/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.apache.giraph.utils;

import it.unimi.dsi.fastutil.ints.Int2ObjectOpenHashMap;

import java.util.concurrent.atomic.AtomicInteger;

import org.apache.giraph.conf.FloatConfOption;
import org.apache.giraph.conf.GiraphConstants;
import org.apache.giraph.conf.ImmutableClassesGiraphConfiguration;
import org.apache.giraph.conf.IntConfOption;

/**
 * Wraps a list of byte array outputs and provides convenient
 * utilities on top of it
 */
public class ExtendedByteArrayOutputBuffer {
  /**
   * This option sets the capacity of an
   * {@link org.apache.giraph.utils.ExtendedDataOutput} instance created in
   * {@link org.apache.giraph.utils.ExtendedByteArrayOutputBuffer}
   */
  public static final IntConfOption CAPACITY_OF_DATAOUT_IN_BUFFER =
      new IntConfOption("giraph.capacityOfDataOutInBuffer",
          1024 * GiraphConstants.ONE_KB,
          "Set the capacity of dataoutputs in dataout buffer");

  /**
   * This option sets the maximum fraction of a
   * {@link org.apache.giraph.utils.ExtendedDataOutput} instance (stored in
   * {@link org.apache.giraph.utils.ExtendedByteArrayOutputBuffer})
   * that can be filled
   */
  public static final FloatConfOption FILLING_THRESHOLD_OF_DATAOUT_IN_BUFFER =
      new FloatConfOption("giraph.fillingThresholdOfDataoutInBuffer", 0.98f,
          "Set the maximum fraction of dataoutput capacity allowed to fill");

  /** Maximum size allowed for one byte array output */
  private final int maxBufSize;
  /** Stop writing to buffer after threshold has been reached */
  private final int threshold;
  /** Giraph configuration */
  private final ImmutableClassesGiraphConfiguration<?, ? , ?> config;

  /** Map of index => byte array outputs */
  private final Int2ObjectOpenHashMap<ExtendedDataOutput>
  bytearrayOutputs = new Int2ObjectOpenHashMap<>();
  /** Size of byte array outputs map */
  private final AtomicInteger mapSize = new AtomicInteger(0);
  /** Thread local variable to get hold of a byte array output stream */
  private final ThreadLocal<IndexAndDataOut> threadLocal =
    new ThreadLocal<IndexAndDataOut>() {
      @Override
      protected IndexAndDataOut initialValue() {
        return newIndexAndDataOutput();
      }
    };

  /**
   * Constructor
   *
   * @param config configuration
   */
  public ExtendedByteArrayOutputBuffer(
    ImmutableClassesGiraphConfiguration<?, ?, ?> config) {
    this.config = config;

    maxBufSize = CAPACITY_OF_DATAOUT_IN_BUFFER.get(config);
    threshold = (int) (FILLING_THRESHOLD_OF_DATAOUT_IN_BUFFER.get(config) *
      maxBufSize);
  }

  /**
   * Return threadLocal indexAndDataOutput instance
   *
   * @return threadLocal indexAndDataOutput instance
   */
  public IndexAndDataOut getIndexAndDataOut() {
    IndexAndDataOut indexAndDataOut = threadLocal.get();
    if (indexAndDataOut.dataOutput.getPos() >= threshold) {
      indexAndDataOut = newIndexAndDataOutput();
      threadLocal.set(indexAndDataOut);
    }
    return indexAndDataOut;
  }

  /**
   * Get dataoutput from bytearrayOutputs
   *
   * @param index index in bytearrayOutputs
   * @return extendeddataoutput at given index
   */
  public ExtendedDataOutput getDataOutput(int index) {
    return bytearrayOutputs.get(index);
  }

  /**
   * Holder for index &amp; DataOutput objects
   */
  public static class IndexAndDataOut {
    /** Index */
    private final int index;
    /** Dataouput instance */
    private final ExtendedDataOutput dataOutput;

    /**
     * Constructor
     *
     * @param index index in bytearrayOutputs
     * @param dataOutput dataoutput
     */
    public IndexAndDataOut(int index, ExtendedDataOutput dataOutput) {
      this.index = index;
      this.dataOutput = dataOutput;
    }

    public int getIndex() {
      return index;
    }

    public ExtendedDataOutput getDataOutput() {
      return dataOutput;
    }
  }

  /**
   * Create a new IndexAndDataOutput instance
   * @return new IndexAndDataOutput instance
   */
  private IndexAndDataOut newIndexAndDataOutput() {
    int index = mapSize.getAndIncrement();
    ExtendedDataOutput output = config.createExtendedDataOutput(
        maxBufSize);
    synchronized (bytearrayOutputs) {
      bytearrayOutputs.put(index, output);
    }
    return new IndexAndDataOut(index, output);
  }
}