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

package org.opensearch.index.similarity;

import org.apache.lucene.index.FieldInvertState;
import org.apache.lucene.misc.search.similarity.LegacyBM25Similarity;
import org.apache.lucene.search.CollectionStatistics;
import org.apache.lucene.search.TermStatistics;
import org.apache.lucene.search.similarities.BooleanSimilarity;
import org.apache.lucene.search.similarities.Similarity;
import org.opensearch.Version;
import org.opensearch.common.settings.Settings;
import org.opensearch.index.IndexSettings;
import org.opensearch.test.IndexSettingsModule;
import org.opensearch.test.OpenSearchTestCase;
import org.hamcrest.Matchers;

import java.util.Collections;

import static org.hamcrest.Matchers.instanceOf;

public class SimilarityServiceTests extends OpenSearchTestCase {
    public void testDefaultSimilarity() {
        Settings settings = Settings.builder().build();
        IndexSettings indexSettings = IndexSettingsModule.newIndexSettings("test", settings);
        SimilarityService service = new SimilarityService(indexSettings, null, Collections.emptyMap());
        assertThat(service.getDefaultSimilarity(), instanceOf(LegacyBM25Similarity.class));
    }

    // Tests #16594
    public void testOverrideBuiltInSimilarity() {
        Settings settings = Settings.builder().put("index.similarity.BM25.type", "classic").build();
        IndexSettings indexSettings = IndexSettingsModule.newIndexSettings("test", settings);
        try {
            new SimilarityService(indexSettings, null, Collections.emptyMap());
            fail("can't override bm25");
        } catch (IllegalArgumentException ex) {
            assertEquals(ex.getMessage(), "Cannot redefine built-in Similarity [BM25]");
        }
    }

    public void testOverrideDefaultSimilarity() {
        Settings settings = Settings.builder().put("index.similarity.default.type", "boolean").build();
        IndexSettings indexSettings = IndexSettingsModule.newIndexSettings("test", settings);
        SimilarityService service = new SimilarityService(indexSettings, null, Collections.emptyMap());
        assertTrue(service.getDefaultSimilarity() instanceof BooleanSimilarity);
    }

    public void testSimilarityValidation() {
        Similarity negativeScoresSim = new Similarity() {

            @Override
            public long computeNorm(FieldInvertState state) {
                return state.getLength();
            }

            @Override
            public SimScorer scorer(float boost, CollectionStatistics collectionStats, TermStatistics... termStats) {
                return new SimScorer() {

                    @Override
                    public float score(float freq, long norm) {
                        return -1;
                    }

                };
            }
        };
        IllegalArgumentException e = expectThrows(
            IllegalArgumentException.class,
            () -> SimilarityService.validateSimilarity(Version.V_2_0_0, negativeScoresSim)
        );
        assertThat(e.getMessage(), Matchers.containsString("Similarities should not return negative scores"));

        Similarity decreasingScoresWithFreqSim = new Similarity() {

            @Override
            public long computeNorm(FieldInvertState state) {
                return state.getLength();
            }

            @Override
            public SimScorer scorer(float boost, CollectionStatistics collectionStats, TermStatistics... termStats) {
                return new SimScorer() {

                    @Override
                    public float score(float freq, long norm) {
                        return 1 / (freq + norm);
                    }

                };
            }
        };
        e = expectThrows(
            IllegalArgumentException.class,
            () -> SimilarityService.validateSimilarity(Version.V_2_0_0, decreasingScoresWithFreqSim)
        );
        assertThat(e.getMessage(), Matchers.containsString("Similarity scores should not decrease when term frequency increases"));

        Similarity increasingScoresWithNormSim = new Similarity() {

            @Override
            public long computeNorm(FieldInvertState state) {
                return state.getLength();
            }

            @Override
            public SimScorer scorer(float boost, CollectionStatistics collectionStats, TermStatistics... termStats) {
                return new SimScorer() {

                    @Override
                    public float score(float freq, long norm) {
                        return freq + norm;
                    }

                };
            }
        };
        e = expectThrows(
            IllegalArgumentException.class,
            () -> SimilarityService.validateSimilarity(Version.V_2_0_0, increasingScoresWithNormSim)
        );
        assertThat(e.getMessage(), Matchers.containsString("Similarity scores should not increase when norm increases"));
    }

}
