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Trino - SQL Server connector
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/*
 * Licensed 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 io.trino.plugin.sqlserver;

import io.trino.matching.Capture;
import io.trino.matching.Captures;
import io.trino.matching.Pattern;
import io.trino.plugin.base.aggregation.AggregateFunctionRule;
import io.trino.plugin.jdbc.JdbcColumnHandle;
import io.trino.plugin.jdbc.JdbcExpression;
import io.trino.plugin.jdbc.expression.ParameterizedExpression;
import io.trino.spi.connector.AggregateFunction;
import io.trino.spi.expression.Variable;
import io.trino.spi.type.DoubleType;

import java.util.Optional;

import static com.google.common.base.Verify.verify;
import static io.trino.matching.Capture.newCapture;
import static io.trino.plugin.base.aggregation.AggregateFunctionPatterns.basicAggregation;
import static io.trino.plugin.base.aggregation.AggregateFunctionPatterns.functionName;
import static io.trino.plugin.base.aggregation.AggregateFunctionPatterns.singleArgument;
import static io.trino.plugin.base.expression.ConnectorExpressionPatterns.type;
import static io.trino.plugin.base.expression.ConnectorExpressionPatterns.variable;
import static io.trino.spi.type.DoubleType.DOUBLE;
import static java.lang.String.format;

public class ImplementSqlServerStdev
        implements AggregateFunctionRule
{
    private static final Capture ARGUMENT = newCapture();

    @Override
    public Pattern getPattern()
    {
        return basicAggregation()
                .with(functionName().equalTo("stddev"))
                .with(singleArgument().matching(
                        variable()
                                .with(type().matching(DoubleType.class::isInstance))
                                .capturedAs(ARGUMENT)));
    }

    @Override
    public Optional rewrite(AggregateFunction aggregateFunction, Captures captures, RewriteContext context)
    {
        Variable argument = captures.get(ARGUMENT);
        JdbcColumnHandle columnHandle = (JdbcColumnHandle) context.getAssignment(argument.getName());
        verify(columnHandle.getColumnType().equals(DOUBLE));
        verify(aggregateFunction.getOutputType().equals(DOUBLE));

        ParameterizedExpression rewrittenArgument = context.rewriteExpression(argument).orElseThrow();
        return Optional.of(new JdbcExpression(
                format("STDEV(%s)", rewrittenArgument.expression()),
                rewrittenArgument.parameters(),
                columnHandle.getJdbcTypeHandle()));
    }
}