// CW3

import $file.lexer

import lexer._ 

case class ~[+A, +B](_1: A, _2: B)

type IsSeq[A] = A => Seq[_]

abstract class Parser[I : IsSeq, T] {

  def parse(ts: I): Set[(T, I)]

  def parse_all(ts: I) : Set[T] =

    for ((head, tail) <- parse(ts); if tail.isEmpty) yield head

}

class SeqParser[I : IsSeq, T, S](p: => Parser[I, T], q: => Parser[I, S]) extends Parser[I, ~[T, S]] {

  def parse(sb: I) = 

    for ((head1, tail1) <- p.parse(sb); 

         (head2, tail2) <- q.parse(tail1)) yield (new ~(head1, head2), tail2)

}

class AltParser[I : IsSeq, T](p: => Parser[I, T], q: => Parser[I, T]) extends Parser[I, T] {

  def parse(sb: I) = p.parse(sb) ++ q.parse(sb)   

}

class FunParser[I : IsSeq, T, S](p: => Parser[I, T], f: T => S) extends Parser[I, S] {

  def parse(sb: I) = 

    for ((head, tail) <- p.parse(sb)) yield (f(head), tail)

}

// New parser that takes as input a list of tokens

case class TokenListParser(ts: List[Token]) extends Parser[List[Token], List[Token]] {

    def parse(tsb: List[Token]) = {

        val (prefix, suffix) = tsb.splitAt(ts.length)

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

    }

}

// Implicit definitions to go from a token 

// or a list of tokens to a TokenListParser

implicit def token2parser(t: Token) = TokenListParser(List(t))

implicit def tokenList2parser(ts: List[Token]) = TokenListParser(ts)

implicit def ParserOps[I : IsSeq, T](p: Parser[I, T]) = new {

  def || (q : => Parser[I, T]) = new AltParser[I, T](p, q)

  def ==>[S] (f: => T => S) = new FunParser[I, T, S](p, f)

  def ~[S] (q : => Parser[I, S]) = new SeqParser[I, T, S](p, q)

}

implicit def TokenOps(t: Token) = new {

    def || (q : => Parser[List[Token], List[Token]]) = new AltParser[List[Token], List[Token]](List(t), q)

    def || (qs : List[Token]) = new AltParser[List[Token], List[Token]](List(t), qs)

    def ==>[S] (f: => List[Token] => S) = new FunParser[List[Token], List[Token], S](List(t), f)

    def ~[S](q : => Parser[List[Token], S]) =

        new SeqParser[List[Token], List[Token], S](List(t), q)

    def ~ (qs : List[Token]) =

        new SeqParser[List[Token], List[Token], List[Token]](List(t), qs)

}

implicit def TokenListOps(ts: List[Token]) = new {

    def || (q : => Parser[List[Token], List[Token]]) = new AltParser[List[Token], List[Token]](ts, q)

    def || (qs : List[Token]) = new AltParser[List[Token], List[Token]](ts, qs)

    def ==>[S] (f: => List[Token] => S) = new FunParser[List[Token], List[Token], S](ts, f)

    def ~[S](q : => Parser[List[Token], S]) =

        new SeqParser[List[Token], List[Token], S](ts, q)

    def ~ (qs : List[Token]) =

        new SeqParser[List[Token], List[Token], List[Token]](ts, qs)

}

// Abstract Syntax Trees

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 Read(s: String) extends Stmt

case class WriteId(s: String) extends Stmt  // for printing values of variables

case class WriteString(s: String) extends Stmt  // for printing words

case class For(counter: String, lower: AExp, upper: AExp, code: Block) 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

case class IdParser() extends Parser[List[Token], String] {

    def parse(tsb: List[Token]) = tsb match {

        case T_ID(id) :: rest => Set((id, rest))

        case _ => Set()

    }

}

case class NumParser() extends Parser[List[Token], Int] {

    def parse(tsb: List[Token]) = tsb match {

        case T_NUM(n) :: rest => Set((n, rest))

        case _ => Set()

    }

}

case class StringParser() extends Parser[List[Token], String] {

    def parse(tsb: List[Token]) = tsb match {

        case T_STRING(s) :: rest => Set((s, rest))

        case _ => Set()

