ios: fix exporting files (CSV exports, log export, notes export)

Similar to Android, we set `ExportsDir()` to `""` and let
the backend environment `getSaveFilename()` construct the full path.

Mobile handling of the dirs/files is a big hack and works on implicit
assumptions, e.g. that `getSaveFilename()` is always called with
`filepath.Join(exportsDir, filename)`, which is only the filename on
mobile as `ExportsDir()` returns `""`. This should be cleaned up, but
for now iOS is made to behave like Android in this regard.

frontends/ios/BitBoxApp/BitBoxApp/BitBoxAppApp.swift

@@ -38,10 +38,11 @@ protocol SetMessageHandlersProtocol {
     func setMessageHandlers(handlers: MessageHandlersProtocol)
 }
 
-class GoEnvironment: NSObject, MobileserverGoEnvironmentInterfaceProtocol {
-    func getSaveFilename(_ p0: String?) -> String {
-        // TODO
-        return ""
+class GoEnvironment: NSObject, MobileserverGoEnvironmentInterfaceProtocol, UIDocumentInteractionControllerDelegate {
+    func getSaveFilename(_ fileName: String?) -> String {
+        let cacheDirectory = FileManager.default.urls(for: .cachesDirectory, in: .userDomainMask).first!
+        let fileURL = cacheDirectory.appendingPathComponent(fileName!)
+        return fileURL.path()
     }
 
     func auth() {
@@ -75,10 +76,47 @@ class GoEnvironment: NSObject, MobileserverGoEnvironmentInterfaceProtocol {
     func setDarkTheme(_ p0: Bool) {
     }
 
-    func systemOpen(_ url: String?) throws {
-        guard let url = URL(string: url!) else { return }
-        if UIApplication.shared.canOpenURL(url) {
-            UIApplication.shared.open(url)
+    // Helper method to get the root view controller
+    private func getRootViewController() -> UIViewController? {
+        guard let scene = UIApplication.shared.connectedScenes
+                .filter({ $0.activationState == .foregroundActive })
+                .first as? UIWindowScene else {
+            return nil
+        }
+
+        return scene.windows.first(where: { $0.isKeyWindow })?.rootViewController
+    }
+
+    func systemOpen(_ urlString: String?) throws {
+        guard let urlString = urlString else { return }
+        // Check if it's a local file path (not a URL)
+        var url: URL
+        if urlString.hasPrefix("/") {
+            // This is a local file path, construct a file URL
+            url = URL(fileURLWithPath: urlString)
+        } else if let potentialURL = URL(string: urlString), potentialURL.scheme != nil {
+            // This is already a valid URL with a scheme
+            url = potentialURL
+        } else {
+            // Invalid URL or path
+            return
+        }
+        // Ensure all UIKit actions run on the main thread
+        DispatchQueue.main.async {
+            if url.isFileURL {
+                // Local file path, use UIDocumentInteractionController
+                if let rootViewController = self.getRootViewController() {
+                    //let documentController = UIDocumentInteractionController(url: url)
+                    //documentController.delegate = self // Ensure GoEnvironment conforms to UIDocumentInteractionControllerDelegate
+                    //documentController.presentOptionsMenu(from: rootViewController.view.frame, in: rootViewController.view, animated: true)
+                    let activityViewController = UIActivityViewController(activityItems: [url], applicationActivities: nil)
+                    rootViewController.present(activityViewController, animated: true, completion: nil)
+                }
+            } else {
+                if UIApplication.shared.canOpenURL(url) {
+                    UIApplication.shared.open(url)
+                }
+            }
         }
     }
 

util/config/appdir.go

@@ -83,8 +83,8 @@ func AppDir() string {
 
 // ExportsDir returns the absolute path to the folder which can be used to export files.
 func ExportsDir() (string, error) {
-	if runtime.GOOS == "android" {
-		// Android apps are sandboxed, we don't need to specify a folder.
+	if runtime.GOOS == "android" || runtime.GOOS == "ios" {
+		// Android/iOS apps are sandboxed, we don't need to specify a folder.
 		return "", nil
 	}
 	homeFolder := os.Getenv("HOME")