import PromiseKit

final class LinkDeviceVC : BaseVC, UIPageViewControllerDataSource, UIPageViewControllerDelegate, OWSQRScannerDelegate {
    private let pageVC = UIPageViewController(transitionStyle: .scroll, navigationOrientation: .horizontal, options: nil)
    private var pages: [UIViewController] = []
    private var targetVCIndex: Int?
    private var tabBarTopConstraint: NSLayoutConstraint!
    private var activityIndicatorModal: ModalActivityIndicatorViewController?
    
    // MARK: Components
    private lazy var tabBar: TabBar = {
        let tabs = [
            TabBar.Tab(title: NSLocalizedString("vc_link_device_recovery_phrase_tab_title", comment: "")) { [weak self] in
                guard let self = self else { return }
                self.pageVC.setViewControllers([ self.pages[0] ], direction: .forward, animated: false, completion: nil)
            },
            TabBar.Tab(title: NSLocalizedString("vc_link_device_scan_qr_code_tab_title", comment: "")) { [weak self] in
                guard let self = self else { return }
                self.pageVC.setViewControllers([ self.pages[1] ], direction: .forward, animated: false, completion: nil)
            }
        ]
        return TabBar(tabs: tabs)
    }()
    
    private lazy var recoveryPhraseVC: RecoveryPhraseVC = {
        let result = RecoveryPhraseVC()
        result.linkDeviceVC = self
        return result
    }()
    
    private lazy var scanQRCodePlaceholderVC: ScanQRCodePlaceholderVC = {
        let result = ScanQRCodePlaceholderVC()
        result.linkDeviceVC = self
        return result
    }()
    
    private lazy var scanQRCodeWrapperVC: ScanQRCodeWrapperVC = {
        let message = NSLocalizedString("vc_link_device_scan_qr_code_explanation", comment: "")
        let result = ScanQRCodeWrapperVC(message: message)
        result.delegate = self
        return result
    }()
    
    // MARK: Lifecycle
    override func viewDidLoad() {
        super.viewDidLoad()
        setUpGradientBackground()
        setUpNavBarStyle()
        setNavBarTitle(NSLocalizedString("vc_link_device_title", comment: ""))
        let navigationBar = navigationController!.navigationBar
        // Page VC
        let hasCameraAccess = (AVCaptureDevice.authorizationStatus(for: .video) == .authorized)
        pages = [ recoveryPhraseVC, (hasCameraAccess ? scanQRCodeWrapperVC : scanQRCodePlaceholderVC) ]
        pageVC.dataSource = self
        pageVC.delegate = self
        pageVC.setViewControllers([ recoveryPhraseVC ], direction: .forward, animated: false, completion: nil)
        // Tab bar
        view.addSubview(tabBar)
        tabBar.pin(.leading, to: .leading, of: view)
        tabBarTopConstraint = tabBar.autoPinEdge(toSuperviewSafeArea: .top)
        view.pin(.trailing, to: .trailing, of: tabBar)
        // Page VC constraints
        let pageVCView = pageVC.view!
        view.addSubview(pageVCView)
        pageVCView.pin(.leading, to: .leading, of: view)
        pageVCView.pin(.top, to: .bottom, of: tabBar)
        view.pin(.trailing, to: .trailing, of: pageVCView)
        view.pin(.bottom, to: .bottom, of: pageVCView)
        let screen = UIScreen.main.bounds
        pageVCView.set(.width, to: screen.width)
        let statusBarHeight = UIApplication.shared.statusBarFrame.height
        let height = navigationController!.view.bounds.height - navigationBar.height() - TabBar.snHeight - statusBarHeight
        pageVCView.set(.height, to: height)
        recoveryPhraseVC.constrainHeight(to: height)
        scanQRCodePlaceholderVC.constrainHeight(to: height)
    }
    
    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        tabBarTopConstraint.constant = navigationController!.navigationBar.height()
    }
    
    deinit {
        NotificationCenter.default.removeObserver(self)
    }
    
    // MARK: General
    func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {
        guard let index = pages.firstIndex(of: viewController), index != 0 else { return nil }
        return pages[index - 1]
    }
    
    func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? {
        guard let index = pages.firstIndex(of: viewController), index != (pages.count - 1) else { return nil }
        return pages[index + 1]
    }
    
    fileprivate func handleCameraAccessGranted() {
        pages[1] = scanQRCodeWrapperVC
        pageVC.setViewControllers([ scanQRCodeWrapperVC ], direction: .forward, animated: false, completion: nil)
    }
    