    }

}

// WHILE Language Parsing

lazy val AExp: Parser[List[Token], AExp] = 

  (Te ~ T_OP("+") ~ AExp) ==> { case x ~ _ ~ z => Aop("+", x, z): AExp } ||

  (Te ~ T_OP("-") ~ AExp) ==> { case x ~ _ ~ z => Aop("-", x, z): AExp } || Te

lazy val Te: Parser[List[Token], AExp] = 

  (Fa ~ T_OP("*") ~ Te) ==> { case x ~ _ ~ z => Aop("*", x, z): AExp } || 

  (Fa ~ T_OP("/") ~ Te) ==> { case x ~ _ ~ z => Aop("/", x, z): AExp } || 

  (Fa ~ T_OP("%") ~ Te) ==> { case x ~ _ ~ z => Aop("%", x, z): AExp } || Fa  

lazy val Fa: Parser[List[Token], AExp] = 

   (T_PAREN("(") ~ AExp ~ T_PAREN(")")) ==> { case _ ~ y ~ _ => y } || 

   IdParser() ==> Var  || 

   NumParser() ==> Num

lazy val BExp: Parser[List[Token], BExp] = 

   (AExp ~ T_OP("==") ~ AExp) ==> { case x ~ _ ~ z => Bop("==", x, z): BExp } || 

   (AExp ~ T_OP("!=") ~ AExp) ==> { case x ~ _ ~ z => Bop("!=", x, z): BExp } || 

   (AExp ~ T_OP("<") ~ AExp) ==> { case x ~ _ ~ z => Bop("<", x, z): BExp } || 

   (AExp ~ T_OP(">") ~ AExp) ==> { case x ~ _ ~ z => Bop(">", x, z): BExp } ||

   (T_PAREN("(") ~ BExp ~ List(T_PAREN(")"), T_OP("&&")) ~ BExp) ==> { case _ ~ y ~ _ ~ v => And(y, v): BExp } ||

   (T_PAREN("(") ~ BExp ~ List(T_PAREN(")"), T_OP("||")) ~ BExp) ==> { case _ ~ y ~ _ ~ v => Or(y, v): BExp } ||

   (T_KEYWORD("true") ==> (_ => True: BExp )) || 

   (T_KEYWORD("false") ==> (_ => False: BExp )) ||

   (T_PAREN("(") ~ BExp ~ T_PAREN(")")) ==> { case _ ~ x ~ _ => x }

lazy val Stmt: Parser[List[Token], Stmt] =

    T_KEYWORD("skip") ==> (_ => Skip: Stmt) ||

    (IdParser() ~ T_OP(":=") ~ AExp) ==> { case id ~ _ ~ z => Assign(id, z): Stmt } ||

    (T_KEYWORD("if") ~ BExp ~ T_KEYWORD("then") ~ Block ~ T_KEYWORD("else") ~ Block) ==> { case _ ~ y ~ _ ~ u ~ _ ~ w => If(y, u, w): Stmt } ||

    (T_KEYWORD("while") ~ BExp ~ T_KEYWORD("do") ~ Block) ==> { case _ ~ y ~ _ ~ w => While(y, w) : Stmt } ||

    (T_KEYWORD("read") ~ IdParser()) ==> { case _ ~ id => Read(id): Stmt} ||

    (T_KEYWORD("write") ~ IdParser()) ==> { case _ ~ id => WriteId(id): Stmt} ||

    (T_KEYWORD("write") ~ StringParser()) ==> { case _ ~ s => WriteString(s): Stmt} ||

    (T_KEYWORD("for") ~ IdParser() ~ T_OP(":=") ~ AExp ~ T_KEYWORD("upto") ~ AExp ~ T_KEYWORD("do") ~ Block) ==> {

      case _ ~ id ~ _ ~ lower ~ _ ~ upper ~ _ ~ blck => For(id, lower, upper, blck): Stmt

    }

lazy val Stmts: Parser[List[Token], Block] =

    (Stmt ~ T_SEMI ~ Stmts) ==> { case x ~ _ ~ z => x :: z : Block } ||

    (Stmt ==> (s => List(s) : Block))

lazy val Block: Parser[List[Token], Block] =

    (T_PAREN("{") ~ Stmts ~ T_PAREN("}")) ==> { case x ~ y ~ z => y} ||

    (Stmt ==> (s => List(s)))