#!/usr/bin/env python3
import argparse
from datetime import datetime, timedelta


parser = argparse.ArgumentParser(formatter_class=argparse.ArgumentDefaultsHelpFormatter)
parser.add_argument(
    "-p", "--principle",
    default=10_000,
    type=int,
    help='The starting principal amount in dollars',
    )
parser.add_argument(
    "-r", "--rate",
    default=15,
    type=int,
    help='The annual interest rate in percent',
    )
parser.add_argument(
    "-c", "--annual-contribution",
    default=20_000,
    type=int,
    help='The annual contribution rate in dollars',
    )
parser.add_argument(
    "-C", "--contribution-increase-rate",
    default=3,
    type=int,
    help='The rate at which the annual contribution rate increases in percent',
    )
parser.add_argument(
    "-f", "--front-load-to-month",
    default=12,
    type=int,
    help='Front load to month',
    )
parser.add_argument(
    "-y", "--years",
    default=20,
    type=int,
    help='How many years to render out to',
    )
parser.add_argument(
    "-l", "--cost-of-living",
    default=60_000,
    type=int,
    help='The current cost of living in dollars',
    )
parser.add_argument(
    "-L", "--cost-of-living-increase-rate",
    default=2,
    type=int,
    help='The cost of living annual increase rate in percent',
    )
parser.add_argument(
    "-i", "--cost-of-living-retire-ratio",
    default=4,
    type=int,
    help='Used to find the point at which to retire: interest_income > cost of living * cost of living retire ratio',
    )

args = parser.parse_args()

principle = args.principle
annual_contribution = args.annual_contribution
rate = args.rate
front_load_to_month = args.front_load_to_month
years = args.years
contribution_increase_rate = args.contribution_increase_rate
cost_of_living = args.cost_of_living
cost_of_living_increase_rate = args.cost_of_living_increase_rate

rate = (rate / 100) / 12   #reduce APR to MPR
months = 12 * years

results = []
now = datetime.now()

def date_gen(number_of_months):
    for month in range(1, number_of_months + 1):
        yield now + timedelta(days=round(month*365.25/12))


total_contribution = principle
total_interest = 0
total_draw = 0

for t in date_gen(months):
    current_month = round((t - now).days / 365.25 * 12)

    initial_principle = principle
    principle = principle*(1-rate**(current_month+1))/(1-rate)      #expression for generating interest
    interest_income = principle - initial_principle
    total_interest += interest_income
    cost_of_living *= cost_of_living_increase_rate / 12 / 100 + 1
    # If retired
    if interest_income > cost_of_living / 12 * args.cost_of_living_retire_ratio:
        principle -= cost_of_living / 12
        total_draw += cost_of_living / 12
    # Elif making a contribution this month
    elif (current_month - 1) % 12 in range(front_load_to_month):
        contribution = annual_contribution / front_load_to_month
        total_contribution += contribution
        principle += contribution

    if current_month % 12 == 0:
        annual_contribution *= contribution_increase_rate / 100 + 1
        print("year {}, balance: {:,} total_contribution: {:,} total_interest: {:,} total_draw: {:,}".format(
            t.year,
            int(principle),
            int(total_contribution),
            int(total_interest),
            int(total_draw),
            ))