// Parser Combinators:

// Simple Version for WHILE-language

//====================================

//

// with some added convenience for

// map-parsers and grammar rules

//

// call with

//

//    amm comb2.sc

// more convenience for the map parsers later on;

// it allows writing nested patterns as

// case x ~ y ~ z => ...

// parser combinators

}

// atomic parser for (particular) strings

case class StrParser(s: String) extends Parser[String, String] {

  def parse(sb: String) = {

    val (prefix, suffix) = sb.splitAt(s.length)

    if (prefix == s) Set((prefix, suffix)) else Set()

  }

}

// atomic parser for identifiers (variable names)

case object IdParser extends Parser[String, String] {

  val reg = "[a-z][a-z,0-9]*".r

  def parse(sb: String) = reg.findPrefixOf(sb) match {

    case None => Set()

    case Some(s) => Set(sb.splitAt(s.length))

  }

}

// atomic parser for numbers (transformed into Ints)

case object NumParser extends Parser[String, Int] {

  val reg = "[0-9]+".r

  def parse(sb: String) = reg.findPrefixOf(sb) match {

    case None => Set()

    case Some(s) => {

      val (hd, tl) = sb.splitAt(s.length)

      Set((hd.toInt, tl)) 

    }

  }

}

// the following string interpolation allows us to write 

// StrParser(_some_string_) more conveniently as 

//

// p"<_some_string_>" 

extension (sc: StringContext) 

  def p(args: Any*) = StrParser(sc.s(args*))

// the abstract syntax trees for the WHILE language

abstract class Stmt

abstract class AExp

abstract class BExp 

type Block = List[Stmt]

case object Skip extends Stmt

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

case class Write(s: String) extends Stmt

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 object True extends BExp

case object False extends BExp

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

case class And(b1: BExp, b2: BExp) extends BExp

case class Or(b1: BExp, b2: BExp) extends BExp

// arithmetic expressions

lazy val AExp: Parser[String, AExp] = 

lazy val Te: Parser[String, AExp] = 

lazy val Fa: Parser[String, AExp] = 

   IdParser.map(Var(_)) || 

   NumParser.map(Num(_))

// boolean expressions with some simple nesting

lazy val BExp: Parser[String, BExp] = 

lazy val Stmt: Parser[String, Stmt] =

  ((p"skip".map[Stmt]{_ => Skip }) ||

lazy val Stmts: Parser[String, Block] =

  (Stmt ~ p";" ~ Stmts).map[Block]{ case x ~ _ ~ z => x :: z } ||

  (Stmt.map[Block]{ s => List(s) })

lazy val Block: Parser[String, Block] =

  ((p"{" ~ Stmts ~ p"}").map{ case _ ~ y ~ _ => y } || 

// Examples

println(AExp.parse_all("2*2*2"))

println(BExp.parse_all("5+3"))

println(Stmt.parse_all("5==3"))

println(Stmt.parse_all("x2:=5+3"))

println(Block.parse_all("{x:=5;y:=8}"))

println(Block.parse_all("if(false)then{x:=5}else{x:=10}"))

val fib = """n := 10;

             minus1 := 0;

             minus2 := 1;

             temp := 0;

             while (n > 0) do {

                 temp := minus2;

                 minus2 := minus1 + minus2;

                 minus1 := temp;

                 n := n - 1

             };

             result := minus2""".replaceAll("\\s+", "")

println("fib testcase:")

println(Stmts.parse_all(fib))

// an interpreter for the WHILE language

type Env = Map[String, Int]

def eval(bl: Block) : Env = eval_bl(bl, Map())

// parse + evaluate fib program; then lookup what is

// stored under the variable "result" 

println(eval(Stmts.parse_all(fib).head)("result"))

// calculate and print all factors bigger 

// than 1 and smaller than n

println("Factors")

val factors =  

   """n := 12;

      f := 2;

      while (f < n / 2 + 1) do {

        if ((n / f) * f == n) then  { write(f) } else { skip };

        f := f + 1

      }""".replaceAll("\\s+", "")

println(eval(Stmts.parse_all(factors).head))

// calculate all prime numbers up to a number 

println("Primes")

val primes =  

   """end := 100;

      n := 2;

      while (n < end) do {

        f := 2;

        tmp := 0;

        while ((f < n / 2 + 1) && (tmp == 0)) do {

          if ((n / f) * f == n) then  { tmp := 1 } else { skip };

          f := f + 1

        };

        if (tmp == 0) then { write(n) } else { skip };

        n  := n + 1

      }""".replaceAll("\\s+", "")

println(eval(Stmts.parse_all(primes).head))