exchange.py

"""The currency exchange module.

This script solves the following challenge: https://exercism.org/tracks/python/exercises/currency-exchange
"""


def exchange_money(budget: float, exchange_rate: float) -> float:
    """

    :param budget: float - amount of money you are planning to exchange.
    :param exchange_rate: float - unit value of the foreign currency.
    :return: float - exchanged value of the foreign currency you can receive.
    """

    return budget / exchange_rate


def get_change(budget: float, exchanging_value: float) -> float:
    """

    :param budget: float - amount of money you own.
    :param exchanging_value: float - amount of your money you want to exchange now.
    :return: float - amount left of your starting currency after exchanging.
    """

    return budget - exchanging_value


def get_value_of_bills(denomination: int, number_of_bills: int) -> int:
    """

    :param denomination: int - the value of a bill.
    :param number_of_bills: int - amount of bills you received.
    :return: int - total value of bills you now have.
    """

    return int(denomination * number_of_bills)


def get_number_of_bills(budget: float, denomination: int) -> int:
    """

    :param budget: float - the amount of money you are planning to exchange.
    :param denomination: int - the value of a single bill.
    :return: int - number of bills after exchanging all your money.
    """

    return budget // denomination


def get_leftover_of_bills(budget: float, denomination: int) -> float:
    """

    :param budget: float - the amount of money you are planning to exchange.
    :param denomination: int - the value of a single bill.
    :return: float - the leftover amount that cannot be exchanged given the current denomination.
    """

    num_bills = get_number_of_bills(budget, denomination)

    return budget - denomination * num_bills


def exchangeable_value(
    budget: float, exchange_rate: float, spread: int, denomination: int
) -> int:
    """

    :param budget: float - the amount of your money you are planning to exchange.
    :param exchange_rate: float - the unit value of the foreign currency.
    :param spread: int - percentage that is taken as an exchange fee.
    :param denomination: int - the value of a single bill.
    :return: int - maximum value you can get.
    """

    rate_after_spread = exchange_rate * (1 + spread / 100)
    max_after_exchange = exchange_money(budget, rate_after_spread)
    num_bills = get_number_of_bills(max_after_exchange, denomination)

    return get_value_of_bills(denomination, num_bills)