space-ios/iOSClient/Viewer/NCViewerImage/NCViewerImagePageContainer.swift

//
//  NCViewerImagePageContainer.swift
//  Nextcloud
//
//  Created by Marino Faggiana on 24/10/2020.
//  Copyright © 2020 Marino Faggiana. All rights reserved.
//
//  Author Marino Faggiana <marino.faggiana@nextcloud.com>
//
//  This program is free software: you can redistribute it and/or modify
//  it under the terms of the GNU General Public License as published by
//  the Free Software Foundation, either version 3 of the License, or
//  (at your option) any later version.
//
//  This program is distributed in the hope that it will be useful,
//  but WITHOUT ANY WARRANTY; without even the implied warranty of
//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//  GNU General Public License for more details.
//
//  You should have received a copy of the GNU General Public License
//  along with this program.  If not, see <http://www.gnu.org/licenses/>.
//

import UIKit
import SVGKit
import NCCommunication

class NCViewerImagePageContainer: UIViewController, UIGestureRecognizerDelegate {

    @IBOutlet weak var progressView: UIProgressView!
    @IBOutlet weak var toolBar: UIToolbar!

    enum ScreenMode {
        case full, normal
    }
    var currentMode: ScreenMode = .normal
        
    var pageViewController: UIPageViewController {
        return self.children[0] as! UIPageViewController
    }
    
    var currentViewController: NCViewerImageZoom {
        return self.pageViewController.viewControllers![0] as! NCViewerImageZoom
    }
    
    var metadatas: [tableMetadata] = []
    var currentMetadata: tableMetadata = tableMetadata()
    var currentIndex = 0
    var nextIndex: Int?
   
    var startPanLocation = CGPoint.zero
    let panDistanceForPopViewController: CGFloat = 150
    var defaultImageViewTopConstraint: CGFloat = 0
    var defaultImageViewBottomConstraint: CGFloat = 0
    
    var currentViewerImageZoom: NCViewerImageZoom?
    var panGestureRecognizer: UIPanGestureRecognizer!
    var singleTapGestureRecognizer: UITapGestureRecognizer!
    var longtapGestureRecognizer: UILongPressGestureRecognizer!
    
    private var playerVideo: AVPlayer?
    private var videoLayer: AVPlayerLayer?
    private var durationVideo: Float = 0
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        singleTapGestureRecognizer = UITapGestureRecognizer(target: self, action: #selector(didSingleTapWith(gestureRecognizer:)))
        panGestureRecognizer = UIPanGestureRecognizer(target: self, action: #selector(didPanWith(gestureRecognizer:)))
        longtapGestureRecognizer = UILongPressGestureRecognizer()
        longtapGestureRecognizer.delaysTouchesBegan = true
        longtapGestureRecognizer.minimumPressDuration = 0.3
        longtapGestureRecognizer.delegate = self
        longtapGestureRecognizer.addTarget(self, action: #selector(didLongpressGestureEvent(gestureRecognizer:)))
        
        pageViewController.delegate = self
        pageViewController.dataSource = self
        pageViewController.view.addGestureRecognizer(panGestureRecognizer)
        pageViewController.view.addGestureRecognizer(singleTapGestureRecognizer)
        pageViewController.view.addGestureRecognizer(longtapGestureRecognizer)
        
        let viewerImageZoom = UIStoryboard(name: "NCViewerImage", bundle: nil).instantiateViewController(withIdentifier: "NCViewerImageZoom") as! NCViewerImageZoom
                
        viewerImageZoom.index = currentIndex
        viewerImageZoom.image = getImageMetadata(metadatas[currentIndex])
        viewerImageZoom.metadata = metadatas[currentIndex]
        viewerImageZoom.delegate = self

        singleTapGestureRecognizer.require(toFail: viewerImageZoom.doubleTapGestureRecognizer)
        
        pageViewController.setViewControllers([viewerImageZoom], direction: .forward, animated: true, completion: nil)
        
