bot.js

const Telegraf = require('telegraf');
const config = require('./config'); // Holds Telegram API token plus YouTube API token

var youtube = require('./models/youtube');  // Provides easy access to YouTube API

const bot = new Telegraf(config.telegraf_token);

bot.telegram.getMe().then((bot_informations) => {
    bot.options.username = bot_informations.username;
    console.log("Server has initialized bot nickname. Nick: "+bot_informations.username);
});

// Usage: @yourbot channel. Retrieves: a list of last videos of 'channel' query input.
bot.on('inline_query', ctx => {
    let nickname = ctx.update.inline_query.query;  // Take the nickname out of Telegraf context structure.
    if(nickname.length > 3){  // If user input is longer than 3 characters
        // Search channel based on nickname. If there is one with same user query, let's retrieve its channel ID.
        youtube.get_id_from_nickname(nickname).then(channel_id => {
            // Let's get last uploaded videos as data structure through YouTube API (thanks to our written model).
            youtube.fetch_channel_uploads(channel_id).then(structured_data => {
                // Let's parse those structured data to get only essential informations for video listing.
                youtube.parse_list_videos(structured_data).then(video_info => {
                    // Let's encapsulate those informations in a list that Telegraf API can digest.
                    let new_arr = [];
                    // For each video, extract retrieved informations for extra elaborations.
                    for(let k in video_info){
                        new_arr[k] = {
                            type: 'video',
                            id: k,
                            title: video_info[k].title,
                            description: video_info[k].description,
                            video_url: video_info[k].url,
                            mime_type: "video/mp4",
                            thumb_url: video_info[k].thumb,
                            input_message_content: {message_text: "[BOT] "+video_info[k].url}
                        }
                    }
                    // Let's show this list to the user. Cache time is set to zero for development purposes.
                    return ctx.answerInlineQuery(new_arr, {cache_time: 0});
                }).catch(error => {console.log("Promise error: "+error)});
            }).catch(error => {console.log("Promise error: "+error)});
        }).catch(error => {console.log("Promise error: "+error)});
    }
});

bot.startPolling();