// Part 2 about an Interpreter for the Brainf*** language
//========================================================

object CW8b {

type Mem = Map[Int, Int]

// (2a) Complete the functions for safely reading  
// and writing brainf*** memory. Safely read should
// Return the value stored in the Map for a given memory
// pointer, if it exists; otherwise Returns 0. The
// writing function generates a new Map with the
// same data, except at the given memory pointer the
// a value v is stored.


def sread(mem: Mem, mp: Int) : Int = 
  mem.getOrElse(mp, 0)

def write(mem: Mem, mp: Int, v: Int) : Mem =
  mem.updated(mp, v)


// (2b) Implement the two jumping instructions in the 
// brainf*** language. In jumpRight, given a program and 
// a program counter move the program counter to the right 
// until after the *matching* ]-command. Similarly, 
// jumpLeft implements the move to the left to just after
// the *matching* [--command.

def jumpRight(prog: String, pc: Int, level: Int) : Int = {
  if (prog.length <= pc) pc 
  else (prog(pc), level) match {
    case (']', 0) => pc + 1
    case (']', l) => jumpRight(prog, pc + 1, l - 1)
    case ('[', l) => jumpRight(prog, pc + 1, l + 1)
    case (_, l) => jumpRight(prog, pc + 1, l)
  }
}

def jumpLeft(prog: String, p: Int, level: Int) : Int = {
  if (p < 0) p 
  else (prog(p), level) match {
    case ('[', 0) => p + 1
    case ('[', l) => jumpLeft(prog, p - 1, l - 1)
    case (']', l) => jumpLeft(prog, p - 1, l + 1)
    case (_, l) => jumpLeft(prog, p - 1, l)
  }
}


// (2c) Complete the run function that interpretes (runs) a brainf***
// program: the arguments are a program, a program counter,
// a memory counter and a brainf*** memory. It Returns the
// memory at the stage when the excution of the brainf*** program
// finishes. The interpretation finishes once the program counter
// pc is pointing to something outside the program string.
// If the pc points to a character inside the program, the pc, 
// memory pointer and memory need to be updated according to 
// rules of the brainf*** language. Then, recursively, run 
// function continues with the command at the new program
// counter. 
// Implement the start function that calls run with the program
// counter and memory counter set to 0.

def run(prog: String, pc: Int, mp: Int, mem: Mem) : Mem = {
  if (0 <= pc && pc < prog.length) { 
    val (new_pc, new_mp, new_mem) = prog(pc) match {
      case '>' => (pc + 1, mp + 1, mem)
      case '<' => (pc + 1, mp - 1, mem)
      case '+' => (pc + 1, mp, write(mem, mp, sread(mem, mp) + 1))
      case '-' => (pc + 1, mp, write(mem, mp, sread(mem, mp) - 1))
      case '.' => { print(sread(mem, mp).toChar); (pc + 1, mp, mem) }
      case ',' => (pc + 1, mp, write(mem, mp, Console.in.read().toByte))
      case '['  => 
	if (sread(mem, mp) == 0) (jumpRight(prog, pc + 1, 0), mp, mem) else (pc + 1, mp, mem) 
      case ']'  => 
	if (sread(mem, mp) != 0) (jumpLeft(prog, pc - 1, 0), mp, mem) else (pc + 1, mp, mem) 
      case _ => (pc + 1, mp, mem)
    }		     
    run(prog, new_pc, new_mp, new_mem)	
  }
  else mem
}

def start(prog: String, m: Mem) = run(prog, 0, 0, m)

// some sample programs collected from the Internet
//==================================================


/*
// first some contrived (small) programs

// clears the 0-cell
start("[-]", Map(0 -> 100)) 

// copies content of the 0-cell to 1-cell
start("[->+<]", Map(0 -> 10))

// copies content of the 0-cell to 2-cell and 4-cell
start("[>>+>>+<<<<-]", Map(0 -> 42))


// prints out numbers 0 to 9
start("""+++++[->++++++++++<]>--<+++[->>++++++++++<<]>>++<<----------[+>.>.<+<]""", Map())


// some more "useful" programs

// hello world program 1
start("""++++++++[>++++[>++>+++>+++>+<<<<-]>+>+>->>+[<]<-]>>.>---.+++++++
       ..+++.>>.<-.<.+++.------.--------.>>+.>++.""", Map())

// hello world program 2
start("""++++++++++[>+++++++>++++++++++>+++>+<<<<-]>++.>+.+++++++..+++.>+
      +.<<+++++++++++++++.>.+++.------.--------.>+.>.""", Map())


// draws the Sierpinski triangle
start("""++++++++[>+>++++<<-]>++>>+<[-[>>+<<-]+>>]>+[-<<<[
      ->[+[-]+>++>>>-<<]<[<]>>++++++[<<+++++>>-]+<<++.[-]<<
      ]>.>+[>>]>+]""", Map())

