/*
 * 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 {SCBulkRequest, SCThingType} from '@openstapps/core';
import {Logger} from '@openstapps/logger';
import moment from 'moment';
import NodeCache from 'node-cache';
import {v4} from 'uuid';
import {Database} from './database';

/**
 * Possible operations with a bulk
 */
export type BulkOperation = 'create' | 'expired' | 'update';

/**
 * Describes an indexing process
 */
export class Bulk implements SCBulkRequest {
  /**
   * Expiration of the bulk
   *
   * If the bulk is not finished before the expiration date is hit, the bulk
   * and all data associated with it will be deleted
   */
  expiration: string;

  /**
   * The data source of the bulk
   *
   * Bulks with same type and source will be replaced and the data will be
   * updated when the bulk is marked as done
   */
  source: string;

  /**
   * State of the bulk
   *
   * Data can be indexed for this bulk as long as the state is `in progress`
   * and the bulk is not expired
   *
   * When the bulk is marked as `done` it replaces the previous bulk with
   * the same source and type. The data will be availabe to the user when
   * the bulk switches to done
   */
  state: 'in progress' | 'done';

  /**
   * Type of data in the bulk
   */
  type: SCThingType;

  /**
   * Unique identifier of the bulk
   */
  uid: string;

  /**
   * Creates a new bulk process
   *
   * @param request Data needed for requesting a bulk
   */
  constructor(request: SCBulkRequest) {
    this.uid = v4();
    this.state = 'in progress';

    this.expiration =
      typeof request.expiration === 'string' ? request.expiration : moment().add(1, 'hour').toISOString();
    // when should this process be finished
    // where does the process come from
    this.source = request.source;
    // which type of data is this process about to index
    this.type = request.type;
  }
}

/**
 * Cache for bulk-processes
 */
export class BulkStorage {
  /**
   * Cache for temporary storage
   */
  private readonly cache: NodeCache;

  /**
   * Creates a new BulkStorage
   *
   * @param database the database that is controlled by this bulk storage
   */
  constructor(public database: Database) {
    // a bulk lives 60 minutes if no expiration is given
    // the cache is checked every 60 seconds
    this.cache = new NodeCache({stdTTL: 3600, checkperiod: 60});

    this.cache.on('expired', async (_key, bulk: Bulk) => {
      // if the bulk is not done
      if (bulk.state !== 'done') {
        // the database can delete the data associated with this bulk
        await this.database.bulkExpired(bulk);
      }
    });
  }

  /**
   * Saves a bulk process and assigns to it a user-defined ttl (time-to-live)
   *
   * @param bulk the bulk process to save
   * @returns the bulk process that was saved
   */
  private save(bulk: Bulk): Bulk {
    const expirationInSeconds = moment(bulk.expiration).diff(moment.now()) / 1000;
    Logger.info('Bulk expires in ', expirationInSeconds, 'seconds');

    // save the item in the cache with it's expected expiration
    this.cache.set(bulk.uid, bulk, expirationInSeconds);

    return bulk;
  }

  /**
   * Create and save a new bulk process
   *
   * @param bulkRequest a request for a new bulk process
   * @returns a promise that contains the new bulk process
   */
  public async create(bulkRequest: SCBulkRequest): Promise<Bulk> {
    const bulk = new Bulk(bulkRequest);
    bulk.source = bulkRequest.source;
    bulk.type = bulkRequest.type;

    this.save(bulk);

    // tell the database that the bulk was created
    await this.database.bulkCreated(bulk);

    return bulk;
  }

  /**
   * Delete a bulk process
   *
   * @param uid uid of the bulk process
   * @returns a promise that contains the deleted bulk process
   */
  public async delete(uid: string): Promise<Bulk> {
    const bulk = this.read(uid);

    if (typeof bulk === 'undefined') {
      throw new TypeError(`Bulk that should be deleted was not found. UID was "${uid}"`);
    }

    // delete the bulk process from the cache
    this.cache.del(uid);

    // tell the database to handle the expiration of the bulk
    await this.database.bulkExpired(bulk);

    return bulk;
  }

  /**
   * Update an old bulk process (replace it with the new one)
   *
   * @param bulk new bulk process
   * @returns an empty promise
   */
  public async markAsDone(bulk: Bulk): Promise<void> {
    bulk.state = 'done';
    this.save(bulk);

    // tell the database that this is the new bulk
    await this.database.bulkUpdated(bulk);

    return;
  }

  /**
   * Read an existing bulk process
   *
   * @param uid uid of the bulk process
   * @returns a promise that contains a bulk
   */
  public read(uid: string): Bulk | undefined {
    return this.cache.get(uid);
  }
}