import UIKit

final class RDEPUBImageViewController: UIViewController {

    struct Configuration {
        let image: UIImage
        let sourceRect: CGRect?
        let altText: String?
        let theme: RDEPUBReaderTheme

        init(image: UIImage, sourceRect: CGRect? = nil, altText: String? = nil, theme: RDEPUBReaderTheme) {
            self.image = image
            self.sourceRect = sourceRect
            self.altText = altText
            self.theme = theme
        }
    }

    // MARK: - Properties

    private let configuration: Configuration
    private let scrollView = UIScrollView()
    private let imageView = UIImageView()
    private let closeButton = UIButton(type: .system)
    private let backgroundView = UIView()

    private var isShowingChrome = true

    // MARK: - Init

    init(configuration: Configuration) {
        self.configuration = configuration
        super.init(nibName: nil, bundle: nil)
        modalPresentationStyle = .fullScreen
        modalTransitionStyle = .crossDissolve
    }

    @available(*, unavailable)
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    // MARK: - Lifecycle

    override func viewDidLoad() {
        super.viewDidLoad()
        setupBackground()
        setupScrollView()
        setupImageView()
        setupCloseButton()
    }

    override func viewDidLayoutSubviews() {
        super.viewDidLayoutSubviews()
        centerImage()
    }

    override var prefersStatusBarHidden: Bool { true }

    // MARK: - Setup

    private func setupBackground() {
        backgroundView.translatesAutoresizingMaskIntoConstraints = false
        backgroundView.backgroundColor = configuration.theme.imageViewerBackgroundColor
        view.addSubview(backgroundView)
        NSLayoutConstraint.activate([
            backgroundView.topAnchor.constraint(equalTo: view.topAnchor),
            backgroundView.bottomAnchor.constraint(equalTo: view.bottomAnchor),
            backgroundView.leadingAnchor.constraint(equalTo: view.leadingAnchor),
            backgroundView.trailingAnchor.constraint(equalTo: view.trailingAnchor)
        ])

        let tap = UITapGestureRecognizer(target: self, action: #selector(dismissViewer))
        backgroundView.addGestureRecognizer(tap)
    }

    private func setupScrollView() {
        scrollView.translatesAutoresizingMaskIntoConstraints = false
        scrollView.delegate = self
        scrollView.minimumZoomScale = 1.0
        scrollView.maximumZoomScale = 5.0
        scrollView.showsVerticalScrollIndicator = false
        scrollView.showsHorizontalScrollIndicator = false
        scrollView.alwaysBounceVertical = false
        scrollView.alwaysBounceHorizontal = false
        scrollView.decelerationRate = .fast
        view.addSubview(scrollView)
        NSLayoutConstraint.activate([
            scrollView.topAnchor.constraint(equalTo: view.topAnchor),
            scrollView.bottomAnchor.constraint(equalTo: view.bottomAnchor),
            scrollView.leadingAnchor.constraint(equalTo: view.leadingAnchor),
            scrollView.trailingAnchor.constraint(equalTo: view.trailingAnchor)
        ])

        let swipeDown = UISwipeGestureRecognizer(target: self, action: #selector(dismissViewer))
        swipeDown.direction = .down
        scrollView.addGestureRecognizer(swipeDown)
    }

    private func setupImageView() {
        imageView.image = configuration.image
        imageView.contentMode = .scaleAspectFit
        imageView.isUserInteractionEnabled = true
        imageView.accessibilityLabel = configuration.altText
        imageView.isAccessibilityElement = configuration.altText != nil
        scrollView.addSubview(imageView)

        let doubleTap = UITapGestureRecognizer(target: self, action: #selector(handleDoubleTap(_:)))
        doubleTap.numberOfTapsRequired = 2
        imageView.addGestureRecognizer(doubleTap)

        let singleTap = UITapGestureRecognizer(target: self, action: #selector(toggleChrome))
        singleTap.numberOfTapsRequired = 1
        singleTap.require(toFail: doubleTap)
        imageView.addGestureRecognizer(singleTap)
    }