        NotificationCenter.default.addObserver(self, selector: #selector(changeTheming), name: NSNotification.Name(rawValue: k_notificationCenter_changeTheming), object: nil)
        NotificationCenter.default.addObserver(self, selector: #selector(downloadedFile(_:)), name: NSNotification.Name(rawValue: k_notificationCenter_downloadedFile), object: nil)
        NotificationCenter.default.addObserver(self, selector: #selector(triggerProgressTask(_:)), name: NSNotification.Name(rawValue: k_notificationCenter_progressTask), object:nil)
        NotificationCenter.default.addObserver(self, selector: #selector(deleteFile(_:)), name: NSNotification.Name(rawValue: k_notificationCenter_deleteFile), object: nil)
        NotificationCenter.default.addObserver(self, selector: #selector(renameFile(_:)), name: NSNotification.Name(rawValue: k_notificationCenter_renameFile), object: nil)
        NotificationCenter.default.addObserver(self, selector: #selector(moveFile(_:)), name: NSNotification.Name(rawValue: k_notificationCenter_moveFile), object: nil)
        NotificationCenter.default.addObserver(self, selector: #selector(saveLivePhoto(_:)), name: NSNotification.Name(rawValue: k_notificationCenter_menuSaveLivePhoto), object: nil)
        
        NotificationCenter.default.addObserver(self, selector: #selector(viewUnload), name: NSNotification.Name(rawValue: k_notificationCenter_menuDetailClose), object: nil)
        
        progressView.tintColor = NCBrandColor.sharedInstance.brandElement
        progressView.trackTintColor = .clear
        progressView.progress = 0
    }
    
    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)

        let buttonMore = UIBarButtonItem.init(image: CCGraphics.changeThemingColorImage(UIImage(named: "more"), width: 50, height: 50, color: NCBrandColor.sharedInstance.textView), style: .plain, target: self, action: #selector(self.openMenuMore))
        navigationItem.rightBarButtonItem = buttonMore
        
        navigationController?.setNavigationBarHidden(false, animated: true)
        navigationController?.navigationBar.prefersLargeTitles = false
    }
    
    @objc func viewUnload() {
        
        navigationController?.popViewController(animated: true)
    }
    
    //MARK: - NotificationCenter

    @objc func downloadedFile(_ notification: NSNotification) {
        if self.view?.window == nil { return }
        
        if let userInfo = notification.userInfo as NSDictionary? {
            if let metadata = userInfo["metadata"] as? tableMetadata, let errorCode = userInfo["errorCode"] as? Int {
                if metadata.ocId == currentViewerImageZoom?.metadata.ocId && errorCode == 0 {
                    let image = getImageMetadata(metadata)
                    currentViewerImageZoom?.updateImage(image)
                }
                if self.metadatas.first(where: { $0.ocId == metadata.ocId }) != nil {
                    progressView.progress = 0
                }
            }
        }
    }
    
    @objc func triggerProgressTask(_ notification: NSNotification) {
        if self.view?.window == nil { return }
        
        if let userInfo = notification.userInfo as NSDictionary? {
            if let ocId = userInfo["ocId"] as? String {
                if self.metadatas.first(where: { $0.ocId == ocId }) != nil {
                    let progressNumber = userInfo["progress"] as? NSNumber ?? 0
                    let progress = progressNumber.floatValue
                    if progress == 1 {
                        self.progressView.progress = 0
                    } else {
                        self.progressView.progress = progress
                    }
                }
            }
        }
    }
    
    @objc func deleteFile(_ notification: NSNotification) {
        if self.view?.window == nil { return }
        
        if let userInfo = notification.userInfo as NSDictionary? {
            if let metadata = userInfo["metadata"] as? tableMetadata {
                let metadatas = self.metadatas.filter { $0.ocId != metadata.ocId }
                if self.metadatas.count == metadatas.count { return }
                self.metadatas = metadatas
                
                if metadata.ocId == currentViewerImageZoom?.metadata.ocId {
                    if !shiftCurrentPage() {
                        self.viewUnload()
                    }
                }
            }
        }
    }
    
