/*
 * 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 com.facebook.presto.operator.aggregation;

import com.facebook.presto.spi.block.Block;
import com.facebook.presto.spi.block.BlockBuilder;
import com.facebook.presto.spi.type.ArrayType;
import com.facebook.presto.spi.type.RowType;
import com.facebook.presto.spi.type.Type;
import com.google.common.collect.ImmutableList;
import org.openjdk.jol.info.ClassLayout;

import java.util.Optional;

import static com.facebook.presto.spi.type.BigintType.BIGINT;
import static com.google.common.base.Preconditions.checkArgument;
import static io.airlift.slice.SizeOf.sizeOf;
import static java.lang.Math.toIntExact;

public class TypedKeyValueHeap
{
    private static final int INSTANCE_SIZE = ClassLayout.parseClass(TypedKeyValueHeap.class).instanceSize();

    private static final int COMPACT_THRESHOLD_BYTES = 32768;
    private static final int COMPACT_THRESHOLD_RATIO = 3; // when 2/3 of elements in keyBlockBuilder is unreferenced, do compact

    private final BlockComparator keyComparator;
    private final Type keyType;
    private final Type valueType;
    private final int capacity;

    private int positionCount;
    private final int[] heapIndex;
    private BlockBuilder keyBlockBuilder;
    private BlockBuilder valueBlockBuilder;

    public TypedKeyValueHeap(BlockComparator keyComparator, Type keyType, Type valueType, int capacity)
    {
        this.keyComparator = keyComparator;
        this.keyType = keyType;
        this.valueType = valueType;
        this.capacity = capacity;
        this.heapIndex = new int[capacity];
        this.keyBlockBuilder = keyType.createBlockBuilder(null, capacity);
        this.valueBlockBuilder = valueType.createBlockBuilder(null, capacity);
    }

    public static Type getSerializedType(Type keyType, Type valueType)
    {
        return new RowType(ImmutableList.of(BIGINT, new ArrayType(keyType), new ArrayType(valueType)), Optional.empty());
    }

    public int getCapacity()
    {
        return capacity;
    }

    public long getEstimatedSize()
    {
        return INSTANCE_SIZE + keyBlockBuilder.getRetainedSizeInBytes() + valueBlockBuilder.getRetainedSizeInBytes() + sizeOf(heapIndex);
    }

    public boolean isEmpty()
    {
        return positionCount == 0;
    }

    public void serialize(BlockBuilder out)
    {
        BlockBuilder blockBuilder = out.beginBlockEntry();
        BIGINT.writeLong(blockBuilder, getCapacity());

        BlockBuilder keyElements = blockBuilder.beginBlockEntry();
        for (int i = 0; i < positionCount; i++) {
            keyType.appendTo(keyBlockBuilder, heapIndex[i], keyElements);
        }
        blockBuilder.closeEntry();

        BlockBuilder valueElements = blockBuilder.beginBlockEntry();
        for (int i = 0; i < positionCount; i++) {
            valueType.appendTo(valueBlockBuilder, heapIndex[i], valueElements);
        }
        blockBuilder.closeEntry();

        out.closeEntry();
    }

    public static TypedKeyValueHeap deserialize(Block block, Type keyType, Type valueType, BlockComparator blockComparator)
    {
        int capacity = toIntExact(BIGINT.getLong(block, 0));
        Block keysBlock = new ArrayType(keyType).getObject(block, 1);
        Block valuesBlock = new ArrayType(valueType).getObject(block, 2);
        TypedKeyValueHeap heap = new TypedKeyValueHeap(blockComparator, keyType, valueType, capacity);
        heap.addAll(keysBlock, valuesBlock);
        return heap;
    }

    public void popAll(BlockBuilder resultBlockBuilder)
    {
        while (positionCount > 0) {
            pop(resultBlockBuilder);
        }
    }

    public void pop(BlockBuilder resultBlockBuilder)
    {
        valueType.appendTo(valueBlockBuilder, heapIndex[0], resultBlockBuilder);
        remove();
    }

    private void remove()
    {
        positionCount--;
        heapIndex[0] = heapIndex[positionCount];
        siftDown();
    }

