mic-bot/bot/normal_mode/captcha.ts

import { Filter } from "https://deno.land/x/grammy/mod.ts";
import { BotConfig } from "../../cfg/config.ts";
import { Ctx } from "../ctx.ts";
import { LangManager } from "../lang/export.ts";
import { Kysely } from 'npm:kysely';
import { Database } from "../../repo/scheme.ts";
import { checkUserRestrictions } from "../../core/users.ts";
import type { CheckUserOnStartOut } from "./user_managment.ts";

const CAPTCHA_FAILS_LIMIT = 3
const TIMEOUT_AFTER_FAIL_MINS = 5

export interface CaptchaSessionData {
  message_id: number,
  tries_failed: number,
  generated_at: number,
  // Captcha can be changed from a simple matematical ones
  // to a more complicated images or even science-related questions
  solution:     string, 
}

const randInt = (min: number, max: number): number =>
  Math.floor(Math.random() * (max - min) + min)

// Returns captcha task (string) and the solution (number)
const genCaptcha = (): [string, number] => {
  const number1 = randInt(-100, 100)
  const number2 = randInt(-100, 100)
  return [
    `Captcha: ${number1}+${number2}=?`,
    number1 + number2
  ]
}

// User captcha response sanitizer/parser/validator
const isSolutionCorrect = (expectSolution: string, solution: string): boolean => {
  solution = solution.replace(' ','').replace('\t','') // Sanitizing
  return parseInt(solution, 10) == parseInt(expectSolution, 10) ? true : false
}


const captchaPassed = async (ctx: Ctx, db: Kysely<Database>, cfg: BotConfig) => {
  if (ctx.chatId && ctx.session.captcha_data) {
    await ctx.api.deleteMessage(
      ctx.chatId, ctx.session.captcha_data.message_id
    )
  }
  ctx.session.captcha_data = undefined

  const linkValidUntil = new Date()
  linkValidUntil.setHours(linkValidUntil.getHours() + 12)

  const link = await ctx.api.createChatInviteLink(cfg.chat_id, {
    member_limit: 1,
    expire_date: Math.floor(linkValidUntil.getTime() / 1000),
  })

  await db.transaction().execute(async trx => {
    await trx.updateTable('users').where('tg_id', '=', ctx.from!.id)
      .set({ is_captcha_passed: true }).execute()

    await trx.insertInto('invite_links').values({
      link:              link.invite_link,
      expect_user_tg_id: ctx.from!.id,
      valid_until:       linkValidUntil
    }).execute()
  })

  ctx.reply(LangManager.getLang(ctx.from!.language_code)
    .replies.captcha.passed(link.invite_link))
  ctx.session.captcha_data = undefined
}


const initUserCaptcha = async (ctx: Ctx, db: Kysely<Database>, user: CheckUserOnStartOut, cfg: BotConfig) => {
  if (user.isChatParticipant) {
    ctx.reply(LangManager.getLang(ctx.from!.language_code)
      .replies.captcha.already_in_chat)
  } else if (user.activeInviteLink) {
    await ctx.reply(user.activeInviteLink)
  } else if (user.isCaptchaSolved) {
    await captchaPassed(ctx, db, cfg)
  } else {
    const [captchaText, captchaSolution] = genCaptcha()
    const msg = await ctx.reply(captchaText)
    ctx.session.captcha_data = {
      message_id: msg.message_id,
      tries_failed: 0,
      generated_at: new Date().getTime(),
      solution: captchaSolution.toString(),
    }
  }
}


// returns true if captcha is response to a captcha; else -- returns false
const checkCaptchaSolution = async (ctx: Filter<Ctx, "message:text">, db: Kysely<Database>, cfg: BotConfig) => {
  if (!ctx.msg) return
  const users = await db.selectFrom('users').selectAll().where('tg_id', '=', ctx.msg.from.id).execute()
  if (users.length < 1) return // TODO: Maybe create new user here, idk

  const user = users[0]
  const userRestrictions = await checkUserRestrictions(db, user)
  if (userRestrictions.isBlocked || userRestrictions.isTimeout) return

  if (isSolutionCorrect(ctx.session.captcha_data!.solution, ctx.message.text)) {
    await captchaPassed(ctx, db, cfg)
  } else {
    ctx.session.captcha_data!.tries_failed++
    await ctx.api.deleteMessage(ctx.chatId, ctx.msg.message_id)
    if (ctx.session.captcha_data!.tries_failed > CAPTCHA_FAILS_LIMIT) {
      ctx.reply(LangManager.getLang(ctx.msg.from.language_code)
        .replies.captcha.failed(TIMEOUT_AFTER_FAIL_MINS))
      await ctx.api.deleteMessage(ctx.chatId, ctx.session.captcha_data!.message_id)
      // TODO: Add timeout
    } 
  }
  return
}


export { checkCaptchaSolution, initUserCaptcha }