    @objc func renameFile(_ notification: NSNotification) {
        if self.view?.window == nil { return }
        
        if let userInfo = notification.userInfo as NSDictionary? {
            if let metadata = userInfo["metadata"] as? tableMetadata {
                if let index = metadatas.firstIndex(where: {$0.ocId == metadata.ocId}) {
                    metadatas[index] = metadata
                    if index == currentIndex {
                        navigationItem.title = metadata.fileNameView
                        currentViewerImageZoom?.metadata = metadata
                    }
                }
            }
        }
    }
    
    @objc func moveFile(_ notification: NSNotification) {
        if self.view?.window == nil { return }
        
        if let userInfo = notification.userInfo as NSDictionary? {
            if let metadata = userInfo["metadata"] as? tableMetadata {
                if metadatas.firstIndex(where: {$0.ocId == metadata.ocId}) != nil {
                    deleteFile(notification)
                }
            }
        }
    }
    
    @objc func saveLivePhoto(_ notification: NSNotification) {
        if self.view?.window == nil { return }
        
        if let userInfo = notification.userInfo as NSDictionary? {
            if let metadata = userInfo["metadata"] as? tableMetadata, let metadataMov = userInfo["metadataMov"] as? tableMetadata {
                let fileNameImage = URL(fileURLWithPath: CCUtility.getDirectoryProviderStorageOcId(metadata.ocId, fileNameView: metadata.fileNameView)!)
                let fileNameMov = URL(fileURLWithPath: CCUtility.getDirectoryProviderStorageOcId(metadataMov.ocId, fileNameView: metadataMov.fileNameView)!)
                
                NCLivePhoto.generate(from: fileNameImage, videoURL: fileNameMov, progress: { progress in
                    DispatchQueue.main.async {
                        self.progressView.progress = Float(progress)
                    }
                }, completion: { livePhoto, resources in
                    self.progressView.progress = 0
                    if resources != nil {
                        NCLivePhoto.saveToLibrary(resources!) { (result) in
                            if !result {
                                NCContentPresenter.shared.messageNotification("_error_", description: "_livephoto_save_error_", delay: TimeInterval(k_dismissAfterSecond), type: NCContentPresenter.messageType.error, errorCode: Int(k_CCErrorInternalError))
                            }
                        }
                    } else {
                        NCContentPresenter.shared.messageNotification("_error_", description: "_livephoto_save_error_", delay: TimeInterval(k_dismissAfterSecond), type: NCContentPresenter.messageType.error, errorCode: Int(k_CCErrorInternalError))
                    }
                })
            }
        }
    }
    
    @objc func changeTheming() {
        
        if currentMode == .normal {
            view.backgroundColor = NCBrandColor.sharedInstance.backgroundView
        }
    }
    
    //MARK: - Gesture

    func gestureRecognizerShouldBegin(_ gestureRecognizer: UIGestureRecognizer) -> Bool {
        
        if let gestureRecognizer = gestureRecognizer as? UIPanGestureRecognizer {
            let velocity = gestureRecognizer.velocity(in: self.view)
            
            var velocityCheck : Bool = false
            
            if UIDevice.current.orientation.isLandscape {
                velocityCheck = velocity.x < 0
            }
            else {
                velocityCheck = velocity.y < 0
            }
            if velocityCheck {
                return false
            }
        }
        
        return true
    }
    
    func gestureRecognizer(_ gestureRecognizer: UIGestureRecognizer, shouldRecognizeSimultaneouslyWith otherGestureRecognizer: UIGestureRecognizer) -> Bool {
        
        if otherGestureRecognizer == currentViewController.scrollView.panGestureRecognizer {
            if self.currentViewController.scrollView.contentOffset.y == 0 {
                return true
            }
        }
        
