From fb2dac9b3f4b21a1765e15da0840b8f0bec04230 Mon Sep 17 00:00:00 2001
From: Sarah Gerweck <sarah.a180@gmail.com>
Date: Mon, 18 Apr 2016 20:18:45 -0700
Subject: [PATCH] Code to make an `Observable` from a `Future`

---
 .../scalafx/util/FutureObservable.scala       | 39 +++++++++++++++++++
 1 file changed, 39 insertions(+)
 create mode 100644 src/main/scala/org/gerweck/scalafx/util/FutureObservable.scala

diff --git a/src/main/scala/org/gerweck/scalafx/util/FutureObservable.scala b/src/main/scala/org/gerweck/scalafx/util/FutureObservable.scala
new file mode 100644
index 0000000..9fd7cbb
--- /dev/null
+++ b/src/main/scala/org/gerweck/scalafx/util/FutureObservable.scala
@@ -0,0 +1,39 @@
+package org.gerweck.scalafx.util
+
+import scala.concurrent._
+
+import org.log4s._
+
+import scalafx.application.Platform.runLater
+import scalafx.beans.property._
+
+/** An [[scalafx.beans.value.ObservableValue]] that pulls its value from a future.
+  *
+  * @author Sarah Gerweck <sarah.a180@gmail.com>
+  */
+object FutureObservable {
+  private[this] val logger = getLogger
+
+  /** Construct an observable that gives the value of the future on success.
+    *
+    * Until the future completes successfully, the value will be that of
+    * `defaultValue`. If there is an error, the value will persist as
+    * `defaultValue`.
+    *
+    * If you want to change state in case of an error, I recommend you use
+    * [[scala.concurrent.Future.recover]] to choose the values that will be
+    * used in that case. The `defaultValue` is provided because `Future` has
+    * no equivalent mechanism for this mandatory functionality, but recovery
+    * is already a built-in feature.
+    */
+  def apply[A](defaultValue: A)(future: Future[A])(implicit ec: ExecutionContext): ReadOnlyObjectProperty[A] = {
+    val prop = ObjectProperty[A](defaultValue)
+    future onSuccess { case a =>
+      runLater {
+        logger.trace("Updating property value after Future's success")
+        prop.value = a
+      }
+    }
+    prop
+  }
+}