Add window level (#116)

* set window level

* fmt fixes

src/appkit/window/enums.rs

@@ -134,3 +134,47 @@ impl From<WindowToolbarStyle> for NSUInteger {
         }
     }
 }
+
+/// Describe the level of the window. Stacking of window levels take precedence over stacking
+/// of windows withing each level.
+#[derive(Clone, Copy, Debug)]
+pub enum WindowLevel {
+    /// The default level for NSWindow objects.
+    Normal,
+
+    /// Useful for floating palettes.
+    Floating,
+
+    /// The level for a modal panel.
+    ModalPanel,
+
+    /// Reserved for the application’s main menu.
+    MainMenu,
+
+    /// The level for a status window.
+    Status,
+
+    /// The level for the dock.
+    DockWindow,
+
+    /// The level for a pop-up menu.
+    PopUpMenu,
+
+    /// The level for a screen saver.
+    ScreenSaver
+}
+
+impl From<WindowLevel> for NSInteger {
+    fn from(mode: WindowLevel) -> Self {
+        match mode {
+            WindowLevel::Normal => 0,
+            WindowLevel::Floating => 3,
+            WindowLevel::ModalPanel => 8,
+            WindowLevel::MainMenu => 24,
+            WindowLevel::Status => 25,
+            WindowLevel::DockWindow => 100,
+            WindowLevel::PopUpMenu => 101,
+            WindowLevel::ScreenSaver => 1000
+        }
+    }
+}

src/appkit/window/mod.rs

@@ -312,6 +312,21 @@ impl<T> Window<T> {
         }
     }
 
+    /// Sets the window level, which determines the stacking order of windows on the screen.
+    pub fn set_level(&self, value: WindowLevel) {
+        let value: NSInteger = value.into();
+        unsafe {
+            let _: () = msg_send![&*self.objc, setLevel: value];
+        }
+    }
+
+    /// Removes window from the screen making it effectively hidden.
+    pub fn order_out(&self) {
+        unsafe {
+            let _: () = msg_send![&*self.objc, orderOut: nil];
+        }
+    }
+
     /// Set whether the toolbar toggle button is shown. Has no effect if no toolbar exists on this
     /// window.
     pub fn set_shows_toolbar_button(&self, shows: bool) {