// A crawler which checks whether there are 

// dead links in web-pages

import io.Source

import scala.util.matching.Regex

import scala.util._

// gets the first 10K of a web-page

def get_page(url: String) : String = {

  Try(Source.fromURL(url)("ISO-8859-1").take(10000).mkString).

    getOrElse { println(s"  Problem with: $url"); ""}

}

// e.g. get_page("https://nms.kcl.ac.uk/christiana.urban/")

// regex for URLs

val http_pattern = """"https?://[^"]*"""".r /*@\label{httpline}@*/ 

// drops the first and last characters from a string

def unquote(s: String) = s.drop(1).dropRight(1)

def get_all_URLs(page: String) : Set[String] = 

  http_pattern.findAllIn(page).map(unquote).toSet /*@\label{findallline}@*/

// a very naive version of crawl - searches until a given 

// depth, visits pages potentially more than once

def crawl(url: String, n: Int) : Unit = {

  if (n == 0) ()

  else {

    println(s"Visiting: $n $url")

    for (u <- get_all_URLs(get_page(url))) crawl(u, n - 1)

  }

}

// some starting URLs for the crawler

val startURL = """https://nms.kcl.ac.uk/christian.urban/"""

//val startURL = """https://nms.kcl.ac.uk/luc.moreau/"""

crawl(startURL, 2)