// Part 2 about a "Compiler" for the Brainf*** language
//======================================================

object CW10b {

// !!! Copy any function you need from file bf.scala !!!
//
// If you need any auxiliary function, feel free to 
// implement it, but do not make any changes to the
// templates below.


def time_needed[T](n: Int, code: => T) = {
  val start = System.nanoTime()
  for (i <- 0 until n) code
  val end = System.nanoTime()
  (end - start)/(n * 1.0e9)
}

type Mem = Map[Int, Int]


import io.Source
import scala.util._

def load_bff(name: String) : String = 
  Try(Source.fromFile(name)("ISO-8859-1").mkString).getOrElse("")

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

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

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

def compute(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)
    }		     
    compute(prog, new_pc, new_mp, new_mem)	
  }
  else mem
}

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


// The baseline to what we can compare our "compiler"
// implemented below. It should require something like 
// 60 seconds for the calculation on my laptop
//
//time_needed(1, run(load_bff("benchmark.bf")))



// DEBUGGING INFORMATION!!!
//
// Compiler, even real ones, are fiedishly difficult to get
// to prduce correct code. The point is that for example for
// the sierpinski program, they need to still generate code
// that displays such a triangle. If yes, then one usually
// can take comfort that all is well. If not, then something
// went wrong during the optimisations.



// (5) Write a function jtable that precomputes the "jump
//     table" for a bf-program. This function takes a bf-program 
//     as an argument and Returns a Map[Int, Int]. The 
//     purpose of this map is to record the information
//     that given on the position pc is a '[' or a ']',
//     then to which pc-position do we need to jump next?
// 
//     For example for the program
//    
//       "+++++[->++++++++++<]>--<+++[->>++++++++++<<]>>++<<----------[+>.>.<+<]"
//
//     we obtain the map
//
//       Map(69 -> 61, 5 -> 20, 60 -> 70, 27 -> 44, 43 -> 28, 19 -> 6)
//  
//     This states that for the '[' on position 5, we need to
//     jump to position 20, which is just after the corresponding ']'.
//     Similarly, for the ']' on position 19, we need to jump to
//     position 6, which is just after the '[' on position 5, and so
//     on. The idea is to not calculate this information each time
//     we hit a bracket, but just look up this information in the 
//     jtable. You can use the jumpLeft and jumpRight functions
//     from Part 1 for calculating the jtable.
//
//     Then adapt the compute and run functions from Part 1 in order 
//     to take advantage of the information stored in the jtable. 
//     This means whenever jumpLeft and jumpRight was called previously,
//     you should look up the jump address in the jtable.
 

def jtable(pg: String) : Map[Int, Int] = 
    (0 until pg.length).collect { pc => pg(pc) match {
      case '[' => (pc -> jumpRight(pg, pc + 1, 0))
      case ']' => (pc -> jumpLeft(pg, pc - 1, 0))
    }}.toMap


// testcase
// jtable("""+++++[->++++++++++<]>--<+++[->>++++++++++<<]>>++<<----------[+>.>.<+<]""")
// =>  Map(69 -> 61, 5 -> 20, 60 -> 70, 27 -> 44, 43 -> 28, 19 -> 6)


def compute2(pg: String, tb: Map[Int, Int], pc: Int, mp: Int, mem: Mem) : Mem = {
  if (0 <= pc && pc < pg.length) { 
    val (new_pc, new_mp, new_mem) = pg(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) (tb(pc), mp, mem) else (pc + 1, mp, mem) 
      case ']'  => 
	if (sread(mem, mp) != 0) (tb(pc), mp, mem) else (pc + 1, mp, mem) 
      case _ => (pc + 1, mp, mem)
    }		     
    compute2(pg, tb, new_pc, new_mp, new_mem)	
  }
  else mem
}


def run2(pg: String, m: Mem = Map()) = 
  compute2(pg, jtable(pg), 0, 0, m)

//time_needed(1, run2(load_bff("benchmark.bf")))



// (6) Write a function optimise which deletes "dead code" (everything
// that is not a bf-command) and also replaces substrings of the form
// [-] by a new command 0. The idea is that the loop [-] just resets the
// memory at the current location to 0. In the compute3 and run3 functions
// below you implement this command by writing the number 0 to mem(mp), 
// that is write(mem, mp, 0). 
//
// The easiest way to modify a string in this way is to use the regular
// expression """[^<>+-.,\[\]]""", which recognises everything that is 
// not a bf-command and replace it by the empty string. Similarly the
// regular expression """\[-\]""" finds all occurences of [-] and 
// by using the Scala method .replaceAll you can repplace it with the 
// string "0" standing for the new bf-command.

