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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.index.fielddata.ordinals;

import org.apache.lucene.index.DocValues;
import org.apache.lucene.index.SortedSetDocValues;
import org.apache.lucene.util.Accountable;
import org.apache.lucene.util.Accountables;
import org.apache.lucene.util.BytesRef;
import org.apache.lucene.util.RamUsageEstimator;
import org.apache.lucene.util.packed.PackedInts;
import org.elasticsearch.index.fielddata.AbstractSortedDocValues;

import java.io.IOException;
import java.util.Collection;
import java.util.Collections;

public class SinglePackedOrdinals extends Ordinals {

    // ordinals with value 0 indicates no value
    private final PackedInts.Reader reader;
    private final int valueCount;

    public SinglePackedOrdinals(OrdinalsBuilder builder, float acceptableOverheadRatio) {
        assert builder.getNumMultiValuesDocs() == 0;
        this.valueCount = (int) builder.getValueCount();
        // We don't reuse the builder as-is because it might have been built with a higher overhead ratio
        final PackedInts.Mutable reader = PackedInts.getMutable(
            builder.maxDoc(),
            PackedInts.bitsRequired(valueCount),
            acceptableOverheadRatio
        );
        PackedInts.copy(builder.getFirstOrdinals(), 0, reader, 0, builder.maxDoc(), 8 * 1024);
        this.reader = reader;
    }

    @Override
    public long ramBytesUsed() {
        return RamUsageEstimator.NUM_BYTES_OBJECT_REF + reader.ramBytesUsed();
    }

    @Override
    public Collection getChildResources() {
        return Collections.singleton(Accountables.namedAccountable("reader", reader));
    }

    @Override
    public SortedSetDocValues ordinals(ValuesHolder values) {
        return DocValues.singleton(new Docs(this, values));
    }

    private static class Docs extends AbstractSortedDocValues {

        private final int maxOrd;
        private final PackedInts.Reader reader;
        private final ValuesHolder values;

        private int currentDoc = -1;
        private int currentOrd;

        Docs(SinglePackedOrdinals parent, ValuesHolder values) {
            this.maxOrd = parent.valueCount;
            this.reader = parent.reader;
            this.values = values;
        }

        @Override
        public int getValueCount() {
            return maxOrd;
        }

        @Override
        public BytesRef lookupOrd(int ord) {
            return values.lookupOrd(ord);
        }

        @Override
        public int ordValue() {
            return currentOrd;
        }

        @Override
        public boolean advanceExact(int docID) throws IOException {
            currentDoc = docID;
            currentOrd = (int) (reader.get(docID) - 1);
            return currentOrd != -1;
        }

        @Override
        public int docID() {
            return currentDoc;
        }
    }
}