/*
 * 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 com.google.common.collect.Iterables.transform;
import static com.google.common.collect.Lists.newArrayList;
import static com.google.common.collect.Lists.partition;

import com.google.common.base.Function;
import com.google.common.collect.ImmutableList;
import java.io.IOException;
import java.io.Serializable;
import java.util.Iterator;
import java.util.List;
import javax.annotation.Nullable;
import org.apache.beam.sdk.io.UnboundedSource;

/**
 * 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);
    }

    public static KinesisReaderCheckpoint asCurrentStateOf(Iterable<ShardRecordsIterator>
                                                                   iterators) {
        return new KinesisReaderCheckpoint(transform(iterators,
                new Function<ShardRecordsIterator, ShardCheckpoint>() {

                    @Nullable
                    @Override
                    public ShardCheckpoint apply(@Nullable
                                                 ShardRecordsIterator shardRecordsIterator) {
                        assert shardRecordsIterator != null;
                        return shardRecordsIterator.getCheckpoint();
                    }
                }));
    }

    /**
     * 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();
    }
}