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 * 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
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 */
package org.apache.cassandra.db.rows;

import java.io.IOException;
import java.util.*;

import org.apache.cassandra.db.*;
import org.apache.cassandra.db.partitions.PartitionStatisticsCollector;
import org.apache.cassandra.io.util.DataInputPlus;
import org.apache.cassandra.io.util.DataOutputPlus;

Stats used for the encoding of the rows and tombstones of a given source.
 Those stats are used to optimize the on-wire and on-disk storage of rows. More precisely, the minTimestamp, minLocalDeletionTime and minTTL stats are used to delta-encode those information for the sake of vint encoding. 
 Note that due to their use, those stats can suffer to be somewhat inaccurate (the more incurrate they are, the less effective the storage will be, but provided the stats are not completly wacky, this shouldn't have too huge an impact on performance) and in fact they will not always be accurate for reasons explained in SerializationHeader.make. /**
 * Stats used for the encoding of the rows and tombstones of a given source.
 * <p>
 * Those stats are used to optimize the on-wire and on-disk storage of rows. More precisely,
 * the {@code minTimestamp}, {@code minLocalDeletionTime} and {@code minTTL} stats are used to
 * delta-encode those information for the sake of vint encoding.
 * <p>
 * Note that due to their use, those stats can suffer to be somewhat inaccurate (the more incurrate
 * they are, the less effective the storage will be, but provided the stats are not completly wacky,
 * this shouldn't have too huge an impact on performance) and in fact they will not always be
 * accurate for reasons explained in {@link SerializationHeader#make}.
 */
public class EncodingStats
{
    // Default values for the timestamp, deletion time and ttl. We use this both for NO_STATS, but also to serialize
    // an EncodingStats. Basically, we encode the diff of each value of to these epoch, which give values with better vint encoding.
    private static final long TIMESTAMP_EPOCH;
    private static final int DELETION_TIME_EPOCH;
    private static final int TTL_EPOCH = 0;
    static
    {
        // We want a fixed epoch, but that provide small values when substracted from our timestamp and deletion time.
        // So we somewhat arbitrary use the date of the summit 2015, which should hopefully roughly correspond to 3.0 release.
        Calendar c = Calendar.getInstance(TimeZone.getTimeZone("GMT-0"), Locale.US);
        c.set(Calendar.YEAR, 2015);
        c.set(Calendar.MONTH, Calendar.SEPTEMBER);
        c.set(Calendar.DAY_OF_MONTH, 22);
        c.set(Calendar.HOUR_OF_DAY, 0);
        c.set(Calendar.MINUTE, 0);
        c.set(Calendar.SECOND, 0);
        c.set(Calendar.MILLISECOND, 0);

        TIMESTAMP_EPOCH = c.getTimeInMillis() * 1000; // timestamps should be in microseconds by convention
        DELETION_TIME_EPOCH = (int)(c.getTimeInMillis() / 1000); // local deletion times are in seconds
    }

    // We should use this sparingly obviously
    public static final EncodingStats NO_STATS = new EncodingStats(TIMESTAMP_EPOCH, DELETION_TIME_EPOCH, TTL_EPOCH);

    public static final Serializer serializer = new Serializer();

    public final long minTimestamp;
    public final int minLocalDeletionTime;
    public final int minTTL;

    public EncodingStats(long minTimestamp,
                         int minLocalDeletionTime,
                         int minTTL)
    {
        // Note that the exact value of those don't impact correctness, just the efficiency of the encoding. So when we
        // get a value for timestamp (resp. minLocalDeletionTime) that means 'no object had a timestamp' (resp. 'a local
        // deletion time'), then what value we store for minTimestamp (resp. minLocalDeletionTime) doesn't matter, and
        // it's thus more efficient to use our EPOCH numbers, since it will result in a guaranteed 1 byte encoding.

        this.minTimestamp = minTimestamp == LivenessInfo.NO_TIMESTAMP ? TIMESTAMP_EPOCH : minTimestamp;
        this.minLocalDeletionTime = minLocalDeletionTime == LivenessInfo.NO_EXPIRATION_TIME ? DELETION_TIME_EPOCH : minLocalDeletionTime;
        this.minTTL = minTTL;
    }

    
Merge this stats with another one.
 The comments of SerializationHeader.make applies here too, i.e. the result of merging will be not totally accurate but we can live with that. /**
     * Merge this stats with another one.
     * <p>
     * The comments of {@link SerializationHeader#make} applies here too, i.e. the result of
     * merging will be not totally accurate but we can live with that.
     */
    public EncodingStats mergeWith(EncodingStats that)
    {
        long minTimestamp = this.minTimestamp == TIMESTAMP_EPOCH
                          ? that.minTimestamp
                          : (that.minTimestamp == TIMESTAMP_EPOCH ? this.minTimestamp : Math.min(this.minTimestamp, that.minTimestamp));

        int minDelTime = this.minLocalDeletionTime == DELETION_TIME_EPOCH
                       ? that.minLocalDeletionTime
                       : (that.minLocalDeletionTime == DELETION_TIME_EPOCH ? this.minLocalDeletionTime : Math.min(this.minLocalDeletionTime, that.minLocalDeletionTime));

        int minTTL = this.minTTL == TTL_EPOCH
                   ? that.minTTL
                   : (that.minTTL == TTL_EPOCH ? this.minTTL : Math.min(this.minTTL, that.minTTL));

        return new EncodingStats(minTimestamp, minDelTime, minTTL);
    }

    @Override
    public boolean equals(Object o)
    {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        EncodingStats that = (EncodingStats) o;

        return this.minLocalDeletionTime == that.minLocalDeletionTime
            && this.minTTL == that.minTTL
            && this.minTimestamp == that.minTimestamp;
    }

