Hacker News API Part 1

  "org.scalaj" %% "scalaj-http" % "2.3.0",
  "com.lihaoyi" %% "upickle" % "0.4.4",
  "org.typelevel" %% "cats" % "0.9.0",
  "org.ocpsoft.prettytime" % "prettytime" % "3.2.7.Final",
  "org.scalatest" %% "scalatest" % "3.0.1" % "test",
  "com.lihaoyi" % "ammonite" % "1.0.0" % "test" cross CrossVersion.full

  object CustomHttp extends BaseHttp(
    proxyConfig = None,
    options = HttpConstants.defaultOptions,
    charset = HttpConstants.utf8,
    sendBufferSize = 4096,
    userAgent = "justinhj/hnfetch/1.0",
    compress = false
  )

  val baseHNURL = "https://hacker-news.firebaseio.com/v0/"

  def getUserURL(userId: HNUserID) = s"${baseHNURL}user/$userId.json"
  def getItemURL(itemId: HNItemID) = s"${baseHNURL}item/$itemId.json"
  val getTopItemsURL = s"${baseHNURL}topstories.json"
  

  type HNUserID = String
  type HNItemID = Int

  val HNMissingItemID : HNItemID = -1
  val HNMissingUserID : HNUserID = ""

  case class HNUser (
                    id : HNUserID, // The user's unique username. Case-sensitive. Required.
                    //delay : Int, // Delay in minutes between a comment's creation and its visibility to other users.
                    created : Int, // Creation date of the user, in Unix Time.
                    karma : Int, // The user's karma.
                    about : String, // The user's optional self-description. HTML.
                    submitted : List[HNItemID] ) // List of the user's stories, polls and comments.

  case class HNItem(
                     id : HNItemID, // The item's unique id.
                     deleted : Boolean = false, // true if the item is deleted.
                     `type` : String, // The type of item. One of "job", "story", "comment", "poll", or "pollopt".
                     by : HNUserID = HNMissingUserID, // The username of the item's author.
                     time : Int, // Creation date of the item, in Unix Time.
                     text : String = "", // The comment, story or poll text. HTML.
                     dead : Boolean = false, // true if the item is dead.
                     parent : HNItemID = HNMissingItemID, // The comment's parent: either another comment or the relevant story.
                     poll : HNItemID = HNMissingItemID, // The pollopt's associated poll.
                     kids : List[HNItemID] = List(), // The ids of the item's comments, in ranked display order.
                     url : String = "", // The URL of the story.
                     score : Int = -1, // The story's score, or the votes for a pollopt.
                     title : String = "", // The title of the story, poll or job.
                     parts : List[HNItemID] = List(), // A list of related pollopts, in display order.
                     descendants : Int = 0 // In the case of stories or polls, the total comment count.
                   )

  def hnRequest[T](url: String)(implicit r: Reader[T]) : Future[Either[String, T]] = {

    Future {CustomHttp(url).asString}.map {
      response =>
        if(response.code == 200) {
          Try(read[T](response.body)) match {
            case Success(good) if good == null =>
              println("got empty")
              Left("Not found")
            case Success(good) =>
              println("got successfully")
              Right(good)
            case Failure(e) =>
              println(s"got parse error ${response.body}")
              Left("Failed to read " + e.getMessage())
          }
        }
        else {
          println("got no response")
          Left(s"Failed to retrieve $url code: ${response.code}")
        }
    }
      .recover {
        case e : Exception =>
          println(s"got exception ${e.getMessage} due to ${e.getCause}")
          Left("Failed to retrieve $url becasue ${e.getMessage}")
      }
  }

  // constuct the query to get an item
  def getUser(userID: HNUserID) : Future[Either[String, HNUser]] = {
    val url = getUserURL(userID)

    println(s"GET $url")
    hnRequest[HNUser](url)
  }

  def getItem(itemId: HNItemID) : Future[Either[String, HNItem]] = {
    val url = getItemURL(itemId)

    println(s"GET $url")
    hnRequest[HNItem](url)
  }

  type HNItemIDList = List[HNItemID]

  def getTopItems() : Future[Either[String, HNItemIDList]] = {
    hnRequest[HNItemIDList](getTopItemsURL)
  }

  def printPage(startPage: Int, numItemsPerPage: Int) : Unit = {

    // helper to show the article rank
    def itemNum(n: Int) = (startPage * numItemsPerPage) + n + 1

    val futureItems = getTopItems().flatMap {
      case Right(items) =>
        val pageOfItems = items.slice(startPage * numItemsPerPage, startPage * numItemsPerPage + numItemsPerPage)
        getItems(pageOfItems)

      case Left(err) =>
        Future.failed(new Exception(err))
    }

    val printItems = futureItems.map {
      _.zipWithIndex.foreach {
        case (Right(item), n) =>
          println(s"${itemNum(n)}. ${item.title} ${getHostName(item.url)}")
          println(s"  ${item.score} points by ${item.by} at ${timestampToPretty(item.time)} ${item.descendants} comments\n")
        case (Left(err), n) => println(s"${itemNum(n)}. No item (err $err)")
      }
    }

    Await.ready(printItems, 10 seconds)
  }

 def getItems(itemIDs : Seq[HNItemID]) : Future[Seq[Either[String, HNItem]]] = {

    val f = itemIDs.map { itemID => getItem(itemID) }
    Future.sequence(f)
  }