owner owner;

  
Creates a storage engine using the given page source, and portabilities.
Params:
width – int or long based engine
source – allocator used for storage allocation
pageSize – internal (constant) page size
keyPortability – key type portability
valuePortability – value type portability/**
   * Creates a storage engine using the given page source, and portabilities.
   *
   * @param width {@code int} or {@code long} based engine
   * @param source allocator used for storage allocation
   * @param pageSize internal (constant) page size
   * @param keyPortability key type portability
   * @param valuePortability value type portability
   */
  public OffHeapBufferStorageEngine(PointerSize width, PageSource source, int pageSize, Portability<? super K> keyPortability, Portability<? super V> valuePortability) {
    this(width, source, pageSize, pageSize, keyPortability, valuePortability);
  }

  public OffHeapBufferStorageEngine(PointerSize width, PageSource source, int pageSize, Portability<? super K> keyPortability, Portability<? super V> valuePortability, float compressThreshold) {
    this(width, source, pageSize, pageSize, keyPortability, valuePortability, compressThreshold);
  }

  public OffHeapBufferStorageEngine(PointerSize width, PageSource source, int initialPageSize, int maximalPageSize, Portability<? super K> keyPortability, Portability<? super V> valuePortability) {
    this(width, source, initialPageSize, maximalPageSize, keyPortability, valuePortability, false, false);
  }

  public OffHeapBufferStorageEngine(PointerSize width, PageSource source, int initialPageSize, int maximalPageSize, Portability<? super K> keyPortability, Portability<? super V> valuePortability, float compressThreshold) {
    this(width, source, initialPageSize, maximalPageSize, keyPortability, valuePortability, false, false, compressThreshold);
  }

  public OffHeapBufferStorageEngine(PointerSize width, PageSource source, int pageSize, Portability<? super K> keyPortability, Portability<? super V> valuePortability, boolean thief, boolean victim) {
    this(width, source, pageSize, pageSize, keyPortability, valuePortability, thief, victim);
  }

  public OffHeapBufferStorageEngine(PointerSize width, PageSource source, int pageSize, Portability<? super K> keyPortability, Portability<? super V> valuePortability, boolean thief, boolean victim, float compressThreshold) {
    this(width, source, pageSize, pageSize, keyPortability, valuePortability, thief, victim, compressThreshold);
  }

  public OffHeapBufferStorageEngine(PointerSize width, PageSource source, int initialPageSize, int maximalPageSize, Portability<? super K> keyPortability, Portability<? super V> valuePortability, boolean thief, boolean victim) {
    super(keyPortability, valuePortability);
    this.storageArea = new OffHeapStorageArea(width, this, source, initialPageSize, maximalPageSize, thief, victim);
  }

  public OffHeapBufferStorageEngine(PointerSize width, PageSource source, int initialPageSize, int maximalPageSize, Portability<? super K> keyPortability, Portability<? super V> valuePortability, boolean thief, boolean victim, float compressThreshold) {
    super(keyPortability, valuePortability);
    this.storageArea = new OffHeapStorageArea(width, this, source, initialPageSize, maximalPageSize, thief, victim, compressThreshold);
  }

  @Override
  protected void clearInternal() {
    storageArea.clear();
  }

  @Override
  protected void free(long address) {
    storageArea.free(address);
  }

  @Override
  public ByteBuffer readKeyBuffer(long address) {
    int length = storageArea.readInt(address + KEY_LENGTH_OFFSET);
    return storageArea.readBuffer(address + DATA_OFFSET, length).asReadOnlyBuffer();
  }

  @Override
  protected WriteContext getKeyWriteContext(long address) {
    int keyLength = storageArea.readInt(address + KEY_LENGTH_OFFSET);
    return getWriteContext(address + DATA_OFFSET, keyLength);
  }

  @Override
  public ByteBuffer readValueBuffer(long address) {
    int keyLength = storageArea.readInt(address + KEY_LENGTH_OFFSET);
    int valueLength = storageArea.readInt(address + VALUE_LENGTH_OFFSET);
    return storageArea.readBuffer(address + DATA_OFFSET + keyLength, valueLength).asReadOnlyBuffer();
  }

