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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.operator.aggregation;

import io.trino.annotation.UsedByGeneratedCode;
import io.trino.operator.aggregation.state.LongAndDoubleState;
import io.trino.spi.block.BlockBuilder;
import io.trino.spi.function.AggregationFunction;
import io.trino.spi.function.AggregationState;
import io.trino.spi.function.CombineFunction;
import io.trino.spi.function.InputFunction;
import io.trino.spi.function.OutputFunction;
import io.trino.spi.function.SqlType;
import io.trino.spi.function.WindowAccumulator;
import io.trino.spi.function.WindowIndex;
import io.trino.spi.type.StandardTypes;

import static io.trino.spi.type.DoubleType.DOUBLE;

@AggregationFunction(value = "avg", windowAccumulator = DoubleAverageAggregations.DoubleAverageWindowAccumulator.class)
public final class DoubleAverageAggregations
{
    private DoubleAverageAggregations() {}

    @InputFunction
    public static void input(@AggregationState LongAndDoubleState state, @SqlType(StandardTypes.DOUBLE) double value)
    {
        state.setLong(state.getLong() + 1);
        state.setDouble(state.getDouble() + value);
    }

    @CombineFunction
    public static void combine(@AggregationState LongAndDoubleState state, @AggregationState LongAndDoubleState otherState)
    {
        state.setLong(state.getLong() + otherState.getLong());
        state.setDouble(state.getDouble() + otherState.getDouble());
    }

    @OutputFunction(StandardTypes.DOUBLE)
    public static void output(@AggregationState LongAndDoubleState state, BlockBuilder out)
    {
        long count = state.getLong();
        if (count == 0) {
            out.appendNull();
        }
        else {
            double value = state.getDouble();
            DOUBLE.writeDouble(out, value / count);
        }
    }

    public static class DoubleAverageWindowAccumulator
            implements WindowAccumulator
    {
        private long count;
        private double sum;

        @UsedByGeneratedCode
        public DoubleAverageWindowAccumulator() {}

        private DoubleAverageWindowAccumulator(long count, double sum)
        {
            this.count = count;
            this.sum = sum;
        }

        @Override
        public long getEstimatedSize()
        {
            return Long.BYTES + Double.BYTES;
        }

        @Override
        public WindowAccumulator copy()
        {
            return new DoubleAverageWindowAccumulator(count, sum);
        }

        @Override
        public void addInput(WindowIndex index, int startPosition, int endPosition)
        {
            for (int i = startPosition; i <= endPosition; i++) {
                if (!index.isNull(0, i)) {
                    sum += index.getDouble(0, i);
                    count++;
                }
            }
        }

        @Override
        public boolean removeInput(WindowIndex index, int startPosition, int endPosition)
        {
            // If sum is finite, all value to be removed are finite
            if (!Double.isFinite(sum)) {
                return false;
            }

            for (int i = startPosition; i <= endPosition; i++) {
                if (!index.isNull(0, i)) {
                    sum -= index.getDouble(0, i);
                    count--;
                }
            }
            return true;
        }

        @Override
        public void output(BlockBuilder blockBuilder)
        {
            if (count == 0) {
                blockBuilder.appendNull();
            }
            else {
                DOUBLE.writeDouble(blockBuilder, sum / count);
            }
        }
    }
}