    // MARK: Updating
    func pageViewController(_ pageViewController: UIPageViewController, willTransitionTo pendingViewControllers: [UIViewController]) {
        guard let targetVC = pendingViewControllers.first, let index = pages.firstIndex(of: targetVC) else { return }
        targetVCIndex = index
    }
    
    func pageViewController(_ pageViewController: UIPageViewController, didFinishAnimating isFinished: Bool, previousViewControllers: [UIViewController], transitionCompleted isCompleted: Bool) {
        guard isCompleted, let index = targetVCIndex else { return }
        tabBar.selectTab(at: index)
    }
    
    // MARK: Interaction
    @objc private func close() {
        dismiss(animated: true, completion: nil)
    }
    
    func controller(_ controller: OWSQRCodeScanningViewController, didDetectQRCodeWith string: String) {
        let seed = Data(hex: string)
        continueWithSeed(seed)
    }
    
    func continueWithSeed(_ seed: Data) {
        let (ed25519KeyPair, x25519KeyPair) = KeyPairUtilities.generate(from: seed)
        Onboarding.Flow.link.preregister(with: seed, ed25519KeyPair: ed25519KeyPair, x25519KeyPair: x25519KeyPair)
        TSAccountManager.sharedInstance().didRegister()
        NotificationCenter.default.addObserver(self, selector: #selector(handleInitialConfigurationMessageReceived), name: .initialConfigurationMessageReceived, object: nil)
        ModalActivityIndicatorViewController.present(fromViewController: navigationController!) { [weak self] modal in
            self?.activityIndicatorModal = modal
        }
    }
    
    @objc private func handleInitialConfigurationMessageReceived(_ notification: Notification) {
        TSAccountManager.sharedInstance().phoneNumberAwaitingVerification = OWSIdentityManager.shared().identityKeyPair()!.hexEncodedPublicKey
        DispatchQueue.main.async {
            self.navigationController!.dismiss(animated: true) {
                let pnModeVC = PNModeVC()
                self.navigationController!.setViewControllers([ pnModeVC ], animated: true)
            }
        }
    }
}

private final class RecoveryPhraseVC : UIViewController {
    weak var linkDeviceVC: LinkDeviceVC!
    private var spacer1HeightConstraint: NSLayoutConstraint!
    private var spacer2HeightConstraint: NSLayoutConstraint!
    private var restoreButtonBottomOffsetConstraint: NSLayoutConstraint!
    private var bottomConstraint: NSLayoutConstraint!
    
    private lazy var mnemonicTextView: TextView = {
        let result = TextView(placeholder: NSLocalizedString("vc_restore_seed_text_field_hint", comment: ""))
        result.layer.borderColor = Colors.text.cgColor
        result.accessibilityLabel = "Recovery phrase text view"
        return result
    }()
    
