How to host your Telegram bot on Google App Script

README.md

Telegram Bot on Google App Script

This is the source code of one of my blog post. To read the full blog post please click here.

bot.js

var token = 'xxx';

function doPost(e) {
  // Make sure to only reply to json requests
  if(e.postData.type == "application/json") {
    
    // Parse the update sent from Telegram
    var update = JSON.parse(e.postData.contents);

    // Instantiate our bot passing the update 
    var bot = new Bot(token, update);
    
    // Building commands
    var bus = new CommandBus();
    bus.on(/\/start/, function () {
      this.replyToSender("Congratulations! It works!");
    });
    
    bus.on(/\/joke\s*([A-Za-z0-9_]+)?\s*([A-Za-z0-9_]+)?/, randomJoke);
    
    // Register the command bus
    bot.register(bus);
    
    // If the update is valid, process it
    if (update) {
      bot.process();
    }   
  }      
}

function setWebhook() {
  var bot = new Bot(token, {});
  var result = bot.request('setWebhook', {
    url: ScriptApp.getService().getUrl()
  });
  
  Logger.log(result);
}

function randomJoke(name, surname) {
  var firstName = name || null;
  var lastName = surname || null;
      
  var url = 'http://api.icndb.com/jokes/random?escape=javascript';
  
  if (firstName) url += '&firstName=' + firstName;
  if (lastName) url += '&lastName=' + lastName;
  
  var data = JSON.parse(UrlFetchApp.fetch(url).getContentText());

  this.replyToSender(data.value.joke);
}

function Bot (token, update) {
  this.token = token;
  this.update = update;
  this.handlers = [];
}

Bot.prototype.register = function ( handler) {
  this.handlers.push(handler);
}

Bot.prototype.process = function () {  
  for (var i in this.handlers) {
    var event = this.handlers[i];
    var result = event.condition(this);
    if (result) {
      return event.handle(this);
    }
  }
}

Bot.prototype.request = function (method, data) {
  var options = {
    'method' : 'post',
    'contentType': 'application/json',
    'payload' : JSON.stringify(data)
  };
  
  var response = UrlFetchApp.fetch('https://api.telegram.org/bot' + this.token + '/' + method, options);
    
  if (response.getResponseCode() == 200) {
    return JSON.parse(response.getContentText());
  }
  
  return false;
}

Bot.prototype.replyToSender = function (text) {
  return this.request('sendMessage', {
    'chat_id': this.update.message.from.id,
    'text': text
  });
}

function CommandBus() {
  this.commands = [];
}

CommandBus.prototype.on = function (regexp, callback) {
  this.commands.push({'regexp': regexp, 'callback': callback});
}

CommandBus.prototype.condition = function (bot) {
  return bot.update.message.text.charAt(0) === '/';
}

CommandBus.prototype.handle = function (bot) {  
  for (var i in this.commands) {
    var cmd = this.commands[i];
    var tokens = cmd.regexp.exec(bot.update.message.text);
    if (tokens != null) {
      return cmd.callback.apply(bot, tokens.splice(1));
    }
  }
  return bot.replyToSender("Invalid command");
}