        return false
    }

    @objc func didPanWith(gestureRecognizer: UIPanGestureRecognizer) {
        let currentLocation = gestureRecognizer.translation(in: self.view)

        switch gestureRecognizer.state {
        case .began:
            startPanLocation = currentLocation
            defaultImageViewTopConstraint = currentViewController.imageViewTopConstraint.constant
            defaultImageViewBottomConstraint = currentViewController.imageViewBottomConstraint.constant
            currentViewController.scrollView.isScrollEnabled = false
        case .ended:
            currentViewController.scrollView.isScrollEnabled = true
            currentViewController.imageViewTopConstraint.constant = defaultImageViewTopConstraint
            currentViewController.imageViewBottomConstraint.constant = defaultImageViewBottomConstraint
        case .changed:
            let dy = currentLocation.y - startPanLocation.y
            currentViewController.imageViewTopConstraint.constant = defaultImageViewTopConstraint + dy
            currentViewController.imageViewBottomConstraint.constant = defaultImageViewBottomConstraint - dy
            if dy >= panDistanceForPopViewController {
                self.navigationController?.popViewController(animated: true)
            }
            print(dy)
        default:
            break
        }
    }
    
    @objc func didSingleTapWith(gestureRecognizer: UITapGestureRecognizer) {
        
        if currentMetadata.typeFile == k_metadataTypeFile_video || currentMetadata.typeFile == k_metadataTypeFile_audio {
            
            videoStop()

            let video = NCViewerVideoAudio()
            video.metadata = currentMetadata
            present(video, animated: false) { }
            
        } else {
        
            if currentMode == .full {
                
                changeScreenMode(to: .normal)
                currentMode = .normal
                
            } else {
                
                changeScreenMode(to: .full)
                currentMode = .full
            }
        }
    }
    
    @objc func didLongpressGestureEvent(gestureRecognizer: UITapGestureRecognizer) {
        
        if gestureRecognizer.state == .began {
            
            let fileName = (currentMetadata.fileNameView as NSString).deletingPathExtension + ".mov"
            if let metadata = NCManageDatabase.sharedInstance.getMetadata(predicate: NSPredicate(format: "account == %@ AND serverUrl == %@ AND fileNameView LIKE[c] %@", currentMetadata.account, currentMetadata.serverUrl, fileName)) {
                
                if CCUtility.fileProviderStorageSize(metadata.ocId, fileNameView: metadata.fileNameView) > 0 {
                    
                    AudioServicesPlaySystemSound(1519) // peek feedback
                    self.playVideo(metadata: metadata)
                    
                } else {
                    
                    let serverUrlFileName = metadata.serverUrl + "/" + metadata.fileNameView
                    let fileNameLocalPath = CCUtility.getDirectoryProviderStorageOcId(metadata.ocId, fileNameView: metadata.fileNameView)!
                                    
                    NCCommunication.shared.download(serverUrlFileName: serverUrlFileName, fileNameLocalPath: fileNameLocalPath, requestHandler: { (_) in
                        
                    }, progressHandler: { (progress) in
                                        
                        self.progressView.progress = Float(progress.fractionCompleted)
                        
                    }) { (account, etag, date, length, error, errorCode, errorDescription) in
                        
                        self.progressView.progress = 0
                        
                        if errorCode == 0 && account == metadata.account {
                            
                            NCManageDatabase.sharedInstance.addLocalFile(metadata: metadata)
                            
                            if gestureRecognizer.state == .began {
                                AudioServicesPlaySystemSound(1519) // peek feedback
                                self.playVideo(metadata: metadata)
                            }
                        }
                    }
                }
            }
            
        } else if gestureRecognizer.state == .ended {
            
            currentViewerImageZoom?.statusViewImage.isHidden = false
            currentViewerImageZoom?.statusLabel.isHidden = false
            videoStop()
            videoLayer?.removeFromSuperlayer()
        }
    }
    
