/**
 * 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.io.DataOutput;
import java.io.IOException;

import org.apache.hadoop.hive.ql.exec.Description;
import org.apache.hadoop.hive.ql.exec.UDFArgumentException;
import org.apache.hadoop.hive.ql.metadata.HiveException;
import org.apache.hadoop.hive.ql.parse.SemanticException;
import org.apache.hadoop.hive.serde2.objectinspector.ObjectInspector;
import org.apache.hadoop.hive.serde2.objectinspector.primitive.LongObjectInspector;
import org.apache.hadoop.hive.serde2.objectinspector.primitive.PrimitiveObjectInspectorFactory;
import org.apache.hadoop.hive.serde2.typeinfo.TypeInfo;
import org.apache.hadoop.io.LongWritable;

import edu.uci.ics.hivesterix.runtime.evaluator.BufferSerDeUtil;
import edu.uci.ics.hivesterix.runtime.evaluator.SerializableBuffer;

/**
 * This class implements the COUNT aggregation function as in SQL.
 */
@Description(name = "count", value = "_FUNC_(*) - Returns the total number of retrieved rows, including "
        + "rows containing NULL values.\n"

        + "_FUNC_(expr) - Returns the number of rows for which the supplied " + "expression is non-NULL.\n"

        + "_FUNC_(DISTINCT expr[, expr...]) - Returns the number of rows for "
        + "which the supplied expression(s) are unique and non-NULL.")
public class GenericUDAFCount implements GenericUDAFResolver2 {

    @Override
    public GenericUDAFEvaluator getEvaluator(TypeInfo[] parameters) throws SemanticException {
        // This method implementation is preserved for backward compatibility.
        return new GenericUDAFCountEvaluator();
    }

    @Override
    public GenericUDAFEvaluator getEvaluator(GenericUDAFParameterInfo paramInfo) throws SemanticException {

        TypeInfo[] parameters = paramInfo.getParameters();

        if (parameters.length == 0) {
            if (!paramInfo.isAllColumns()) {
                throw new UDFArgumentException("Argument expected");
            }
            assert !paramInfo.isDistinct() : "DISTINCT not supported with *";
        } else {
            if (parameters.length > 1 && !paramInfo.isDistinct()) {
                throw new UDFArgumentException("DISTINCT keyword must be specified");
            }
            assert !paramInfo.isAllColumns() : "* not supported in expression list";
        }

        return new GenericUDAFCountEvaluator().setCountAllColumns(paramInfo.isAllColumns());
    }

    /**
     * GenericUDAFCountEvaluator.
     */
    public static class GenericUDAFCountEvaluator extends GenericUDAFEvaluator {
        private boolean countAllColumns = false;
        private LongObjectInspector partialCountAggOI;
        private LongWritable result;

        @Override
        public ObjectInspector init(Mode m, ObjectInspector[] parameters) throws HiveException {
            super.init(m, parameters);
            partialCountAggOI = PrimitiveObjectInspectorFactory.writableLongObjectInspector;
            result = new LongWritable(0);
            return PrimitiveObjectInspectorFactory.writableLongObjectInspector;
        }

        private GenericUDAFCountEvaluator setCountAllColumns(boolean countAllCols) {
            countAllColumns = countAllCols;
            return this;
        }

        /** class for storing count value. */
        static class CountAgg implements SerializableBuffer {
            long value;

            @Override
            public void deSerializeAggBuffer(byte[] data, int start, int len) {
                value = BufferSerDeUtil.getLong(data, start);
            }

            @Override
            public void serializeAggBuffer(byte[] data, int start, int len) {
                BufferSerDeUtil.writeLong(value, data, start);
            }

            @Override
            public void serializeAggBuffer(DataOutput output) throws IOException {
                output.writeLong(value);
            }
        }

        @Override
        public AggregationBuffer getNewAggregationBuffer() throws HiveException {
            CountAgg buffer = new CountAgg();
            reset(buffer);
            return buffer;
        }

        @Override
        public void reset(AggregationBuffer agg) throws HiveException {
            ((CountAgg) agg).value = 0;
        }

        @Override
        public void iterate(AggregationBuffer agg, Object[] parameters) throws HiveException {
            // parameters == null means the input table/split is empty
            if (parameters == null) {
                return;
            }
            if (countAllColumns) {
                assert parameters.length == 0;
                ((CountAgg) agg).value++;
            } else {
                assert parameters.length > 0;
                boolean countThisRow = true;
                for (Object nextParam : parameters) {
                    if (nextParam == null) {
                        countThisRow = false;
                        break;
                    }
                }
                if (countThisRow) {
                    ((CountAgg) agg).value++;
                }
            }
        }

        @Override
        public void merge(AggregationBuffer agg, Object partial) throws HiveException {
            if (partial != null) {
                long p = partialCountAggOI.get(partial);
                ((CountAgg) agg).value += p;
            }
        }

        @Override
        public Object terminate(AggregationBuffer agg) throws HiveException {
            result.set(((CountAgg) agg).value);
            return result;
        }

        @Override
        public Object terminatePartial(AggregationBuffer agg) throws HiveException {
            return terminate(agg);
        }
    }
}