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

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

// !!! 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._

// !! COPY from your bf.scala !!

// def load_bff(name: String) : String = ...

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

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

// def jumpRight(prog: String, pc: Int, level: Int) : Int = ...

// def jumpLeft(prog: String, pc: Int, level: Int) : Int = ...

// def compute(prog: String, pc: Int, mp: Int, mem: Mem) : Mem = ...

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

// 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 fiendishly difficult to get

// to produce 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.

// ADVANCED 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

//     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] = ...

// 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()) = ... 

//testcase

//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 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  // => 11203

//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[[....."""

//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")))