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/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF 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.apache.metamodel.elasticsearch.nativeclient;

import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Comparator;
import java.util.List;
import java.util.Map;

import org.apache.metamodel.DataContext;
import org.apache.metamodel.MetaModelException;
import org.apache.metamodel.QueryPostprocessDataContext;
import org.apache.metamodel.UpdateScript;
import org.apache.metamodel.UpdateableDataContext;
import org.apache.metamodel.data.DataSet;
import org.apache.metamodel.data.DataSetHeader;
import org.apache.metamodel.data.Row;
import org.apache.metamodel.data.SimpleDataSetHeader;
import org.apache.metamodel.elasticsearch.common.ElasticSearchMetaData;
import org.apache.metamodel.elasticsearch.common.ElasticSearchUtils;
import org.apache.metamodel.query.FilterItem;
import org.apache.metamodel.query.LogicalOperator;
import org.apache.metamodel.query.SelectItem;
import org.apache.metamodel.schema.Column;
import org.apache.metamodel.schema.MutableColumn;
import org.apache.metamodel.schema.MutableSchema;
import org.apache.metamodel.schema.MutableTable;
import org.apache.metamodel.schema.Schema;
import org.apache.metamodel.schema.Table;
import org.apache.metamodel.util.SimpleTableDef;
import org.elasticsearch.Version;
import org.elasticsearch.action.admin.cluster.state.ClusterStateRequestBuilder;
import org.elasticsearch.action.count.CountResponse;
import org.elasticsearch.action.get.GetResponse;
import org.elasticsearch.action.search.SearchRequestBuilder;
import org.elasticsearch.action.search.SearchResponse;
import org.elasticsearch.client.Client;
import org.elasticsearch.cluster.ClusterState;
import org.elasticsearch.cluster.metadata.IndexMetaData;
import org.elasticsearch.cluster.metadata.MappingMetaData;
import org.elasticsearch.common.collect.ImmutableOpenMap;
import org.elasticsearch.common.hppc.ObjectLookupContainer;
import org.elasticsearch.common.hppc.cursors.ObjectCursor;
import org.elasticsearch.common.unit.TimeValue;
import org.elasticsearch.index.query.QueryBuilder;
import org.elasticsearch.index.query.QueryBuilders;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * DataContext implementation for ElasticSearch analytics engine.
 *
 * ElasticSearch has a data storage structure hierarchy that briefly goes like
 * this:
 * 
 * Index
 * Document type (short: Type) (within an index)
 * Documents (of a particular type)
 * 
 *
 * When instantiating this DataContext, an index name is provided. Within this
 * index, each document type is represented as a table.
 *
 * This implementation supports either automatic discovery of a schema or manual
 * specification of a schema, through the {@link SimpleTableDef} class.
 */
public class ElasticSearchDataContext extends QueryPostprocessDataContext implements DataContext, UpdateableDataContext {

    private static final Logger logger = LoggerFactory.getLogger(ElasticSearchDataContext.class);

    public static final TimeValue TIMEOUT_SCROLL = TimeValue.timeValueSeconds(60);

    private final Client elasticSearchClient;
    private final String indexName;
    // Table definitions that are set from the beginning, not supposed to be changed.
    private final List staticTableDefinitions;

    // Table definitions that are discovered, these can change
    private final List dynamicTableDefinitions = new ArrayList<>();

    /**
     * Constructs a {@link ElasticSearchDataContext}. This constructor accepts a
     * custom array of {@link SimpleTableDef}s which allows the user to define
     * his own view on the indexes in the engine.
     *
     * @param client
     *            the ElasticSearch client
     * @param indexName
     *            the name of the ElasticSearch index to represent
     * @param tableDefinitions
     *            an array of {@link SimpleTableDef}s, which define the table
     *            and column model of the ElasticSearch index.
     */
    public ElasticSearchDataContext(Client client, String indexName, SimpleTableDef... tableDefinitions) {
        if (client == null) {
            throw new IllegalArgumentException("ElasticSearch Client cannot be null");
        }
        if (indexName == null || indexName.trim().length() == 0) {
            throw new IllegalArgumentException("Invalid ElasticSearch Index name: " + indexName);
        }
        this.elasticSearchClient = client;
        this.indexName = indexName;
        this.staticTableDefinitions = Arrays.asList(tableDefinitions);
        this.dynamicTableDefinitions.addAll(Arrays.asList(detectSchema()));
    }

    /**
     * Constructs a {@link ElasticSearchDataContext} and automatically detects
     * the schema structure/view on all indexes (see
     * {@link #detectTable(ClusterState, String, String)}).
     *
     * @param client
     *            the ElasticSearch client
     * @param indexName
     *            the name of the ElasticSearch index to represent
     */
    public ElasticSearchDataContext(Client client, String indexName) {
        this(client, indexName, new SimpleTableDef[0]);
    }

