⭐️ Impl: RNIModalManager.computeModalIndex

Summary:
* Impl. `RNIModalManager.computeModalIndex`
* Refactor: `RNIModal+Helpers` - Update to use `RNIModalManager.computeModalIndex`.

ios/src_library/React Native/RNIModal/RNIModal+Helpers.swift

@@ -55,26 +55,23 @@ extension RNIModalState where Self: RNIModalPresentation {
 
   /// Programmatically get the "modal index"
   public var synthesizedModalIndex: Int {
-    let listPresentedVC =
-      RNIModalManager.getPresentedViewControllers(for: self.window);
-
-    var index = -1;
+    guard let window = self.window,
+          let modalVC = self.modalViewController
+    else { return -1 };
 
-    for vc in listPresentedVC {
-      if vc.presentingViewController != nil {
-        index += 1;
-      };
-
-      guard vc === self.modalViewController else { continue };
-      return index;
-    };
-
-    return -1;
+    return RNIModalManager.computeModalIndex(
+      forWindow: window,
+      forViewController: modalVC
+    );
   };
 
   public var synthesizedCurrentModalIndex: Int {
-    guard let window = self.window else { return -1 };
-    return RNIModalManagerShared.getCurrentModalIndex(for: window);
+    RNIModalManager.computeModalIndex(forWindow: self.window);
+  };
+
+  internal var synthesizedWindowMapData: RNIWindowMapData? {
+    guard let window = self.window else { return nil };
+    return RNIModalWindowMapShared.get(forWindow: window);
   };
 };
 

ios/src_library/React Native/RNIModal/RNIModalManager.swift

@@ -201,6 +201,46 @@ public class RNIModalManager {
     return Self.getPresentedViewControllers(for: window).last;
   };
 
+  static func computeModalIndex(
+    forWindow window: UIWindow,
+    forViewController viewController: UIViewController? = nil
+  ) -> Int {
+
+    let listPresentedVC =
+      RNIModalManager.getPresentedViewControllers(for: window);
+
+    var index = -1;
+
+    for vc in listPresentedVC {
+      if vc.presentingViewController != nil {
+        index += 1;
+      };
+
+      /// A - no `viewController` arg., keep counting until all items in
+      ///     `listPresentedVC` have been exhausted.
+      guard viewController == nil else { continue };
+
+      /// B - `viewController` arg. specified, stop counting if found matching
+      ///      instance of `viewController` in `listPresentedVC`.
+      guard viewController !== vc
+      else { break };
+    };
+
+    return index;
+  };
+
+  static func computeModalIndex(
+    forWindow window: UIWindow?,
+    forViewController viewController: UIViewController? = nil
+  ) -> Int {
+    guard let window = window else { return -1 };
+
+    return Self.computeModalIndex(
+      forWindow: window,
+      forViewController: viewController
+    );
+  };
+
   // MARK: - Properties
   // ------------------