    //MARK: - Delegate Image Zoom

    func viewWillAppearImageZoom(viewerImageZoom: NCViewerImageZoom, metadata: tableMetadata) {

        navigationItem.title = metadata.fileNameView

        currentMetadata = metadata
        currentViewerImageZoom = viewerImageZoom
        toolBar.isHidden = true
        
        videoStop()
        
        if (currentMetadata.typeFile == k_metadataTypeFile_video || currentMetadata.typeFile == k_metadataTypeFile_audio) {

            if CCUtility.fileProviderStorageSize(metadata.ocId, fileNameView: metadata.fileNameView) > 0 {
                toolBar.isHidden = false
                playVideo(metadata: metadata)
            }
        }
    }
    
    func viewDidAppearImageZoom(viewerImageZoom: NCViewerImageZoom, metadata: tableMetadata) {
                
        if !NCOperationQueue.shared.downloadExists(metadata: metadata) {
            self.progressView.progress = 0
        }
        
        let isFolderEncrypted = CCUtility.isFolderEncrypted(metadata.serverUrl, e2eEncrypted: metadata.e2eEncrypted, account: metadata.account, urlBase: metadata.urlBase)
        let ext = CCUtility.getExtension(metadata.fileNameView)
        
        if ((metadata.contentType == "image/heic" &&  metadata.hasPreview == false) || ext == "GIF" || ext == "SVG" || isFolderEncrypted) && metadata.session == "" {
            NCOperationQueue.shared.download(metadata: metadata, selector: "", setFavorite: false, forceDownload: false)
        }
        
        if !CCUtility.fileProviderStoragePreviewIconExists(metadata.ocId, etag: metadata.etag) && metadata.hasPreview {
            
            let fileNamePath = CCUtility.returnFileNamePath(fromFileName: metadata.fileName, serverUrl: metadata.serverUrl, urlBase: metadata.urlBase, account: metadata.account)!
            let fileNamePreviewLocalPath = CCUtility.getDirectoryProviderStoragePreviewOcId(metadata.ocId, etag: metadata.etag)!
            let fileNameIconLocalPath = CCUtility.getDirectoryProviderStorageIconOcId(metadata.ocId, etag: metadata.etag)!
            
            NCCommunication.shared.downloadPreview(fileNamePathOrFileId: fileNamePath, fileNamePreviewLocalPath: fileNamePreviewLocalPath, widthPreview: Int(k_sizePreview), heightPreview: Int(k_sizePreview), fileNameIconLocalPath: fileNameIconLocalPath, sizeIcon: Int(k_sizeIcon)) { (account, imagePreview, imageIcon,  errorCode, errorMessage) in
                if errorCode == 0 {
                    viewerImageZoom.updateImage(imagePreview)
                }
            }
        }
    }
    
    //MARK: - Function
    
    func changeScreenMode(to: ScreenMode) {
        
        if to == .full {
            
            navigationController?.setNavigationBarHidden(true, animated: false)
            view.backgroundColor = .black
            progressView.isHidden = true
            
        } else {
            
            navigationController?.setNavigationBarHidden(false, animated: false)
            view.backgroundColor = NCBrandColor.sharedInstance.backgroundView
            progressView.isHidden = false
        }
    }
    
    func getImageMetadata(_ metadata: tableMetadata) -> UIImage? {
                
        if let image = getImage(metadata: metadata) {
            return image
        }
        
        if metadata.typeFile == k_metadataTypeFile_video && !metadata.hasPreview {
            CCGraphics.createNewImage(from: metadata.fileNameView, ocId: metadata.ocId, etag: metadata.etag, typeFile: metadata.typeFile)
        }
        
        if CCUtility.fileProviderStoragePreviewIconExists(metadata.ocId, etag: metadata.etag) {
            if let imagePreviewPath = CCUtility.getDirectoryProviderStoragePreviewOcId(metadata.ocId, etag: metadata.etag) {
                return UIImage.init(contentsOfFile: imagePreviewPath)
            } 
        }
        
        return nil
    }
    
    private func getImage(metadata: tableMetadata) -> UIImage? {
        
        let ext = CCUtility.getExtension(metadata.fileNameView)
        var image: UIImage?
        
