import scala.language.implicitConversions    

import scala.language.reflectiveCalls

import scala.annotation.tailrec   

import scala.io.Source

import scala.util.parsing.combinator._

abstract class Rexp 

case object ZERO extends Rexp 

case object ONE extends Rexp

case class CHAR(c: Char) extends Rexp {

  override def toString = c.toString 

}

case object ANYCHAR extends Rexp {

  override def toString = "." 

}

case class ALT(r1: Rexp, r2: Rexp) extends Rexp {

  override def toString = "(" + r1.toString + "|" + r2.toString + ")" 

}

case class SEQ(r1: Rexp, r2: Rexp) extends Rexp {

  override def toString = "(" + r1.toString + r2.toString +")"

} 

case class STAR(r: Rexp) extends Rexp 

case class RECD(x: String, r: Rexp) extends Rexp {

  override def toString = "[" + r.toString +"]"

}

abstract class Val

case object Empty extends Val

case class Chr(c: Char) extends Val

case class Sequ(v1: Val, v2: Val) extends Val

case class Left(v: Val) extends Val

case class Right(v: Val) extends Val

case class Stars(vs: List[Val]) extends Val

// nullable function: tests whether the regular 

// expression can recognise the empty string

def nullable (r: Rexp) : Boolean = r match {

  case ZERO => false

  case ONE => true

  case CHAR(_) => false

  case ANYCHAR => false

  case ALT(r1, r2) => nullable(r1) || nullable(r2)

  case SEQ(r1, r2) => nullable(r1) && nullable(r2)

  case STAR(_) => true

  case RECD(_, r1) => nullable(r1)

}

// derivative of a regular expression w.r.t. a character

def der (c: Char, r: Rexp) : Rexp = r match {

  case ZERO => ZERO

  case ONE => ZERO

  case CHAR(d) => if (c == d) ONE else ZERO

  case ANYCHAR => ONE

  case ALT(r1, r2) => ALT(der(c, r1), der(c, r2))

  case SEQ(r1, r2) => 

    if (nullable(r1)) ALT(SEQ(der(c, r1), r2), der(c, r2))

    else SEQ(der(c, r1), r2)

  case STAR(r) => SEQ(der(c, r), STAR(r))

  case RECD(_, r1) => der(c, r1)

}

// derivative w.r.t. a string (iterates der)

def ders (s: List[Char], r: Rexp) : Rexp = s match {

  case Nil => r

  case c::s => ders(s, der(c, r))

}

// extracts a string from value

def flatten(v: Val) : String = v match {

  case Empty => ""

  case Chr(c) => c.toString

  case Left(v) => flatten(v)

  case Right(v) => flatten(v)

  case Sequ(v1, v2) => flatten(v1) + flatten(v2)

  case Stars(vs) => vs.map(flatten).mkString

}

// extracts an environment from a value

def env(v: Val, r: Rexp) : List[(String, String)] = (v, r) match {

  case (Empty, ONE) => Nil

  case (Chr(c), CHAR(_)) => Nil

  case (Chr(c), ANYCHAR) => Nil

  case (Left(v), ALT(r1, r2)) => env(v, r1)

  case (Right(v), ALT(r1, r2)) => env(v, r2)

  case (Sequ(v1, v2), SEQ(r1, r2)) => env(v1, r1) ::: env(v2, r2)

  case (Stars(vs), STAR(r)) => vs.flatMap(env(_, r))

  case (v, RECD(x, r)) => (x, flatten(v))::env(v, r)

}

// extracts indices for the underlying strings

def env2(v: Val, r: Rexp, n: Int) : (List[(Int, Int)], Int) = (v, r) match {

  case (Empty, ONE) => (Nil, n)

  case (Chr(c), CHAR(_)) => (Nil, n + 1)

  case (Chr(c), ANYCHAR) => (Nil, n + 1)

  case (Left(v), ALT(r1, r2)) => env2(v, r1, n)

  case (Right(v), ALT(r1, r2)) => env2(v, r2, n)

  case (Sequ(v1, v2), SEQ(r1, r2)) => {

   val (e1, n1) = env2(v1, r1, n) 

   val (e2, n2) = env2(v2, r2, n1)

   (e1 ::: e2, n2)

