frenzy-ios/Reader/Screens/Items/ItemsViewController.swift

//
//  ItemsViewController.swift
//  Reader
//
//  Created by Shadowfacts on 1/9/22.
//

import UIKit
import CoreData
import SafariServices

protocol ItemsViewControllerDelegate: AnyObject {
    func showReadItem(_ item: Item)
}

class ItemsViewController: UIViewController {
    
    weak var delegate: ItemsViewControllerDelegate?
    
    let fervorController: FervorController
    let fetchRequest: NSFetchRequest<Item>
    
    private var collectionView: UICollectionView!
    private var resultsController: NSFetchedResultsController<Item>!
    
    private var batchUpdates: [() -> Void] = []
    
    init(fetchRequest: NSFetchRequest<Item>, fervorController: FervorController) {
        self.fervorController = fervorController
        self.fetchRequest = fetchRequest
        
        super.init(nibName: nil, bundle: nil)
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        
        if UIDevice.current.userInterfaceIdiom != .mac {
            view.backgroundColor = .appBackground
        }
            
        var configuration = UICollectionLayoutListConfiguration(appearance: .plain)
        configuration.backgroundColor = .clear
        let layout = UICollectionViewCompositionalLayout.list(using: configuration)
        collectionView = UICollectionView(frame: view.bounds, collectionViewLayout: layout)
        collectionView.delegate = self
        collectionView.dataSource = self
        collectionView.translatesAutoresizingMaskIntoConstraints = false
        collectionView.register(ItemCollectionViewCell.self, forCellWithReuseIdentifier: "itemCell")
        view.addSubview(collectionView)
        
        NSLayoutConstraint.activate([
            collectionView.leadingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.leadingAnchor),
            collectionView.trailingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.trailingAnchor),
            collectionView.topAnchor.constraint(equalTo: view.topAnchor),
            collectionView.bottomAnchor.constraint(equalTo: view.bottomAnchor),
        ])
        
        fetchRequest.sortDescriptors = [NSSortDescriptor(key: "published", ascending: false)]
        fetchRequest.fetchBatchSize = 20
        resultsController = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: fervorController.persistentContainer.viewContext, sectionNameKeyPath: nil, cacheName: nil)
        resultsController.delegate = self
        try! resultsController.performFetch()
    }

}

extension ItemsViewController: UICollectionViewDataSource {
    func numberOfSections(in collectionView: UICollectionView) -> Int {
        return 1
    }
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return resultsController.fetchedObjects?.count ?? 0
    }
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "itemCell", for: indexPath) as! ItemCollectionViewCell
        cell.delegate = self
        cell.scrollView = collectionView
        cell.updateUI(item: resultsController.fetchedObjects![indexPath.row])
        return cell
    }
}

extension ItemsViewController: NSFetchedResultsControllerDelegate {
    func controllerWillChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
        batchUpdates = []
    }
    func controllerDidChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
        collectionView.performBatchUpdates {
            for update in self.batchUpdates {
                update()
            }
        }
        // clear to prevent retain cycles
        batchUpdates = []
    }
    func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChange anObject: Any, at indexPath: IndexPath?, for type: NSFetchedResultsChangeType, newIndexPath: IndexPath?) {
        guard let indexPath = indexPath else {
            return
        }
        batchUpdates.append {
            switch type {
            case .insert:
                self.collectionView.insertItems(at: [indexPath])
            case .delete:
                self.collectionView.deleteItems(at: [indexPath])
            case .move:
                if let newIndexPath = newIndexPath {
                    self.collectionView.moveItem(at: indexPath, to: newIndexPath)
                }
            case .update:
                self.collectionView.reloadItems(at: [indexPath])
            @unknown default:
                break
            }
        }
    }
}

extension ItemsViewController: UICollectionViewDelegate {
    func collectionView(_ collectionView: UICollectionView, contextMenuConfigurationForItemAt indexPath: IndexPath, point: CGPoint) -> UIContextMenuConfiguration? {
        let item = resultsController.fetchedObjects![indexPath.row]
        return UIContextMenuConfiguration(identifier: nil, previewProvider: {
            ReadViewController(item: item, fervorController: self.fervorController)
        }, actionProvider: { _ in
            var children: [UIAction] = []
            if let url = item.url {
                children.append(UIAction(title: "Open in Safari", image: UIImage(systemName: "safari"), handler: { [weak self] _ in
                    let vc = SFSafariViewController(url: url)
                    vc.preferredControlTintColor = .appTintColor
                    self?.present(vc, animated: true)
                }))
                children.append(UIAction(title: "Share", image: UIImage(systemName: "square.and.arrow.up"), handler: { [weak self] _ in
                    self?.present(UIActivityViewController(activityItems: [url], applicationActivities: nil), animated: true)
                }))
            }
            if item.read {
                children.append(UIAction(title: "Mark as Unread", image: UIImage(systemName: "checkmark.circle"), handler: { _ in
                    item.read = false
                }))
            } else {
                children.append(UIAction(title: "Mark as Read", image: UIImage(systemName: "checkmark.circle.fill"), handler: { _ in
                    item.read = true
                }))
            }
            return UIMenu(children: children)
        })
    }
    
    func collectionView(_ collectionView: UICollectionView, willPerformPreviewActionForMenuWith configuration: UIContextMenuConfiguration, animator: UIContextMenuInteractionCommitAnimating) {
        guard let vc = animator.previewViewController else {
            return
        }
        animator.preferredCommitStyle = .pop
        animator.addCompletion {
            self.show(vc, sender: nil)
        }
    }
}

extension ItemsViewController: ItemCollectionViewCellDelegate {
    func itemCellSelected(cell: ItemCollectionViewCell, item: Item) {
        cell.setRead(true, animated: true)
        if let delegate = delegate {
            delegate.showReadItem(item)
        } else {
            show(ReadViewController(item: item, fervorController: fervorController), sender: nil)
        }
    }
}