final class PathVC : BaseVC {
    
    // MARK: Lifecycle
    override func viewDidLoad() {
        super.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 close button
        let closeButton = UIBarButtonItem(image: #imageLiteral(resourceName: "X"), style: .plain, target: self, action: #selector(close))
        closeButton.tintColor = Colors.text
        navigationItem.leftBarButtonItem = closeButton
        // Customize title
        let titleLabel = UILabel()
        titleLabel.text = NSLocalizedString("Path", comment: "")
        titleLabel.textColor = Colors.text
        titleLabel.font = .boldSystemFont(ofSize: Values.veryLargeFontSize)
        navigationItem.titleView = titleLabel
        // Set up explanation label
        let explanationLabel = UILabel()
        explanationLabel.textColor = Colors.text.withAlphaComponent(Values.unimportantElementOpacity)
        explanationLabel.font = .systemFont(ofSize: Values.smallFontSize)
        explanationLabel.text = NSLocalizedString("Session hides your IP by routing your messages through several Service Nodes in Session's decentralized Service Node network before sending them to their destination. The Service Nodes currently being used by your device are shown below.", comment: "")
        explanationLabel.numberOfLines = 0
        explanationLabel.textAlignment = .center
        explanationLabel.lineBreakMode = .byWordWrapping
        view.addSubview(explanationLabel)
        explanationLabel.pin(.leading, to: .leading, of: view, withInset: Values.largeSpacing)
        explanationLabel.pin(.top, to: .top, of: view, withInset: Values.mediumSpacing)
        explanationLabel.pin(.trailing, to: .trailing, of: view, withInset: -Values.largeSpacing)
        // Set up path stack view
        guard let mainPath = OnionRequestAPI.paths.first else {
            return close() // TODO: Show path establishing UI
        }
        let dotAnimationRepeatInterval = (Double(mainPath.count) + 2) * 0.5
        let snodeRows = mainPath.enumerated().reversed().map { index, snode in
            getPathRow(snode: snode, location: .middle, dotAnimationStartDelay: (Double(index) + 1) * 0.5, dotAnimationRepeatInterval: dotAnimationRepeatInterval)
        }
        let destinationRow = getPathRow(title: NSLocalizedString("Destination", comment: ""), subtitle: nil, location: .top, dotAnimationStartDelay: (Double(mainPath.count) + 1) * 0.5, dotAnimationRepeatInterval: dotAnimationRepeatInterval)
        let youRow = getPathRow(title: NSLocalizedString("You", comment: ""), subtitle: nil, location: .bottom, dotAnimationStartDelay: 0, dotAnimationRepeatInterval: dotAnimationRepeatInterval)
        let rows = [ destinationRow ] + snodeRows + [ youRow ]
        let pathStackView = UIStackView(arrangedSubviews: rows)
        pathStackView.axis = .vertical
        let pathStackViewContainer = UIView()
        pathStackViewContainer.addSubview(pathStackView)
        pathStackView.pin([ UIView.VerticalEdge.top, UIView.VerticalEdge.bottom ], to: pathStackViewContainer)
        pathStackView.center(in: pathStackViewContainer)
        pathStackView.leadingAnchor.constraint(greaterThanOrEqualTo: pathStackViewContainer.leadingAnchor).isActive = true
        pathStackViewContainer.trailingAnchor.constraint(greaterThanOrEqualTo: pathStackView.trailingAnchor).isActive = true
        // Set up rebuild path button
        let rebuildPathButton = Button(style: .prominentOutline, size: .large)
        rebuildPathButton.setTitle(NSLocalizedString("Rebuild Path", comment: ""), for: UIControl.State.normal)
        rebuildPathButton.addTarget(self, action: #selector(rebuildPath), for: UIControl.Event.touchUpInside)
        let rebuildPathButtonContainer = UIView()
        rebuildPathButtonContainer.addSubview(rebuildPathButton)
        rebuildPathButton.pin(.leading, to: .leading, of: rebuildPathButtonContainer, withInset: 80)
        rebuildPathButton.pin(.top, to: .top, of: rebuildPathButtonContainer)
        rebuildPathButtonContainer.pin(.trailing, to: .trailing, of: rebuildPathButton, withInset: 80)
        rebuildPathButtonContainer.pin(.bottom, to: .bottom, of: rebuildPathButton)
        // Set up main stack view
        let mainStackView = UIStackView(arrangedSubviews: [ explanationLabel, UIView.spacer(withHeight: Values.mediumSpacing), pathStackViewContainer, UIView.vStretchingSpacer(), rebuildPathButtonContainer ])
        mainStackView.axis = .vertical
        mainStackView.alignment = .fill
        mainStackView.layoutMargins = UIEdgeInsets(top: Values.largeSpacing, left: Values.largeSpacing, bottom: Values.largeSpacing, right: Values.largeSpacing)
        mainStackView.isLayoutMarginsRelativeArrangement = true
        view.addSubview(mainStackView)
        mainStackView.pin(to: view)
    }