  }

  case (Stars(Nil), STAR(r)) => (Nil, n)

  case (Stars(v :: vs), STAR(r)) => {

   val (e1, n1) = env2(v, r, n) 

   val (e2, n2) = env2(Stars(vs), STAR(r), n1)

   (e1 ::: e2, n2)

  }

  case (v, RECD(x, r)) => {

    val (e1, n1) = env2(v, r, n)

    ((n, n + flatten(v).length) :: e1, n1)

  }

}

// injection part

def mkeps(r: Rexp) : Val = r match {

  case ONE => Empty

  case ALT(r1, r2) => 

    if (nullable(r1)) Left(mkeps(r1)) else Right(mkeps(r2))

  case SEQ(r1, r2) => Sequ(mkeps(r1), mkeps(r2))

  case STAR(r) => Stars(Nil)

  case RECD(x, r) => mkeps(r)

}

def inj(r: Rexp, c: Char, v: Val) : Val = (r, v) match {

  case (STAR(r), Sequ(v1, Stars(vs))) => Stars(inj(r, c, v1)::vs)

  case (SEQ(r1, r2), Sequ(v1, v2)) => Sequ(inj(r1, c, v1), v2)

  case (SEQ(r1, r2), Left(Sequ(v1, v2))) => Sequ(inj(r1, c, v1), v2)

  case (SEQ(r1, r2), Right(v2)) => Sequ(mkeps(r1), inj(r2, c, v2))

  case (ALT(r1, r2), Left(v1)) => Left(inj(r1, c, v1))

  case (ALT(r1, r2), Right(v2)) => Right(inj(r2, c, v2))

  case (CHAR(d), Empty) => Chr(c) 

  case (ANYCHAR, Empty) => Chr(c) 

  case (RECD(x, r1), _) => inj(r1, c, v)

}

// main lexing function (produces a value)

def lex(r: Rexp, s: List[Char]) : Val = s match {

  case Nil => if (nullable(r)) mkeps(r) else throw new Exception("Not matched")

  case c::cs => inj(r, c, lex(der(c, r), cs))

}

def lexing(r: Rexp, s: String) : Val = lex(r, s.toList)

// Regular expression parser

case class Parser(s: String) {

  var i = 0

  def peek() = s(i)

  def eat(c: Char) = 

    if (c == s(i)) i = i + 1 else throw new Exception("Expected " + c + " got " + s(i))

  def next() = { i = i + 1; s(i - 1) }

  def more() = s.length - i > 0

  def Regex() : Rexp = {

    val t = Term();

    if (more() && peek() == '|') {

      eat ('|') ; 

      ALT(t, Regex()) 

    } 

    else t

  }

  def Term() : Rexp = {

    var f : Rexp = 

      if (more() && peek() != ')' && peek() != '|') Factor() else ONE;

    while (more() && peek() != ')' && peek() != '|') {

      f = SEQ(f, Factor()) ;

    }

    f

  }

  def Factor() : Rexp = {

    var b = Base();

    while (more() && peek() == '*') {

      eat('*') ;

      b = STAR(b) ;

    }

    while (more() && peek() == '?') {

      eat('?') ;

      b = ALT(b, ONE) ;

    }

    while (more() && peek() == '+') {

      eat('+') ;

      b = SEQ(b, STAR(b)) ;

    }

    b

  }

  def Base() : Rexp = {

    peek() match {

      case '(' => { eat('(') ; val r = Regex(); eat(')') ; RECD("",r) }

      case '.' => { eat('.'); ANYCHAR }

      case _ => CHAR(next())

    }

  }

}

println(Parser("a|(bc)*").Regex())

  if (line.head == '#') "#" else

    {

      val line_split = line.split("\\t+")

      val reg_str = line_split(1)

      val reg = RECD("", Parser(reg_str).Regex())

      val in_str = if (line_split(2) == "-") "" else line_split(2)

      val res_str = line_split(3)

      val our_val = lexing(reg, in_str)

      val our_result = env2(our_val, reg, 0)._1.mkString("") 

      if (our_result != res_str) 

        { 

          reg_str + ":   " + 

          reg.toString + ": " + 

          in_str + "   \n " + 

          our_result +  

          " => \n" + res_str + " ! " +

          our_val + ":" + reg + "\n" 

        }

      else "*"

    }

}