/*
 * 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.index.get;

import org.apache.lucene.index.Term;
import org.elasticsearch.ElasticsearchException;
import org.elasticsearch.common.Nullable;
import org.elasticsearch.common.bytes.BytesReference;
import org.elasticsearch.common.collect.Tuple;
import org.elasticsearch.common.lucene.uid.VersionsAndSeqNoResolver.DocIdAndVersion;
import org.elasticsearch.common.metrics.CounterMetric;
import org.elasticsearch.common.metrics.MeanMetric;
import org.elasticsearch.common.util.set.Sets;
import org.elasticsearch.common.xcontent.XContentFactory;
import org.elasticsearch.common.xcontent.XContentHelper;
import org.elasticsearch.common.xcontent.XContentType;
import org.elasticsearch.common.xcontent.support.XContentMapValues;
import org.elasticsearch.index.IndexSettings;
import org.elasticsearch.index.VersionType;
import org.elasticsearch.index.engine.Engine;
import org.elasticsearch.index.fieldvisitor.CustomFieldsVisitor;
import org.elasticsearch.index.fieldvisitor.FieldsVisitor;
import org.elasticsearch.index.mapper.DocumentMapper;
import org.elasticsearch.index.mapper.FieldMapper;
import org.elasticsearch.index.mapper.MapperService;
import org.elasticsearch.index.mapper.ParentFieldMapper;
import org.elasticsearch.index.mapper.SourceFieldMapper;
import org.elasticsearch.index.mapper.Uid;
import org.elasticsearch.index.mapper.UidFieldMapper;
import org.elasticsearch.index.shard.AbstractIndexShardComponent;
import org.elasticsearch.index.shard.IndexShard;
import org.elasticsearch.search.fetch.subphase.FetchSourceContext;
import org.elasticsearch.search.fetch.subphase.ParentFieldSubFetchPhase;

import java.io.IOException;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.concurrent.TimeUnit;

public final class ShardGetService extends AbstractIndexShardComponent {
    private final MapperService mapperService;
    private final MeanMetric existsMetric = new MeanMetric();
    private final MeanMetric missingMetric = new MeanMetric();
    private final CounterMetric currentMetric = new CounterMetric();
    private final IndexShard indexShard;

    public ShardGetService(IndexSettings indexSettings, IndexShard indexShard,
                           MapperService mapperService) {
        super(indexShard.shardId(), indexSettings);
        this.mapperService = mapperService;
        this.indexShard = indexShard;
    }

    public GetStats stats() {
        return new GetStats(existsMetric.count(), TimeUnit.NANOSECONDS.toMillis(existsMetric.sum()), missingMetric.count(), TimeUnit.NANOSECONDS.toMillis(missingMetric.sum()), currentMetric.count());
    }

    public GetResult get(String type, String id, String[] gFields, boolean realtime, long version, VersionType versionType, FetchSourceContext fetchSourceContext) {
        currentMetric.inc();
        try {
            long now = System.nanoTime();
            GetResult getResult = innerGet(type, id, gFields, realtime, version, versionType, fetchSourceContext);

            if (getResult.isExists()) {
                existsMetric.inc(System.nanoTime() - now);
            } else {
                missingMetric.inc(System.nanoTime() - now);
            }
            return getResult;
        } finally {
            currentMetric.dec();
        }
    }

    /**
     * Returns {@link GetResult} based on the specified {@link org.elasticsearch.index.engine.Engine.GetResult} argument.
     * This method basically loads specified fields for the associated document in the engineGetResult.
     * This method load the fields from the Lucene index and not from transaction log and therefore isn't realtime.
     * <p>
     * Note: Call <b>must</b> release engine searcher associated with engineGetResult!
     */
    public GetResult get(Engine.GetResult engineGetResult, String id, String type, String[] fields, FetchSourceContext fetchSourceContext) {
        if (!engineGetResult.exists()) {
            return new GetResult(shardId.getIndexName(), type, id, -1, false, null, null);
        }

        currentMetric.inc();
        try {
            long now = System.nanoTime();
            fetchSourceContext = normalizeFetchSourceContent(fetchSourceContext, fields);
            GetResult getResult = innerGetLoadFromStoredFields(type, id, fields, fetchSourceContext, engineGetResult, mapperService);
            if (getResult.isExists()) {
                existsMetric.inc(System.nanoTime() - now);
            } else {
                missingMetric.inc(System.nanoTime() - now); // This shouldn't happen...
            }
            return getResult;
        } finally {
            currentMetric.dec();
        }
    }

    /**
     * decides what needs to be done based on the request input and always returns a valid non-null FetchSourceContext
     */
    private FetchSourceContext normalizeFetchSourceContent(@Nullable FetchSourceContext context, @Nullable String[] gFields) {
        if (context != null) {
            return context;
        }
        if (gFields == null) {
            return FetchSourceContext.FETCH_SOURCE;
        }
        for (String field : gFields) {
            if (SourceFieldMapper.NAME.equals(field)) {
                return FetchSourceContext.FETCH_SOURCE;
            }
        }
        return FetchSourceContext.DO_NOT_FETCH_SOURCE;
    }

    private GetResult innerGet(String type, String id, String[] gFields, boolean realtime, long version, VersionType versionType, FetchSourceContext fetchSourceContext) {
        fetchSourceContext = normalizeFetchSourceContent(fetchSourceContext, gFields);

