// A Transpiler for the Brainf*** language

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

//

// This version "optimises" the code by replacing 

// for example +++ by (*ptr) += 3, instead of three

// separate (*ptr)++, (*ptr)++, (*ptr)++

// 

// Call with

//

//  amm bfc1.sc <<bf_program.bf>>

//

// generate "compound" c-instructions 

def instr2(c: Char, n: Int) : String = c match {

  case '>' => s"ptr += $n ;"

  case '<' => s"ptr -= $n ;"

  case '+' => s"(*ptr) += $n ;"

  case '-' => s"(*ptr) -= $n ;"

  case '.' => "putchar(*ptr);" * n

  case ',' => "*ptr = getchar(); " * n

  case '['  => "while(*ptr){" * n

  case ']'  => "}" * n

  case _ => ""

}

// "splicing" a BF program into "spans" 

// and counting the number of occurrences in

// each span; then generate the new intruction

// accordingly

def splice(cs: List[Char], acc: List[String]) : List[String] = cs match {

  case Nil => acc

  case hd :: _ => {

    val (hds, rest) = cs.span(_ == hd)

    splice(rest, instr2(hd, hds.length) :: acc) 

  }

}

def instrs2(prog: String) : String =

  splice(prog.toList, Nil).reverse.mkString

// adding boilerplate

def compile(prog: String) : String = 

  s"""#include <string.h> 

      #include <stdio.h> 

      char field[30000]; 

      char *ptr = &field[15000]; 

      int main() { 

      memset(field, '\\0', 30000); 

      ${instrs2(prog)} 

      return 0;}"""

def compile_to_file(name: String, prog: String) = 

  os.write.over(os.pwd / name, compile(prog))

// running the c-compiler over the transpiled

// BF program and running the resulting binary

def compile_and_run(prog: String) = {

  val tn = "tmp"

  compile_to_file(s"${tn}.c", prog)

  os.proc("gcc", "-O0", "-o", tn, s"${tn}.c").call() // call gcc

  os.proc("./tmp").call(stdout = os.Inherit)         // run binary

}

// Running Testcases

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

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)

}

@doc(" the argument should be a BF program ")

@main

def main(fname: String) = {

  val bf_str = os.read(os.pwd / fname)

  println(s"${time_needed(1, compile_and_run(bf_str))} secs")

}