import UIKit

public final class RDURLReaderController: UIViewController {
    private let bookURL: URL
    private let epubConfiguration: RDEPUBReaderConfiguration
    private var embeddedController: UIViewController?

    public init(
        bookURL: URL,
        epubConfiguration: RDEPUBReaderConfiguration = RDEPUBReaderConfiguration()
    ) {
        self.bookURL = bookURL
        self.epubConfiguration = epubConfiguration
        super.init(nibName: nil, bundle: nil)
    }

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

    public override func viewDidLoad() {
        super.viewDidLoad()
        view.backgroundColor = .systemBackground
        title = bookURL.deletingPathExtension().lastPathComponent
        embedReaderController()
    }

    private func embedReaderController() {
        let controller: UIViewController
        if bookURL.pathExtension.lowercased() == "epub" {
            controller = RDEPUBReaderController(
                epubURL: bookURL,
                configuration: epubConfiguration
            )
        } else {
            let bookIdentifier = bookURL.lastPathComponent
            let bookTitle = bookURL.deletingPathExtension().lastPathComponent
            let pageSize = currentTextPageSize()
            let renderStyle = currentTextRenderStyle()
            let builder = RDPlainTextBookBuilder()
            if let textBook = try? builder.build(textFileURL: bookURL, pageSize: pageSize, style: renderStyle) {
                controller = RDEPUBReaderController(
                    textBook: textBook,
                    bookIdentifier: bookIdentifier,
                    title: bookTitle,
                    textFileURL: bookURL,
                    configuration: epubConfiguration
                )
            } else {
                // 分页失败时回退到纯文本展示
                let fallback = UIViewController()
                let textView = UITextView()
                textView.isEditable = false
                textView.text = rd_decodeTextFile(url: bookURL)
                fallback.view = textView
                controller = fallback
            }
        }
        embeddedController = controller
        addChild(controller)
        controller.view.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(controller.view)
        NSLayoutConstraint.activate([
            controller.view.topAnchor.constraint(equalTo: view.topAnchor),
            controller.view.leadingAnchor.constraint(equalTo: view.leadingAnchor),
            controller.view.trailingAnchor.constraint(equalTo: view.trailingAnchor),
            controller.view.bottomAnchor.constraint(equalTo: view.bottomAnchor),
        ])
        controller.didMove(toParent: self)
    }

    private func currentTextPageSize() -> CGSize {
        let viewportSize = UIScreen.main.bounds.size
        let insets = epubConfiguration.reflowableContentInsets
        return CGSize(
            width: max(viewportSize.width - insets.left - insets.right, 1),
            height: max(viewportSize.height - insets.top - insets.bottom, 1)
        )
    }

    private func currentTextRenderStyle() -> RDEPUBTextRenderStyle {
        let font = UIFont.systemFont(ofSize: epubConfiguration.fontSize)
        let lineSpacing = max(font.lineHeight * (epubConfiguration.lineHeightMultiple - 1), 4)
        return RDEPUBTextRenderStyle(
            font: font,
            lineSpacing: lineSpacing,
            textColor: epubConfiguration.theme.contentTextColor,
            backgroundColor: epubConfiguration.theme.contentBackgroundColor
        )
    }

    private func rd_decodeTextFile(url: URL) -> String {
        if let content = try? NSString(contentsOf: url, encoding: String.Encoding.utf8.rawValue) as String {
            return content
        }
        if let content = try? NSString(contentsOf: url, encoding: 0x80000632) as String {
            return content
        }
        if let content = try? NSString(contentsOf: url, encoding: 0x80000631) as String {
            return content
        }
        return ""
    }
}