stats.ts

import { Bot, Context, session, SessionFlavor } from 'grammy'

// This bot will collect some basic statistics about each chat. They can be
// retrieved with the `/stats` command.

// This is the data that will be saved per chat.
interface SessionData {
    messages: number
    edits: number
}

// flavor the context type to include sessions
type MyContext = Context & SessionFlavor<SessionData>

// Create a bot
const bot = new Bot<MyContext>('') // <-- place your token inside this string

// Note that using `session()` will only save the data in-memory. If the Node.js
// process terminates, all data will be lost. A bot running in production will
// need some sort of database or file storage to persist data between restarts.
// Confer the grammY documentation to find out how to store data with your bot.
bot.use(session({ initial: () => ({ messages: 1, edits: 0 }) }))

// Collect statistics
bot.on('message', async (ctx, next) => {
    ctx.session.messages++
    await next()
})
bot.on('edited_message', async (ctx, next) => {
    ctx.session.edits++
    await next()
})

bot.filter(ctx => ctx.chat?.type === 'private').command('start', ctx =>
    ctx.reply(
        'Hi there! I will count the messages in this chat so you can get your /stats!'
    )
)

bot.on(':new_chat_members:me', ctx =>
    ctx.reply(
        'Hi everyone! I will count the messages in this chat so you can get your /stats!'
    )
)

// Send statistics upon `/stats`
bot.command('stats', async ctx => {
    const stats = ctx.session

    // Format stats to string
    const message = `You sent <b>${
        stats.messages
    } messages</b> since I'm here! You edited messages <b>${
        stats.edits
    } times</b>—that is <b>${
        stats.edits / stats.messages
    } edits</b> per message on average!`

    // Send message in same chat using `reply` shortcut. Don't forget to `await`!
    await ctx.reply(message, { parse_mode: 'HTML' })
})

// Catch errors and log them
bot.catch(err => console.error(err))

// Start bot!
bot.start()