/*
 * 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.similarity;

import org.apache.lucene.index.FieldInvertState;
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.elasticsearch.common.settings.Settings;
import org.elasticsearch.index.IndexSettings;
import org.elasticsearch.index.IndexVersion;
import org.elasticsearch.lucene.similarity.LegacyBM25Similarity;
import org.elasticsearch.test.ESTestCase;
import org.elasticsearch.test.IndexSettingsModule;
import org.hamcrest.Matchers;

import java.util.Collections;

import static org.hamcrest.Matchers.instanceOf;

public class SimilarityServiceTests extends ESTestCase {
    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(IndexVersion.V_7_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(IndexVersion.V_7_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(IndexVersion.V_7_0_0, increasingScoresWithNormSim)
        );
        assertThat(e.getMessage(), Matchers.containsString("Similarity scores should not increase when norm increases"));
    }

}