    public void add(Block keyBlock, Block valueBlock, int position)
    {
        checkArgument(!keyBlock.isNull(position));
        if (positionCount == capacity) {
            if (keyComparator.compareTo(keyBlockBuilder, heapIndex[0], keyBlock, position) >= 0) {
                return; // and new element is not larger than heap top: do not add
            }
            heapIndex[0] = keyBlockBuilder.getPositionCount();
            keyType.appendTo(keyBlock, position, keyBlockBuilder);
            valueType.appendTo(valueBlock, position, valueBlockBuilder);
            siftDown();
        }
        else {
            heapIndex[positionCount] = keyBlockBuilder.getPositionCount();
            positionCount++;
            keyType.appendTo(keyBlock, position, keyBlockBuilder);
            valueType.appendTo(valueBlock, position, valueBlockBuilder);
            siftUp();
        }
        compactIfNecessary();
    }

    public void addAll(TypedKeyValueHeap otherHeap)
    {
        addAll(otherHeap.keyBlockBuilder, otherHeap.valueBlockBuilder);
    }

    public void addAll(Block keysBlock, Block valuesBlock)
    {
        for (int i = 0; i < keysBlock.getPositionCount(); i++) {
            add(keysBlock, valuesBlock, i);
        }
    }

    private void siftDown()
    {
        int position = 0;
        while (true) {
            int leftPosition = position * 2 + 1;
            if (leftPosition >= positionCount) {
                break;
            }
            int rightPosition = leftPosition + 1;
            int smallerChildPosition;
            if (rightPosition >= positionCount) {
                smallerChildPosition = leftPosition;
            }
            else {
                smallerChildPosition = keyComparator.compareTo(keyBlockBuilder, heapIndex[leftPosition], keyBlockBuilder, heapIndex[rightPosition]) >= 0 ? rightPosition : leftPosition;
            }
            if (keyComparator.compareTo(keyBlockBuilder, heapIndex[smallerChildPosition], keyBlockBuilder, heapIndex[position]) >= 0) {
                break; // child is larger or equal
            }
            int swapTemp = heapIndex[position];
            heapIndex[position] = heapIndex[smallerChildPosition];
            heapIndex[smallerChildPosition] = swapTemp;
            position = smallerChildPosition;
        }
    }

    private void siftUp()
    {
        int position = positionCount - 1;
        while (position != 0) {
            int parentPosition = (position - 1) / 2;
            if (keyComparator.compareTo(keyBlockBuilder, heapIndex[position], keyBlockBuilder, heapIndex[parentPosition]) >= 0) {
                break; // child is larger or equal
            }
            int swapTemp = heapIndex[position];
            heapIndex[position] = heapIndex[parentPosition];
            heapIndex[parentPosition] = swapTemp;
            position = parentPosition;
        }
    }

    private void compactIfNecessary()
    {
        // Byte size check is needed. Otherwise, if size * 3 is small, BlockBuilder can be reallocate too often.
        // Position count is needed. Otherwise, for large elements, heap will be compacted every time.
        // Size instead of retained size is needed because default allocation size can be huge for some block builders. And the first check will become useless in such case.
        if (keyBlockBuilder.getSizeInBytes() < COMPACT_THRESHOLD_BYTES || keyBlockBuilder.getPositionCount() / positionCount < COMPACT_THRESHOLD_RATIO) {
            return;
        }
        BlockBuilder newHeapKeyBlockBuilder = keyType.createBlockBuilder(null, keyBlockBuilder.getPositionCount());
        BlockBuilder newHeapValueBlockBuilder = valueType.createBlockBuilder(null, valueBlockBuilder.getPositionCount());
        for (int i = 0; i < positionCount; i++) {
            keyType.appendTo(keyBlockBuilder, heapIndex[i], newHeapKeyBlockBuilder);
            valueType.appendTo(valueBlockBuilder, heapIndex[i], newHeapValueBlockBuilder);
            heapIndex[i] = i;
        }
        keyBlockBuilder = newHeapKeyBlockBuilder;
        valueBlockBuilder = newHeapValueBlockBuilder;
    }
}