        if CCUtility.fileProviderStorageSize(metadata.ocId, fileNameView: metadata.fileNameView) > 0 && metadata.typeFile == k_metadataTypeFile_image {
           
            let previewPath = CCUtility.getDirectoryProviderStoragePreviewOcId(metadata.ocId, etag: metadata.etag)!
            let imagePath = CCUtility.getDirectoryProviderStorageOcId(metadata.ocId, fileNameView: metadata.fileNameView)!
            
            if ext == "GIF" {
                if !FileManager().fileExists(atPath: previewPath) {
                    CCGraphics.createNewImage(from: metadata.fileNameView, ocId: metadata.ocId, etag: metadata.etag, typeFile: metadata.typeFile)
                }
                image = UIImage.animatedImage(withAnimatedGIFURL: URL(fileURLWithPath: imagePath))
            } else if ext == "SVG" {
                if let svgImage = SVGKImage(contentsOfFile: imagePath) {
                    let scale = svgImage.size.height / svgImage.size.width
                    svgImage.size = CGSize(width: CGFloat(k_sizePreview), height: (CGFloat(k_sizePreview) * scale))
                    if let image = svgImage.uiImage {
                        if !FileManager().fileExists(atPath: previewPath) {
                            do {
                                try image.pngData()?.write(to: URL(fileURLWithPath: previewPath), options: .atomic)
                            } catch { }
                        }
                        return image
                    } else {
                        return nil
                    }
                } else {
                    return nil
                }
            } else {
                if !FileManager().fileExists(atPath: previewPath) {
                    CCGraphics.createNewImage(from: metadata.fileNameView, ocId: metadata.ocId, etag: metadata.etag, typeFile: metadata.typeFile)
                }
                image = UIImage.init(contentsOfFile: imagePath)
            }
        }
        
        return image
    }
    
    func playVideo(metadata: tableMetadata) {
                
        currentViewerImageZoom?.statusViewImage.isHidden = true
        currentViewerImageZoom?.statusLabel.isHidden = true
        
        playerVideo = AVPlayer(url: URL(fileURLWithPath: CCUtility.getDirectoryProviderStorageOcId(metadata.ocId, fileNameView: metadata.fileNameView)!))
        videoLayer = AVPlayerLayer(player: playerVideo)
        
        if videoLayer != nil && currentViewerImageZoom != nil {
            
            videoLayer!.frame = currentViewerImageZoom!.imageView.bounds
            videoLayer!.videoGravity = AVLayerVideoGravity.resizeAspectFill
            
            currentViewerImageZoom!.imageView.layer.addSublayer(videoLayer!)
            
            // At end go back to start
            NotificationCenter.default.addObserver(forName: .AVPlayerItemDidPlayToEndTime, object: nil, queue: nil) { (notification) in
                self.playerVideo?.seek(to: CMTime.zero)
            }
                        
            playerVideo?.addObserver(self, forKeyPath: "rate", options: [], context: nil)
            videoPlay()
        }
    }
    
    /*
    @objc func updateTimer() {
        if let durationVideo = playerVideo?.currentItem?.asset.duration {
            timerCounter += 1
            let floatTime = Float(CMTimeGetSeconds(durationVideo))
            progressView.progress = timerCounter / floatTime
        }
    }
    */
    
    //MARK: - Action
    
    override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
        
        if keyPath != nil && keyPath == "rate" {
            
            if playerVideo?.rate == 1 {
                print("start")
                let item = UIBarButtonItem(barButtonSystemItem: UIBarButtonItem.SystemItem.pause, target: self, action: #selector(videoPause))
                toolBar.setItems([item], animated: true)
            } else {
                print("pause")
                let item = UIBarButtonItem(barButtonSystemItem: UIBarButtonItem.SystemItem.play, target: self, action: #selector(self.videoPlay))
                toolBar.setItems([item], animated: true)
            }
        }
    }
    
