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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.plain;

import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import org.apache.lucene.index.DirectoryReader;
import org.apache.lucene.index.LeafReaderContext;
import org.apache.lucene.index.OrdinalMap;
import org.apache.lucene.index.SortedSetDocValues;
import org.apache.lucene.index.Terms;
import org.apache.lucene.index.TermsEnum;
import org.apache.lucene.util.BytesRef;
import org.elasticsearch.ElasticsearchException;
import org.elasticsearch.index.fielddata.IndexFieldDataCache;
import org.elasticsearch.index.fielddata.IndexOrdinalsFieldData;
import org.elasticsearch.index.fielddata.LeafOrdinalsFieldData;
import org.elasticsearch.index.fielddata.RamAccountingTermsEnum;
import org.elasticsearch.index.fielddata.ordinals.GlobalOrdinalsBuilder;
import org.elasticsearch.index.fielddata.ordinals.GlobalOrdinalsIndexFieldData;
import org.elasticsearch.indices.breaker.CircuitBreakerService;
import org.elasticsearch.script.field.ToScriptFieldFactory;
import org.elasticsearch.search.aggregations.support.ValuesSourceType;

import java.io.IOException;

public abstract class AbstractIndexOrdinalsFieldData implements IndexOrdinalsFieldData {
    private static final Logger logger = LogManager.getLogger(AbstractIndexOrdinalsFieldData.class);

    private final String fieldName;
    private final ValuesSourceType valuesSourceType;
    private final IndexFieldDataCache cache;
    protected final CircuitBreakerService breakerService;
    protected final ToScriptFieldFactory toScriptFieldFactory;

    protected AbstractIndexOrdinalsFieldData(
        String fieldName,
        ValuesSourceType valuesSourceType,
        IndexFieldDataCache cache,
        CircuitBreakerService breakerService,
        ToScriptFieldFactory toScriptFieldFactory
    ) {
        this.fieldName = fieldName;
        this.valuesSourceType = valuesSourceType;
        this.cache = cache;
        this.breakerService = breakerService;
        this.toScriptFieldFactory = toScriptFieldFactory;
    }

    @Override
    public String getFieldName() {
        return this.fieldName;
    }

    @Override
    public ValuesSourceType getValuesSourceType() {
        return valuesSourceType;
    }

    @Override
    public OrdinalMap getOrdinalMap() {
        return null;
    }

    @Override
    public LeafOrdinalsFieldData load(LeafReaderContext context) {
        if (context.reader().getFieldInfos().fieldInfo(fieldName) == null) {
            // Some leaf readers may be wrapped and report different set of fields and use the same cache key.
            // If a field can't be found then it doesn't mean it isn't there,
            // so if a field doesn't exist then we don't cache it and just return an empty field data instance.
            // The next time the field is found, we do cache.
            return AbstractLeafOrdinalsFieldData.empty(toScriptFieldFactory);
        }

        try {
            return cache.load(context, this);
        } catch (Exception e) {
            if (e instanceof ElasticsearchException) {
                throw (ElasticsearchException) e;
            } else {
                throw new ElasticsearchException(e);
            }
        }
    }

    @Override
    public IndexOrdinalsFieldData loadGlobal(DirectoryReader indexReader) {
        IndexOrdinalsFieldData fieldData = loadGlobalInternal(indexReader);
        if (fieldData instanceof GlobalOrdinalsIndexFieldData) {
            // we create a new instance of the cached value for each consumer in order
            // to avoid creating new TermsEnums for each segment in the cached instance
            return ((GlobalOrdinalsIndexFieldData) fieldData).newConsumer(indexReader);
        } else {
            return fieldData;
        }
    }

    private IndexOrdinalsFieldData loadGlobalInternal(DirectoryReader indexReader) {
        if (indexReader.leaves().size() <= 1) {
            // ordinals are already global
            return this;
        }
        boolean fieldFound = false;
        for (LeafReaderContext context : indexReader.leaves()) {
            if (context.reader().getFieldInfos().fieldInfo(getFieldName()) != null) {
                fieldFound = true;
                break;
            }
        }
        if (fieldFound == false) {
            // Some directory readers may be wrapped and report different set of fields and use the same cache key.
            // If a field can't be found then it doesn't mean it isn't there,
            // so if a field doesn't exist then we don't cache it and just return an empty field data instance.
            // The next time the field is found, we do cache.
            try {
                return GlobalOrdinalsBuilder.buildEmpty(indexReader, this, toScriptFieldFactory);
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }
        try {
            return cache.load(indexReader, this);
        } catch (Exception e) {
            if (e instanceof ElasticsearchException) {
                throw (ElasticsearchException) e;
            } else {
                throw new ElasticsearchException(e);
            }
        }
    }

    @Override
    public IndexOrdinalsFieldData loadGlobalDirect(DirectoryReader indexReader) throws Exception {
        return GlobalOrdinalsBuilder.build(indexReader, this, breakerService, logger, toScriptFieldFactory);
    }

    @Override
    public boolean supportsGlobalOrdinalsMapping() {
        return false;
    }

    /**
     * A {@code PerValueEstimator} is a sub-class that can be used to estimate
     * the memory overhead for loading the data. Each field data
     * implementation should implement its own {@code PerValueEstimator} if it
     * intends to take advantage of the CircuitBreaker.
     * 
     * Note that the .beforeLoad(...) and .afterLoad(...) methods must be
     * manually called.
     */
    public interface PerValueEstimator {

        /**
         * @return the number of bytes for the given term
         */
        long bytesPerValue(BytesRef term);

        /**
         * Execute any pre-loading estimations for the terms. May also
         * optionally wrap a {@link TermsEnum} in a
         * {@link RamAccountingTermsEnum}
         * which will estimate the memory on a per-term basis.
         *
         * @param terms terms to be estimated
         * @return A TermsEnum for the given terms
         */
        TermsEnum beforeLoad(Terms terms) throws IOException;

        /**
         * Possibly adjust a circuit breaker after field data has been loaded,
         * now that the actual amount of memory used by the field data is known
         *
         * @param termsEnum  terms that were loaded
         * @param actualUsed actual field data memory usage
         */
        void afterLoad(TermsEnum termsEnum, long actualUsed);
    }
}