iOS: Add file picker (#747)

* iOS: Add file picker

* Fix lock placement

src/pandios/Pandios/ContentView.swift

@@ -3,6 +3,47 @@ import SwiftUI
 import MetalKit
 import Darwin
 
+var emulatorLock = NSLock()
+
+class DocumentViewController: UIViewController, DocumentDelegate {
+    var documentPicker: DocumentPicker!
+
+    override func viewDidLoad() {
+        super.viewDidLoad()
+
+        /// set up the document picker
+        documentPicker = DocumentPicker(presentationController: self, delegate: self)
+        /// When the view loads (ie user opens the app) show the file picker
+        show()
+    }
+    
+    /// callback from the document picker
+    func didPickDocument(document: Document?) {
+        if let pickedDoc = document {
+            let fileURL = pickedDoc.fileURL
+            
+            print("Loading ROM", fileURL)
+            emulatorLock.lock()
+            iosLoadROM(fileURL.path(percentEncoded: false))
+            emulatorLock.unlock()
+        }
+    }
+    
+    func show() {
+        documentPicker.displayPicker()
+    }
+}
+
+struct DocumentView: UIViewControllerRepresentable {
+    func makeUIViewController(context: Context) -> DocumentViewController {
+        return DocumentViewController()
+    }
+    
+    func updateUIViewController(_ uiViewController: DocumentViewController, context: Context) {
+        // No update needed
+    }
+}
+
 struct ContentView: UIViewRepresentable {
     @State var showFileImporter = true
 
@@ -32,7 +73,9 @@ struct ContentView: UIViewRepresentable {
             iosCreateEmulator()
             
             while (true) {
+                emulatorLock.lock()
                 iosRunFrame(metalLayer);
+                emulatorLock.unlock()
             }
         }
 
@@ -46,6 +89,7 @@ struct ContentView: UIViewRepresentable {
 
 struct ContentView_Previews: PreviewProvider {
     static var previews: some View {
-        ContentView()
+        DocumentView();
+        ContentView();
     }
 }