    // MARK: Lifecycle
    override func viewDidLoad() {
        view.backgroundColor = .clear
        // Title label
        let titleLabel = UILabel()
        titleLabel.textColor = Colors.text
        titleLabel.font = .boldSystemFont(ofSize: isIPhone5OrSmaller ? Values.largeFontSize : Values.veryLargeFontSize)
        titleLabel.text = NSLocalizedString("vc_enter_recovery_phrase_title", comment: "")
        titleLabel.numberOfLines = 0
        titleLabel.lineBreakMode = .byWordWrapping
        // Explanation label
        let explanationLabel = UILabel()
        explanationLabel.textColor = Colors.text
        explanationLabel.font = .systemFont(ofSize: Values.smallFontSize)
        explanationLabel.text = NSLocalizedString("vc_enter_recovery_phrase_explanation", comment: "")
        explanationLabel.numberOfLines = 0
        explanationLabel.lineBreakMode = .byWordWrapping
        // Spacers
        let topSpacer = UIView.vStretchingSpacer()
        let spacer1 = UIView()
        spacer1HeightConstraint = spacer1.set(.height, to: isIPhone5OrSmaller ? Values.smallSpacing : Values.veryLargeSpacing)
        let spacer2 = UIView()
        spacer2HeightConstraint = spacer2.set(.height, to: isIPhone5OrSmaller ? Values.smallSpacing : Values.veryLargeSpacing)
        let bottomSpacer = UIView.vStretchingSpacer()
        let restoreButtonBottomOffsetSpacer = UIView()
        restoreButtonBottomOffsetConstraint = restoreButtonBottomOffsetSpacer.set(.height, to: Values.onboardingButtonBottomOffset)
        // Continue button
        let continueButton = Button(style: .prominentFilled, size: .large)
        continueButton.setTitle(NSLocalizedString("continue_2", comment: ""), for: UIControl.State.normal)
        continueButton.titleLabel!.font = .boldSystemFont(ofSize: Values.mediumFontSize)
        continueButton.addTarget(self, action: #selector(handleContinueButtonTapped), for: UIControl.Event.touchUpInside)
        // Continue button container
        let continueButtonContainer = UIView()
        continueButtonContainer.addSubview(continueButton)
        continueButton.pin(.leading, to: .leading, of: continueButtonContainer, withInset: Values.massiveSpacing)
        continueButton.pin(.top, to: .top, of: continueButtonContainer)
        continueButtonContainer.pin(.trailing, to: .trailing, of: continueButton, withInset: Values.massiveSpacing)
        continueButtonContainer.pin(.bottom, to: .bottom, of: continueButton)
        // Top stack view
        let topStackView = UIStackView(arrangedSubviews: [ titleLabel, spacer1, explanationLabel, spacer2, mnemonicTextView ])
        topStackView.axis = .vertical
        topStackView.alignment = .fill
        // Top stack view container
        let topStackViewContainer = UIView()
        topStackViewContainer.addSubview(topStackView)
        topStackView.pin(.leading, to: .leading, of: topStackViewContainer, withInset: Values.veryLargeSpacing)
        topStackView.pin(.top, to: .top, of: topStackViewContainer)
        topStackViewContainer.pin(.trailing, to: .trailing, of: topStackView, withInset: Values.veryLargeSpacing)
        topStackViewContainer.pin(.bottom, to: .bottom, of: topStackView)
        // Main stack view
        let mainStackView = UIStackView(arrangedSubviews: [ topSpacer, topStackViewContainer, bottomSpacer, continueButtonContainer, restoreButtonBottomOffsetSpacer ])
        mainStackView.axis = .vertical
        mainStackView.alignment = .fill
        view.addSubview(mainStackView)
        mainStackView.pin(.leading, to: .leading, of: view)
        mainStackView.pin(.top, to: .top, of: view)
        mainStackView.pin(.trailing, to: .trailing, of: view)
        bottomConstraint = mainStackView.pin(.bottom, to: .bottom, of: view)
        topSpacer.heightAnchor.constraint(equalTo: bottomSpacer.heightAnchor, multiplier: 1).isActive = true
        // Dismiss keyboard on tap
        let tapGestureRecognizer = UITapGestureRecognizer(target: self, action: #selector(dismissKeyboard))
        view.addGestureRecognizer(tapGestureRecognizer)
        // Listen to keyboard notifications
        let notificationCenter = NotificationCenter.default
        notificationCenter.addObserver(self, selector: #selector(handleKeyboardWillChangeFrameNotification(_:)), name: UIResponder.keyboardWillChangeFrameNotification, object: nil)
        notificationCenter.addObserver(self, selector: #selector(handleKeyboardWillHideNotification(_:)), name: UIResponder.keyboardWillHideNotification, object: nil)
        // Set up width constraint
        view.set(.width, to: UIScreen.main.bounds.width)
    }
    
    deinit {
        NotificationCenter.default.removeObserver(self)
    }
    
    // MARK: General
    func constrainHeight(to height: CGFloat) {
        view.set(.height, to: height)
    }
    
    @objc private func dismissKeyboard() {
        mnemonicTextView.resignFirstResponder()
    }
    
