final class RegisterVC : UIViewController {
    private var seed: Data! { didSet { updateKeyPair() } }
    private var keyPair: ECKeyPair! { didSet { updatePublicKeyLabel() } }
    
    // MARK: Components
    private lazy var publicKeyLabel: UILabel = {
        let result = UILabel()
        result.textColor = Colors.text
        result.font = Fonts.spaceMono(ofSize: isSmallScreen ? Values.mediumFontSize : Values.largeFontSize)
        result.numberOfLines = 0
        result.lineBreakMode = .byCharWrapping
        return result
    }()
    
    private lazy var copyPublicKeyButton: Button = {
        let result = Button(style: .prominentOutline, size: .large)
        result.setTitle(NSLocalizedString("Copy", comment: ""), for: UIControl.State.normal)
        result.addTarget(self, action: #selector(copyPublicKey), for: UIControl.Event.touchUpInside)
        return result
    }()
    
    private lazy var legalLabel: UILabel = {
        let result = UILabel()
        result.textColor = Colors.text
        result.font = .systemFont(ofSize: Values.verySmallFontSize)
        let text = "By using this service, you agree to our Terms and Conditions and Privacy Statement"
        let attributedText = NSMutableAttributedString(string: text)
        attributedText.addAttribute(.font, value: UIFont.boldSystemFont(ofSize: Values.verySmallFontSize), range: (text as NSString).range(of: "Terms and Conditions"))
        attributedText.addAttribute(.font, value: UIFont.boldSystemFont(ofSize: Values.verySmallFontSize), range: (text as NSString).range(of: "Privacy Statement"))
        result.attributedText = attributedText
        result.numberOfLines = 0
        result.textAlignment = .center
        result.lineBreakMode = .byWordWrapping
        return result
    }()
    
    // MARK: Settings
    override var preferredStatusBarStyle: UIStatusBarStyle { return .lightContent }
    
    // MARK: Lifecycle
    override func viewDidLoad() {
        // Set gradient background
        view.backgroundColor = .clear
        let gradient = Gradients.defaultLokiBackground
        view.setGradient(gradient)
        // Set up navigation bar
        let navigationBar = navigationController!.navigationBar
        navigationBar.setBackgroundImage(UIImage(), for: UIBarMetrics.default)
        navigationBar.shadowImage = UIImage()
        navigationBar.isTranslucent = false
        navigationBar.barTintColor = Colors.navigationBarBackground
        // Set up logo image view
        let logoImageView = UIImageView()
        logoImageView.image = #imageLiteral(resourceName: "Session")
        logoImageView.contentMode = .scaleAspectFit
        logoImageView.set(.width, to: 32)
        logoImageView.set(.height, to: 32)
        navigationItem.titleView = logoImageView
        // Set up title label
        let titleLabel = UILabel()
        titleLabel.textColor = Colors.text
        titleLabel.font = .boldSystemFont(ofSize: isSmallScreen ? Values.largeFontSize : Values.veryLargeFontSize)
        titleLabel.text = NSLocalizedString("Say hello to your Session ID", comment: "")
        titleLabel.numberOfLines = 0
        titleLabel.lineBreakMode = .byWordWrapping
        // Set up explanation label
        let explanationLabel = UILabel()
        explanationLabel.textColor = Colors.text
        explanationLabel.font = .systemFont(ofSize: Values.smallFontSize)
        explanationLabel.text = NSLocalizedString("Your Session ID is the unique address that people can use to contact you on Session. With no connection to your real identity, your Session ID is totally anonymous and private by design.", comment: "")
        explanationLabel.numberOfLines = 0
        explanationLabel.lineBreakMode = .byWordWrapping
        // Set up public key label container
        let publicKeyLabelContainer = UIView()
        publicKeyLabelContainer.addSubview(publicKeyLabel)
        publicKeyLabel.pin(to: publicKeyLabelContainer, withInset: Values.mediumSpacing)
        publicKeyLabelContainer.layer.cornerRadius = Values.textFieldCornerRadius
        publicKeyLabelContainer.layer.borderWidth = Values.borderThickness
        publicKeyLabelContainer.layer.borderColor = Colors.text.cgColor
        // Set up spacers
        let topSpacer = UIView.vStretchingSpacer()
        let bottomSpacer = UIView.vStretchingSpacer()
        // Set up register button
        let registerButton = Button(style: .prominentFilled, size: .large)
        registerButton.setTitle(NSLocalizedString("Continue", comment: ""), for: UIControl.State.normal)
        registerButton.titleLabel!.font = .boldSystemFont(ofSize: Values.mediumFontSize)
        registerButton.addTarget(self, action: #selector(register), for: UIControl.Event.touchUpInside)
        // Set up button stack view
        let buttonStackView = UIStackView(arrangedSubviews: [ registerButton, copyPublicKeyButton ])
        buttonStackView.axis = .vertical
        buttonStackView.spacing = isSmallScreen ? Values.smallSpacing : Values.mediumSpacing
        buttonStackView.alignment = .fill
        // Set up button stack view container
        let buttonStackViewContainer = UIView()
        buttonStackViewContainer.addSubview(buttonStackView)
        buttonStackView.pin(.leading, to: .leading, of: buttonStackViewContainer, withInset: Values.massiveSpacing)
        buttonStackView.pin(.top, to: .top, of: buttonStackViewContainer)
        buttonStackViewContainer.pin(.trailing, to: .trailing, of: buttonStackView, withInset: Values.massiveSpacing)
        buttonStackViewContainer.pin(.bottom, to: .bottom, of: buttonStackView)
        // Set up legal label
        legalLabel.isUserInteractionEnabled = true
        let tapGestureRecognizer = UITapGestureRecognizer(target: self, action: #selector(handleLegalLabelTapped))
        legalLabel.addGestureRecognizer(tapGestureRecognizer)
        // Set up legal label container
        let legalLabelContainer = UIView()
        legalLabelContainer.set(.height, to: Values.onboardingButtonBottomOffset)
        legalLabelContainer.addSubview(legalLabel)
        legalLabel.pin(.leading, to: .leading, of: legalLabelContainer, withInset: Values.massiveSpacing)
        legalLabel.pin(.top, to: .top, of: legalLabelContainer)
        legalLabelContainer.pin(.trailing, to: .trailing, of: legalLabel, withInset: Values.massiveSpacing)
        legalLabelContainer.pin(.bottom, to: .bottom, of: legalLabel, withInset: isSmallScreen ? 6 : 10)
        // Set up top stack view
        let topStackView = UIStackView(arrangedSubviews: [ titleLabel, explanationLabel, publicKeyLabelContainer ])
        topStackView.axis = .vertical
        topStackView.spacing = isSmallScreen ? Values.smallSpacing : Values.veryLargeSpacing
        topStackView.alignment = .fill
        // Set up 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)
        // Set up main stack view
        let mainStackView = UIStackView(arrangedSubviews: [ topSpacer, topStackViewContainer, bottomSpacer, buttonStackViewContainer, legalLabelContainer ])
        mainStackView.axis = .vertical
        mainStackView.alignment = .fill
        view.addSubview(mainStackView)
        mainStackView.pin(to: view)
        topSpacer.heightAnchor.constraint(equalTo: bottomSpacer.heightAnchor, multiplier: 1).isActive = true
        // Peform initial seed update
        updateSeed()
    }
    
