// A Web-Crawler
//================

// call parallel version with
//
// scala -cp scala-parallel-collections_2.13-0.2.0.jar crawler.scala 


import io.Source
import scala.util._
import scala.collection.parallel.CollectionConverters._

// the idea is to look for links using the
// regular expression "https?://[^"]*" and for
// email addresses using yet another regex.


// 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"); ""}
}

// regex for URLs and emails
val http_pattern = """"https?://[^"]*"""".r
val email_pattern = """([a-z0-9_\.-]+)@([\da-z\.-]+)\.([a-z\.]{2,6})""".r

//  val s = "foo bla christian@kcl.ac.uk 1234567"
//  email_pattern.findAllIn(s).toList

// drops the first and last character 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

// a 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")
    val page = get_page(url)
    for (u <- get_all_URLs(get_page(url)).par) crawl(u, n - 1)
  }
}

// some starting URLs for the crawler
val startURL = """https://nms.kcl.ac.uk/christian.urban/"""

//crawl(startURL, 2)

// a primitive email harvester
def emails(url: String, n: Int) : Set[String] = {
  if (n == 0) Set()
  else {
    println(s"  Visiting: $n $url")
    val page = get_page(url)
    val new_emails = email_pattern.findAllIn(page).toSet
    new_emails ++ (for (u <- get_all_URLs(page).par) yield emails(u, n - 1)).flatten
  }
}

println(emails(startURL, 3))