/*
 * The Alluxio Open Foundation licenses this work under the Apache License, version 2.0
 * (the "License"). You may not use this work except in compliance with the License, which is
 * available at www.apache.org/licenses/LICENSE-2.0
 *
 * This software is distributed on an "AS IS" basis, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
 * either express or implied, as more fully set forth in the License.
 *
 * See the NOTICE file distributed with this work for information regarding copyright ownership.
 */

package alluxio.client.file.policy;

import alluxio.Configuration;
import alluxio.PropertyKey;
import alluxio.client.block.BlockWorkerInfo;
import alluxio.client.block.policy.BlockLocationPolicy;
import alluxio.client.block.policy.options.GetWorkerOptions;
import alluxio.util.network.NetworkAddressUtils;
import alluxio.wire.WorkerNetAddress;

import com.google.common.base.Objects;
import com.google.common.collect.Lists;

import java.util.Collections;
import java.util.List;

import javax.annotation.concurrent.ThreadSafe;
/**
 * A policy that returns local host first, and if the local worker doesn't have enough availability,
 * it randomly picks a worker from the active workers list for each block write.
 * If No worker meets the demands, return local host.
 * USER_FILE_WRITE_AVOID_EVICTION_POLICY_RESERVED_BYTES is used to reserve some space of the worker
 * to store the block, for the values mCapacityBytes minus mUsedBytes is not the available bytes.
 */
// TODO(peis): Move the BlockLocationPolicy implementation to alluxio.client.block.policy.
@ThreadSafe
public final class LocalFirstAvoidEvictionPolicy
    implements FileWriteLocationPolicy, BlockLocationPolicy {
  private String mLocalHostName;

  /**
   * Constructs a {@link LocalFirstAvoidEvictionPolicy}.
   */
  public LocalFirstAvoidEvictionPolicy() {
    mLocalHostName = NetworkAddressUtils.getClientHostName();
  }

  @Override
  public WorkerNetAddress getWorkerForNextBlock(Iterable<BlockWorkerInfo> workerInfoList,
      long blockSizeBytes) {
    // try the local host first
    WorkerNetAddress localWorkerNetAddress = null;
    for (BlockWorkerInfo workerInfo : workerInfoList) {
      if (workerInfo.getNetAddress().getHost().equals(mLocalHostName)) {
        localWorkerNetAddress = workerInfo.getNetAddress();
        if (getAvailableBytes(workerInfo) >= blockSizeBytes) {
          return localWorkerNetAddress;
        }
      }
    }

    // otherwise randomly pick a worker that has enough availability
    List<BlockWorkerInfo> shuffledWorkers = Lists.newArrayList(workerInfoList);
    Collections.shuffle(shuffledWorkers);
    for (BlockWorkerInfo workerInfo : shuffledWorkers) {
      if (getAvailableBytes(workerInfo) >= blockSizeBytes) {
        return workerInfo.getNetAddress();
      }
    }
    if (localWorkerNetAddress == null && shuffledWorkers.size() > 0) {
      return shuffledWorkers.get(0).getNetAddress();
    }
    return localWorkerNetAddress;
  }

  @Override
  public WorkerNetAddress getWorker(GetWorkerOptions options) {
    return getWorkerForNextBlock(options.getBlockWorkerInfos(), options.getBlockSize());
  }

  /**
   * The information of BlockWorkerInfo is update after a file complete write. To avoid evict,
   * user should configure "alluxio.user.file.write.avoid.eviction.policy.reserved.size.bytes"
   * to reserve some space to store the block.
   *
   * @param workerInfo BlockWorkerInfo of the worker
   * @return the available bytes of the worker
   */
  private long getAvailableBytes(BlockWorkerInfo workerInfo) {
    long mUserFileWriteCapacityReserved = Configuration
            .getBytes(PropertyKey.USER_FILE_WRITE_AVOID_EVICTION_POLICY_RESERVED_BYTES);
    long mCapacityBytes = workerInfo.getCapacityBytes();
    long mUsedBytes = workerInfo.getUsedBytes();
    return mCapacityBytes - mUsedBytes - mUserFileWriteCapacityReserved;
  }

  @Override
  public boolean equals(Object o) {
    if (this == o) {
      return true;
    }
    if (!(o instanceof LocalFirstAvoidEvictionPolicy)) {
      return false;
    }
    LocalFirstAvoidEvictionPolicy that = (LocalFirstAvoidEvictionPolicy) o;
    return Objects.equal(mLocalHostName, that.mLocalHostName);
  }

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

  @Override
  public String toString() {
    return Objects.toStringHelper(this)
        .add("localHostName", mLocalHostName)
        .toString();
  }
}