// A Small Compiler for the WHILE Language

//

// - this compiler contains support for "static" integer 

//   arrays (they are mutable but cannot be re-sized)

//

// Call with 

//

// amm compile_arrays.sc

// the abstract syntax trees for WHILE

abstract class Stmt

abstract class AExp

abstract class BExp 

type Block = List[Stmt]

// statements

case object Skip extends Stmt

case class ArrayDef(s: String, n: Int) extends Stmt            // array definition

case class If(a: BExp, bl1: Block, bl2: Block) extends Stmt

case class While(b: BExp, bl: Block) extends Stmt

case class Assign(s: String, a: AExp) extends Stmt             // var := exp

case class AssignA(s: String, a1: AExp, a2: AExp) extends Stmt // arr[exp1] := exp2

case class Write(s: String) extends Stmt

// arithmetic expressions

case class Var(s: String) extends AExp

case class Num(i: Int) extends AExp

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

case class Ref(s: String, a: AExp) extends AExp

// boolean expressions

case object True extends BExp

case object False extends BExp

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

// compiler headers needed for the JVM

//

// - contains a main method and a method for writing out an integer

//

// - the stack and locals are hard-coded

//

val beginning = """

.class public XXX.XXX

.super java/lang/Object

.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/print(I)V

    return 

.end method

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

   .limit locals 200

   .limit stack 200

; COMPILED CODE STARTS   

"""

val ending = """

; COMPILED CODE ENDS

   return

.end method

"""

// for generating new labels

var counter = -1

def Fresh(x: String) = {

  counter += 1

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

}

// environments for variables and indices

type Env = Map[String, Int]

// convenient string interpolations 

// for generating instructions and labels

extension (sc: StringContext) {

}

def compile_op(op: String) = op match {

  case "+" => i"iadd"

  case "-" => i"isub"

  case "*" => i"imul"

}

// arithmetic expression compilation

def compile_aexp(a: AExp, env : Env) : String = a match {

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

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

  case Aop(op, a1, a2) => 

    compile_aexp(a1, env) ++ compile_aexp(a2, env) ++ compile_op(op)

  case Ref(s, a) =>

    i"aload ${env(s)}" ++ compile_aexp(a, env) ++  i"iaload"

}

// boolean expression compilation

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

  case True => ""

  case False => i"goto $jmp"

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

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

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

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

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

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

}

// statement compilation

def compile_stmt(s: Stmt, env: Env) : (String, Env) = s match {

  case Skip => ("", env)

  case Assign(x, a) => {

    (compile_aexp(a, env) ++ i"istore $index \t\t; $x", env + (x -> index)) 

  } 

  case If(b, bl1, bl2) => {

    val if_else = Fresh("If_else")

    val if_end = Fresh("If_end")

    val (instrs1, env1) = compile_block(bl1, env)

    val (instrs2, env2) = compile_block(bl2, env1)

    (compile_bexp(b, env, if_else) ++

     instrs1 ++

     i"goto $if_end" ++

     l"$if_else" ++

     instrs2 ++

     l"$if_end", env2)

  }

  case While(b, bl) => {

    val loop_begin = Fresh("Loop_begin")

    val loop_end = Fresh("Loop_end")

    val (instrs1, env1) = compile_block(bl, env)

    (l"$loop_begin" ++

     compile_bexp(b, env, loop_end) ++

     instrs1 ++

     i"goto $loop_begin" ++

     l"$loop_end", env1)

  }

  case Write(x) => 

    (i"iload ${env(x)} \t\t; $x" ++ 

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

  case ArrayDef(s: String, n: Int) => {

    val index = if (env.isDefinedAt(s)) throw new Exception("array def error") else 

                    env.keys.size

    (i"ldc $n" ++

     i"newarray int" ++

     i"astore $index", env + (s -> index))

  }

  case AssignA(s, a1, a2) => {

    val index = if (env.isDefinedAt(s)) env(s) else 

                    throw new Exception("array not defined")

    (i"aload ${env(s)}" ++

     compile_aexp(a1, env) ++

     compile_aexp(a2, env) ++

     i"iastore", env)

  } 

}

// compile a block (i.e. list of statements)

def compile_block(bl: Block, env: Env) : (String, Env) = bl match {

  case Nil => ("", env)

  case s::bl => {

    val (instrs1, env1) = compile_stmt(s, env)

    val (instrs2, env2) = compile_block(bl, env1)

    (instrs1 ++ instrs2, env2)

  }

}

// main compile function for blocks (adds headers and proper JVM names)

def compile(bl: Block, class_name: String) : String = {

  val instructions = compile_block(bl, Map())._1

  (beginning ++ instructions ++ ending).replace("XXX", class_name)

}

// contrived example involving arrays

val array_test = 

  List(ArrayDef("a", 10),               // array a[10]

       ArrayDef("b", 2),                // array b[2]

       AssignA("a", Num(0), Num(10)),   // a[0] := 10

       Assign("x", Ref("a", Num(0))),   // x := a[0]

       Write("x"),            

       AssignA("b", Num(1), Num(5)),    // b[1] := 5

       Assign("x", Ref("b", Num(1))),   // x := b[1] 

       Write("x"))                     

// prints out the JVM-assembly instructions for fib above

//

//    println(compile(array_test, "arr"))

//

// can be assembled by hand with 

//

//    java -jar jasmin.jar arr.j

//

// and run with

//

//    java arr/arr

// automating the above

def compile_to_file(bl: Block, class_name: String) : Unit = 

  write.over(pwd / s"$class_name.j", compile(bl, class_name))  

def compile_and_run(bl: Block, class_name: String) : Unit = {

  println(s"Start of compilation")

  compile_to_file(bl, class_name)

  println(s"generated $class_name.j file")

  os.proc("java", "-jar", "jasmin.jar", s"$class_name.j").call()

  println(s"generated $class_name.class file ")

  //println(os.proc("java", s"${class_name}/${class_name}").call().out.text())

  os.proc("java", s"${class_name}/${class_name}").call(stdout = os.Inherit)

  println(s"done.")

}

//@main def main() = {

//  compile_and_run(array_test, "arr")

//}