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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.hadoop.hive.ql.udf.generic;

import java.util.ArrayList;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.hive.ql.exec.Description;
import org.apache.hadoop.hive.ql.exec.UDFArgumentTypeException;
import org.apache.hadoop.hive.ql.exec.WindowFunctionDescription;
import org.apache.hadoop.hive.ql.metadata.HiveException;
import org.apache.hadoop.hive.ql.parse.SemanticException;
import org.apache.hadoop.hive.ql.udf.generic.GenericUDAFEvaluator.AggregationBuffer;
import org.apache.hadoop.hive.serde2.objectinspector.ObjectInspector;
import org.apache.hadoop.hive.serde2.objectinspector.ObjectInspectorFactory;
import org.apache.hadoop.hive.serde2.objectinspector.primitive.PrimitiveObjectInspectorFactory;
import org.apache.hadoop.hive.serde2.typeinfo.TypeInfo;
import org.apache.hadoop.io.IntWritable;

@WindowFunctionDescription
(
		description = @Description(
								name = "row_number",
								value = "_FUNC_() - The ROW_NUMBER function assigns a unique number (sequentially, starting from 1, as defined by ORDER BY) to each row within the partition."
								),
		supportsWindow = false,
		pivotResult = true
)
public class GenericUDAFRowNumber extends AbstractGenericUDAFResolver
{
	static final Log LOG = LogFactory.getLog(GenericUDAFRowNumber.class.getName());

	@Override
	public GenericUDAFEvaluator getEvaluator(TypeInfo[] parameters)
			throws SemanticException
	{
		if (parameters.length != 0)
		{
			throw new UDFArgumentTypeException(parameters.length - 1,
					"No argument is expected.");
		}
		return new GenericUDAFRowNumberEvaluator();
	}

	static class RowNumberBuffer implements AggregationBuffer
	{
		ArrayList rowNums;
		int nextRow;

		void init()
		{
			rowNums = new ArrayList();
		}

		RowNumberBuffer()
		{
			init();
			nextRow = 1;
		}

		void incr()
		{
			rowNums.add(new IntWritable(nextRow++));
		}
	}

	public static class GenericUDAFRowNumberEvaluator extends
			GenericUDAFEvaluator
	{

		@Override
		public ObjectInspector init(Mode m, ObjectInspector[] parameters)
				throws HiveException
		{
			super.init(m, parameters);
			if (m != Mode.COMPLETE)
			{
				throw new HiveException("Only COMPLETE mode supported for row_number function");
			}

			return ObjectInspectorFactory.getStandardListObjectInspector(
					PrimitiveObjectInspectorFactory.writableIntObjectInspector);
		}

		@Override
		public AggregationBuffer getNewAggregationBuffer() throws HiveException
		{
			return new RowNumberBuffer();
		}

		@Override
		public void reset(AggregationBuffer agg) throws HiveException
		{
			((RowNumberBuffer) agg).init();
		}

		@Override
		public void iterate(AggregationBuffer agg, Object[] parameters)
				throws HiveException
		{
			((RowNumberBuffer) agg).incr();
		}

		@Override
		public Object terminatePartial(AggregationBuffer agg)
				throws HiveException
		{
			throw new HiveException("terminatePartial not supported");
		}

		@Override
		public void merge(AggregationBuffer agg, Object partial)
				throws HiveException
		{
			throw new HiveException("merge not supported");
		}

		@Override
		public Object terminate(AggregationBuffer agg) throws HiveException
		{
			return ((RowNumberBuffer) agg).rowNums;
		}

	}
}