//:load matcher.scala

// some regular expressions

val SYM = RANGE("""ABCDEFGHIJKLMNOPQRSTUVXYZabcdefghijklmnopqrstuvwxyz.,!?-{[()]}':;%0123456789""")

val WORD = PLUS(SYM)

val BTAG = SEQS("<", WORD, ">") 

val ETAG = SEQS("</", WORD, ">")

val WHITESPACE = PLUS(RANGE(" \n"))

// for classifying the strings that have been recognised

abstract class Token

case object T_WHITESPACE extends Token

case class T_WORD(s: String) extends Token

case class T_ETAG(s: String) extends Token

case class T_BTAG(s: String) extends Token

case class T_NT(s: String, rhs: List[Token]) extends Token

val lexing_rules: List[Rule[Token]] = 

  List((BTAG, (s) => T_BTAG(s.mkString)),

       (ETAG, (s) => T_ETAG(s.mkString)),

       (WORD, (s) => T_WORD(s.mkString)),

       (WHITESPACE, (s) => T_WHITESPACE))

// the tokenizer

val T = Tokenizer(lexing_rules)

// width for printing

val WIDTH = 60

def interpret(ts: List[Token], c: Int, ctr: List[String]) : Unit= ts match {

  case Nil => println(Console.RESET)

  case T_WHITESPACE::rest => print(Console.RESET + " "); interpret(rest, c + 1, ctr)

  case T_WORD(s)::rest => {

    val newstr = Console.RESET + ctr.reverse.mkString + s

    if (c + s.length < WIDTH) {

      print(newstr);

      interpret(rest, c + s.length, ctr)

    }

    else {

      print("\n" + newstr)

      interpret(rest, s.length, ctr)

    } 

  }

  case T_BTAG("<p>")::rest => print("\n"); interpret(rest, 0, ctr)

  case T_ETAG("</p>")::rest => print("\n"); interpret(rest, 0, ctr)

  case T_BTAG("<b>")::rest => interpret(rest, c, Console.BOLD :: ctr)

  case T_BTAG("<a>")::rest => interpret(rest, c, Console.UNDERLINED :: ctr)

  case T_BTAG("<cyan>")::rest => interpret(rest, c, Console.CYAN :: ctr)

  case T_BTAG("<red>")::rest => interpret(rest, c, Console.RED :: ctr)

  case T_BTAG("<blink>")::rest => interpret(rest, c, Console.BLINK :: ctr)

  case T_ETAG(_)::rest => interpret(rest, c, ctr.tail)

  case _::rest => interpret(rest, c, ctr)

}

val test_string = """

<b>MSc Projects</b>

<p>

start of paragraph. <cyan> a <red>cyan</red> word</cyan> normal again something longer.

</p> 

 <p><b>Description:</b>  

  <a>Regular expressions</a> are extremely useful for many text-processing tasks such as finding patterns in texts,

  lexing programs, syntax highlighting and so on. Given that regular expressions were

  introduced in 1950 by <a>Stephen Kleene</a>, you might think 

  regular expressions have since been studied and implemented to death. But you would definitely be mistaken: in fact they are still

  an active research area. For example

  <a>this paper</a> 

  about regular expression matching and partial derivatives was presented this summer at the international 

  PPDP'12 conference. The task in this project is to implement the results from this paper.</p>

  <p>The background for this project is that some regular expressions are 

  <a>evil</a>

  and can stab you in the back; according to

  this <a>blog post</a>.

  For example, if you use in <a>Python</a> or 

  in <a>Ruby</a> (probably also in other mainstream programming languages) the 

  innocently looking regular expression a?{28}a{28} and match it, say, against the string 

  <red>aaaaaaaaaa<cyan>aaaaaaa</cyan>aaaaaaaaaaa</red> (that is 28 as), you will soon notice that your CPU usage goes to 100%. In fact,

  Python and Ruby need approximately 30 seconds of hard work for matching this string. You can try it for yourself:

  <a>re.py</a> (Python version) and 

  <a>re.rb</a> 

  (Ruby version). You can imagine an attacker

  mounting a nice <a>DoS attack</a> against 

  your program if it contains such an evil regular expression. Actually 

  <a>Scala</a> (and also Java) are almost immune from such

  attacks as they can deal with strings of up to 4,300 as in less than a second. But if you scale

  the regular expression and string further to, say, 4,600 as, then you get a 

  StackOverflowError 

  potentially crashing your program.

  </p>

"""

interpret(T.fromString(test_string), 0, Nil)