canoe

Overview

canoe is a purely functional, compositional library for building Telegram bots. It provides functional streaming interface over Telegram Bot API and allows you to build interactive chatbots using idiomatic Scala code.

Getting started

sbt dependency:

libraryDependencies += "org.augustjune" %% "canoe" % "<version>"

You can find the latest version in releases tab or by clicking on the maven-central badge.

Imports:

import canoe.api._
import canoe.syntax._

The problem

Building interactive chatbots requires maintaining the state of each conversation, with possible interaction across them and/or using shared resources. The complexity of this task grows rapidly with the advancement of the bot. canoe solves this problem by decomposing behavior of the bot into the set of scenarios which the chatbot will follow.

Example

Here's a quick example of how the definition of simple bot behavior looks like in canoe. More samples can be found here.

import canoe.api._
import canoe.syntax._
import cats.effect.ConcurrentEffect
import fs2.Stream

def app[F[_]: ConcurrentEffect]: F[Unit] = 
  Stream
    .resource(TelegramClient.global[F](token))
    .flatMap { implicit client => Bot.polling[F].follow(greetings) }
    .compile.drain

def greetings[F[_]: TelegramClient]: Scenario[F, Unit] =
    for {
      chat  <- Scenario.start(command("hi").chat)
      _     <- Scenario.eval(chat.send("Hello. What's your name?"))
      name  <- Scenario.next(text)
      _     <- Scenario.eval(chat.send(s"Nice to meet you, $name"))
    } yield ()

Regardless of whether you decide to use scenarios for steering the bot, you are still able to use all functionality of Telegram Bot API in a streaming context, as it is demonstrated here.

Telegram Bot API methods

Low level abstractions are available through standalone Telegram Bot API methods from canoe.methods package. Having instance of TelegramClient in implicit scope, you can use call method on constructed action in order to execute it in effect F.

def sendText[F[_]: TelegramClient](chatId: Long, text: String): F[TextMessage] = 
  SendMessage(chatId, text).call

As an alternative, all the methods from Telegram Bot API are available from corresponding models, e.g.chat.kickUser(user.id), message.editText("edited").

Webhook support

canoe also provides support for obtaining messages from Telegram by setting a webhook. The same app described above would look this way using webhook version. Full example may be found here.

import canoe.api._
import canoe.syntax._
import cats.effect.{ConcurrentEffect, Timer}
import fs2.Stream

val url: String = "<your server url>"

def app[F[_]: ConcurrentEffect: Timer]: F[Unit] =
    Stream
      .resource(TelegramClient.global[F](token))
      .flatMap { implicit client =>
        Stream.resource(Bot.hook[F](url)).flatMap(_.follow(greetings))
      }
      .compile.drain

def greetings[F[_]: TelegramClient]: Scenario[F, Unit] = ???  // Scenario stays unchanged

Setting a webhook you have to specify the url to which Telegram updates will be sent. This address must be reachable for the Telegram, so in case you're using local environment you'd have to expose your local host to the Internet. It can be achieved using ngrok simply following this comprehensive guide.

Handling errors

There's a lot of things that may go wrong during your scenarios executions, from user input to the network issues. For this reason, Scenario forms a MonadError for any F having ApplicativeError instance. If you're not familiar with this kind of abstractions, you can just use built-in handleErrorWith and attempt methods, in order to react to the raised error or ensure that bot workflow won't break. Full example may be found here.

Contribution

If you're interested in the project PRs are very welcomed. In case it's a feature you'd like to introduce, it is recommended to discuss it first by raising an issue or simply using gitter.

codingblazes/canoe