MIN_RATE = 8.0
RATE_WINDOW = 12.0
INITIAL_PRINCIPLE = 50.0
PERIODS = 36

def get_new_rate
  return MIN_RATE + rand(RATE_WINDOW)
end

def add_loans(loans, account_balance)
  new_loan_count = account_balance / INITIAL_PRINCIPLE
  new_loan_count.to_i.times do
    rate = get_new_rate
    loans << {:principle => INITIAL_PRINCIPLE, :rate => rate, :min_payment => calc_minimum_payment(INITIAL_PRINCIPLE,rate)}
    account_balance -= INITIAL_PRINCIPLE
  end
  account_balance
end

def calc_minimum_payment(principle, interest)
  per_int = interest / 12.0 / 100
  (per_int * principle * (1 + per_int)**PERIODS) / ((1 + per_int)**PERIODS - 1)
end

def calc_payment(loan, months=1)
  if loan[:principle] < loan[:min_payment]
    payment = loan[:principle]
    loan[:principle] = 0
    return payment
  end
  
  interest = loan[:principle] * loan[:rate] / 100.0 / 12
  loan[:principle] -= loan[:min_payment] - interest
  return loan[:min_payment]
end

def calc_average(coll)
  sum = coll.inject(0) {|sum, n| sum + n}
  sum / coll.size
end

account_balance = ARGV[0].to_f if ARGV[0]
account_balance ||= 0.0

monthly_deposit = ARGV[1].to_f if ARGV[1]
monthly_deposit ||= 100.0

number_of_years = ARGV[2].to_i if ARGV[2]
number_of_years ||= 1

loans = []
for i in (1..number_of_years*12)
  old_loans = loans.size
  account_balance = add_loans loans, account_balance
  print "Month #{i}\n"
  print "Number of loans: #{loans.size} (#{loans.size - old_loans})\n"
  print "Average Rate: #{calc_average(loans.collect {|i| i[:rate]})}\n"
  income= loans.inject(0) {|bal, i| bal + calc_payment(i)}
  print "Account balance: #{account_balance}\n"
  print "Income: #{income}\n"
  account_balance += income  + monthly_deposit
  print "Account value: #{loans.collect {|i| i[:principle]}.inject(account_balance) {|sum, i| sum + i}}\n"
  print "\n"
  loans.delete_if {|item| item[:principle] == 0}
end