    @Override
    public int hashCode()
    {
        return Objects.hash(minTimestamp, minLocalDeletionTime, minTTL);
    }

    @Override
    public String toString()
    {
        return String.format("EncodingStats(ts=%d, ldt=%d, ttl=%d)", minTimestamp, minLocalDeletionTime, minTTL);
    }

    public static class Collector implements PartitionStatisticsCollector
    {
        private boolean isTimestampSet;
        private long minTimestamp = Long.MAX_VALUE;

        private boolean isDelTimeSet;
        private int minDeletionTime = Integer.MAX_VALUE;

        private boolean isTTLSet;
        private int minTTL = Integer.MAX_VALUE;

        public void update(LivenessInfo info)
        {
            if (info.isEmpty())
                return;

            updateTimestamp(info.timestamp());

            if (info.isExpiring())
            {
                updateTTL(info.ttl());
                updateLocalDeletionTime(info.localExpirationTime());
            }
        }

        public void update(Cell cell)
        {
            updateTimestamp(cell.timestamp());
            if (cell.isExpiring())
            {
                updateTTL(cell.ttl());
                updateLocalDeletionTime(cell.localDeletionTime());
            }
            else if (cell.isTombstone())
            {
                updateLocalDeletionTime(cell.localDeletionTime());
            }
        }

        public void update(DeletionTime deletionTime)
        {
            if (deletionTime.isLive())
                return;

            updateTimestamp(deletionTime.markedForDeleteAt());
            updateLocalDeletionTime(deletionTime.localDeletionTime());
        }

        public void updateTimestamp(long timestamp)
        {
            isTimestampSet = true;
            minTimestamp = Math.min(minTimestamp, timestamp);
        }

        public void updateLocalDeletionTime(int deletionTime)
        {
            isDelTimeSet = true;
            minDeletionTime = Math.min(minDeletionTime, deletionTime);
        }

        public void updateTTL(int ttl)
        {
            isTTLSet = true;
            minTTL = Math.min(minTTL, ttl);
        }

        public void updateColumnSetPerRow(long columnSetInRow)
        {
        }

        public void updateHasLegacyCounterShards(boolean hasLegacyCounterShards)
        {
            // We don't care about this but this come with PartitionStatisticsCollector
        }

        public EncodingStats get()
        {
            return new EncodingStats(isTimestampSet ? minTimestamp : TIMESTAMP_EPOCH,
                                     isDelTimeSet ? minDeletionTime : DELETION_TIME_EPOCH,
                                     isTTLSet ? minTTL : TTL_EPOCH);
        }

        public static EncodingStats collect(Row staticRow, Iterator<Row> rows, DeletionInfo deletionInfo)
        {
            Collector collector = new Collector();
            deletionInfo.collectStats(collector);
            if (!staticRow.isEmpty())
                Rows.collectStats(staticRow, collector);
            while (rows.hasNext())
                Rows.collectStats(rows.next(), collector);
            return collector.get();
        }
    }

    public static class Serializer
    {
        public void serialize(EncodingStats stats, DataOutputPlus out) throws IOException
        {
            out.writeUnsignedVInt(stats.minTimestamp - TIMESTAMP_EPOCH);
            out.writeUnsignedVInt(stats.minLocalDeletionTime - DELETION_TIME_EPOCH);
            out.writeUnsignedVInt(stats.minTTL - TTL_EPOCH);
        }

        public int serializedSize(EncodingStats stats)
        {
            return TypeSizes.sizeofUnsignedVInt(stats.minTimestamp - TIMESTAMP_EPOCH)
                   + TypeSizes.sizeofUnsignedVInt(stats.minLocalDeletionTime - DELETION_TIME_EPOCH)
                   + TypeSizes.sizeofUnsignedVInt(stats.minTTL - TTL_EPOCH);
        }

        public EncodingStats deserialize(DataInputPlus in) throws IOException
        {
            long minTimestamp = in.readUnsignedVInt() + TIMESTAMP_EPOCH;
            int minLocalDeletionTime = (int)in.readUnsignedVInt() + DELETION_TIME_EPOCH;
            int minTTL = (int)in.readUnsignedVInt() + TTL_EPOCH;
            return new EncodingStats(minTimestamp, minLocalDeletionTime, minTTL);
        }
    }
}