import UIKit
import CoreData

class ConverterTableViewController: UITableViewController {
    
    private var fetchedResultsController: NSFetchedResultsController<Currency>!
    private let coreDataManager = CurrencyCoreDataManager()
    private var currencyManager = CurrencyManager()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        setupFetchedResultsController()
    }
    
    func setupFetchedResultsController() {
        let predicate = NSPredicate(format: "isForConverter == YES")
        fetchedResultsController = createCurrencyFetchedResultsController(and: predicate)
        fetchedResultsController.delegate = self
        try? fetchedResultsController.performFetch()
    }

    func createCurrencyFetchedResultsController(with request: NSFetchRequest<Currency> = Currency.fetchRequest(), and predicate: NSPredicate? = nil, sortDescriptor: [NSSortDescriptor] = [NSSortDescriptor(key: "shortName", ascending: true)]) -> NSFetchedResultsController<Currency> {
        request.predicate = predicate
        request.sortDescriptors = sortDescriptor
        
        return NSFetchedResultsController(fetchRequest: request, managedObjectContext: context, sectionNameKeyPath: nil, cacheName: nil)
    }

    // MARK: - TableView DataSource Methods
    
    override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        let currency = fetchedResultsController.sections![section]
        print(currency.numberOfObjects)
        return currency.numberOfObjects
    }
    
    override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCell(withIdentifier: "converterCell", for: indexPath) as! ConverterTableViewCell
        
        let currency = fetchedResultsController.object(at: indexPath)
        cell.flag.image = currencyManager.showCurrencyFlag(currency.shortName ?? "notFound")
        cell.shortName.text = currency.shortName
        cell.fullName.text = currency.fullName
        
        return cell
    }
}

//MARK: - NSFetchedResultsController Delegates

extension ConverterTableViewController: NSFetchedResultsControllerDelegate {
    func controllerWillChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
        tableView.beginUpdates()
    }
    
    func controllerDidChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
        tableView.endUpdates()
    }
    
    func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChange anObject: Any, at indexPath: IndexPath?, for type: NSFetchedResultsChangeType, newIndexPath: IndexPath?) {
        if let indexPath = indexPath, let newIndexPath = newIndexPath {
            switch type {
            case .update:
                tableView.reloadRows(at: [indexPath], with: .none)
            case .move:
                tableView.moveRow(at: indexPath, to: newIndexPath)
            case .delete:
                tableView.deleteRows(at: [indexPath], with: .none)
            case .insert:
                tableView.insertRows(at: [indexPath], with: .none)
            default:
                tableView.reloadData()
            }
        }
    }
}