import fetch from 'node-fetch';
import {JSDOM} from 'jsdom';

/**
 * Given a product id, will try to find the current price of the item on the
 * Amazon page.
 */
export class AmazonPriceChecker {

  private readonly url: string;

  constructor(id: string) {
    this.url = `https://www.amazon.com/gp/product/${id}`;
  }

  /**
   * Returns a payload of the url for the product and it's current price, if
   * found. If the price cannot be determined, it will be `NaN`.
   */
  async check() {
    try {
      const response = await this.fetchProductPage();
      const body = await response.text();
      const doc = new JSDOM(body).window.document;
      let price = Number(doc.querySelector('#priceblock_ourprice')?.textContent?.trim().replace('$',''));
      return {url: this.url, price};
    } catch(e) {
      throw new Error(e);
    }
  }

  private async fetchProductPage() {
    return await fetch(this.url, {
      method: 'get',
      headers: {
        'accept-language': 'en-US',
        'Accept': 'text/html,application/xhtml+xml',
        // Make our request look like a browser.
        'User-Agent': 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/88.0.4324.11 Safari/537.36',
      }
    });
  }
}

import fetch from 'node-fetch';

/**
 * Super simple telegram wrapper that sends messages to a bot specific chat.
 */
export class TelegramBot {

  constructor(private botApiKey: string, private chatId: string) {}

  async sendMessage(text: string) {
    return await fetch(`https://api.telegram.org/bot${this.botApiKey}/sendMessage?chat_id=${this.chatId}&text=${encodeURIComponent(text)}`);
  }
}

import {AmazonPriceChecker} from './amazon_watcher';
import {TelegramBot} from './telegrambot';

const TELEGRAM_API_KEY = 'YOUR_API_KEY';
const TELEGRAM_CHAT_ID = 'YOUR_API_KEYCHAT_ID';

// The Amazon product id. The XXX in
// https://www.amazon.com/dp/XXX or https://www.amazon.com/gp/product/XXX
const AMAZON_PRODUCT_ID = 'B08KB652Q2';
const TARGET_PRICE = 300;

const MS_MINUTES = 1000 * 60;
const BASE_TIMEOUT = MS_MINUTES * 2;

const telegram = new TelegramBot(TELEGRAM_API_KEY, TELEGRAM_CHAT_ID);
const priceChecker = new AmazonPriceChecker(AMAZON_PRODUCT_ID);

/**
 * Checks the price with `priceChecker`, issues a message with `telegram` if
 * it meets our threshold, and schedules another check.
 */
async function check() {
  let timeout = BASE_TIMEOUT;
  try {
    const {url, price} = await priceChecker.check();

    if (price) {
      if (price <= TARGET_PRICE) {
        telegram.sendMessage(`Price is: ${price}. Checking again in ${timeout / MS_MINUTES} minutes. ${url}`);
      }
    } else {
      // If we can't parse the price, maybe something's wrong. We'll slow down
      // our interval a bit.
      timeout += MS_MINUTES * 5;
      telegram.sendMessage(`Could not parse price. Trying again in ${timeout / MS_MINUTES}. ${url}`);
    }

  } catch(e) {
    timeout += MS_MINUTES * 5;
    telegram.sendMessage(`There was an error fetching the price. Will check again in ${timeout / MS_MINUTES} minutes.`);
    console.error(e);
  }

  // Rinse & repeat.
  setTimeout(() => { check(); }, timeout);
}

// Start it!
check();

console.log('Checker Started. Stop with Ctrl + C.');