/*
 * 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", the "GNU Affero General Public License v3.0 only", 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", the "GNU Affero General Public
 * License v3.0 only", or the "Server Side Public License, v 1".
 */

package org.elasticsearch.search.fetch.subphase.highlight;

import org.apache.lucene.search.vectorhighlight.FastVectorHighlighter;
import org.apache.lucene.search.vectorhighlight.FieldFragList.WeightedFragInfo;
import org.apache.lucene.search.vectorhighlight.FieldFragList.WeightedFragInfo.SubInfo;
import org.apache.lucene.search.vectorhighlight.FragmentsBuilder;
import org.apache.lucene.util.CollectionUtil;

import java.util.List;

/**
 * Simple helper class for {@link FastVectorHighlighter} {@link FragmentsBuilder} implementations.
 */
public final class FragmentBuilderHelper {

    private FragmentBuilderHelper() {
        // no instance
    }

    /**
     * Fixes problems with broken analysis chains if positions and offsets are messed up that can lead to
     * {@link StringIndexOutOfBoundsException} in the {@link FastVectorHighlighter}
     */
    public static WeightedFragInfo fixWeightedFragInfo(WeightedFragInfo fragInfo) {
        assert fragInfo != null : "FragInfo must not be null";
        if (fragInfo.getSubInfos().isEmpty() == false) {
            /* This is a special case where broken analysis like WDF is used for term-vector creation at index-time
             * which can potentially mess up the offsets. To prevent a SAIIOBException we need to resort
             * the fragments based on their offsets rather than using solely the positions as it is done in
             * the FastVectorHighlighter. Yet, this is really a lucene problem and should be fixed in lucene rather
             * than in this hack... aka. "we are are working on in!" */
            final List<SubInfo> subInfos = fragInfo.getSubInfos();
            CollectionUtil.introSort(subInfos, (o1, o2) -> {
                int startOffset = o1.termsOffsets().get(0).getStartOffset();
                int startOffset2 = o2.termsOffsets().get(0).getStartOffset();
                return Integer.compare(startOffset, startOffset2);
            });
            return new WeightedFragInfo(
                Math.min(fragInfo.getSubInfos().get(0).termsOffsets().get(0).getStartOffset(), fragInfo.getStartOffset()),
                fragInfo.getEndOffset(),
                subInfos,
                fragInfo.getTotalBoost()
            );
        } else {
            return fragInfo;
        }
    }

}