//fibonacci numbers below 100
start("""+++++++++++
      >+>>>>++++++++++++++++++++++++++++++++++++++++++++
      >++++++++++++++++++++++++++++++++<<<<<<[>[>>>>>>+>
      +<<<<<<<-]>>>>>>>[<<<<<<<+>>>>>>>-]<[>++++++++++[-
      <-[>>+>+<<<-]>>>[<<<+>>>-]+<[>[-]<[-]]>[<<[>>>+<<<
      -]>>[-]]<<]>>>[>>+>+<<<-]>>>[<<<+>>>-]+<[>[-]<[-]]
      >[<<+>>[-]]<<<<<<<]>>>>>[+++++++++++++++++++++++++
      +++++++++++++++++++++++.[-]]++++++++++<[->-<]>++++
      ++++++++++++++++++++++++++++++++++++++++++++.[-]<<
      <<<<<<<<<<[>>>+>+<<<<-]>>>>[<<<<+>>>>-]<-[>>.>.<<<
      [-]]<<[>>+>+<<<-]>>>[<<<+>>>-]<<[<+>-]>[<+>-]<<<-]""", Map())


//outputs the square numbers up to 10000
start("""++++[>+++++<-]>[<+++++>-]+<+[
    >[>+>+<<-]++>>[<<+>>-]>>>[-]++>[-]+
    >>>+[[-]++++++>>>]<<<[[<++++++++<++>>-]+<.<[>----<-]<]
    <<[>>>>>[>>>[-]+++++++++<[>-<-]+++++++++>[-[<->-]+[<<<]]<[>+<-]>]<<-]<<-]""", Map())


//collatz numbers (need to be typed in)
start(""">,[[----------[
      >>>[>>>>]+[[-]+<[->>>>++>>>>+[>>>>]++[->+<<<<<]]<<<]
      ++++++[>------<-]>--[>>[->>>>]+>+[<<<<]>-],<]>]>>>++>+>>[
      <<[>>>>[-]+++++++++<[>-<-]+++++++++>[-[<->-]+[<<<<]]<[>+<-]>]
      >[>[>>>>]+[[-]<[+[->>>>]>+<]>[<+>[<<<<]]+<<<<]>>>[->>>>]+>+[<<<<]]
      >[[>+>>[<<<<+>>>>-]>]<<<<[-]>[-<<<<]]>>>>>>>
      ]>>+[[-]++++++>>>>]<<<<[[<++++++++>-]<.[-]<[-]<[-]<]<,]""", Map())


// infinite collatz (never stops)
start(""">>+>+<[[->>[>>]>>>[>>]+[<<]<<<[<<]>[>[>>]>>+>[>>]<+<[<<]<<<[<
      <]>-]>[>>]>>[<<<<[<<]>+>[>>]>>-]<<<<[<<]+>>]<<[+++++[>+++++++
      +<-]>.<++++++[>--------<-]+<<]>>[>>]+[>>>>[<<+>+>-]<-[>+<-]+<
      [<<->>-[<<+>>[-]]]>>>[<<<+<<+>>>>>-]<<<[>>>+<<<-]<<[[-]>+>>->
      [<+<[<<+>>-]<[>+<-]<[>+<-]>>>>-]<[>+<-]+<[->[>>]<<[->[<+++>-[
      <+++>-[<+++>-[<[-]++>>[-]+>+<<-[<+++>-[<+++>-[<[-]+>>>+<<-[<+
      ++>-[<+++>-]]]]]]]]]<[>+<-]+<<]>>>+<[->[<+>-[<+>-[<+>-[<+>-[<
      +>-[<+>-[<+>-[<+>-[<+>-[<[-]>>[-]+>+<<-[<+>-]]]]]]]]]]]<[>+<-
      ]+>>]<<[<<]>]<[->>[->+>]<[-[<+>-[<->>+<-[<+>-[<->>+<-[<+>-[<-
      >>+<-[<+>-[<->>+<-[<+>-[<->>+<-[<+>-[<->>+<-[<+>-[<->>+<-[<+>
      -[<->>+<-[<+>-[<->>+<-[<+>-]]]]]]]]]]]]]]]]]]]>[<+>-]<+<[<+++
      +++++++>-]<]>>[<+>->>]<<[>+>+<<-]>[<+>-]+>[<->[-]]<[-<<-]<<[<
      <]]++++++[>+++++++<-]>++.------------.[-]>[>>]<<[+++++[>+++++
      +++<-]>.<++++++[>--------<-]+<<]+<]>[<+>-]<]>>>[>>]<<[>[-]<-<
      <]++++++++++.[-]<<<[<<]>>>+<[->[<+>-[<+>-[<+>-[<+>-[<+>-[<+>-
      [<+>-[<+>-[<+>-[<[-]>>[-]+>+<<-]]]]]]]]]]<[>+<-]+>>]<<[<<]>>]""", Map())


*/ 

}