def optimise(s: String) : String = 
  s.replaceAll("""[^<>+-.,\[\]]""","").replaceAll("""\[-\]""", "0")


def compute3(pg: String, tb: Map[Int, Int], pc: Int, mp: Int, mem: Mem) : Mem = {
  if (0 <= pc && pc < pg.length) { 
    val (new_pc, new_mp, new_mem) = pg(pc) match {
      case '0' => (pc + 1, mp, write(mem, mp, 0))
      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) (tb(pc), mp, mem) else (pc + 1, mp, mem) 
      case ']'  => 
	if (sread(mem, mp) != 0) (tb(pc), mp, mem) else (pc + 1, mp, mem) 
      case _ => (pc + 1, mp, mem)
    }		     
    compute3(pg, tb, new_pc, new_mp, new_mem)	
  }
  else mem
}

def run3(pg: String, m: Mem = Map()) = { 
  val pg_opt = optimise(pg)
  compute3(pg_opt, jtable(pg_opt), 0, 0, m)
}


// testcases

//optimise(load_bff("benchmark.bf"))          // should have inserted 0's
//optimise(load_bff("benchmark.bf")).length   // => 181  
//optimise(load_bff("mandelbrot.bf")).length  // => 11203
 
//time_needed(1, run3(load_bff("benchmark.bf")))



// (7)  Write a function combine which replaces sequences
// of repated increment and decrement commands by appropriate
// two-character commands. For example for sequences of +
//
//              orig bf-cmds  | replacement
//            ------------------------------
//              +             | +A 
//              ++            | +B
//              +++           | +C
//                            |
//              ...           |
//                            | 
//              +++....+++    | +Z
//                (where length = 26)
//
//  Similar for the bf-command -, > and <. All other commands should
//  be unaffected by this change.
//
//  Adapt the compute4 and run4 functions such that they can deal
//  appropriately with such two-character commands.

def splice(cs: List[Char], acc: List[(Char, Int)]) : List[(Char, Int)] = (cs, acc) match {
  case (Nil, acc) => acc  
  case ('[' :: cs, acc) => splice(cs, ('[', 1) :: acc)
  case (']' :: cs, acc) => splice(cs, (']', 1) :: acc)
  case ('.' :: cs, acc) => splice(cs, ('.', 1) :: acc)
  case (',' :: cs, acc) => splice(cs, (',', 1) :: acc)
  case ('0' :: cs, acc) => splice(cs, ('0', 1) :: acc)
  case (c :: cs, Nil) => splice(cs, List((c, 1)))
  case (c :: cs, (d, n) :: acc) => 
    if (c == d && n < 26) splice(cs, (c, n + 1) :: acc)
    else splice(cs, (c, 1) :: (d, n) :: acc)
}

def spl(s: String) = splice(s.toList, Nil).reverse

//spl(load_bff("benchmark.bf"))

def combine(s: String) : String = {
  (for ((c, n) <- spl(s)) yield c match {
    case '>' => List('>', (n + '@').toChar)
    case '<' => List('<', (n + '@').toChar)
    case '+' => List('+', (n + '@').toChar)
    case '-' => List('-', (n + '@').toChar)
    case _ => List(c)
  }).flatten.mkString
}


//combine(load_bff("benchmark.bf"))

def compute4(pg: String, tb: Map[Int, Int], pc: Int, mp: Int, mem: Mem) : Mem = {
  if (0 <= pc && pc < pg.length) { 
    val (new_pc, new_mp, new_mem) = pg(pc) match {
      case '0' => (pc + 1, mp, write(mem, mp, 0))
      case '>' => (pc + 2, mp + (pg(pc + 1) - '@'), mem)
      case '<' => (pc + 2, mp - (pg(pc + 1) - '@'), mem)
      case '+' => (pc + 2, mp, write(mem, mp, sread(mem, mp) + (pg(pc + 1) - '@')))
      case '-' => (pc + 2, mp, write(mem, mp, sread(mem, mp) - (pg(pc + 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) (tb(pc), mp, mem) else (pc + 1, mp, mem) 
      case ']'  => 
	if (sread(mem, mp) != 0) (tb(pc), mp, mem) else (pc + 1, mp, mem) 
      case _ => (pc + 1, mp, mem)
    }		     
    compute4(pg, tb, new_pc, new_mp, new_mem)	
  }
  else mem
}

def run4(pg: String, m: Mem = Map()) = { 
  val pg_opt = combine(optimise(pg))
  compute4(pg_opt, jtable(pg_opt), 0, 0, m)
}

// testcases
//combine(optimise(load_bff("benchmark.bf"))) // => """>A+B[<A+M>A-A]<A[[....."""
//combine(optimise(load_bff("benchmark.bf"))).length // => 134
//combine(optimise(load_bff("mandelbrot.bf"))).length // => 6509

//time_needed(1, run4(load_bff("benchmark.bf")))

//time_needed(1, run(load_bff("sierpinski.bf"))) 
//time_needed(1, run4(load_bff("sierpinski.bf"))) 

//time_needed(1, run4(load_bff("mandelbrot.bf")))


}