/*
 * Copyright (C) 2019 StApps
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as
 * published by the Free Software Foundation, either version 3 of the
 * License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */
import {
  SCBulkResponse,
  SCConfigFile,
  SCFacet,
  SCSearchQuery,
  SCSearchResponse,
  SCThings,
  SCThingTypes,
  SCUuid,
} from '@openstapps/core';
import * as ES from 'elasticsearch';
import * as moment from 'moment';
import { logger } from '../../common';
import { MailQueue } from '../../notification/MailQueue';
import { Bulk } from '../BulkStorage';
import { Database } from '../Database';
import { buildAggregations, parseAggregations } from './aggregations';
import { AggregationSchema, ElasticsearchConfig, ElasticsearchObject } from './common';
import * as Monitoring from './monitoring';
import { buildQuery, buildSort } from './query';
import { putTemplate } from './templating';

// this will match index names such as stapps_<type>_<source>_<random suffix>
const indexRegex = /^stapps_([A-z0-9_]+)_([a-z0-9-_]+)_([-a-z0-9^_]+)$/;

/**
 * A database interface for elasticsearch
 */
export class Elasticsearch implements Database {

  aggregationsSchema: AggregationSchema;

  /**
   * Holds a map of all elasticsearch indices that are available to search
   */
  aliasMap: {
    // each scType has a alias which can contain multiple sources
    [scType: string]: {
      // each source is assigned a index name in elasticsearch
      [source: string]: string;
    },
  };
  client: ES.Client;
  ready: boolean;

  /**
   * Create a new interface for elasticsearch
   * @param config an assembled config file
   * @param mailQueue a mailqueue for monitoring
   */
  constructor(private config: SCConfigFile, mailQueue?: MailQueue) {

    if (!config.internal.database || typeof config.internal.database.version === 'undefined') {
      throw new Error('Database version is undefined. Check you config file');
    }

    const options = {
      apiVersion: config.internal.database.version,
      host: this.getElasticsearchUrl(),
      log: 'error',
    };

    // enable verbose logging for all request to elasticsearch
    if (process.env.ES_DEBUG === 'true') {
      options.log = 'trace';
    }

    this.client = new ES.Client(options);
    this.aliasMap = {};
    this.ready = false;

    this.aggregationsSchema = buildAggregations(this.config.internal.aggregations);

    this.getAliasMap();

    const monitoringConfiguration = this.config.internal.monitoring;

    if (typeof monitoringConfiguration !== 'undefined') {
      if (typeof mailQueue === 'undefined') {
        throw new Error('Monitoring is defined, but MailQueue is undefined. A MailQueue is obligatory for monitoring.');
      }
      // read all watches and schedule searches on the client
      Monitoring.setUp(monitoringConfiguration, this.client, mailQueue);
    }

  }

  /**
   * Tests if an object already exists
   *
   * Returns Elasticsearch Object if it exists
   */
  private async doesItemExist(object: SCThings): Promise<{exists: boolean; object?: ElasticsearchObject<SCThings>}> {
    const searchResponse = await this.client.search<SCThings>({
      body: {
        query: {
          term: {
            'uid.raw': {
              value: object.uid,
            },
          },
        },
      },
      from: 0,
      index: this.getListOfAllIndices(),
      size: 1,
    });

    if (searchResponse.hits.total > 1) {
      return {
        exists: true,
        object: searchResponse.hits.hits[0],
      };
    }

    return {
      exists: false,
    };
  }

  /**
   * Gets a map which contains each alias and all indices that are associated with each alias
   */
  private async getAliasMap() {

    // create a list of old indices that are not in use
    const oldIndicesToDelete: string[] = [];

    let aliases: {
      [index: string]: {
        aliases: {
          [K in SCThingTypes]: any
        },
      },
    };

    try {
      aliases = await this.client.indices.getAlias({});
    } catch (error) {
      logger.error('Failed getting alias map:', error);
      setTimeout(() => {
        this.getAliasMap();
      }, 5000); // retry in 5 seconds
      return;
    }

    for (const index in aliases) {
      if (aliases.hasOwnProperty(index)) {

        const matches = indexRegex.exec(index);
        if (matches !== null) {
          const type = matches[1];
          const source = matches[2];

          // check if there is an alias for the current index
          // check that alias equals type
          const hasAlias = type in aliases[index].aliases;
          if (hasAlias) {
            if (typeof this.aliasMap[type] === 'undefined') {
              this.aliasMap[type] = {};
            }
            this.aliasMap[type][source] = index;
          } else {
            oldIndicesToDelete.push(index);
          }
        }
      }
    }

    this.ready = true;