        Engine.GetResult get = null;
        if (type == null || type.equals("_all")) {
            for (String typeX : mapperService.types()) {
                get = indexShard.get(new Engine.Get(realtime, new Term(UidFieldMapper.NAME, Uid.createUidAsBytes(typeX, id)))
                        .version(version).versionType(versionType));
                if (get.exists()) {
                    type = typeX;
                    break;
                } else {
                    get.release();
                }
            }
            if (get == null) {
                return new GetResult(shardId.getIndexName(), type, id, -1, false, null, null);
            }
            if (!get.exists()) {
                // no need to release here as well..., we release in the for loop for non exists
                return new GetResult(shardId.getIndexName(), type, id, -1, false, null, null);
            }
        } else {
            get = indexShard.get(new Engine.Get(realtime, new Term(UidFieldMapper.NAME, Uid.createUidAsBytes(type, id)))
                    .version(version).versionType(versionType));
            if (!get.exists()) {
                get.release();
                return new GetResult(shardId.getIndexName(), type, id, -1, false, null, null);
            }
        }

        try {
            // break between having loaded it from translog (so we only have _source), and having a document to load
            return innerGetLoadFromStoredFields(type, id, gFields, fetchSourceContext, get, mapperService);
        } finally {
            get.release();
        }
    }

    private GetResult innerGetLoadFromStoredFields(String type, String id, String[] gFields, FetchSourceContext fetchSourceContext, Engine.GetResult get, MapperService mapperService) {
        Map<String, GetField> fields = null;
        BytesReference source = null;
        DocIdAndVersion docIdAndVersion = get.docIdAndVersion();
        FieldsVisitor fieldVisitor = buildFieldsVisitors(gFields, fetchSourceContext);
        if (fieldVisitor != null) {
            try {
                docIdAndVersion.context.reader().document(docIdAndVersion.docId, fieldVisitor);
            } catch (IOException e) {
                throw new ElasticsearchException("Failed to get type [" + type + "] and id [" + id + "]", e);
            }
            source = fieldVisitor.source();

            if (!fieldVisitor.fields().isEmpty()) {
                fieldVisitor.postProcess(mapperService);
                fields = new HashMap<>(fieldVisitor.fields().size());
                for (Map.Entry<String, List<Object>> entry : fieldVisitor.fields().entrySet()) {
                    fields.put(entry.getKey(), new GetField(entry.getKey(), entry.getValue()));
                }
            }
        }

        DocumentMapper docMapper = mapperService.documentMapper(type);
        if (docMapper.parentFieldMapper().active()) {
            String parentId = ParentFieldSubFetchPhase.getParentId(docMapper.parentFieldMapper(), docIdAndVersion.context.reader(), docIdAndVersion.docId);
            if (fields == null) {
                fields = new HashMap<>(1);
            }
            fields.put(ParentFieldMapper.NAME, new GetField(ParentFieldMapper.NAME, Collections.singletonList(parentId)));
        }

        if (gFields != null && gFields.length > 0) {
            for (String field : gFields) {
                FieldMapper fieldMapper = docMapper.mappers().smartNameFieldMapper(field);
                if (fieldMapper == null) {
                    if (docMapper.objectMappers().get(field) != null) {
                        // Only fail if we know it is a object field, missing paths / fields shouldn't fail.
                        throw new IllegalArgumentException("field [" + field + "] isn't a leaf field");
                    }
                }
            }
        }

        if (!fetchSourceContext.fetchSource()) {
            source = null;
        } else if (fetchSourceContext.includes().length > 0 || fetchSourceContext.excludes().length > 0) {
            Map<String, Object> sourceAsMap;
            XContentType sourceContentType = null;
            // TODO: The source might parsed and available in the sourceLookup but that one uses unordered maps so different. Do we care?
            Tuple<XContentType, Map<String, Object>> typeMapTuple = XContentHelper.convertToMap(source, true);
            sourceContentType = typeMapTuple.v1();
            sourceAsMap = typeMapTuple.v2();
            sourceAsMap = XContentMapValues.filter(sourceAsMap, fetchSourceContext.includes(), fetchSourceContext.excludes());
            try {
                source = XContentFactory.contentBuilder(sourceContentType).map(sourceAsMap).bytes();
            } catch (IOException e) {
                throw new ElasticsearchException("Failed to get type [" + type + "] and id [" + id + "] with includes/excludes set", e);
            }
        }

        return new GetResult(shardId.getIndexName(), type, id, get.version(), get.exists(), source, fields);
    }

    private static FieldsVisitor buildFieldsVisitors(String[] fields, FetchSourceContext fetchSourceContext) {
        if (fields == null || fields.length == 0) {
            return fetchSourceContext.fetchSource() ? new FieldsVisitor(true) : null;
        }

        return new CustomFieldsVisitor(Sets.newHashSet(fields), fetchSourceContext.fetchSource());
    }
}
