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There is a newer version: 8.16.0
/*
 * 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.plugins;

import org.apache.lucene.util.Accountable;
import org.apache.lucene.util.RamUsageEstimator;
import org.elasticsearch.cluster.metadata.MappingMetadata;

import java.util.function.Predicate;

/**
 * Filter for visible fields.
 */
public interface FieldPredicate extends Accountable, Predicate {
    /**
     * The default field predicate applied, which doesn't filter anything. That means that by default get mappings, get index
     * get field mappings and field capabilities API will return every field that's present in the mappings.
     */
    FieldPredicate ACCEPT_ALL = new FieldPredicate() {
        @Override
        public boolean test(String field) {
            return true;
        }

        @Override
        public String modifyHash(String hash) {
            return hash;
        }

        @Override
        public long ramBytesUsed() {
            return 0; // Shared
        }

        @Override
        public String toString() {
            return "accept all";
        }
    };

    /**
     * Should this field be included?
     */
    @Override
    boolean test(String field);

    /**
     * Modify the {@link MappingMetadata#getSha256} to track any filtering this predicate
     * has performed on the list of fields.
     */
    String modifyHash(String hash);

    class And implements FieldPredicate {
        private static final long SHALLOW_RAM_BYTES_USED = RamUsageEstimator.shallowSizeOfInstance(And.class);

        private final FieldPredicate first;
        private final FieldPredicate second;

        public And(FieldPredicate first, FieldPredicate second) {
            this.first = first;
            this.second = second;
        }

        @Override
        public boolean test(String field) {
            return first.test(field) && second.test(field);
        }

        @Override
        public String modifyHash(String hash) {
            return second.modifyHash(first.modifyHash(hash));
        }

        @Override
        public long ramBytesUsed() {
            return SHALLOW_RAM_BYTES_USED + first.ramBytesUsed() + second.ramBytesUsed();
        }

        @Override
        public String toString() {
            return first + " then " + second;
        }
    }
}