/*
 * 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.aggregations.bucket.histogram;

import org.apache.lucene.index.LeafReaderContext;
import org.apache.lucene.util.CollectionUtil;
import org.elasticsearch.common.inject.internal.Nullable;
import org.elasticsearch.common.lease.Releasables;
import org.elasticsearch.common.util.LongHash;
import org.elasticsearch.index.fielddata.SortedNumericDoubleValues;
import org.elasticsearch.search.DocValueFormat;
import org.elasticsearch.search.aggregations.Aggregator;
import org.elasticsearch.search.aggregations.AggregatorFactories;
import org.elasticsearch.search.aggregations.InternalAggregation;
import org.elasticsearch.search.aggregations.LeafBucketCollector;
import org.elasticsearch.search.aggregations.LeafBucketCollectorBase;
import org.elasticsearch.search.aggregations.bucket.BucketsAggregator;
import org.elasticsearch.search.aggregations.bucket.histogram.InternalHistogram.EmptyBucketInfo;
import org.elasticsearch.search.aggregations.pipeline.PipelineAggregator;
import org.elasticsearch.search.aggregations.support.ValuesSource;
import org.elasticsearch.search.internal.SearchContext;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Map;

/**
 * An aggregator for numeric values. For a given {@code interval},
 * {@code offset} and {@code value}, it returns the highest number that can be
 * written as {@code interval * x + offset} and yet is less than or equal to
 * {@code value}.
 */
class HistogramAggregator extends BucketsAggregator {

    private final ValuesSource.Numeric valuesSource;
    private final DocValueFormat formatter;
    private final double interval, offset;
    private final InternalOrder order;
    private final boolean keyed;
    private final long minDocCount;
    private final double minBound, maxBound;

    private final LongHash bucketOrds;

    HistogramAggregator(String name, AggregatorFactories factories, double interval, double offset,
            InternalOrder order, boolean keyed, long minDocCount, double minBound, double maxBound,
            @Nullable ValuesSource.Numeric valuesSource, DocValueFormat formatter,
            SearchContext context, Aggregator parent,
            List<PipelineAggregator> pipelineAggregators, Map<String, Object> metaData) throws IOException {

        super(name, factories, context, parent, pipelineAggregators, metaData);
        if (interval <= 0) {
            throw new IllegalArgumentException("interval must be positive, got: " + interval);
        }
        this.interval = interval;
        this.offset = offset;
        this.order = order;
        this.keyed = keyed;
        this.minDocCount = minDocCount;
        this.minBound = minBound;
        this.maxBound = maxBound;
        this.valuesSource = valuesSource;
        this.formatter = formatter;

        bucketOrds = new LongHash(1, context.bigArrays());
    }

    @Override
    public boolean needsScores() {
        return (valuesSource != null && valuesSource.needsScores()) || super.needsScores();
    }

    @Override
    public LeafBucketCollector getLeafCollector(LeafReaderContext ctx,
            final LeafBucketCollector sub) throws IOException {
        if (valuesSource == null) {
            return LeafBucketCollector.NO_OP_COLLECTOR;
        }

        final SortedNumericDoubleValues values = valuesSource.doubleValues(ctx);
        return new LeafBucketCollectorBase(sub, values) {
            @Override
            public void collect(int doc, long bucket) throws IOException {
                assert bucket == 0;
                if (values.advanceExact(doc)) {
                    final int valuesCount = values.docValueCount();

                    double previousKey = Double.NEGATIVE_INFINITY;
                    for (int i = 0; i < valuesCount; ++i) {
                        double value = values.nextValue();
                        double key = Math.floor((value - offset) / interval);
                        assert key >= previousKey;
                        if (key == previousKey) {
                            continue;
                        }
                        long bucketOrd = bucketOrds.add(Double.doubleToLongBits(key));
                        if (bucketOrd < 0) { // already seen
                            bucketOrd = -1 - bucketOrd;
                            collectExistingBucket(sub, doc, bucketOrd);
                        } else {
                            collectBucket(sub, doc, bucketOrd);
                        }
                        previousKey = key;
                    }
                }
            }
        };
    }

    @Override
    public InternalAggregation buildAggregation(long bucket) throws IOException {
        assert bucket == 0;
        List<InternalHistogram.Bucket> buckets = new ArrayList<>((int) bucketOrds.size());
        for (long i = 0; i < bucketOrds.size(); i++) {
            double roundKey = Double.longBitsToDouble(bucketOrds.get(i));
            double key = roundKey * interval + offset;
            buckets.add(new InternalHistogram.Bucket(key, bucketDocCount(i), keyed, formatter, bucketAggregations(i)));
        }

        // the contract of the histogram aggregation is that shards must return buckets ordered by key in ascending order
        CollectionUtil.introSort(buckets, InternalOrder.KEY_ASC.comparator());

        EmptyBucketInfo emptyBucketInfo = null;
        if (minDocCount == 0) {
            emptyBucketInfo = new EmptyBucketInfo(interval, offset, minBound, maxBound, buildEmptySubAggregations());
        }
        return new InternalHistogram(name, buckets, order, minDocCount, emptyBucketInfo, formatter, keyed, pipelineAggregators(), metaData());
    }

    @Override
    public InternalAggregation buildEmptyAggregation() {
        EmptyBucketInfo emptyBucketInfo = null;
        if (minDocCount == 0) {
            emptyBucketInfo = new EmptyBucketInfo(interval, offset, minBound, maxBound, buildEmptySubAggregations());
        }
        return new InternalHistogram(name, Collections.emptyList(), order, minDocCount, emptyBucketInfo, formatter, keyed, pipelineAggregators(), metaData());
    }

    @Override
    public void doClose() {
        Releasables.close(bucketOrds);
    }
}
