//
//  File.swift
//  Star Wars DB
//
//  Created by Mark Townsend on 4/22/19.
//  Copyright © 2019 Mark Townsend. All rights reserved.
//

import Foundation
import CoreData

public class DataManager {
    static let shared = DataManager()

    private init() {}

    // MARK: - Core Data stack

    lazy var persistentContainer: 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.
         */
        let container = NSPersistentContainer(name: "Star_Wars_DB")
        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.
                 */
                fatalError("Unresolved error \(error), \(error.userInfo)")
            }
        })
        return container
    }()

    // MARK: - Core Data Saving support

    func saveContext () {
        let context = persistentContainer.viewContext
        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.
                let nserror = error as NSError
                fatalError("Unresolved error \(nserror), \(nserror.userInfo)")
            }
        }
    }

    func fetchAll(managedObject: NSManagedObject.Type) -> [NSManagedObject]? {
        let moc = persistentContainer.viewContext
        let fetchRequest = managedObject.fetchRequest()
        let sortDescriptor = NSSortDescriptor(key: "url", ascending: true)
        fetchRequest.sortDescriptors = [sortDescriptor]
        do {
            let result = try moc.fetch(fetchRequest)
            return result as? [NSManagedObject]
        } catch let error as NSError {
            print (error)
            return nil
        }
    }

    func clear(managedObject: NSManagedObject.Type) {
        let moc  = persistentContainer.viewContext
        
        let fetchRequest = managedObject.fetchRequest()
        let batchDeleteRequest = NSBatchDeleteRequest(fetchRequest: fetchRequest)
        DispatchQueue.main.async {
            do {
                try moc.execute(batchDeleteRequest)
                try moc.save()
            } catch let error as NSError {
                print(error)
            }
        }
    }
}
