// 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))