telegram-channel-events.js

var request = require('request-promise');
var Events  = require('events');

var emitter  = new Events();
var endpoint = 'https://t.me/spbmetro/';
var last_mid = 2288;
var pending  = 0;

function parseMessage(id) {
    return request(endpoint + id).then((res) => {
        var body = res.toString();
        var start = '<meta property="og:description" content="';
        var startPos = body.indexOf(start) + start.length;
        var endPos = body.substr(startPos, 4000).indexOf('">');
        var message = body.substr(startPos, endPos);

        if (/View In Channel/.test(body)) {
            return { id, message };
        } else {
            throw { code: 404, res: body };
        }
    });
}

function findMessage(message_id) {
    return parseMessage(message_id).catch((e) => {
        if (e && e.code !== 404) {
            throw e;
        }
        return parseMessage(message_id + 1);
    }).catch((e) => {
        if (e && e.code !== 404) {
            throw e;
        }
        return parseMessage(message_id + 2);
    });
}

setInterval(() => {
    if (pending) return;
    pending = findMessage(last_mid).then(({ message_id, description }) => {
        last_mid = message_id + 1;
        emitter.emit('update', { message_id, description });
        pending = false;
    }).catch((e) => {
        if (e.code !== 404) {
            console.error(e);
        }
        pending = false;
    });
}, 1000);



emitter.on('update', (event) => {
    console.log(event);
});