    private func getPathRow(title: String, subtitle: String?, location: LineView.Location, dotAnimationStartDelay: Double, dotAnimationRepeatInterval: Double) -> UIStackView {
        let lineView = LineView(location: location, dotAnimationStartDelay: dotAnimationStartDelay, dotAnimationRepeatInterval: dotAnimationRepeatInterval)
        lineView.set(.width, to: Values.pathRowDotSize)
        lineView.set(.height, to: Values.pathRowHeight)
        let titleLabel = UILabel()
        titleLabel.textColor = Colors.text
        titleLabel.font = .systemFont(ofSize: Values.mediumFontSize)
        titleLabel.text = title
        titleLabel.lineBreakMode = .byTruncatingTail
        let titleStackView = UIStackView(arrangedSubviews: [ titleLabel ])
        titleStackView.axis = .vertical
        if let subtitle = subtitle {
            let subtitleLabel = UILabel()
            subtitleLabel.textColor = Colors.text
            subtitleLabel.font = .systemFont(ofSize: Values.verySmallFontSize)
            subtitleLabel.text = subtitle
            subtitleLabel.lineBreakMode = .byTruncatingTail
            titleStackView.addArrangedSubview(subtitleLabel)
        }
        let stackView = UIStackView(arrangedSubviews: [ lineView, titleStackView ])
        stackView.axis = .horizontal
        stackView.spacing = Values.largeSpacing
        stackView.alignment = .center
        return stackView
    }

    private func getPathRow(snode: LokiAPITarget, location: LineView.Location, dotAnimationStartDelay: Double, dotAnimationRepeatInterval: Double) -> UIStackView {
        var snodeIP = snode.description
        if snodeIP.hasPrefix("https://") { snodeIP.removeFirst(8) }
        if let colonIndex = snodeIP.lastIndex(of: ":") {
            snodeIP = String(snodeIP[snodeIP.startIndex..<colonIndex])
        }
        return getPathRow(title: NSLocalizedString("Service Node", comment: ""), subtitle: snodeIP, location: location, dotAnimationStartDelay: dotAnimationStartDelay, dotAnimationRepeatInterval: dotAnimationRepeatInterval)
    }
    
    // MARK: Interaction
    @objc private func close() {
        dismiss(animated: true, completion: nil)
    }

    @objc private func rebuildPath() {
        // TODO: Implement
    }
}

// MARK: Line View
private final class LineView : UIView {
    private let location: Location
    private let dotAnimationStartDelay: Double
    private let dotAnimationRepeatInterval: Double
    private var dotViewWidthConstraint: NSLayoutConstraint!
    private var dotViewHeightConstraint: NSLayoutConstraint!
    private var dotViewAnimationTimer: Timer!

