WebClientAppInstance.scala

package cs214.webapp
package client
package graphics

import scala.scalajs.concurrent.JSExecutionContext.Implicits.queue
import org.scalajs.dom

import scalatags.JsDom.all.Frag

/** General web graphics UI, basically a wrapper around raw ScalaJS API */
abstract class WebClientAppInstance[Event, View](
    userId: UserId,
    sendMessage: ujson.Value => Unit,
    target: Target
) extends StateMachineClientAppInstance[Event, View](userId, sendMessage), DOMClientUI[View], PatchableUI:
  /** The currently-rendered view, if one exists. */
  private var currentView: Option[View] = None

  /** Renders a [[View]] received from the server. The method also takes a
    * [[UserId]] to get information on the context and an [[onEvent]] callback
    * which it uses to send server events when specific actions are triggered on
    * the UI (click on a button for example)
    * @param userId
    *   The user id used by the client.
    * @param view
    *   The view to render.
    * @return
    *   The rendered view.
    */
  protected def render(userId: UserId, view: View): Frag

  override def displayView(view: View): Unit =
    if Some(view) != currentView then
      currentView = Some(view)
      patchUI(target, render(userId, view))

  override def patchUI(target: dom.Element, fr: Frag): Unit =
    target.replaceChildren(fr.render)

trait PatchableUI:
  def patchUI(target: dom.Element, fr: Frag): Unit