/*
 * 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.sampler;

import org.apache.lucene.index.LeafReaderContext;
import org.elasticsearch.common.ParseField;
import org.elasticsearch.common.lease.Releasables;
import org.elasticsearch.search.aggregations.AggregationExecutionException;
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.bucket.DeferringBucketCollector;
import org.elasticsearch.search.aggregations.bucket.SingleBucketAggregator;
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.List;
import java.util.Map;

/**
 * Aggregate on only the top-scoring docs on a shard.
 *
 * TODO currently the diversity feature of this agg offers only 'script' and
 * 'field' as a means of generating a de-dup value. In future it would be nice
 * if users could use any of the "bucket" aggs syntax (geo, date histogram...)
 * as the basis for generating de-dup values. Their syntax for creating bucket
 * values would be preferable to users having to recreate this logic in a
 * 'script' e.g. to turn a datetime in milliseconds into a month key value.
 */
public class SamplerAggregator extends SingleBucketAggregator {

    public static final ParseField SHARD_SIZE_FIELD = new ParseField("shard_size");
    public static final ParseField MAX_DOCS_PER_VALUE_FIELD = new ParseField("max_docs_per_value");
    public static final ParseField EXECUTION_HINT_FIELD = new ParseField("execution_hint");

    public enum ExecutionMode {

        MAP(new ParseField("map")) {

            @Override
            Aggregator create(String name, AggregatorFactories factories, int shardSize, int maxDocsPerValue, ValuesSource valuesSource,
                    SearchContext context, Aggregator parent, List<PipelineAggregator> pipelineAggregators,
                    Map<String, Object> metaData) throws IOException {

                return new DiversifiedMapSamplerAggregator(name, shardSize, factories, context, parent, pipelineAggregators, metaData,
                        valuesSource,
                        maxDocsPerValue);
            }

            @Override
            boolean needsGlobalOrdinals() {
                return false;
            }

        },
        BYTES_HASH(new ParseField("bytes_hash")) {

            @Override
            Aggregator create(String name, AggregatorFactories factories, int shardSize, int maxDocsPerValue, ValuesSource valuesSource,
                    SearchContext context, Aggregator parent, List<PipelineAggregator> pipelineAggregators,
                    Map<String, Object> metaData) throws IOException {

                return new DiversifiedBytesHashSamplerAggregator(name, shardSize, factories, context, parent, pipelineAggregators,
                        metaData,
                        valuesSource,
                        maxDocsPerValue);
            }

            @Override
            boolean needsGlobalOrdinals() {
                return false;
            }

        },
        GLOBAL_ORDINALS(new ParseField("global_ordinals")) {

            @Override
            Aggregator create(String name, AggregatorFactories factories, int shardSize, int maxDocsPerValue, ValuesSource valuesSource,
                    SearchContext context, Aggregator parent, List<PipelineAggregator> pipelineAggregators,
                    Map<String, Object> metaData) throws IOException {
                return new DiversifiedOrdinalsSamplerAggregator(name, shardSize, factories, context, parent, pipelineAggregators, metaData,
                        (ValuesSource.Bytes.WithOrdinals.FieldData) valuesSource, maxDocsPerValue);
            }

            @Override
            boolean needsGlobalOrdinals() {
                return true;
            }

        };

        public static ExecutionMode fromString(String value) {
            for (ExecutionMode mode : values()) {
                if (mode.parseField.match(value)) {
                    return mode;
                }
            }
            throw new IllegalArgumentException("Unknown `execution_hint`: [" + value + "], expected any of " + values());
        }

        private final ParseField parseField;

        ExecutionMode(ParseField parseField) {
            this.parseField = parseField;
        }

        abstract Aggregator create(String name, AggregatorFactories factories, int shardSize, int maxDocsPerValue,
                ValuesSource valuesSource, SearchContext context, Aggregator parent, List<PipelineAggregator> pipelineAggregators,
                Map<String, Object> metaData) throws IOException;

        abstract boolean needsGlobalOrdinals();

        @Override
        public String toString() {
            return parseField.getPreferredName();
        }
    }


    protected final int shardSize;
    protected BestDocsDeferringCollector bdd;

    SamplerAggregator(String name, int shardSize, AggregatorFactories factories, SearchContext context,
            Aggregator parent, List<PipelineAggregator> pipelineAggregators, Map<String, Object> metaData) throws IOException {
        super(name, factories, context, parent, pipelineAggregators, metaData);
        this.shardSize = shardSize;
    }

    @Override
    public boolean needsScores() {
        return true;
    }

    @Override
    public DeferringBucketCollector getDeferringCollector() {
        bdd = new BestDocsDeferringCollector(shardSize, context.bigArrays());
        return bdd;
    }

    @Override
    protected boolean shouldDefer(Aggregator aggregator) {
        return true;
    }

    @Override
    public InternalAggregation buildAggregation(long owningBucketOrdinal) throws IOException {
        runDeferredCollections(owningBucketOrdinal);
        return new InternalSampler(name, bdd == null ? 0 : bdd.getDocCount(owningBucketOrdinal), bucketAggregations(owningBucketOrdinal),
                pipelineAggregators(),
                metaData());
    }

    @Override
    public InternalAggregation buildEmptyAggregation() {
        return new InternalSampler(name, 0, buildEmptySubAggregations(), pipelineAggregators(), metaData());
    }

    @Override
    protected LeafBucketCollector getLeafCollector(LeafReaderContext ctx, LeafBucketCollector sub) throws IOException {
        if (bdd == null) {
            throw new AggregationExecutionException("Sampler aggregation must be used with child aggregations.");
        }
        return bdd.getLeafCollector(ctx);
    }

    @Override
    protected void doClose() {
        Releasables.close(bdd);
        super.doClose();
    }

}
