Add popover for entering session length

client/src/activities_view.vala

@@ -81,6 +81,50 @@ namespace StudySystemClient {
 			content.append(button);
 
 			set_child(content);
+
+			var log_session_popover = new LogSessionPopover();
+			log_session_popover.set_parent(button);
+			button.clicked.connect(() => log_session_popover.popup());
+		}
+	}
+
+	private class LogSessionPopover : Gtk.Popover {
+		private const int DEFAULT_LENGTH = 30;
+
+		private Gtk.SpinButton input;
+
+		public LogSessionPopover() {
+			var content = new Gtk.Box(Gtk.Orientation.HORIZONTAL, 6);
+
+			var label = new Gtk.Label("Minutes");
+			label.halign = Gtk.Align.START;
+			content.append(label);
+
+			var adjustment
+				= new Gtk.Adjustment(DEFAULT_LENGTH, 10, 480, 10, 10, 0);
+			input = new Gtk.SpinButton(adjustment, 1, 0);
+			input.numeric = true;
+			content.append(input);
+
+			var button = new Gtk.Button.from_icon_name("emblem-ok-symbolic");
+			button.halign = Gtk.Align.END;
+			button.set_tooltip_text("Submit");
+			button.add_css_class("suggested-action");
+			button.clicked.connect(submit);
+			content.append(button);
+
+			set_child(content);
+
+			closed.connect(reset);
+		}
+
+		private void submit() {
+			reset();
+			popdown();
+		}
+
+		private void reset() {
+			input.value = DEFAULT_LENGTH;
 		}
 	}
 }