/*
 * 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.
 */

package org.elasticsearch.search.controller;

import org.apache.lucene.search.FieldComparator;
import org.apache.lucene.search.FieldDoc;
import org.apache.lucene.search.SortField;
import org.apache.lucene.util.BytesRef;
import org.apache.lucene.util.PriorityQueue;
import org.elasticsearch.ElasticsearchIllegalStateException;

import java.io.IOException;

/**
 *
 */
// LUCENE TRACK, Had to copy over in order ot improve same order tie break to take shards into account
public class ShardFieldDocSortedHitQueue extends PriorityQueue<FieldDoc> {

    volatile SortField[] fields = null;

    // used in the case where the fields are sorted by locale
    // based strings
    //volatile Collator[] collators = null;

    FieldComparator[] comparators = null;

    /**
     * Creates a hit queue sorted by the given list of fields.
     *
     * @param fields Fieldable names, in priority order (highest priority first).
     * @param size   The number of hits to retain.  Must be greater than zero.
     */
    public ShardFieldDocSortedHitQueue(SortField[] fields, int size) {
        super(size);
        setFields(fields);
    }


    /**
     * Allows redefinition of sort fields if they are <code>null</code>.
     * This is to handle the case using ParallelMultiSearcher where the
     * original list contains AUTO and we don't know the actual sort
     * type until the values come back.  The fields can only be set once.
     * This method should be synchronized external like all other PQ methods.
     *
     * @param fields
     */
    public void setFields(SortField[] fields) {
        this.fields = fields;
        //this.collators = hasCollators(fields);
        try {
            comparators = new FieldComparator[fields.length];
            for (int fieldIDX = 0; fieldIDX < fields.length; fieldIDX++) {
                comparators[fieldIDX] = fields[fieldIDX].getComparator(1, fieldIDX);
            }
        } catch (IOException e) {
            throw new ElasticsearchIllegalStateException("failed to get comparator", e);
        }
    }


    /**
     * Returns the fields being used to sort.
     */
    SortField[] getFields() {
        return fields;
    }

    /**
     * Returns whether <code>a</code> is less relevant than <code>b</code>.
     *
     * @param docA ScoreDoc
     * @param docB ScoreDoc
     * @return <code>true</code> if document <code>a</code> should be sorted after document <code>b</code>.
     */
    @SuppressWarnings("unchecked")
    @Override
    protected final boolean lessThan(final FieldDoc docA, final FieldDoc docB) {
        final int n = fields.length;
        int c = 0;
        for (int i = 0; i < n && c == 0; ++i) {
            final SortField.Type type = fields[i].getType();
            if (type == SortField.Type.STRING) {
                final BytesRef s1 = (BytesRef) docA.fields[i];
                final BytesRef s2 = (BytesRef) docB.fields[i];
                // null values need to be sorted first, because of how FieldCache.getStringIndex()
                // works - in that routine, any documents without a value in the given field are
                // put first.  If both are null, the next SortField is used
                if (s1 == null) {
                    c = (s2 == null) ? 0 : -1;
                } else if (s2 == null) {
                    c = 1;
                } else { //if (fields[i].getLocale() == null) {
                    c = s1.compareTo(s2);
                }
//                } else {
//                    c = collators[i].compare(s1, s2);
//                }
            } else {
                c = comparators[i].compareValues(docA.fields[i], docB.fields[i]);
            }
            // reverse sort
            if (fields[i].getReverse()) {
                c = -c;
            }
        }

        // avoid random sort order that could lead to duplicates (bug #31241):
        if (c == 0) {
            // CHANGE: Add shard base tie breaking
            c = docA.shardIndex - docB.shardIndex;
            if (c == 0) {
                return docA.doc > docB.doc;
            }
        }

        return c > 0;
    }
}
