Wrapped CoreData stack

DataManager.swift

//
//  DataManager.swift
//
//  Created by Marcos Santos on 8/30/18.
//  Copyright © 2018 Marcos Santos 2018. All rights reserved.
//

import CoreData

public class DataManager {
    public static var shared = DataManager()
    
    public var bundle: Bundle?
    public var modelName: String?
    
    private init(){}
    
    lazy public var persistentContainer: NSPersistentContainer? = {
        
        guard let bundle = self.bundle else{
            if let modelName = self.modelName{
                return loadContainer(modelName: modelName)
            }
            else{
                return loadContainer()
            }
        }
        guard let modelName = self.modelName else{
            return loadContainer(bundle: bundle)
        }
        
        return loadContainer(bundle: bundle, modelName: modelName)
    }()
    
    public class func getContext() throws -> NSManagedObjectContext {
        if let context = shared.persistentContainer?.viewContext {
            return context
        }
        throw Errors.wrongContext
    }
    
    public func loadContainer(bundle: Bundle = Bundle(for: DataManager.self), modelName: String = "ModelName") -> NSPersistentContainer? {
        /*
         The persistent container for the application. This implementation
         creates and returns a container, having loaded the store for the
         application to it. This property is optional since there are legitimate
         error conditions that could cause the creation of the store to fail.
         */
        
        guard let modelURL = bundle.url(forResource: modelName, withExtension:"momd"), let model = NSManagedObjectModel(contentsOf: modelURL) else {
            print("Error loading model from bundle")
            return nil
        }
        
        
        var container: NSPersistentContainer? = NSPersistentContainer(name: modelName, managedObjectModel: model)
        
        container?.loadPersistentStores(completionHandler: { (storeDescription, error) in
            if let error = error as NSError? {
                // Replace this implementation with code to handle the error appropriately.
                // fatalError() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
                
                /*
                 Typical reasons for an error here include:
                 * The parent directory does not exist, cannot be created, or disallows writing.
                 * The persistent store is not accessible, due to permissions or data protection when the device is locked.
                 * The device is out of space.
                 * The store could not be migrated to the current model version.
                 Check the error message to determine what the actual problem was.
                 */
                print("Unresolved error \(error), \(error.userInfo)")
                container = nil
            }
        })
        return container
    }
    
    // MARK: - Core Data Saving support
    public func saveContext() throws {
        guard let context = persistentContainer?.viewContext else{
            throw Errors.wrongContainer
        }
        if context.hasChanges {
            do {
                try context.save()
            } catch {
                // Replace this implementation with code to handle the error appropriately.
                // fatalError() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
                
                throw Errors.cantSave
            }
        }
    }
    
}