    // MARK: General
    @objc private func enableCopyButton() {
        copyPublicKeyButton.isUserInteractionEnabled = true
        UIView.transition(with: copyPublicKeyButton, duration: 0.25, options: .transitionCrossDissolve, animations: {
            self.copyPublicKeyButton.setTitle(NSLocalizedString("Copy", comment: ""), for: UIControl.State.normal)
        }, completion: nil)
    }
    
    // MARK: Updating
    private func updateSeed() {
        seed = Randomness.generateRandomBytes(16)
    }
    
    private func updateKeyPair() {
        keyPair = Curve25519.generateKeyPair(fromSeed: seed + seed)
    }
    
    private func updatePublicKeyLabel() {
        let hexEncodedPublicKey = keyPair.hexEncodedPublicKey
        let characterCount = hexEncodedPublicKey.count
        var count = 0
        let limit = 32
        func animate() {
            let numberOfIndexesToShuffle = 32 - count
            let indexesToShuffle = (0..<characterCount).shuffled()[0..<numberOfIndexesToShuffle]
            var mangledHexEncodedPublicKey = hexEncodedPublicKey
            for index in indexesToShuffle {
                let startIndex = mangledHexEncodedPublicKey.index(mangledHexEncodedPublicKey.startIndex, offsetBy: index)
                let endIndex = mangledHexEncodedPublicKey.index(after: startIndex)
                mangledHexEncodedPublicKey.replaceSubrange(startIndex..<endIndex, with: "0123456789abcdef__".shuffled()[0..<1])
            }
            count += 1
            if count < limit {
                publicKeyLabel.text = mangledHexEncodedPublicKey
                Timer.scheduledTimer(withTimeInterval: 0.032, repeats: false) { _ in
                    animate()
                }
            } else {
                publicKeyLabel.text = hexEncodedPublicKey
            }
        }
        animate()
    }
    
    // MARK: Interaction
    @objc private func register() {
        let identityManager = OWSIdentityManager.shared()
        let databaseConnection = identityManager.value(forKey: "dbConnection") as! YapDatabaseConnection
        databaseConnection.setObject(seed.toHexString(), forKey: "LKLokiSeed", inCollection: OWSPrimaryStorageIdentityKeyStoreCollection)
        databaseConnection.setObject(keyPair!, forKey: OWSPrimaryStorageIdentityKeyStoreIdentityKey, inCollection: OWSPrimaryStorageIdentityKeyStoreCollection)
        TSAccountManager.sharedInstance().phoneNumberAwaitingVerification = keyPair!.hexEncodedPublicKey
        let displayNameVC = DisplayNameVC()
        navigationController!.pushViewController(displayNameVC, animated: true)
    }
    
    @objc private func copyPublicKey() {
        UIPasteboard.general.string = keyPair.hexEncodedPublicKey
        copyPublicKeyButton.isUserInteractionEnabled = false
        UIView.transition(with: copyPublicKeyButton, duration: 0.25, options: .transitionCrossDissolve, animations: {
            self.copyPublicKeyButton.setTitle(NSLocalizedString("Copied", comment: ""), for: UIControl.State.normal)
        }, completion: nil)
        Timer.scheduledTimer(timeInterval: 4, target: self, selector: #selector(enableCopyButton), userInfo: nil, repeats: false)
    }
    
    @objc private func handleLegalLabelTapped(_ tapGestureRecognizer: UITapGestureRecognizer) {
        let url = URL(string: "https://github.com/loki-project/loki-messenger-ios/blob/master/privacy-policy.md")!
        UIApplication.shared.open(url)
    }
}