/*
 * 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.beam.sdk.io.kinesis;

import static org.apache.beam.vendor.guava.v20_0.com.google.common.collect.Lists.newArrayList;
import static org.apache.beam.vendor.guava.v20_0.com.google.common.collect.Lists.partition;

import java.io.IOException;
import java.io.Serializable;
import java.util.Iterator;
import java.util.List;
import org.apache.beam.sdk.io.UnboundedSource;
import org.apache.beam.vendor.guava.v20_0.com.google.common.collect.ImmutableList;

/**
 * Checkpoint representing a total progress in a set of shards in single stream. The set of shards
 * covered by {@link KinesisReaderCheckpoint} may or may not be equal to set of all shards present
 * in the stream. This class is immutable.
 */
class KinesisReaderCheckpoint
    implements Iterable<ShardCheckpoint>, UnboundedSource.CheckpointMark, Serializable {

  private final List<ShardCheckpoint> shardCheckpoints;

  public KinesisReaderCheckpoint(Iterable<ShardCheckpoint> shardCheckpoints) {
    this.shardCheckpoints = ImmutableList.copyOf(shardCheckpoints);
  }

  /**
   * Splits given multi-shard checkpoint into partitions of approximately equal size.
   *
   * @param desiredNumSplits - upper limit for number of partitions to generate.
   * @return list of checkpoints covering consecutive partitions of current checkpoint.
   */
  public List<KinesisReaderCheckpoint> splitInto(int desiredNumSplits) {
    int partitionSize = divideAndRoundUp(shardCheckpoints.size(), desiredNumSplits);

    List<KinesisReaderCheckpoint> checkpoints = newArrayList();
    for (List<ShardCheckpoint> shardPartition : partition(shardCheckpoints, partitionSize)) {
      checkpoints.add(new KinesisReaderCheckpoint(shardPartition));
    }
    return checkpoints;
  }

  private int divideAndRoundUp(int nominator, int denominator) {
    return (nominator + denominator - 1) / denominator;
  }

  @Override
  public void finalizeCheckpoint() throws IOException {}

  @Override
  public String toString() {
    return shardCheckpoints.toString();
  }

  @Override
  public Iterator<ShardCheckpoint> iterator() {
    return shardCheckpoints.iterator();
  }
}