    // delete old indices that are not used in any alias
    if (oldIndicesToDelete.length > 0) {
      await this.client.indices.delete({
        index: oldIndicesToDelete,
      });
      logger.warn('Deleted old indices: ' + oldIndicesToDelete);
    }

    logger.ok('Read alias map from elasticsearch: ' + JSON.stringify(this.aliasMap, null, 2));
  }

  /**
   * Get the url of elasticsearch
   */
  private getElasticsearchUrl(): string {
    // check if we have a docker link
    if (process.env.ES_PORT_9200_TCP_ADDR !== undefined && process.env.ES_PORT_9200_TCP_PORT !== undefined) {
      return process.env.ES_PORT_9200_TCP_ADDR + ':' + process.env.ES_PORT_9200_TCP_PORT;
    }

    // default
    return 'localhost:9200';
  }

  /**
   * Gets the index name in elasticsearch for one SCThingType
   * @param type SCThingType of data in the index
   * @param source source of data in the index
   * @param bulk bulk process which created this index
   */
  private getIndex(type: SCThingTypes, source: string, bulk: SCBulkResponse) {
    return `stapps_${type.toLowerCase().replace(' ', '_')}_${source}_${bulk.uid.substring(0, 8)}`;
  }

  /**
   * Generates a string which matches all indices
   */
  private getListOfAllIndices(): string {
    // map each SC type in upper camel case
    return 'stapps_*_*_*';
  }

  /**
   * Should be called, when a new bulk was created. Creates a new index and applies a the mapping to the index
   * @param bulk the bulk process that was created
   */
  public async bulkCreated(bulk: Bulk): Promise<void> {
    // if our es instance is not ready yet, we cannot serve this request
    if (!this.ready) {
      throw new Error('No connection to elasticsearch established yet.');
    }

    // index name for elasticsearch
    const index: string = this.getIndex(bulk.type, bulk.source, bulk);

    // there already is an index with this type and source. We will index the new one and switch the alias to it
    // the old one is deleted
    const alias = bulk.type;

    if (typeof this.aliasMap[alias] === 'undefined') {
      this.aliasMap[alias] = {};
    }

    if (!indexRegex.test(index)) {
      throw new Error(
          'Index names can only consist of lowercase letters from a-z, "-", "_" and integer numbers.\n' +
          'Make sure to set the bulk "source" and "type" to names consisting of the characters above.',
      );
    }

    // re-apply the index template before each new bulk operation
    await putTemplate(this.client);
    await this.client.indices.create({
      index,
    });

    logger.info('Created index', index);
  }

  /**
   * Should be called when a bulk process is expired. The index that was created with this bulk gets deleted
   * @param bulk the bulk process that is expired
   */
  public async bulkExpired(bulk: Bulk): Promise<void> {
    // index name for elasticsearch
    const index: string = this.getIndex(bulk.type, bulk.source, bulk);

    logger.info('Bulk expired. Deleting index', index);

    // don't delete indices that are in use already
    if (bulk.state !== 'done') {
      logger.info('deleting obsolete index', index);
      return await this.client.indices.delete({ index });
    }
  }

  /**
   * Should be called when a bulk process is updated (replaced by a newer bulk). This will replace the old
   * index and publish all data, that was index in the new instead
   * @param bulk the new bulk process that should replace the old one with same type and source
   */
  public async bulkUpdated(bulk: Bulk): Promise<void> {
    // if our es instance is not ready yet, we cannot serve this request
    if (!this.ready) {
      throw new Error('Elasticsearch not ready');
    }

    // index name for elasticsearch
    const index: string = this.getIndex(bulk.type, bulk.source, bulk);

    // alias for the indices
    const alias = bulk.type;

    if (typeof this.aliasMap[alias] === 'undefined') {
      this.aliasMap[alias] = {};
    }

    if (!indexRegex.test(index)) {
      throw new Error(
          'Index names can only consist of lowercase letters from a-z, "-", "_" and integer numbers.\n' +
          'Make sure to set the bulk "source" and "type" to names consisting of the characters above.',
      );
    }

    // create the new index if it does not exists
    if (!(await this.client.indices.exists({ index }))) {
      // re-apply the index template before each new bulk operation
      await putTemplate(this.client);
      await this.client.indices.create({
        index,
      });
    }

    // get the old index from our aliasMap
    const oldIndex: string = this.aliasMap[alias][bulk.source];

    // add our new index to the alias
    const actions: ES.IndicesUpdateAliasesParamsAction[] = [
      {
        add: { index: index, alias: alias },
      },
    ];

