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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;

import com.google.common.annotations.VisibleForTesting;
import io.trino.Session;
import io.trino.spi.Page;
import io.trino.spi.block.Block;
import io.trino.spi.block.RunLengthEncodedBlock;
import io.trino.spi.type.BooleanType;
import io.trino.spi.type.Type;

import java.util.List;

import static com.google.common.base.Preconditions.checkState;
import static io.trino.operator.GroupByHash.createGroupByHash;

public class MarkDistinctHash
{
    private final GroupByHash groupByHash;
    private long nextDistinctId;

    public MarkDistinctHash(Session session, List types, boolean hasPrecomputedHash, FlatHashStrategyCompiler hashStrategyCompiler, UpdateMemory updateMemory)
    {
        this.groupByHash = createGroupByHash(session, types, hasPrecomputedHash, 10_000, hashStrategyCompiler, updateMemory);
    }

    public long getEstimatedSize()
    {
        return groupByHash.getEstimatedSize();
    }

    public Work markDistinctRows(Page page)
    {
        return new TransformWork<>(groupByHash.getGroupIds(page), groupIds -> processNextGroupIds(groupByHash.getGroupCount(), groupIds, page.getPositionCount()));
    }

    @VisibleForTesting
    public int getCapacity()
    {
        return groupByHash.getCapacity();
    }

    private Block processNextGroupIds(int groupCount, int[] ids, int positions)
    {
        if (positions > 1) {
            // must have > 1 positions to benefit from using a RunLengthEncoded block
            if (nextDistinctId == groupCount) {
                // no new distinct positions
                return RunLengthEncodedBlock.create(BooleanType.createBlockForSingleNonNullValue(false), positions);
            }
            if (nextDistinctId + positions == groupCount) {
                // all positions are distinct
                nextDistinctId = groupCount;
                return RunLengthEncodedBlock.create(BooleanType.createBlockForSingleNonNullValue(true), positions);
            }
        }
        byte[] distinctMask = new byte[positions];
        for (int position = 0; position < distinctMask.length; position++) {
            if (ids[position] == nextDistinctId) {
                distinctMask[position] = 1;
                nextDistinctId++;
            }
            else {
                distinctMask[position] = 0;
            }
        }
        checkState(nextDistinctId == groupCount);
        return BooleanType.wrapByteArrayAsBooleanBlockWithoutNulls(distinctMask);
    }
}