// A Small Compiler for a Simple Functional Language

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

//

val library = """

.class public XXX.XXX

.super java/lang/Object

.method public <init>()V

        aload_0

        invokenonvirtual java/lang/Object/<init>()V

        return

.end method

.method public static write(I)V 

        .limit locals 1 

        .limit stack 2 

        getstatic java/lang/System/out Ljava/io/PrintStream; 

        iload 0

        invokevirtual java/io/PrintStream/println(I)V 

        return 

.end method

"""

// calculating the maximal needed stack size

def max_stack_exp(e: Exp): Int = e match {

  case Call(_, args) => args.map(max_stack_exp).sum

  case If(a, e1, e2) => max_stack_bexp(a) + (List(max_stack_exp(e1), max_stack_exp(e2)).max)

  case Write(e) => max_stack_exp(e) + 1

  case Var(_) => 1

  case Num(_) => 1

  case Aop(_, a1, a2) => max_stack_exp(a1) + max_stack_exp(a2)

  case Sequence(e1, e2) => List(max_stack_exp(e1), max_stack_exp(e2)).max

}

def max_stack_bexp(e: BExp): Int = e match {

  case Bop(_, a1, a2) => max_stack_exp(a1) + max_stack_exp(a2)

}

// 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

def compile_exp(a: Exp, env : Env) : String = a match {

  case Num(i) => i"ldc $i"

  case Var(s) => i"iload ${env(s)}"

  case Aop("+", a1, a2) => compile_exp(a1, env) ++ compile_exp(a2, env) ++ i"iadd"

  case Aop("-", a1, a2) => compile_exp(a1, env) ++ compile_exp(a2, env) ++ i"isub"

  case Aop("*", a1, a2) => compile_exp(a1, env) ++ compile_exp(a2, env) ++ i"imul"

  case Aop("/", a1, a2) => compile_exp(a1, env) ++ compile_exp(a2, env) ++ i"idiv"

  case Aop("%", a1, a2) => compile_exp(a1, env) ++ compile_exp(a2, env) ++ i"irem"

  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)

}

  val instructions = ast.map(compile_decl).mkString

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

}

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

}

import scala.sys.process._

def compile_run(class_name: String) : Unit = {

  (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_file("fact")

//compile_run("defs")