Port 'Progress Bar' demo to Vala (#168)

src/Progress Bar/main.vala

@@ -0,0 +1,67 @@
+#! /usr/bin/env -S vala workbench.vala --pkg libadwaita-1
+
+public void main () {
+
+    var first_bar = (Gtk.ProgressBar) workbench.builder.get_object ("first");
+    var second_bar = (Gtk.ProgressBar) workbench.builder.get_object ("second");
+    var play = (Gtk.Button) workbench.builder.get_object ("play");
+    var progress_tracker = (Gtk.Label) workbench.builder.get_object ("progress_tracker");
+
+    var target = new Adw.PropertyAnimationTarget (first_bar, "fraction");
+
+    var animation = new Adw.TimedAnimation (
+                                            first_bar, // widget
+                                            0.2, // value_from
+                                            1, // value_to
+                                            11000, // duration
+                                            target // target
+        ) {
+        easing = LINEAR
+    };
+
+    animation.done.connect (() => {
+        animation.reset ();
+    });
+
+    play.clicked.connect (() => {
+        animation.play ();
+        update_tracker (second_bar);
+        pulse_progress (progress_tracker);
+    });
+}
+
+void update_tracker (Gtk.ProgressBar second_bar) {
+    double counter = 0.0;
+    const int pulse_period = 500;
+    const int duration = 10000;
+    double increment = (double) pulse_period / duration;
+
+    Timeout.add (pulse_period, () => {
+        if (counter >= 1.0) {
+            counter = 0.0;
+            second_bar.fraction = 0.0;
+            return false;
+        }
+
+        second_bar.pulse ();
+        counter += increment;
+        return true;
+    }, Priority.DEFAULT);
+}
+
+void pulse_progress (Gtk.Label progress_tracker) {
+
+    int time = 10;
+
+    Timeout.add (1000, () => {
+        if (time == 0) {
+            progress_tracker.label = ("");
+            message (@"Operation complete!");
+            return false;
+        }
+
+        progress_tracker.label = (@"$time seconds remaining…");
+        time -= 1;
+        return true;
+    }, Priority.DEFAULT);
+}