// A Small Compiler for a Simple Functional Language

// (includes an external lexer and parser)

//

// call with 

//

//     scala fun.scala fact

//

//     scala fun.scala defs

//

// this will generate a .j file and run the jasmin

// assembler (installed at jvm/jasmin-2.4/jasmin.jar)

// it runs the resulting JVM file twice for timing 

// purposes.

import java.io._  

import scala.util._

import scala.sys.process._

// Abstract syntax trees for the Fun language

abstract class Exp extends Serializable 

abstract class BExp extends Serializable 

abstract class Decl extends Serializable 

case class Def(name: String, args: List[String], body: Exp) extends Decl

case class Main(e: Exp) extends Decl

case class Call(name: String, args: List[Exp]) extends Exp

case class If(a: BExp, e1: Exp, e2: Exp) extends Exp

case class Write(e: Exp) extends Exp

case class Var(s: String) extends Exp

case class Num(i: Int) extends Exp

case class Aop(o: String, a1: Exp, a2: Exp) extends Exp

case class Sequence(e1: Exp, e2: Exp) extends Exp

case class Bop(o: String, a1: Exp, a2: Exp) extends BExp

// compiler - built-in functions 

// copied from http://www.ceng.metu.edu.tr/courses/ceng444/link/jvm-cpm.html

//

// for generating new labels

var counter = -1

def Fresh(x: String) = {

  counter += 1

  x ++ "_" ++ counter.toString()

}

// convenient string interpolations 

// for instructions, labels and methods

import scala.language.implicitConversions

import scala.language.reflectiveCalls

implicit def sring_inters(sc: StringContext) = new {

    def i(args: Any*): String = "   " ++ sc.s(args:_*) ++ "\n"

    def l(args: Any*): String = sc.s(args:_*) ++ ":\n"

    def m(args: Any*): String = sc.s(args:_*) ++ "\n"

}

type Env = Map[String, Int]

// compile expressions

  case If(b, a1, a2) => {

    val if_else = Fresh("If_else")

    val if_end = Fresh("If_end")

    compile_bexp(b, env, if_else) ++

    compile_exp(a1, env) ++

    i"goto $if_end" ++

    l"$if_else" ++

    compile_exp(a2, env) ++

    l"$if_end"

  }

  case Call(name, args) => {

    val is = "I" * args.length

    args.map(a => compile_exp(a, env)).mkString ++

    i"invokestatic XXX/XXX/$name($is)I"

  }

  case Sequence(a1, a2) => {

    compile_exp(a1, env) ++ i"pop" ++ compile_exp(a2, env)

  }

  case Write(a1) => {

    compile_exp(a1, env) ++

    i"dup" ++

    i"invokestatic XXX/XXX/write(I)V"

  }

}

// compile boolean expressions

def compile_bexp(b: BExp, env : Env, jmp: String) : String = b match {

  case Bop("==", a1, a2) => 

    compile_exp(a1, env) ++ compile_exp(a2, env) ++ i"if_icmpne $jmp"

  case Bop("!=", a1, a2) => 

    compile_exp(a1, env) ++ compile_exp(a2, env) ++ i"if_icmpeq $jmp"

  case Bop("<", a1, a2) => 

    compile_exp(a1, env) ++ compile_exp(a2, env) ++ i"if_icmpge $jmp"

  case Bop("<=", a1, a2) => 

    compile_exp(a1, env) ++ compile_exp(a2, env) ++ i"if_icmpgt $jmp"

}

// compile function for declarations and main

def compile_decl(d: Decl) : String = d match {

  case Def(name, args, a) => { 

    val env = args.zipWithIndex.toMap

    val is = "I" * args.length

    m".method public static $name($is)I" ++

    m".limit locals ${args.length.toString}" ++

    m".limit stack ${1 + max_stack_exp(a)}" ++

    l"${name}_Start" ++   

    compile_exp(a, env) ++

    i"ireturn" ++

    m".end method\n"

  }

  case Main(a) => {

    m".method public static main([Ljava/lang/String;)V" ++

    m".limit locals 200" ++

    m".limit stack 200" ++

    compile_exp(a, Map()) ++

    i"invokestatic XXX/XXX/write(I)V" ++

    i"return" ++

    m".end method\n"

  }

}

// main compiler functions

def time_needed[T](i: Int, code: => T) = {

  val start = System.nanoTime()

  for (j <- 1 to i) code

  val end = System.nanoTime()

  (end - start)/(i * 1.0e9)

}

def deserialise[T](fname: String) : Try[T] = {

  import scala.util.Using

  Using(new ObjectInputStream(new FileInputStream(fname))) {

    in => in.readObject.asInstanceOf[T]

  }

}

def compile(class_name: String) : String = {

  val ast = deserialise[List[Decl]](class_name ++ ".prs").getOrElse(Nil) 

  val instructions = ast.map(compile_decl).mkString

  (library + instructions).replaceAllLiterally("XXX", class_name)

}

def compile_to_file(class_name: String) = {

  val output = compile(class_name)

  scala.tools.nsc.io.File(s"${class_name}.j").writeAll(output)

}

def compile_and_run(class_name: String) : Unit = {

  compile_to_file(class_name)

  (s"java -jar jvm/jasmin-2.4/jasmin.jar ${class_name}.j").!!

  println("Time: " + time_needed(2, (s"java ${class_name}/${class_name}").!))

}

// some examples of .fun files

//compile_to_file("fact")

//compile_and_run("fact")

//compile_and_run("defs")

def main(args: Array[String]) = 

   compile_and_run(args(0))

}