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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.mapper;

import org.apache.lucene.index.LeafReaderContext;
import org.elasticsearch.search.fetch.subphase.FetchFieldsPhase;
import org.elasticsearch.search.lookup.SourceLookup;

import java.io.IOException;
import java.util.List;

/**
 * A helper class for fetching field values during the {@link FetchFieldsPhase}. Each {@link MappedFieldType}
 * is in charge of defining a value fetcher through {@link MappedFieldType#valueFetcher}.
 */
public interface ValueFetcher {
    /**
    * Given access to a document's _source, return this field's values.
    *
    * In addition to pulling out the values, they will be parsed into a standard form.
    * For example numeric field mappers make sure to parse the source value into a number
    * of the right type.
    *
    * Note that for array values, the order in which values are returned is undefined and
    * should not be relied on.
    *
    * @param lookup a lookup structure over the document's source.
    * @param ignoredValues a mutable list to collect any ignored values as they were originally presented in source
    * @return a list a standardized field values.
    */
    List