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 *     Redistributions of source code must retain the above copyright notice,
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package com.salesforce.phoenix.expression.function;

import java.sql.SQLException;
import java.util.List;

import org.apache.hadoop.hbase.io.ImmutableBytesWritable;

import com.salesforce.phoenix.exception.SQLExceptionCode;
import com.salesforce.phoenix.exception.SQLExceptionInfo;
import com.salesforce.phoenix.expression.Expression;
import com.salesforce.phoenix.parse.FunctionParseNode.Argument;
import com.salesforce.phoenix.parse.FunctionParseNode.BuiltInFunction;
import com.salesforce.phoenix.schema.PDataType;
import com.salesforce.phoenix.schema.tuple.Tuple;


/**
 * 
 * Function used to provide an alternative value when the first argument is null.
 * Usage:
 * COALESCE(expr1,expr2)
 * If expr1 is not null, then it is returned, otherwise expr2 is returned. 
 *
 * TODO: better bind parameter type matching, since arg2 must be coercible
 * to arg1. consider allowing a common base type?
 * @author jtaylor
 * @since 0.1
 */
@BuiltInFunction(name=CoalesceFunction.NAME, args= {
    @Argument(),
    @Argument()} )
public class CoalesceFunction extends ScalarFunction {
    public static final String NAME = "COALESCE";

    public CoalesceFunction() {
    }

    public CoalesceFunction(List<Expression> children) throws SQLException {
        super(children);
        if (!children.get(1).getDataType().isCoercibleTo(children.get(0).getDataType())) {
            throw new SQLExceptionInfo.Builder(SQLExceptionCode.CANNOT_CONVERT_TYPE)
                .setMessage(getName() + " expected " + children.get(0).getDataType() + ", but got " + children.get(1).getDataType())
                .build().buildException();
        }
    }

    @Override
    public boolean evaluate(Tuple tuple, ImmutableBytesWritable ptr) {
        if (children.get(0).evaluate(tuple, ptr)) {
            return true;
        }
        return children.get(1).evaluate(tuple, ptr);
    }

    @Override
    public PDataType getDataType() {
        return children.get(0).getDataType();
    }

    @Override
    public Integer getByteSize() {
        Integer maxByteSize1 = children.get(0).getByteSize();
        if (maxByteSize1 != null) {
            Integer maxByteSize2 = children.get(1).getByteSize();
            if (maxByteSize2 != null) {
                return maxByteSize1 > maxByteSize2 ? maxByteSize1 : maxByteSize2;
            }
        }
        return null;
    }

    @Override
    public boolean isNullable() {
        return children.get(0).isNullable() && children.get(1).isNullable();
    }

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