  @Override
  protected WriteContext getValueWriteContext(long address) {
    int keyLength = storageArea.readInt(address + KEY_LENGTH_OFFSET);
    int valueLength = storageArea.readInt(address + VALUE_LENGTH_OFFSET);
    return getWriteContext(address + DATA_OFFSET + keyLength, valueLength);
  }

  private WriteContext getWriteContext(final long address, final int max) {
    return new WriteContext() {

      @Override
      public void setLong(int offset, long value) {
        if (offset < 0 || offset > max) {
          throw new IllegalArgumentException();
        } else {
          storageArea.writeLong(address + offset, value);
        }
      }

      @Override
      public void flush() {
        //no-op
      }
    };
  }
  @Override
  protected Long writeMappingBuffers(ByteBuffer keyBuffer, ByteBuffer valueBuffer, int hash) {
    int keyLength = keyBuffer.remaining();
    int valueLength = valueBuffer.remaining();
    long address = storageArea.allocate(keyLength + valueLength + HEADER_SIZE);

    if (address >= 0) {
      storageArea.writeInt(address + KEY_HASH_OFFSET, hash);
      storageArea.writeInt(address + KEY_LENGTH_OFFSET, keyLength);
      storageArea.writeInt(address + VALUE_LENGTH_OFFSET, valueLength);
      storageArea.writeBuffer(address + DATA_OFFSET, keyBuffer);
      storageArea.writeBuffer(address + DATA_OFFSET + keyLength, valueBuffer);
      return address;
    } else {
      return null;
    }
  }

  @Override
  protected Long writeMappingBuffersGathering(ByteBuffer[] keyBuffers, ByteBuffer[] valueBuffers, int hash) {
    int keyLength = totalLength(keyBuffers);
    int valueLength = totalLength(valueBuffers);
    long address = storageArea.allocate(keyLength + valueLength + HEADER_SIZE);

    if (address >= 0) {
      storageArea.writeInt(address + KEY_HASH_OFFSET, hash);
      storageArea.writeInt(address + KEY_LENGTH_OFFSET, keyLength);
      storageArea.writeInt(address + VALUE_LENGTH_OFFSET, valueLength);
      storageArea.writeBuffers(address + DATA_OFFSET, keyBuffers);
      storageArea.writeBuffers(address + DATA_OFFSET + keyLength, valueBuffers);
      return address;
    } else {
      return null;
    }
  }

  @Override
  public long getAllocatedMemory() {
    return storageArea.getAllocatedMemory();
  }

  @Override
  public long getOccupiedMemory() {
    return storageArea.getOccupiedMemory();
  }

  @Override
  public long getVitalMemory() {
    return getAllocatedMemory();
  }

  @Override
  public long getDataSize() {
    //TODO This is an overestimate.
    return getOccupiedMemory();
  }

  @Override
  public String toString() {
    return "OffHeapBufferStorageEngine allocated=" + DebuggingUtils.toBase2SuffixedString(getAllocatedMemory()) + "B "
           + "occupied=" + DebuggingUtils.toBase2SuffixedString(getOccupiedMemory()) + "B\n"
           + "Storage Area: " + storageArea;
  }

  @Override
  public void destroy() {
    storageArea.destroy();
  }

  @Override
  public boolean shrink() {
    return storageArea.shrink();
  }

  @Override
  public Collection<Long> evictAtAddress(long address, boolean shrink) {
    int hash = storageArea.readInt(address + KEY_HASH_OFFSET);
    int slot = owner.getSlotForHashAndEncoding(hash, address, ~0);
    if (owner.evict(slot, shrink)) {
      return singleton(address);
    } else {
      return emptyList();
    }
  }

  @Override
  public boolean isThief() {
    return owner.isThiefForTableAllocations();
  }

  @Override
  public int readKeyHash(long encoding) {
    return storageArea.readInt(encoding + KEY_HASH_OFFSET);
  }

  @Override
  public boolean moved(long from, long to) {
    return owner.updateEncoding(readKeyHash(to), from, to, ~0);
  }

  @Override
  public int sizeOf(long address) {
    int keyLength = storageArea.readInt(address + KEY_LENGTH_OFFSET);
    int valueLength = storageArea.readInt(address + VALUE_LENGTH_OFFSET);
    return DATA_OFFSET + keyLength + valueLength;
  }

  @Override
  public void bind(Owner m) {
    if (owner != null) {
      throw new AssertionError();
    }
    owner = m;
  }

  @Override
  public Lock writeLock() {
    return owner.writeLock();
  }
}