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/*
 * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
 * or more contributor license agreements. Licensed under the Elastic License
 * 2.0 and the Server Side Public License, v 1; you may not use this file except
 * in compliance with, at your election, the Elastic License 2.0 or the Server
 * Side Public License, v 1.
 */

package org.elasticsearch.common.util;

import org.apache.lucene.util.ArrayUtil;
import org.apache.lucene.util.RamUsageEstimator;
import org.elasticsearch.common.recycler.Recycler;
import org.elasticsearch.core.Releasables;

import java.lang.reflect.Array;
import java.util.Arrays;

/** Common implementation for array lists that slice data into fixed-size blocks. */
abstract class AbstractBigArray extends AbstractArray {

    private final PageCacheRecycler recycler;
    private Recycler.V[] cache;

    private final int pageShift;
    private final int pageMask;
    protected long size;

    protected AbstractBigArray(int pageSize, BigArrays bigArrays, boolean clearOnResize) {
        super(bigArrays, clearOnResize);
        this.recycler = bigArrays.recycler;
        if (pageSize < 128) {
            throw new IllegalArgumentException("pageSize must be >= 128");
        }
        if ((pageSize & (pageSize - 1)) != 0) {
            throw new IllegalArgumentException("pageSize must be a power of two");
        }
        this.pageShift = Integer.numberOfTrailingZeros(pageSize);
        this.pageMask = pageSize - 1;
        size = 0;
        if (this.recycler != null) {
            cache = new Recycler.V[16];
        } else {
            cache = null;
        }
    }

    final int numPages(long capacity) {
        final long numPages = (capacity + pageMask) >>> pageShift;
        if (numPages > Integer.MAX_VALUE) {
            throw new IllegalArgumentException("pageSize=" + (pageMask + 1) + " is too small for such as capacity: " + capacity);
        }
        return (int) numPages;
    }

    final int pageSize() {
        return pageMask + 1;
    }

    final int pageIndex(long index) {
        return (int) (index >>> pageShift);
    }

    final int indexInPage(long index) {
        return (int) (index & pageMask);
    }

    @Override
    public final long size() {
        return size;
    }

    public abstract void resize(long newSize);

    protected abstract int numBytesPerElement();

    @Override
    public final long ramBytesUsed() {
        return ramBytesEstimated(size);
    }

    /** Given the size of the array, estimate the number of bytes it will use. */
    public final long ramBytesEstimated(final long size) {
        // rough approximate, we only take into account the size of the values, not the overhead of the array objects
        return ((long) pageIndex(size - 1) + 1) * pageSize() * numBytesPerElement();
    }

    private static  T[] grow(T[] array, int minSize) {
        if (array.length < minSize) {
            final int newLen = ArrayUtil.oversize(minSize, RamUsageEstimator.NUM_BYTES_OBJECT_REF);
            array = Arrays.copyOf(array, newLen);
        }
        return array;
    }

    private  T registerNewPage(Recycler.V v, int page, int expectedSize) {
        cache = grow(cache, page + 1);
        assert cache[page] == null;
        cache[page] = v;
        assert Array.getLength(v.v()) == expectedSize;
        return v.v();
    }

    protected final byte[] newBytePage(int page) {
        if (recycler != null) {
            final Recycler.V v = recycler.bytePage(clearOnResize);
            return registerNewPage(v, page, PageCacheRecycler.BYTE_PAGE_SIZE);
        } else {
            return new byte[PageCacheRecycler.BYTE_PAGE_SIZE];
        }
    }

    protected final int[] newIntPage(int page) {
        if (recycler != null) {
            final Recycler.V v = recycler.intPage(clearOnResize);
            return registerNewPage(v, page, PageCacheRecycler.INT_PAGE_SIZE);
        } else {
            return new int[PageCacheRecycler.INT_PAGE_SIZE];
        }
    }

    protected final long[] newLongPage(int page) {
        if (recycler != null) {
            final Recycler.V v = recycler.longPage(clearOnResize);
            return registerNewPage(v, page, PageCacheRecycler.LONG_PAGE_SIZE);
        } else {
            return new long[PageCacheRecycler.LONG_PAGE_SIZE];
        }
    }

    protected final Object[] newObjectPage(int page) {
        if (recycler != null) {
            final Recycler.V v = recycler.objectPage();
            return registerNewPage(v, page, PageCacheRecycler.OBJECT_PAGE_SIZE);
        } else {
            return new Object[PageCacheRecycler.OBJECT_PAGE_SIZE];
        }
    }

    protected final void releasePage(int page) {
        if (recycler != null) {
            cache[page].close();
            cache[page] = null;
        }
    }

    @Override
    protected final void doClose() {
        if (recycler != null) {
            Releasables.close(cache);
            cache = null;
        }
    }

}