// A Small Compiler for a Simple Functional Language

import $file.fun_tokens, fun_tokens._

import $file.fun_parser, fun_parser._ 

// 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 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 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]

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

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

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

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

    val if_else = Fresh("If_else")

    val if_end = Fresh("If_end")

    compile_bexpT(b, env, if_else) ++

    compile_expT(a1, env, name) ++

    i"goto $if_end" ++

    l"$if_else" ++

    compile_expT(a2, env, name) ++

    l"$if_end"

  }

  case Call(n, args) => if (name == n) { 

    val stores = args.zipWithIndex.map { case (x, y) => i"istore $y" } 

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

    stores.reverse.mkString ++ 

    i"goto ${n}_Start" 

  } else {

    val is = "I" * args.length

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

    i"invokestatic XXX/XXX/${n}(${is})I"

  }

  case Sequence(a1, a2) => {

    compile_expT(a1, env, "") ++ i"pop" ++ compile_expT(a2, env, name)

  }

  case Write(a1) => {

    compile_expT(a1, env, "") ++

    i"dup" ++

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

  }

}

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

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

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

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

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

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

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

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

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

}

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}" ++

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

    l"${name}_Start" ++   

    compile_expT(a, env, name) ++

    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_expT(a, Map(), "") ++

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

    i"return" ++

    m".end method"

  }

}

// main compiler functions

def compile(prog: List[Decl], class_name: String) : String = {

  val instructions = prog.map(compile_decl).mkString

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

}

@main

def main(fname: String) = {

    val path = os.pwd / fname

    val class_name = fname.stripSuffix("." ++ path.ext)

    val tks = tokenise(os.read(path))

    val ast = parse_tks(tks)

    println(compile(ast, class_name))

}

}