Add TitlebarClickAwareWindow class (#1)

NSWindow subclass honoring the titlebar double click action

Sources/WindowTreatment/Window subclasses/TitlebarClickAwareWindow.swift

@@ -0,0 +1,45 @@
+import AppKit
+
+private extension NSWindow {
+    /// Key of double click action. It can be customized in macOS System Settings app within the Dock subsettings.
+    static let actionOnDoubleClickKey: String = "AppleActionOnDoubleClick"
+    /// Value of zoom action for the ``actionOnDoubleClickKey`` key typically set by the macOS System Settings app.
+    static let zoomActionOnDoubleClickValue: String = "Maximize"
+    /// Value of minimize action for the ``actionOnDoubleClickKey`` key typically set by the macOS System Settings app.
+    static let miniaturizeActionOnDoubleClickValue: String = "Minimize"
+}
+
+/// Simple NSWindow subclass honoring the titlebar double click action from the macOS System Settings app.
+open class TitlebarClickAwareWindow: NSWindow {
+    override open func mouseDown(with event: NSEvent) {
+        if event.clickCount > 1, isEventLocationEligible(event.locationInWindow) {
+            zoomOrMiniaturize(self)
+        }
+        super.mouseDown(with: event)
+    }
+}
+
+private extension TitlebarClickAwareWindow {
+    func isEventLocationEligible(_ location: CGPoint) -> Bool {
+        guard let windowFrame = contentView?.frame else {
+            return false
+        }
+        var titleBarRect = contentLayoutRect
+        titleBarRect.origin.y += contentLayoutRect.height
+        titleBarRect.size.height = windowFrame.height - contentLayoutRect.height
+        return titleBarRect.contains(location)
+    }
+
+    func zoomOrMiniaturize(_ sender: Any?) {
+        let actionOnDoubleClickValue = UserDefaults.standard.string(forKey: Self.actionOnDoubleClickKey)
+
+        switch actionOnDoubleClickValue {
+        case Self.zoomActionOnDoubleClickValue:
+            zoom(sender)
+        case Self.miniaturizeActionOnDoubleClickValue:
+            miniaturize(sender)
+        default:
+            zoom(sender)
+        }
+    }
+}