    /**
     * Performs an analysis of the available indexes in an ElasticSearch cluster
     * {@link Client} instance and detects the elasticsearch types structure
     * based on the metadata provided by the ElasticSearch java client.
     *
     * @see {@link #detectTable(ClusterState, String, String)}
     * @return a mutable schema instance, useful for further fine tuning by the
     *         user.
     */
    private SimpleTableDef[] detectSchema() {
        logger.info("Detecting schema for index '{}'", indexName);

        final ClusterState cs;
        final ClusterStateRequestBuilder clusterStateRequestBuilder =
                getElasticSearchClient().admin().cluster().prepareState();

        // different methods here to set the index name, so we have to use
        // reflection :-/
        try {
            final byte majorVersion = Version.CURRENT.major;
            final Object methodArgument = new String[] { indexName };
            if (majorVersion == 0) {
                final Method method = ClusterStateRequestBuilder.class.getMethod("setFilterIndices", String[].class);
                method.invoke(clusterStateRequestBuilder, methodArgument);
            } else {
                final Method method = ClusterStateRequestBuilder.class.getMethod("setIndices", String[].class);
                method.invoke(clusterStateRequestBuilder, methodArgument);
            }
        } catch (Exception e) {
            logger.error("Failed to set index name on ClusterStateRequestBuilder, version {}", Version.CURRENT, e);
            throw new MetaModelException("Failed to create request for index information needed to detect schema", e);
        }
        cs = clusterStateRequestBuilder.execute().actionGet().getState();

        final List result = new ArrayList<>();

        final IndexMetaData imd = cs.getMetaData().index(indexName);
        if (imd == null) {
            // index does not exist
            logger.warn("No metadata returned for index name '{}' - no tables will be detected.");
        } else {
            final ImmutableOpenMap mappings = imd.getMappings();
            final ObjectLookupContainer documentTypes = mappings.keys();

            for (final Object documentTypeCursor : documentTypes) {
                final String documentType = ((ObjectCursor) documentTypeCursor).value.toString();
                try {
                    final SimpleTableDef table = detectTable(cs, indexName, documentType);
                    result.add(table);
                } catch (Exception e) {
                    logger.error("Unexpected error during detectTable for document type '{}'", documentType, e);
                }
            }
        }
        final SimpleTableDef[] tableDefArray = result.toArray(new SimpleTableDef[result.size()]);
        Arrays.sort(tableDefArray, new Comparator() {
            @Override
            public int compare(SimpleTableDef o1, SimpleTableDef o2) {
                return o1.getName().compareTo(o2.getName());
            }
        });

        return tableDefArray;
    }

    /**
     * Performs an analysis of an available index type in an ElasticSearch
     * {@link Client} client and tries to detect the index structure based on
     * the metadata provided by the java client.
     *
     * @param cs
     *            the ElasticSearch cluster
     * @param indexName
     *            the name of the index
     * @param documentType
     *            the name of the index type
     * @return a table definition for ElasticSearch.
     */
    public static SimpleTableDef detectTable(ClusterState cs, String indexName, String documentType) throws Exception {
        logger.debug("Detecting table for document type '{}' in index '{}'", documentType, indexName);
        final IndexMetaData imd = cs.getMetaData().index(indexName);
        if (imd == null) {
            // index does not exist
            throw new IllegalArgumentException("No such index: " + indexName);
        }
        final MappingMetaData mappingMetaData = imd.mapping(documentType);
        if (mappingMetaData == null) {
            throw new IllegalArgumentException("No such document type in index '" + indexName + "': " + documentType);
        }
        final Map mp = mappingMetaData.getSourceAsMap();
        final Object metadataProperties = mp.get("properties");
        if (metadataProperties != null && metadataProperties instanceof Map) {
            @SuppressWarnings("unchecked")
            final Map metadataPropertiesMap = (Map) metadataProperties;
            final ElasticSearchMetaData metaData = ElasticSearchMetaDataParser.parse(metadataPropertiesMap);
            final SimpleTableDef std = new SimpleTableDef(documentType, metaData.getColumnNames(),
                    metaData.getColumnTypes());
            return std;
        }
        throw new IllegalArgumentException("No mapping properties defined for document type '" + documentType
                + "' in index: " + indexName);
    }

