mainBot.py

import telebot
import db
import BOT_KEY

bot = telebot.TeleBot(BOT_KEY.KEY)

# main menu keyboard creation
menu_keyboard = telebot.types.ReplyKeyboardMarkup(resize_keyboard=True).add(
    telebot.types.KeyboardButton("Exchange"),
    telebot.types.KeyboardButton("Rates"),
    # telebot.types.KeyboardButton("Graphs"), # will be added later, when code for visualisation is made
)

# takes keys from rates dictionary made in db.py file and uses them to create keys for currencies
currency_keyboard = telebot.types.ReplyKeyboardMarkup(resize_keyboard=True).add(
    *[telebot.types.KeyboardButton(currency) for currency in db.rates.keys()]
)


# used to start/reset bot
@bot.message_handler(commands=['start'])
def handle_start(message):
    bot.send_message(message.chat.id, "Welcome to the currency converter bot! Please select an option:",
                     reply_markup=menu_keyboard)


# after "Exchange" is either sent by a button click or manually user is asked question below
@bot.message_handler(func=lambda message: message.text == "Exchange")
def handle_exchange(message):
    bot.send_message(message.chat.id, "How much do you want to convert?")
    bot.register_next_step_handler(message, handle_exchange_amount)


# user gave a number, now this function sends a message asking [...] and showing a keyboard with currency codes
def handle_exchange_amount(message):
    amount = float(message.text)
    bot.send_message(message.chat.id,
                     f"From which currency do you want to convert {amount:.2f}? Please select from the options below:",
                     reply_markup=currency_keyboard)
    # passing all we got so far to the function below
    bot.register_next_step_handler(message, handle_exchange_source, amount)


# again a currency codes keyboard is shown, user picks one
def handle_exchange_source(message, amount):
    source_currency = message.text
    bot.send_message(message.chat.id,
                     f"What currency do you want to convert {amount:.2f} {source_currency} to? Please select from the options below:",
                     reply_markup=currency_keyboard)
    # and everything is passed to the function below
    bot.register_next_step_handler(message, handle_exchange_target, amount, source_currency)


# here all collected data is converted into what user will see in the end
def handle_exchange_target(message, amount, source_currency):
    target_currency = message.text
    conversion_rates = db.rates
    rate = conversion_rates[target_currency] / conversion_rates[source_currency]  # conversion rate is calculated here
    converted_amount = amount * rate
    # final response with converted value
    bot.send_message(message.chat.id,
                     f"{amount:.2f} {source_currency} is equivalent to {converted_amount:.2f} {target_currency}")
    # after the work is done user sees menu keys again so there's no need to use /start
    bot.send_message(message.chat.id, "What else can I help you with?", reply_markup=menu_keyboard)


# handling user picking "Rates" option and is shown a currency code keyboard, after clicking one function bellow is triggered
@bot.message_handler(func=lambda message: message.text == "Rates")
def handle_rates(message):
    bot.send_message(message.chat.id, "Please select the source currency:", reply_markup=currency_keyboard)
    bot.register_next_step_handler(message, handle_rates_source)


# user clicks a button for their target currency
def handle_rates_source(message):
    source_currency = message.text
    bot.send_message(message.chat.id, f"Please select the target currency for {source_currency}:",
                     reply_markup=currency_keyboard)
    bot.register_next_step_handler(message, handle_rates_target, source_currency)


# previous function sends both target and source here, this function calculates rate
def handle_rates_target(message, source_currency):
    target_currency = message.text
    conversion_rates = db.rates
    # here
    exchange_rate = conversion_rates[target_currency] / conversion_rates[source_currency]
    # and sends it to the chat
    bot.send_message(message.chat.id,
                     f"The exchange rate between {source_currency} and {target_currency} is {exchange_rate:.4f}")
    # and shows menu keyboard again
    bot.send_message(message.chat.id, "What else can I help you with?", reply_markup=menu_keyboard)


# bot start
bot.polling()

# keys basically send set messages to the chat and message.text collects them and puts in variables, so they can be used
# that's why user can also just send a message manually and if for some reason keyboard doesn't show, if the message
# is correct everything will work if not it'll be just ignored until correct message is provided. What I used for buttons
# works only on mobile, stuff that theoretically should work both on mobile and web app doesn't work in neither of those
# places (and didn't work in class too) and this version looks nicer.