listener-rss/src/listener-rss.ts

import Parser from "rss-parser";
import {
  ListenerRSSInfos as ListenerInfo,
  ListenerRSSInfos,
} from "./Models/ListenerRSSInfos";
import EventEmitter from "events";

const DEFAULT_TIMELOOP: number = 5 * 60; // default timeloop is 5 min

/**
 * Emit 'update' when he's making a fetch during the start fun
 * Emit 'error' when the fetch has an issue
 * Emit 'newEntries' when the fetch has new entris
 */
export class ListenerRss extends EventEmitter {
  address: string = "";
  timeloop: number = DEFAULT_TIMELOOP; // time in seconds
  customfields?: { [key: string]: string[] | string };

  // private fields
  parser: Parser;
  loopRunning: boolean = false;
  lastEntriesLinks: string[] = [];

  /**
   * @brief constructor
   * @param config ListenerRSSInfos interface who contains the ListenerInfos
   */
  constructor(config: ListenerInfo) {
    super();

    this.address = config.address;
    this.timeloop =
      config.timeloop === undefined ? DEFAULT_TIMELOOP : config.timeloop;
    this.customfields = config.customfields;
    this.lastEntriesLinks =
      config.lastEntriesLinks === undefined ? [] : config.lastEntriesLinks;

    this.parser = this.generateParser();
  }

  /**
   * @brief Private function. Is used to initilize the parser object with the customfields var
   */
  generateParser() {
    const parserConfig = this.customfields && {
      customFields: {
        feed: [],
        item: Object.entries(this.customfields).map(([, value]) => {
          return Array.isArray(value) ? value[0] : value;
        }),
      },
    };
    return new Parser(parserConfig);
  }

  /**
   * @brief use the parseURL function from rss-parser with the objects data
   * @return return a promise with the received data
   */
  fetchRSS(): Promise<Parser.Output<any>> {
    return this.parser.parseURL(this.address);
  }

  /**
   * @brief call the callback function each looptime
   */
  start(): void {
    this.loopRunning = true;

    const fun: () => void = async () => {
      await Promise.resolve(
        this.fetchRSS()
          .then((obj: { [key: string]: any }) => {
            this.emit("update", obj);
            const updatedEntriesLinks = obj.items.map(
              (item: { link: string }) => item.link
            );

            const newEntries = obj.items.filter(
              (item: { link: string }) =>
                !this.lastEntriesLinks.includes(item.link)
            );

            if (newEntries.length !== 0) {
              this.emit("newEntries", newEntries);
            }
            this.lastEntriesLinks = updatedEntriesLinks;
          })
          .catch((err) => this.emit("error", err))
      );
    };

    (async () => {
      while (this.loopRunning) {
        await fun();
        await new Promise((res) => setTimeout(res, this.timeloop * 1000));
      }
    })();
  }

  /**
   * @brief stop the async function
   */
  stop(): void {
    this.loopRunning = false;
  }

  /**
   *  @brief parse the datas inti a ListenerRSSInfos object
   *  @return return a ListenerRSSInfos object
   */
  getProperty(): ListenerRSSInfos {
    return {
      address: this.address,
      customfields: this.customfields,
      lastEntriesLinks: this.lastEntriesLinks,
      timeloop: this.timeloop,
    };
  }
}