#
# Program: interest.py
# Author:  James Tam
# Version: February 15, 2013
# A simple interest calculator (it won't work for compound or interest on
# on interest calculations).
# Learning concepts:
# 1) Return values

# function: introduction
# @introduction(none)
# @returns(nothing)
# Describes how the program works to the user.
def introduction():
    print("""
Simple interest calculator
-------------------------------
With given values for the principle, rate and time period this program
will calculate the interest accrued as well as the new amount (principle
plus interest).
    """)

# function: getInputs
# @getInputs(none)
# @returns(float,float,int)
# Prompt the user for the inputs to the operation: principle, rate, time
# These values must be returned back to the caller of this function so
# they can be used to derive interest and the amount.
def getInputs ():
    principle = float(input("Enter the original principle: "))
    rate = float(input("Enter the yearly interest rate %"))
    rate = rate / 100.0
    time = int(input("Enter the number of years that money will be invested: "))
    return(principle, rate, time)

# function: calculate
# @calculate(float,float,int)
# @returns(float,float)
# Based on the values entered by the user for the principle, rate and time
# this function will calculate the interest earned as well as the new
# amount in the user's bank account.
# Precondition: Principle, rate, time have been set to meaningful values.
def calculate(principle, rate, time):
    interest = principle * rate * time
    amount = principle + interest
    return(interest,amount)

# function: display
# @fun(float,float,int,float,float)
# @returns(nothing)
# Shows but doesn't modify the results of the calculation (amount and interest)
# as well as the original inputs to the operation (principle, rate, time).
def display (principle, rate, time, interest, amount):
    temp = rate * 100
    print("")    
    print("With an investment of $", principle, " at a rate of", temp, "%", end="")
    print(" over", time, " years...")
    print("Interest accrued $", interest)
    print("Amount in your account $", amount)

# @start(none)
# @returns(nothing)
def start():
    principle = 0
    rate = 0
    time = 0
    interest = 0
    amount = 0

    introduction ()
    principle,rate,time = getInputs ()
    interest,amount = calculate (principle, rate, time)
    display (principle, rate, time, interest, amount)

start()