1 files changed, 55 insertions, 0 deletions
diff --git a/src/main/scala/reading/component/widget/Animate.scala b/src/main/scala/reading/component/widget/Animate.scala
new file mode 100644
index 0000000..0e848aa
--- /dev/null
+++ b/src/main/scala/reading/component/widget/Animate.scala
@@ -0,0 +1,55 @@
+package reading.component.widget
+
+import scala.collection.mutable.Map
+
+import org.scalajs.dom.{ window, document }
+import org.scalajs.dom.raw.HTMLElement
+
+object Animate {
+  val animationFrames: Map[String, Int] = Map.empty
+
+  def apply(
+    id: String,
+    duration: Double,
+    transition: (Double, Double) => Double,
+    animate: (Double, HTMLElement) => Unit,
+    onEnd: => Unit = ()
+  ): Unit = {
+    animationFrames.get(id) match {
+      case Some(animationFrame) => window.cancelAnimationFrame(animationFrame)
+      case None => ()
+    }
+    val animationFrame = window.requestAnimationFrame(ts =>
+      frame(id, ts, duration, transition, animate, onEnd)(ts))
+    animationFrames.put(id, animationFrame)
+    ()
+  }
+
+  private def frame(
+    id: String,
+    start: Double,
+    duration: Double,
+    transition: (Double, Double) => Double,
+    animate: (Double, HTMLElement) => Unit,
+    onEnd: => Unit
+  )(
+    timestamp: Double
+  ): Unit = {
+    document.getElementById(id).asInstanceOf[HTMLElement] match {
+      case element: HTMLElement =>
+        val elapsed = timestamp - start
+        if (elapsed < duration) {
+          animate(Transition.easeOut(elapsed, duration), element)
+          val animationFrame = window.requestAnimationFrame(frame(id, start, duration, transition, animate, onEnd))
+          animationFrames.put(id, animationFrame)
+        } else {
+          animate(1, element)
+          onEnd
+        }
+      case _ =>
+        val animationFrame = window.requestAnimationFrame(ts => frame(id, ts, duration, transition, animate, onEnd)(ts))
+        animationFrames.put(id, animationFrame)
+    }
+    ()
+  }
+}