import os, sys

# https://www.investopedia.com/terms/t/timevalueofmoney.asp

# Formula for Time Value of Money

# FV = PV x [1 + (i / n)]^(n x t)

# Assume a sum of $10,000 is invested for one year at 10% interest compounded annually. 
# The future value of that money is:

# FV = $10,000 x [1 + (10% / 1)] ^ (1 x 1) = $11,000

compounding_periods = {"annual" : 1, "monthly" : 12, "quarterly" : 4, "daily" :365}

if 'INVESTMENT' not in os.environ:
    print("Cannot run the script. Investment is missing.")
    sys.exit()

if 'INTEREST_RATE' not in os.environ:
    print("Cannot run the script. Interest rate is missing.")
    sys.exit()

if 'COMPOUNDING_PERIOD' not in os.environ:
    print("Cannot run the script. Compounding period is missing.")
    sys.exit()

if 'YEARS' not in os.environ:
    print("Cannot run the script. Number of years are missing.")
    sys.exit()

compounding_period  = os.getenv('COMPOUNDING_PERIOD')

if compounding_period not in compounding_periods.keys():
    print("Cannot run the script.", compounding_period," is not a valid period")
    sys.exit()

investment = int(os.getenv('INVESTMENT'))
interest_rate = float(os.getenv('INTEREST_RATE'))
years = int(os.getenv('YEARS'))

n = compounding_periods[compounding_period]

FV = investment * pow((1 + ((interest_rate/100) / n)),n * years)

print("Assume a sum of",investment,"is invested for",years,"year(s) at",interest_rate,"% interest compounded on",compounding_period,"basis. ")
print("The future value of that money is:")
print(FV)