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There is a newer version: 2.18.0

/*
 * SPDX-License-Identifier: Apache-2.0
 *
 * The OpenSearch Contributors require contributions made to
 * this file be licensed under the Apache-2.0 license or a
 * compatible open source license.
 */

/*
 * Licensed to Elasticsearch under one or more contributor
 * license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright
 * ownership. Elasticsearch licenses this file to you under
 * the Apache License, Version 2.0 (the "License"); you may
 * not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

/*
 * Modifications Copyright OpenSearch Contributors. See
 * GitHub history for details.
 */

package org.opensearch.search.suggest;

import org.apache.lucene.search.IndexSearcher;
import org.apache.lucene.util.CharsRefBuilder;
import org.opensearch.common.annotation.PublicApi;

import java.io.IOException;

/**
 * Base class used for all suggester implementations
 *
 * @opensearch.api
 */
@PublicApi(since = "1.0.0")
public abstract class Suggester {

    protected abstract Suggest.Suggestion> innerExecute(
        String name,
        T suggestion,
        IndexSearcher searcher,
        CharsRefBuilder spare
    ) throws IOException;

    protected abstract Suggest.Suggestion> emptySuggestion(
        String name,
        T suggestion,
        CharsRefBuilder spare
    ) throws IOException;

    public Suggest.Suggestion> execute(
        String name,
        T suggestion,
        IndexSearcher searcher,
        CharsRefBuilder spare
    ) throws IOException {

        // we only want to output an empty suggestion on empty shards
        if (searcher.getIndexReader().numDocs() == 0) {
            return emptySuggestion(name, suggestion, spare);
        }
        return innerExecute(name, suggestion, searcher, spare);
    }

}