Calculate Total and IVA

monthly_payments.py

from decimal import Decimal
from pprint import pprint


def cast_int(amount: Decimal) -> int:
    return int(amount * 100)


def cast_decimal(amount: int) -> Decimal:
    return Decimal(amount / 100).quantize(Decimal('1.00'))


def calculate_iva(amount: Decimal) -> int:
    iva = amount * Decimal(0.16)
    return cast_int(iva)


def calculate_monthly_payouts(initial_amount: Decimal, num_months: int) -> dict:
    subtotal_amount = cast_int(initial_amount)
    iva_amount = calculate_iva(initial_amount)
    total_amount = subtotal_amount + iva_amount

    monthly_payment = total_amount // num_months
    unexpected_total = monthly_payment * num_months
    last_payment = monthly_payment - (unexpected_total - total_amount)

    plan = [cast_decimal(monthly_payment) for x in range(num_months - 1)] + [cast_decimal(last_payment)]

    return {
        'subtotal': cast_decimal(subtotal_amount),
        'iva': cast_decimal(iva_amount),
        'total': cast_decimal(total_amount),
        'payments': plan,
    }


def sum_items(items):
    total_sum = 0
    for item in items:
        total_sum += item
    return total_sum


subtotal = Decimal(10585)
result = calculate_monthly_payouts(subtotal, 7)

pprint(result)

# Tests
assert sum_items(result['payments']) == result['total']

# Specific value Tests
assert isinstance(result, dict)
assert result['subtotal'] == Decimal('10585.00')
assert result['iva'] == Decimal('1693.60')
assert result['total'] == Decimal('12278.60')
assert sum_items(result['payments']) == Decimal('12278.60')

print('Ok!')