    // MARK: Updating
    @objc private func handleKeyboardWillChangeFrameNotification(_ notification: Notification) {
        guard let newHeight = (notification.userInfo?[UIResponder.keyboardFrameEndUserInfoKey] as? NSValue)?.cgRectValue.size.height else { return }
        bottomConstraint.constant = -newHeight // Negative due to how the constraint is set up
        restoreButtonBottomOffsetConstraint.constant = isIPhone6OrSmaller ? Values.smallSpacing : Values.largeSpacing
        spacer1HeightConstraint.constant = isIPhone6OrSmaller ? Values.smallSpacing : Values.mediumSpacing
        spacer2HeightConstraint.constant = isIPhone6OrSmaller ? Values.smallSpacing : Values.mediumSpacing
        UIView.animate(withDuration: 0.25) {
            self.view.layoutIfNeeded()
        }
    }
    
    @objc private func handleKeyboardWillHideNotification(_ notification: Notification) {
        bottomConstraint.constant = 0
        restoreButtonBottomOffsetConstraint.constant = Values.onboardingButtonBottomOffset
        spacer1HeightConstraint.constant = isIPhone5OrSmaller ? Values.smallSpacing : Values.veryLargeSpacing
        spacer2HeightConstraint.constant = isIPhone5OrSmaller ? Values.smallSpacing : Values.veryLargeSpacing
        UIView.animate(withDuration: 0.25) {
            self.view.layoutIfNeeded()
        }
    }
    
    // MARK: Interaction
    @objc private func handleContinueButtonTapped() {
        func showError(title: String, message: String = "") {
            let alert = UIAlertController(title: title, message: message, preferredStyle: .alert)
            alert.addAction(UIAlertAction(title: NSLocalizedString("OK", comment: ""), style: .default, handler: nil))
            presentAlert(alert)
        }
        let mnemonic = mnemonicTextView.text!.lowercased()
        do {
            let hexEncodedSeed = try Mnemonic.decode(mnemonic: mnemonic)
            let seed = Data(hex: hexEncodedSeed)
            mnemonicTextView.resignFirstResponder()
            linkDeviceVC.continueWithSeed(seed)
        } catch let error {
            let error = error as? Mnemonic.DecodingError ?? Mnemonic.DecodingError.generic
            showError(title: error.errorDescription!)
        }
    }
}

private final class ScanQRCodePlaceholderVC : UIViewController {
    weak var linkDeviceVC: LinkDeviceVC!
    
    override func viewDidLoad() {
        // Remove background color
        view.backgroundColor = .clear
        // Set up explanation label
        let explanationLabel = UILabel()
        explanationLabel.textColor = Colors.text
        explanationLabel.font = .systemFont(ofSize: Values.smallFontSize)
        explanationLabel.text = NSLocalizedString("vc_scan_qr_code_camera_access_explanation", comment: "")
        explanationLabel.numberOfLines = 0
        explanationLabel.textAlignment = .center
        explanationLabel.lineBreakMode = .byWordWrapping
        // Set up call to action button
        let callToActionButton = UIButton()
        callToActionButton.titleLabel!.font = .boldSystemFont(ofSize: Values.mediumFontSize)
        callToActionButton.setTitleColor(Colors.accent, for: UIControl.State.normal)
        callToActionButton.setTitle(NSLocalizedString("vc_scan_qr_code_grant_camera_access_button_title", comment: ""), for: UIControl.State.normal)
        callToActionButton.addTarget(self, action: #selector(requestCameraAccess), for: UIControl.Event.touchUpInside)
        // Set up stack view
        let stackView = UIStackView(arrangedSubviews: [ explanationLabel, callToActionButton ])
        stackView.axis = .vertical
        stackView.spacing = Values.mediumSpacing
        stackView.alignment = .center
        // Set up constraints
        view.set(.width, to: UIScreen.main.bounds.width)
        view.addSubview(stackView)
        stackView.pin(.leading, to: .leading, of: view, withInset: Values.massiveSpacing)
        view.pin(.trailing, to: .trailing, of: stackView, withInset: Values.massiveSpacing)
        let verticalCenteringConstraint = stackView.center(.vertical, in: view)
        verticalCenteringConstraint.constant = -16 // Makes things appear centered visually
    }
    
    func constrainHeight(to height: CGFloat) {
        view.set(.height, to: height)
    }
    
    @objc private func requestCameraAccess() {
        ows_ask(forCameraPermissions: { [weak self] hasCameraAccess in
            if hasCameraAccess {
                self?.linkDeviceVC.handleCameraAccessGranted()
            } else {
                // Do nothing
            }
        })
    }
}