elpha-ios/elpha-ios/InstancesTableViewController.swift

//
//  InstancesTableViewController.swift
//  elpha-ios
//
//  Created by Dwayne Harris on 8/29/18.
//  Copyright © 2018 Elpha. All rights reserved.
//

import Alamofire
import CoreData
import Kingfisher
import UIKit

class InstancesTableViewController: UITableViewController {
    @IBOutlet var mainNavigationItem: UINavigationItem!
    
    let fetchLimit = 20
    var fetchedResultsController: NSFetchedResultsController<ISInstanceMO>?
    
    var loading: Bool = false {
        didSet {
            DispatchQueue.main.async {
                if self.loading {
                    self.refreshControl?.beginRefreshing()
                } else {
                    self.refreshControl?.endRefreshing()
                }
            }
        }
    }
    
    func initializeFetchedResultsController() {
        let request = NSFetchRequest<ISInstanceMO>(entityName: "ISInstance")
        request.sortDescriptors = [
            NSSortDescriptor(key: "users", ascending: false),
        ]
        
        fetchedResultsController = NSFetchedResultsController(
            fetchRequest: request,
            managedObjectContext: CoreDataManager.shared.context,
            sectionNameKeyPath: nil,
            cacheName: nil
        )
        
        fetchedResultsController!.delegate = self
        
        do {
            try fetchedResultsController!.performFetch()
        } catch {
            print("\(error)")
        }
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        initializeFetchedResultsController()
        
        mainNavigationItem.leftBarButtonItem = UIBarButtonItem(barButtonSystemItem: .done, target: self, action: #selector(done))
        
        registerForPreviewing(with: self, sourceView: tableView)
        refreshControl?.addTarget(self, action: #selector(self.refetchInstances), for: .valueChanged)
        
        if tableView.numberOfRows(inSection: 0) == 0 {
            fetchInstances()
        }
    }
    
    @objc func done() {
        dismiss(animated: true, completion: nil)
    }
    
    @objc func refetchInstances() {
        loading = true
        
        DispatchQueue.main.async {
            InstancesDataManager.shared.clearInstances()
            CoreDataManager.shared.saveContext()
            
            InstancesDataManager.shared.reloadInstances() { error in
                self.loading = false
            }
        }
    }
    
    func fetchInstances() {
        loading = true
        
        DispatchQueue.main.async {
            InstancesDataManager.shared.loadInstances() { error in
                self.loading = false
            }
        }
    }
    
    override func numberOfSections(in tableView: UITableView) -> Int {
        return 1
    }
    
    override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        guard let count = fetchedResultsController?.fetchedObjects?.count else {
            return 0
        }
        
        return count
    }
    
    override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        guard let cell = tableView.dequeueReusableCell(withIdentifier: "InstancesTableViewCell", for: indexPath) as? InstancesTableViewCell else {
            fatalError("Unable to find reusable cell")
        }
        
        guard let instance = fetchedResultsController?.object(at: indexPath) else {
            fatalError("CoreData error")
        }
            
        cell.instanceNameLabel.text = instance.name
        cell.statusesLabel.text = NumberFormatter.localizedString(from: NSNumber(value: instance.statuses), number: .decimal)
        cell.usersLabel.text = NumberFormatter.localizedString(from: NSNumber(value: instance.users), number: .decimal)
        
        if let thumbnail = instance.thumbnail {
            cell.thumbnailImageView.kf.setImage(with: thumbnail)
        }
        
        if indexPath.row > 0 && indexPath.row % fetchLimit == 0 && !loading {
            fetchInstances()
        }
        
        return cell
    }
    
    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        if segue.identifier == "InstanceDetailSegue", let cell = segue.destination as? InstanceViewController {
            if let indexPath = tableView.indexPathForSelectedRow {
                guard let instance = fetchedResultsController?.object(at: indexPath) else {
                    fatalError("CoreData error")
                }
                
                cell.instance = instance
            }
        }
    }
}

extension InstancesTableViewController: UIViewControllerPreviewingDelegate {
    public func previewingContext(_ previewingContext: UIViewControllerPreviewing, commit viewControllerToCommit: UIViewController) {
        navigationController?.pushViewController(viewControllerToCommit, animated: true)
    }
    
    public func previewingContext(_ previewingContext: UIViewControllerPreviewing, viewControllerForLocation location: CGPoint) -> UIViewController? {
        guard let indexPath = tableView.indexPathForRow(at: location) else {
            return nil
        }
        
        guard let instance = fetchedResultsController?.object(at: indexPath) else {
            fatalError("CoreData error")
        }
        
        let storyboard = UIStoryboard(name: "Main", bundle: nil)
        if let detailViewController = storyboard.instantiateViewController(withIdentifier: "InstanceViewController") as? InstanceViewController {
            detailViewController.instance = instance
            return detailViewController
        } else {
            return nil
        }
    }
}

extension InstancesTableViewController: NSFetchedResultsControllerDelegate {
    func controllerDidChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
        self.tableView.reloadData()
    }
}