    // remove our old index if it exists
    if (typeof oldIndex === 'string') {
      actions.push({
        remove: { index: oldIndex, alias: alias },
      });
    }

    // refresh the index (fsync changes)
    await this.client.indices.refresh({
      index,
    });

    // execute our alias actions
    await this.client.indices.updateAliases({
      body: {
        actions,
      },
    });

    // swap the index in our aliasMap
    this.aliasMap[alias][bulk.source] = index;
    if (typeof oldIndex === 'string') {
      // delete the old index
      await this.client.indices.delete({ index: oldIndex });
      logger.info('deleted old index', oldIndex);
    }
    logger.info('swapped alias index alias', oldIndex, '=>', index);
  }

  /**
   * Gets an SCThing from all indexed data
   * @param uid uid of an SCThing
   */
  public async get(uid: SCUuid): Promise<SCThings> {
    const searchResponse = await this.client.search({
      body: {
        query: {
          term: {
            uid,
          },
        },
      },
      index: this.getListOfAllIndices(),
    });

    // get data from response
    const hits = searchResponse.hits.hits;

    if (hits.length !== 1) {
      throw new Error('No unique item found.');
    } else {
      return hits[0]._source as SCThings;
    }
  }

  /**
   * Add an item to an index
   * @param object the SCThing to add to the index
   * @param bulk the bulk process which item belongs to
   */
  public async post(object: SCThings, bulk: Bulk): Promise<void> {

    const obj: SCThings & {creation_date: string} = {
      ...object,
      creation_date: moment().format(),
    };

    const itemMeta = await this.doesItemExist(obj);

    // we have to check that the item will get replaced if the index is rolled over
    if (itemMeta.exists && typeof itemMeta.object !== 'undefined') {
      const indexOfNew = this.getIndex(obj.type, bulk.source, bulk);
      const oldIndex = itemMeta.object._index;

      // new item doesn't replace the old one
      if (oldIndex.substring(0, oldIndex.length - 9) !== indexOfNew.substring(0, indexOfNew.length - 9)) {
        throw new Error(
          'Object \"' + obj.uid + '\" already exists. Object was: ' +
          JSON.stringify(obj, null, 2),
        );
      }
    }

    // regular bulk update (item gets replaced when bulk is updated)
    const searchResponse = await this.client.create({
      body: obj,
      id: obj.uid,
      index: this.getIndex(obj.type, bulk.source, bulk),
      timeout: '90s',
      type: obj.type,
    });

    if (!searchResponse.created) {
      throw new Error('Object creation Error: Instance was: ' + JSON.stringify(obj));
    }
  }

  /**
   * Put (update) an existing item
   * @param object SCThing to put
   */
  public async put(object: SCThings) {

    const itemMeta = await this.doesItemExist(object);

    if (itemMeta.exists && typeof itemMeta.object !== 'undefined') {
      return await this.client.update({
        body: {
          doc: object,
        },
        id: object.uid,
        index: itemMeta.object._index,
        type: object.type.toLowerCase(),
      });
    }

    throw new Error('You tried to PUT an non-existing object. PUT is only supported on existing objects.');
  }

  /**
   * Search all indexed data
   * @param params search query
   */
  public async search(params: SCSearchQuery): Promise<SCSearchResponse> {

    if (typeof this.config.internal.database === 'undefined') {
      throw new Error('Database is undefined. You have to configure the query build');
    }

    const searchRequest: ES.SearchParams = {
      body: {
        aggs: this.aggregationsSchema, // use cached version of aggregations (they only change if config changes)
        query: buildQuery(params, this.config, this.config.internal.database as ElasticsearchConfig),
      },
      from: params.from,
      index: this.getListOfAllIndices(),
      size: params.size,
    };

    if (typeof params.sort !== 'undefined') {
      searchRequest.body.sort = buildSort(params.sort);
    }

    // perform the search against elasticsearch
    const response = await this.client.search<SCThings>(searchRequest);

    // gather pagination information
    const pagination = {
      count: response.hits.hits.length,
      offset: (typeof params.from === 'number') ? params.from : 0,
      total: response.hits.total,
    };

    // gather statistics about this search
    const stats = {
      time: response.took,
    };

    // we only directly return the _source documents
    // elasticsearch provides much more information, the user shouldn't see
    const data = response.hits.hits.map((hit) => {
      return hit._source; // SCThing
    });

    let facets: SCFacet[] = [];

    // read the aggregations from elasticsearch and parse them to facets by our configuration
    if (typeof response.aggregations !== 'undefined') {
      facets = parseAggregations(this.aggregationsSchema, response.aggregations);
    }

    return {
      data,
      facets,
      pagination,
      stats,
    };
  }
}