    @objc func openMenuMore() {
        NCViewer.shared.toggleMoreMenu(viewController: self, metadata: currentMetadata)
    }
    
    @objc func videoPause() {
        playerVideo?.pause()
    }
    
    @objc func videoPlay() {
        playerVideo?.play()
        if let duration = playerVideo?.currentItem?.asset.duration {
            durationVideo = Float(CMTimeGetSeconds(duration))
        }
    }
    
    @objc func videoStop() {
        playerVideo?.pause()
        self.playerVideo?.seek(to: CMTime.zero)
    }
}

extension NCViewerImagePageContainer: UIPageViewControllerDelegate, UIPageViewControllerDataSource {
    
    func shiftCurrentPage() -> Bool {
        if metadatas.count == 0 { return false }
        
        var direction: UIPageViewController.NavigationDirection = .forward
        if currentIndex == metadatas.count {
            currentIndex -= 1
            direction = .reverse
        }
        
        let viewerImageZoom = UIStoryboard(name: "NCViewerImage", bundle: nil).instantiateViewController(withIdentifier: "NCViewerImageZoom") as! NCViewerImageZoom
        
        viewerImageZoom.index = currentIndex
        viewerImageZoom.image = getImageMetadata(metadatas[currentIndex])
        viewerImageZoom.metadata = metadatas[currentIndex]
        viewerImageZoom.delegate = self
        
        singleTapGestureRecognizer.require(toFail: viewerImageZoom.doubleTapGestureRecognizer)
        
        pageViewController.setViewControllers([viewerImageZoom], direction: direction, animated: true, completion: nil)
        
        return true
    }
    
    func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {
        if currentIndex == 0 { return nil }
        
        let viewerImageZoom = UIStoryboard(name: "NCViewerImage", bundle: nil).instantiateViewController(withIdentifier: "NCViewerImageZoom") as! NCViewerImageZoom
                
        viewerImageZoom.index = currentIndex - 1
        viewerImageZoom.image = getImageMetadata(metadatas[currentIndex - 1])
        viewerImageZoom.metadata = metadatas[currentIndex - 1]
        viewerImageZoom.delegate = self
        
        self.singleTapGestureRecognizer.require(toFail: viewerImageZoom.doubleTapGestureRecognizer)
        
        return viewerImageZoom
    }
    
    func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? {
        if currentIndex == metadatas.count - 1 { return nil }
                
        let viewerImageZoom = UIStoryboard(name: "NCViewerImage", bundle: nil).instantiateViewController(withIdentifier: "NCViewerImageZoom") as! NCViewerImageZoom
        
        viewerImageZoom.index = currentIndex + 1
        viewerImageZoom.image = getImageMetadata(metadatas[currentIndex + 1])
        viewerImageZoom.metadata = metadatas[currentIndex + 1]
        viewerImageZoom.delegate = self
        
        singleTapGestureRecognizer.require(toFail: viewerImageZoom.doubleTapGestureRecognizer)

        return viewerImageZoom
    }
    
    func pageViewController(_ pageViewController: UIPageViewController, willTransitionTo pendingViewControllers: [UIViewController]) {
        
        guard let nextVC = pendingViewControllers.first as? NCViewerImageZoom else {
            return
        }
        
        self.nextIndex = nextVC.index
    }
    
    func pageViewController(_ pageViewController: UIPageViewController, didFinishAnimating finished: Bool, previousViewControllers: [UIViewController], transitionCompleted completed: Bool) {
        
        if (completed && self.nextIndex != nil) {
            
            previousViewControllers.forEach { vc in
                let viewerImageZoom = vc as! NCViewerImageZoom
                viewerImageZoom.scrollView.zoomScale = viewerImageZoom.scrollView.minimumZoomScale
            }
            currentIndex = nextIndex!
        }
        
        self.nextIndex = nil
    }
}