    enum Location {
        case top, middle, bottom
    }

    private lazy var dotView: UIView = {
        let result = UIView()
        result.layer.cornerRadius = Values.pathRowDotSize / 2
        let glowConfiguration = UIView.CircularGlowConfiguration(size: Values.pathRowDotSize, color: Colors.accent, isAnimated: true, radius: isLightMode ? 2 : 4)
        result.setCircularGlow(with: glowConfiguration)
        result.backgroundColor = Colors.accent
        return result
    }()
    
    init(location: Location, dotAnimationStartDelay: Double, dotAnimationRepeatInterval: Double) {
        self.location = location
        self.dotAnimationStartDelay = dotAnimationStartDelay
        self.dotAnimationRepeatInterval = dotAnimationRepeatInterval
        super.init(frame: CGRect.zero)
        setUpViewHierarchy()
    }
    
    override init(frame: CGRect) {
        preconditionFailure("Use init(location:dotAnimationStartDelay:dotAnimationRepeatInterval:) instead.")
    }
    
    required init?(coder: NSCoder) {
        preconditionFailure("Use init(location:dotAnimationStartDelay:dotAnimationRepeatInterval:) instead.")
    }
    
    private func setUpViewHierarchy() {
        let lineView = UIView()
        lineView.set(.width, to: Values.pathRowLineThickness)
        lineView.backgroundColor = Colors.text
        addSubview(lineView)
        lineView.center(.horizontal, in: self)
        switch location {
        case .top: lineView.topAnchor.constraint(equalTo: centerYAnchor).isActive = true
        case .middle, .bottom: lineView.pin(.top, to: .top, of: self)
        }
        switch location {
        case .top, .middle: lineView.pin(.bottom, to: .bottom, of: self)
        case .bottom: lineView.bottomAnchor.constraint(equalTo: centerYAnchor).isActive = true
        }
        let dotSize = Values.pathRowDotSize
        dotViewWidthConstraint = dotView.set(.width, to: dotSize)
        dotViewHeightConstraint = dotView.set(.height, to: dotSize)
        addSubview(dotView)
        dotView.center(in: self)
        Timer.scheduledTimer(withTimeInterval: dotAnimationStartDelay, repeats: false) { [weak self] _ in
            guard let strongSelf = self else { return }
            strongSelf.animate()
            strongSelf.dotViewAnimationTimer = Timer.scheduledTimer(withTimeInterval: strongSelf.dotAnimationRepeatInterval, repeats: true) { _ in
                guard let strongSelf = self else { return }
                strongSelf.animate()
            }
        }
    }

    deinit {
        dotViewAnimationTimer?.invalidate()
    }

    private func animate() {
        expandDot()
        Timer.scheduledTimer(withTimeInterval: 0.5, repeats: false) { [weak self] _ in
            self?.collapseDot()
        }
    }

    private func expandDot() {
        let newSize = Values.pathRowExpandedDotSize
        let newGlowRadius: CGFloat = isLightMode ? 6 : 8
        updateDotView(size: newSize, glowRadius: newGlowRadius)
    }

    private func collapseDot() {
        let newSize = Values.pathRowDotSize
        let newGlowRadius: CGFloat = isLightMode ? 2 : 4
        updateDotView(size: newSize, glowRadius: newGlowRadius)
    }

    private func updateDotView(size: CGFloat, glowRadius: CGFloat) {
        let frame = CGRect(center: dotView.center, size: CGSize(width: size, height: size))
        dotViewWidthConstraint.constant = size
        dotViewHeightConstraint.constant = size
        UIView.animate(withDuration: 0.25) {
            self.layoutIfNeeded()
            self.dotView.frame = frame
            self.dotView.layer.cornerRadius = size / 2
            let glowColor = Colors.accent
            let glowConfiguration = UIView.CircularGlowConfiguration(size: size, color: glowColor, isAnimated: true, radius: glowRadius)
            self.dotView.setCircularGlow(with: glowConfiguration)
            self.dotView.backgroundColor = Colors.accent
        }
    }
}