// A Transpiler for the Brainf*** language+
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//=========================================+
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//+
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// This version "optimises" the code by replacing +
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// for example +++ by (*ptr) += 3, instead of three+
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// separate (*ptr)++, (*ptr)++, (*ptr)+++
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// +
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// Call with+
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//+
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//  amm bfc1.sc <<bf_program.bf>>+
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//+
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+
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+
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// generate "compound" c-instructions +
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def instr2(c: Char, n: Int) : String = c match {+
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  case '>' => s"ptr += $n ;"+
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  case '<' => s"ptr -= $n ;"+
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  case '+' => s"(*ptr) += $n ;"+
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  case '-' => s"(*ptr) -= $n ;"+
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  case '.' => "putchar(*ptr);" * n+
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  case ',' => "*ptr = getchar(); " * n+
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  case '['  => "while(*ptr){" * n+
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  case ']'  => "}" * n+
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  case _ => ""+
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}+
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+
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// "splicing" a BF program into "spans" +
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// and counting the number of occurrences in+
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// each span; then generate the new intruction+
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// accordingly+
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+
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def splice(cs: List[Char], acc: List[String]) : List[String] = cs match {+
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  case Nil => acc+
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  case hd :: _ => {+
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    val (hds, rest) = cs.span(_ == hd)+
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    splice(rest, instr2(hd, hds.length) :: acc) +
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  }+
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}+
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+
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def instrs2(prog: String) : String =+
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  splice(prog.toList, Nil).reverse.mkString+
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+
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// adding boilerplate+
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def compile(prog: String) : String = +
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  s"""#include <string.h> +
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      #include <stdio.h> +
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      int field[30000]; +
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      int *ptr = &field[15000]; +
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      int main() { +
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      memset(field, '\\0', 30000); +
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      ${instrs2(prog)} +
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      return 0;}"""+
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+
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def compile_to_file(name: String, prog: String) = +
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  os.write.over(os.pwd / name, compile(prog))+
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+
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+
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// running the c-compiler over the transpiled+
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// BF program and running the resulting binary+
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+
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def compile_and_run(prog: String) = {+
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  val tn = "tmp"+
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  compile_to_file(s"${tn}.c", prog)+
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  os.proc("gcc", "-O0", "-o", tn, s"${tn}.c").call() // call gcc+
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  os.proc("./tmp").call(stdout = os.Inherit)         // run binary+
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}+
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+
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// Running Testcases+
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//===================+
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+
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def time_needed[T](n: Int, code: => T) = {+
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  val start = System.nanoTime()+
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  for (i <- 0 until n) code+
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  val end = System.nanoTime()+
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  (end - start)/(n * 1.0e9)+
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}+
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+
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@doc(" the argument should be a BF program ")+
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@main+
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def main(fname: String) = {+
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  val bf_str = os.read(os.pwd / fname)+
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  println(s"${time_needed(1, compile_and_run(bf_str))} secs")+
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}  +
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+
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