// Main Part 5 about a "Compiler" for the Brainf*** language

//============================================================

object M5b {

// !!! 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.

// DEBUGGING INFORMATION FOR COMPILERS!!!

//

// Compiler, even real ones, are fiendishly difficult to get

// to produce correct code. One way to debug them is to run

// example programs ``unoptimised''; and then optimised. Does

// the optimised version still produce the same result?

// for timing purposes

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._

// TASKS

//=======

// (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 about

//     pc positions where '[' or a ']' are stored. The information

//     is 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 immediately look up the jump address in the jtable.

def jtable(pg: String) : Map[Int, Int] = ???

// 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 = ???

def run2(pg: String, m: Mem = Map()) = ???

// testcases

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

// time_needed(1, run2(load_bff("sierpinski.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 occurrences of [-] and 

// by using the Scala method .replaceAll you can replace it with the 

// string "0" standing for the new bf-command.

def optimise(s: String) : String = ???

def compute3(pg: String, tb: Map[Int, Int], pc: Int, mp: Int, mem: Mem) : Mem = ???

def run3(pg: String, m: Mem = Map()) = ???

// testcases

//

// optimise(load_bff("benchmark.bf"))          // should have inserted 0's

// optimise(load_bff("mandelbrot.bf")).length  // => 11205

// 

// time_needed(1, run3(load_bff("benchmark.bf")))

// (7)  Write a function combine which replaces sequences

// of repeated 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 combine(s: String) : String = ???

// testcase

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

def compute4(pg: String, tb: Map[Int, Int], pc: Int, mp: Int, mem: Mem) : Mem = ???

// should call first optimise and then combine on the input string

//

def run4(pg: String, m: Mem = Map()) = ???

// testcases

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

// testcases (they should now run much faster)

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

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

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

}