    @Override
    protected Schema getMainSchema() throws MetaModelException {
        final MutableSchema theSchema = new MutableSchema(getMainSchemaName());
        for (final SimpleTableDef tableDef : staticTableDefinitions) {
            addTable(theSchema, tableDef);
        }

        final SimpleTableDef[] tables = detectSchema();
        synchronized (this) {
            dynamicTableDefinitions.clear();
            dynamicTableDefinitions.addAll(Arrays.asList(tables));
            for (final SimpleTableDef tableDef : dynamicTableDefinitions) {
                final List tableNames = Arrays.asList(theSchema.getTableNames());

                if (!tableNames.contains(tableDef.getName())) {
                    addTable(theSchema, tableDef);
                }
            }
        }

        return theSchema;
    }

    private void addTable(final MutableSchema theSchema, final SimpleTableDef tableDef) {
        final MutableTable table = tableDef.toTable().setSchema(theSchema);
        final Column idColumn = table.getColumnByName(ElasticSearchUtils.FIELD_ID);
        if (idColumn != null && idColumn instanceof MutableColumn) {
            final MutableColumn mutableColumn = (MutableColumn) idColumn;
            mutableColumn.setPrimaryKey(true);
        }
        theSchema.addTable(table);
    }

    @Override
    protected String getMainSchemaName() throws MetaModelException {
        return indexName;
    }

    @Override
    protected DataSet materializeMainSchemaTable(Table table, List selectItems,
            List whereItems, int firstRow, int maxRows) {
        final QueryBuilder queryBuilder = ElasticSearchUtils.createQueryBuilderForSimpleWhere(whereItems, LogicalOperator.AND);
        if (queryBuilder != null) {
            // where clause can be pushed down to an ElasticSearch query
            final SearchRequestBuilder searchRequest = createSearchRequest(table, firstRow, maxRows, queryBuilder);
            final SearchResponse response = searchRequest.execute().actionGet();
            return new ElasticSearchDataSet(elasticSearchClient, response, selectItems, false);
        }
        return super.materializeMainSchemaTable(table, selectItems, whereItems, firstRow, maxRows);
    }

    @Override
    protected DataSet materializeMainSchemaTable(Table table, Column[] columns, int maxRows) {
        final SearchRequestBuilder searchRequest = createSearchRequest(table, 1, maxRows, null);
        final SearchResponse response = searchRequest.execute().actionGet();
        return new ElasticSearchDataSet(elasticSearchClient, response, columns, false);
    }

    private SearchRequestBuilder createSearchRequest(Table table, int firstRow, int maxRows, QueryBuilder queryBuilder) {
        final String documentType = table.getName();
        final SearchRequestBuilder searchRequest = elasticSearchClient.prepareSearch(indexName).setTypes(documentType);
        if (firstRow > 1) {
            final int zeroBasedFrom = firstRow - 1;
            searchRequest.setFrom(zeroBasedFrom);
        }
        if (limitMaxRowsIsSet(maxRows)) {
            searchRequest.setSize(maxRows);
        } else {
            searchRequest.setScroll(TIMEOUT_SCROLL);
        }

        if (queryBuilder != null) {
            searchRequest.setQuery(queryBuilder);
        }

        return searchRequest;
    }

    @Override
    protected Row executePrimaryKeyLookupQuery(Table table, List selectItems, Column primaryKeyColumn,
            Object keyValue) {
        if (keyValue == null) {
            return null;
        }

        final String documentType = table.getName();
        final String id = keyValue.toString();

        final GetResponse response = elasticSearchClient.prepareGet(indexName, documentType, id).execute().actionGet();

        if (!response.isExists()) {
            return null;
        }

        final Map source = response.getSource();
        final String documentId = response.getId();

        final DataSetHeader header = new SimpleDataSetHeader(selectItems);

        return NativeElasticSearchUtils.createRow(source, documentId, header);
    }

    @Override
    protected Number executeCountQuery(Table table, List whereItems, boolean functionApproximationAllowed) {
        if (!whereItems.isEmpty()) {
            // not supported - will have to be done by counting client-side
            return null;
        }
        final String documentType = table.getName();
        final CountResponse response = elasticSearchClient.prepareCount(indexName)
                .setQuery(QueryBuilders.termQuery("_type", documentType)).execute().actionGet();
        return response.getCount();
    }

    private boolean limitMaxRowsIsSet(int maxRows) {
        return (maxRows != -1);
    }

    @Override
    public void executeUpdate(UpdateScript update) {
        final ElasticSearchUpdateCallback callback = new ElasticSearchUpdateCallback(this);
        update.run(callback);
        callback.onExecuteUpdateFinished();
    }

    /**
     * Gets the {@link Client} that this {@link DataContext} is wrapping.
     *
     * @return
     */
    public Client getElasticSearchClient() {
        return elasticSearchClient;
    }

    /**
     * Gets the name of the index that this {@link DataContext} is working on.
     *
     * @return
     */
    public String getIndexName() {
        return indexName;
    }
}