ITunesIOSImporter: Request authorization synchronously

This is required since the importer will otherwise run before the user
has accepted the prompt and thus import no tracks on first launch.

src/library/itunes/itunesiosimporter.h

@@ -22,4 +22,6 @@ class ITunesIOSImporter : public ITunesImporter {
 
   private:
     std::unique_ptr<ITunesDAO> m_dao;
+
+    void requestAuthorization();
 };

src/library/itunes/itunesiosimporter.mm

@@ -1,6 +1,7 @@
 #include "library/itunes/itunesiosimporter.h"
 
 #import <MediaPlayer/MediaPlayer.h>
+#import <dispatch/dispatch.h>
 #include <gsl/pointers>
 
 #include <QDateTime>
@@ -176,7 +177,37 @@ void importMediaItem(MPMediaItem* item) {
         : ITunesImporter(pParentFeature), m_dao(std::move(dao)) {
 }
 
+void ITunesIOSImporter::requestAuthorization() {
+    dispatch_semaphore_t semaphore = dispatch_semaphore_create(0);
+
+    [MPMediaLibrary requestAuthorization:^(MPMediaLibraryAuthorizationStatus status){
+        switch (status) {
+        case MPMediaLibraryAuthorizationStatusAuthorized:
+            qInfo() << "Successfully authorized iOS media library access";
+            break;
+        case MPMediaLibraryAuthorizationStatusRestricted:
+            qWarning() << "iOS media library access is restricted, Mixxx may not be able to access all tracks";
+            break;
+        case MPMediaLibraryAuthorizationStatusDenied:
+            qWarning() << "iOS media library access is denied, Mixxx will not be able to access any tracks";
+            break;
+        case MPMediaLibraryAuthorizationStatusNotDetermined:
+            qWarning() << "iOS media library access is not determined, Mixxx may not be able to access any tracks";
+            break;
+        default:
+            qWarning() << "Unknown iOS media library authorization status:" << status;
+            break;
+        }
+        dispatch_semaphore_signal(semaphore);
+    }];
+
+    qInfo() << "Requesting authorization for iOS media library access...";
+    dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
+}
+
 ITunesImport ITunesIOSImporter::importLibrary() {
+    requestAuthorization();
+
     ITunesImport iTunesImport;
 
     std::unique_ptr<TreeItem> rootItem = TreeItem::newRoot(m_pParentFeature);