/*
 * 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.cassandra.db;

import java.nio.ByteBuffer;

import org.apache.cassandra.db.composites.CellName;
import org.apache.cassandra.db.composites.CellNameType;
import org.apache.cassandra.db.context.CounterContext;
import org.apache.cassandra.utils.Allocator;
import org.apache.cassandra.utils.ByteBufferUtil;
import org.apache.cassandra.utils.HeapAllocator;

/**
 * A counter update while it hasn't been applied yet by the leader replica.
 *
 * Contains a single counter update. When applied by the leader replica, this
 * is transformed to a relevant CounterCell. This Cell is a temporary data
 * structure that should never be stored inside a memtable or an sstable.
 */
public class CounterUpdateCell extends Cell
{
    public CounterUpdateCell(CellName name, long value, long timestamp)
    {
        this(name, ByteBufferUtil.bytes(value), timestamp);
    }

    public CounterUpdateCell(CellName name, ByteBuffer value, long timestamp)
    {
        super(name, value, timestamp);
    }

    public long delta()
    {
        return value().getLong(value().position());
    }

    @Override
    public Cell diff(Cell cell)
    {
        // Diff is used during reads, but we should never read those columns
        throw new UnsupportedOperationException("This operation is unsupported on CounterUpdateCell.");
    }

    @Override
    public Cell reconcile(Cell cell, Allocator allocator)
    {
        // The only time this could happen is if a batchAdd ships two
        // increment for the same cell. Hence we simply sums the delta.

        assert (cell instanceof CounterUpdateCell) || (cell instanceof DeletedCell) : "Wrong class type.";

        // tombstones take precedence
        if (cell.isMarkedForDelete(Long.MIN_VALUE)) // can't be an expired cell, so the current time is irrelevant
            return timestamp() > cell.timestamp() ? this : cell;

        // neither is tombstoned
        CounterUpdateCell c = (CounterUpdateCell) cell;
        return new CounterUpdateCell(name(), delta() + c.delta(), Math.max(timestamp(), c.timestamp()));
    }

    @Override
    public int serializationFlags()
    {
        return ColumnSerializer.COUNTER_UPDATE_MASK;
    }

    @Override
    public CounterCell localCopy(ColumnFamilyStore cfs)
    {
        return new CounterCell(name.copy(HeapAllocator.instance),
                               CounterContext.instance().createLocal(delta(), HeapAllocator.instance),
                               timestamp(),
                               Long.MIN_VALUE);
    }

    @Override
    public Cell localCopy(ColumnFamilyStore cfs, Allocator allocator)
    {
        return new CounterCell(name.copy(allocator),
                               CounterContext.instance().createLocal(delta(), allocator),
                               timestamp(),
                               Long.MIN_VALUE);
    }

    @Override
    public String getString(CellNameType comparator)
    {
        return String.format("%s:%s@%d", comparator.getString(name), ByteBufferUtil.toLong(value), timestamp);
    }
}