//
// program to track bank balance and transactions
// filename must be given as command-line argument
// file will contain:
//   line with ending balance
//   lines containing transactions (amount followed by description),
//     in reverse order (newest first)
// program then prompts repeatedly for one of the following:
//   't' for transaction -- amount (positive for credit, negative for debit)
//     and description
//   'h' for transaction history
//   'q' to quit
//
// on exit, write initial balance and transactions back to file

if (args.length < 1) {
  println("must give filename as argument")
  sys.exit(1)
}
val filename = args(0)

var (balance, history) = readFile(filename) 

var choice = ' '

do {
  println("current balance $" + balance)
  println("what do you want to do?")
  println("(t for transaction, h for history, q for quit)")
  choice = readChar

  choice match {
    case 't' => 
      println("enter amount (integer, positive for credit, negative for debit)")
      val amt = readInt
      println("enter description (line of text)")
      val text = readLine
      history = (amt, text) :: history
      balance += amt
    case 'h' => 
      for (trans <- history) {
        println(trans) // FIXME format this better
      }
    case 'q' => 
      println("ending balance $" + balance)
      writeFile(filename, balance, history)
    case _ => 
      println("invalid choice")
  }
} while (choice != 'q') 

// returns (balance, history)
def readFile(filename : String) : (Int, List[(Int,String)]) = {
  val source = scala.io.Source.fromFile(filename)
  val lines = source.getLines
  val bal = lines.next.toInt
  val hist = lines.toList.map(line => {
      val firstBlank = line.indexOf(' ')
      val amt = line.substring(0, firstBlank).toInt
      val text = line.substring(firstBlank+1)
      (amt, text)
    })
// ANOTHER WAY
//var hist = List[(Int,String)]()
//for (line <- lines) {
//  val firstBlank = line.indexOf(' ')
//  val amt = line.substring(0, firstBlank)
//  val text = line.substring(firstBlank+1)
//  hist = (amt.toInt, text) :: hist
  source.close
  (bal, hist)
}

def writeFile(filename : String, bal : Int, hist : List[(Int,String)]) {
  val pw = new java.io.PrintWriter(new java.io.File(filename))
  pw.println(bal)
  for (trans <- hist) {
    val (a,t) = trans
    pw.println(a + " " + t)
  }
  pw.close
}