AsyncHomework.scala

package com.evolutiongaming.bootcamp.async

import java.net.URL
import java.util.concurrent.Executors

import scala.concurrent.{ExecutionContext, Future}
import scala.io.Source

/** Application:
  * - takes a web-page URL from arguments (args array)
  * - loads the web-page body, extracts HTTP links from it
  * - for all the found links, tries to fetch a server name header if there is one
  * - prints all the encountered unique server name values in alphabetical order
  *
  * Each link processing should be done in parallel.
  * Validation of arguments is not needed.
  *
  * Try to test it on http://google.com!
  */
object AsyncHomework extends App {
  private implicit val ec: ExecutionContext = ExecutionContext.fromExecutor(Executors.newCachedThreadPool())

  // put your code there

  private def fetchPageBody(url: String): Future[String] = {
    println(f"Fetching $url")
    Future {
      val source = Source.fromURL(url)
      try {
        source.mkString
      } finally {
        source.close()
      }
    }
  }

  private def fetchServerName(url: String): Future[Option[String]] = {
    println(s"Fetching server name header for $url")
    Future {
      Option(new URL(url).openConnection().getHeaderField("Server"))
    }
  }

  private def findLinkUrls(html: String): Future[List[String]] = Future {
    val linkPattern = """href="(http[^"]+)"""".r
    linkPattern.findAllMatchIn(html).map(m => m.group(1)).toList
  }
}