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/*
 * 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.phoenix.expression.function;

import org.apache.hadoop.hbase.Cell;
import org.apache.hadoop.hbase.CellUtil;
import org.apache.hadoop.hbase.io.ImmutableBytesWritable;
import org.apache.phoenix.expression.Determinism;
import org.apache.phoenix.expression.Expression;
import org.apache.phoenix.expression.KeyValueColumnExpression;
import org.apache.phoenix.parse.FunctionParseNode.BuiltInFunction;
import org.apache.phoenix.parse.PhoenixRowTimestampParseNode;
import org.apache.phoenix.schema.tuple.Tuple;
import org.apache.phoenix.schema.types.PDataType;
import org.apache.phoenix.schema.types.PDate;

import java.util.Date;
import java.util.List;

/**
 * Function to return the timestamp of the empty column which functions as the row timestamp. The
 * result returned can be used for debugging(eg. using HBase shell), logging etc.
 * Can also be used in sql predicates.
 */
@BuiltInFunction(name = PhoenixRowTimestampFunction.NAME,
        nodeClass= PhoenixRowTimestampParseNode.class,
        args = {})
public class PhoenixRowTimestampFunction extends ScalarFunction {
    public static final String NAME = "PHOENIX_ROW_TIMESTAMP";

    public PhoenixRowTimestampFunction() {
    }

    /**
     *  @param children An EMPTY_COLUMN key value expression injected thru
     *  {@link org.apache.phoenix.parse.PhoenixRowTimestampParseNode#create create}
     *  will cause the empty column key value to be evaluated during scan filter processing.
     */
    public PhoenixRowTimestampFunction(List children) {
        super(children);
        if ((children.size() != 1) || !children.get(0).getClass().isAssignableFrom(
                KeyValueColumnExpression.class)) {
            throw new IllegalArgumentException(
                    "PhoenixRowTimestampFunction should only have an "
                            + "EMPTY_COLUMN key value expression."
            );
        }
        if (!(children.get(0).getDataType().equals(PDate.INSTANCE))) {
            throw new IllegalArgumentException(
                    "PhoenixRowTimestampFunction should have an "
                            + "EMPTY_COLUMN key value expression of type PDate"
            );
        }
    }

    @Override
    public String getName() {
        return NAME;
    }

    /**
     * The evaluate method is called under the following conditions -
     * 1. When PHOENIX_ROW_TIMESTAMP() is evaluated in the projection list.
     *    Since the EMPTY_COLUMN is not part of the table column list,
     *    emptyColumnKV will be null.
     *    PHOENIX-4179 ensures that the maxTS (which will be EMPTY_COLUMN ts)
     *    is returned for the tuple.
     *
     * 2. When PHOENIX_ROW_TIMESTAMP() is evaluated in the backend as part of the where clause.
     *    Here the emptyColumnKV will not be null, since we ensured that by adding it to
     *    scan column list in PhoenixRowTimestampParseNode.
     *    In this case the emptyColumnKV.getTimestamp() is used.
     */
    @Override
    public boolean evaluate(Tuple tuple, ImmutableBytesWritable ptr) {

        if (tuple == null || tuple.size() == 0) {
            return false;
        }

        byte[] emptyCF = ((KeyValueColumnExpression)children.get(0)).getColumnFamily();
        byte[] emptyCQ = ((KeyValueColumnExpression)children.get(0)).getColumnQualifier();
        long ts;
        // Currently there is no good way to figure out if this function is being evaluated during
        // result or filter processing.
        // For now relying on whether empty column exists,
        // if true indicates filter processing else result processing.
        Cell emptyColumnKV = tuple.getValue(emptyCF, emptyCQ);
        if ((emptyColumnKV != null) && CellUtil.matchingColumn(emptyColumnKV, emptyCF, emptyCQ)) {
            ts = emptyColumnKV.getTimestamp();
        } else {
            ts = tuple.getValue(0).getTimestamp();
        }

        Date rowTimestamp = new Date(ts);
        ptr.set(PDate.INSTANCE.toBytes(rowTimestamp));
        return true;
    }

    @Override
    public PDataType getDataType() {
        return PDate.INSTANCE;
    }

    @Override
    public boolean isStateless() {
        return false;
    }

    @Override
    public Determinism getDeterminism() {
        return Determinism.PER_ROW;
    }

}