package playground

class Balance(months : Int, borrowed : Double, rate : Double){

  def balance_(months : Int, borrowed : Double, rate : Double, payment : Double) : Double =
  {
    if(months == 0) borrowed
    else rate * balance_(months - 1, borrowed, rate, payment) - payment
  }

  val balance = balance_(this.months, this.borrowed, this.rate, _ : Double)

  def bisection(f : Double => Double, reps : Int, guess1 : Double, guess2 : Double) : Double =
  {
    def sign(x : Double) : Int =
    {
      x match{
        case y if y < 0 => -1
        case y if y > 0 => 1
        case _          => 0
      }
    }

    val guess3 = (guess1 + guess2)/2

    if(reps == 0 || f(guess3) == 0) guess3
    else{
      val s = sign(f(guess1)/f(guess3))
      s match{
        case 0    => guess1
        case (-1) => bisection(f, reps - 1, guess1, guess3)
        case _    => bisection(f, reps - 1, guess2, guess3)
      }

    }
  }
}  // End of the Balance class.

object Balance extends App{

  import scala.io.StdIn._

  println("")

  print("How much money are you going to borrow? ")
  val borrowed = readDouble()

  print("How many years will it take to repay the loan? ")
  val years = readInt()

  print("What is the annual interest rate expressed as a percentage? ")
  val percent = readDouble()

  val months = 12*years
  val rate = 1 + percent/1200

  print("How many times do you want to implement the bisection algorithm? ")
  val reps = readInt()

  val mortgage = new Balance(months, borrowed, rate)

  val payment = mortgage.bisection(mortgage.balance, reps, borrowed, 0)

  val totalInterest = months * payment - borrowed

  val balanceEachMonth = for (month <- (0 to months).toList)
  yield (month, mortgage.balance_(month, borrowed, rate, payment))

  printf("\nYour monthly mortgage payment is $%,.2f", payment)

  printf("\nThe total interest on the loan after %d years is $%,.2f", years, totalInterest)

  println("\n")

  balanceEachMonth.foreach(t => { print("Month: \t" + t._1); print(",  \t")
    printf("Amount Owed:  \t$%,.2f", t._2); println(""); Thread.sleep(350L) })

  println("\n")

}  // End of the Balance companion object.