    private func setupCloseButton() {
        let config = UIImage.SymbolConfiguration(pointSize: 16, weight: .semibold)
        closeButton.setImage(UIImage(systemName: "xmark", withConfiguration: config), for: .normal)
        closeButton.tintColor = .white
        closeButton.backgroundColor = UIColor(white: 0.3, alpha: 0.6)
        closeButton.layer.cornerRadius = 16
        closeButton.clipsToBounds = true
        closeButton.addTarget(self, action: #selector(dismissViewer), for: .touchUpInside)
        closeButton.accessibilityLabel = NSLocalizedString("Close image viewer", comment: "Accessibility label for close button in image viewer")

        view.addSubview(closeButton)
        closeButton.translatesAutoresizingMaskIntoConstraints = false
        NSLayoutConstraint.activate([
            closeButton.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor, constant: 12),
            closeButton.trailingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.trailingAnchor, constant: -16),
            closeButton.widthAnchor.constraint(equalToConstant: 32),
            closeButton.heightAnchor.constraint(equalToConstant: 32)
        ])
    }

    // MARK: - Layout

    private func centerImage() {
        guard let image = imageView.image else { return }
        let boundsSize = scrollView.bounds.size
        guard boundsSize.width > 0, boundsSize.height > 0 else { return }

        let imageSize = image.size
        guard imageSize.width > 0, imageSize.height > 0 else { return }

        let widthRatio = boundsSize.width / imageSize.width
        let heightRatio = boundsSize.height / imageSize.height
        let fitScale = min(widthRatio, heightRatio)

        let fitWidth = imageSize.width * fitScale
        let fitHeight = imageSize.height * fitScale

        imageView.frame = CGRect(
            x: 0,
            y: 0,
            width: fitWidth,
            height: fitHeight
        )

        scrollView.contentSize = imageView.frame.size

        let horizontalInset = max(0, (boundsSize.width - fitWidth) / 2)
        let verticalInset = max(0, (boundsSize.height - fitHeight) / 2)
        scrollView.contentInset = UIEdgeInsets(
            top: verticalInset,
            left: horizontalInset,
            bottom: verticalInset,
            right: horizontalInset
        )
    }

    // MARK: - Actions

    @objc private func handleDoubleTap(_ gesture: UITapGestureRecognizer) {
        if scrollView.zoomScale > scrollView.minimumZoomScale {
            scrollView.setZoomScale(scrollView.minimumZoomScale, animated: true)
        } else {
            let point = gesture.location(in: imageView)
            let zoomSize = CGSize(width: 100, height: 100)
            let zoomRect = CGRect(
                x: point.x - zoomSize.width / 2,
                y: point.y - zoomSize.height / 2,
                width: zoomSize.width,
                height: zoomSize.height
            )
            scrollView.zoom(to: zoomRect, animated: true)
        }
    }

    @objc private func toggleChrome() {
        isShowingChrome.toggle()
        UIView.animate(withDuration: 0.25) {
            self.closeButton.alpha = self.isShowingChrome ? 1.0 : 0.0
        }
    }

    @objc private func dismissViewer() {
        dismiss(animated: true)
    }
}

// MARK: - UIScrollViewDelegate

extension RDEPUBImageViewController: UIScrollViewDelegate {

    func viewForZooming(in scrollView: UIScrollView) -> UIView? {
        imageView
    }

    func scrollViewDidZoom(_ scrollView: UIScrollView) {
        guard let image = imageView.image else { return }
        let boundsSize = scrollView.bounds.size
        let imageSize = image.size
        guard imageSize.width > 0, imageSize.height > 0 else { return }

        let widthRatio = boundsSize.width / imageSize.width
        let heightRatio = boundsSize.height / imageSize.height
        let fitScale = min(widthRatio, heightRatio)

        let fitWidth = imageSize.width * fitScale * scrollView.zoomScale
        let fitHeight = imageSize.height * fitScale * scrollView.zoomScale

        imageView.frame = CGRect(
            x: 0,
            y: 0,
            width: fitWidth,
            height: fitHeight
        )

        let horizontalInset = max(0, (boundsSize.width - fitWidth) / 2)
        let verticalInset = max(0, (boundsSize.height - fitHeight) / 2)
        scrollView.contentInset = UIEdgeInsets(
            top: verticalInset,
            left: horizontalInset,
            bottom: verticalInset,
            right: horizontalInset
        )
    }
}