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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.LongState;
import io.trino.spi.block.BlockBuilder;
import io.trino.spi.block.ValueBlock;
import io.trino.spi.function.AggregationFunction;
import io.trino.spi.function.AggregationState;
import io.trino.spi.function.BlockIndex;
import io.trino.spi.function.BlockPosition;
import io.trino.spi.function.CombineFunction;
import io.trino.spi.function.Description;
import io.trino.spi.function.InputFunction;
import io.trino.spi.function.OutputFunction;
import io.trino.spi.function.SqlType;
import io.trino.spi.function.TypeParameter;
import io.trino.spi.function.WindowAccumulator;
import io.trino.spi.function.WindowIndex;

import static io.trino.spi.type.BigintType.BIGINT;

@AggregationFunction(value = "count", windowAccumulator = CountColumn.CountColumnWindowAccumulator.class)
@Description("Counts the non-null values")
public final class CountColumn
{
    private CountColumn() {}

    @InputFunction
    @TypeParameter("T")
    public static void input(
            @AggregationState LongState state,
            @BlockPosition @SqlType("T") ValueBlock block,
            @BlockIndex int position)
    {
        state.setValue(state.getValue() + 1);
    }

    @CombineFunction
    public static void combine(@AggregationState LongState state, LongState otherState)
    {
        state.setValue(state.getValue() + otherState.getValue());
    }

    @OutputFunction("BIGINT")
    public static void output(@AggregationState LongState state, BlockBuilder out)
    {
        BIGINT.writeLong(out, state.getValue());
    }

    public static class CountColumnWindowAccumulator
            implements WindowAccumulator
    {
        private long count;

        @UsedByGeneratedCode
        public CountColumnWindowAccumulator() {}

        private CountColumnWindowAccumulator(long count)
        {
            this.count = count;
        }

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

        @Override
        public WindowAccumulator copy()
        {
            return new CountColumnWindowAccumulator(count);
        }

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

        @Override
        public boolean removeInput(WindowIndex index, int startPosition, int endPosition)
        {
            for (int i = startPosition; i <= endPosition; i++) {
                if (!index.isNull(0, i)) {
                    count--;
                }
            }
            return true;
        }

        @Override
        public void output(BlockBuilder blockBuilder)
        {
            BIGINT.writeLong(blockBuilder, count);
        }
    }
}