extension Friend {

    @nonobjc public class func fetchRequest() -> NSFetchRequest<Friend> {
        let request = NSFetchRequest<Friend>(entityName: "Friend")
        request.sortDescriptors = [NSSortDescriptor(key: "name", ascending: true)]
        return request
    }

    @NSManaged public var name: String?
    @NSManaged public var profileImageName: String?
    @NSManaged public var messages: NSSet?

}

import Foundation
import CoreData

class CoreDataStack {


    lazy var managedObjectContext: NSManagedObjectContext = {
        let container = self.persistentContainer
        return container.viewContext
    }()

//    lazy var managedObjectContext: NSManagedObjectContext = {
//        let coordinator = self.persistentStoreCoordinator
//        var moc = NSManagedObjectContext(concurrencyType: .mainQueueConcurrencyType)
//        moc.persistentStoreCoordinator = coordinator
//        return moc
//    }()
//
//    //MARK: не работает
//    private lazy var privateManagedObjectContext: NSManagedObjectContext = {
//        let moc = NSManagedObjectContext(concurrencyType: .privateQueueConcurrencyType)
//        moc.persistentStoreCoordinator = self.persistentStoreCoordinator
//
//        return moc
//    }()
//    //MARK: moc
//    private(set) lazy var defManagedObjectContext: NSManagedObjectContext = {
//        let moc = NSManagedObjectContext(concurrencyType: .mainQueueConcurrencyType)
//        moc.parent = self.privateManagedObjectContext
//
//        return moc
//    }()

    private lazy var persistentContainer: NSPersistentContainer = {
        let container = NSPersistentContainer(name: "messenger")
        container.loadPersistentStores() { storeDescr, error in
            if let error = error as NSError? {
                fatalError("(error), (error.userInfo)")
            }
        }
        return container
    }()

    private(set) lazy var applicationDocumentsDirectory: URL = {
        let urls = FileManager.default.urls(for: .documentDirectory,
                                            in: .userDomainMask)
        let endIndex = urls.index(before: urls.endIndex)
        return urls[endIndex]
    }()

    private(set) lazy var managedObjectModel: NSManagedObjectModel = {
        let modelUrl = Bundle.main.url(forResource: "messenger", withExtension: "momd")!
        return NSManagedObjectModel(contentsOf: modelUrl)!
    }()

    private(set) lazy var persistentStoreCoordinator: NSPersistentStoreCoordinator = {
        let coordinator = NSPersistentStoreCoordinator(managedObjectModel: self.managedObjectModel)
        let url = self.applicationDocumentsDirectory.appendingPathComponent("messenger.sqlite")

        do {
            try coordinator.addPersistentStore(ofType: NSSQLiteStoreType,
                                               configurationName: nil,
                                               at: url)
        } catch {
            print(error)
            abort()
        }

        return coordinator
    }()


}

extension NSManagedObjectContext {

        func saveChanges() {
            let queue = DispatchQueue.global(qos: .userInitiated)
            queue.async {
                if self.hasChanges {
                    do {
                        try self.save()
                    } catch {
                        fatalError("(error.localizedDescription)")
                    }
                }
            }
        }

}