import Foundation
import Ink
import Splash

typealias VideoSource = (url: String, type: VideoFileType)

final class PageContentParser {

    private let pageLinkMarker = "page:"

    private let swift = SyntaxHighlighter(format: HTMLOutputFormat())

    let results = PageGenerationResults()

    private let content: Content

    private let language: ContentLanguage

    private var largeImageCount: Int = 0

    var largeImageWidth: Int {
        content.settings.pages.largeImageWidth
    }

    var thumbnailWidth: Int {
        content.settings.pages.contentWidth
    }

    init(content: Content, language: ContentLanguage) {
        self.content = content
        self.language = language
    }

    func requestImages(_ generator: ImageGenerator) {
        let thumbnailWidth = CGFloat(thumbnailWidth)
        let largeImageWidth = CGFloat(largeImageWidth)

        for image in results.files {
            guard case .image = image.type else {
                continue
            }
            generator.generateImageSet(
                for: image.id,
                maxWidth: thumbnailWidth, maxHeight: thumbnailWidth)

            generator.generateImageSet(
                for: image.id,
                maxWidth: largeImageWidth, maxHeight: largeImageWidth)
        }
    }

    func reset() {
        results.reset()
        largeImageCount = 0
    }

    func generatePage(from content: String) -> String {
        reset()
        let parser = MarkdownParser(modifiers: [
            Modifier(target: .images, closure: processMarkdownImage),
            Modifier(target: .codeBlocks, closure: handleCode),
            Modifier(target: .links, closure: handleLink),
            Modifier(target: .html, closure: handleHTML),
            Modifier(target: .headings, closure: handleHeadlines)
        ])
        return parser.html(from: content)
    }

    private func handleCode(html: String, markdown: Substring) -> String {
        guard markdown.starts(with: "```swift") else {
            return html // Just use normal code highlighting
        }
        // Highlight swift code using Splash
        let code = markdown.between("```swift", and: "```").trimmed
        return "<pre><code>" + swift.highlight(code) + "</pre></code>"
    }

    private func handleLink(html: String, markdown: Substring) -> String {
        let file = markdown.between("(", and: ")")
        if file.hasPrefix(pageLinkMarker) {
            // Retain links pointing to elements within a page
            let textToChange = file.dropAfterFirst("#")
            let pageId = textToChange.replacingOccurrences(of: pageLinkMarker, with: "")
            guard let page = content.page(pageId) else {
                results.missingPages.insert(pageId)
                // Remove link since the page can't be found
                return markdown.between("[", and: "]")
            }
            results.linkedPages.insert(page)
            let pagePath = content.pageLink(page, language: language)
            return html.replacingOccurrences(of: textToChange, with: pagePath)
        }

        // TODO: Check that linked file exists
//        if let filePath = page.nonAbsolutePathRelativeToRootForContainedInputFile(file) {
//            // The target of the page link must be present after generation is complete
//            results.expect(file: filePath, source: page.path)
//        }
        return html
    }

    private func handleHTML(html: String, markdown: Substring) -> String {
        // TODO: Check HTML code in markdown for required resources
        //print("[HTML] Found in page \(page.path):")
        //print(markdown)
        // Things to check:
        // <img src=
        // <a href=
        //
        return html
    }

    /**
     Modify headlines by extracting an id from the headline and adding it into the html element

     Format: ##<title>#<id>

     The id is created by lowercasing the string, removing all special characters, and replacing spaces with scores
     */
    private func handleHeadlines(html: String, markdown: Substring) -> String {
        let id = markdown
            .last(after: "#")
            .trimmed
            .filter { $0.isNumber || $0.isLetter || $0 == " " }
            .lowercased()
            .components(separatedBy: " ")
            .filter { $0 != "" }
            .joined(separator: "-")
        let parts = html.components(separatedBy: ">")
        return parts[0] + " id=\"\(id)\">" + parts.dropFirst().joined(separator: ">")
    }

    private func processMarkdownImage(html: String, markdown: Substring) -> String {
        // First, check the content type, then parse the remaining arguments
        // Notation:
        //     <abc?> -> Optional argument
        //     <abc...> -> Repeated argument (0 or more)
        // ![url](<url>;<text>)
        // ![image](<imageId>;<caption?>]
        // ![video](<fileId>;<option1...>]
        // ![svg](<fileId>;<<x>;<y>;<width>;<height>?>)
        // ![download](<<fileId>,<text>,<download-filename?>;...)
        // ![box](<title>;<body>)
        // ![model](<file>;<description>)
        // ![page](<pageId>)
        // ![external](<<url>;<text>...>
        // ![html](<fileId>)

        let argumentList = markdown.between(first: "](", andLast: ")").removingPercentEncoding ?? markdown.between(first: "](", andLast: ")")
        let arguments = argumentList.components(separatedBy: ";")


        let rawCommand = markdown.between("![", and: "]").trimmed
        guard rawCommand != "" else {
            return handleImage(arguments)
        }

        guard let convertedCommand = rawCommand.removingPercentEncoding,
              let command = ShorthandMarkdownKey(rawValue: convertedCommand) else {
            // Treat unknown commands as normal links
            results.warnings.append("Unknown markdown command '\(rawCommand)'")
            return html
        }

        switch command {
        case .image:
            return handleImage(arguments)
        case .hikingStatistics:
            return handleHikingStatistics(arguments)
        case .downloadButtons:
            return handleDownloadButtons(arguments)
        case .video:
            return handleVideo(arguments)
        case .externalLink:
            return handleExternalButtons(arguments)
            /*
        case .includedHtml:
            return handleExternalHTML(file: content)
        case .box:
            return handleSimpleBox(content: content)
        case .pageLink:
            return handlePageLink(pageId: content)
        case .model:
            return handle3dModel(content: content)
             */
        default:
            results.warnings.append("Unhandled command '\(command.rawValue)'")
            return ""

        }
    }

    private func handleImage(_ arguments: [String]) -> String {
        // [image](<imageId>;<caption?>]
        guard (1...2).contains(arguments.count) else {
            results.invalidCommandArguments.append((.image , arguments))
            return ""
        }
        let imageId = arguments[0]

        guard let image = content.image(imageId) else {
            results.missingFiles.insert(imageId)
            return ""
        }
        results.files.insert(image)

        let caption = arguments.count == 2 ? arguments[1] : nil
        let altText = image.getDescription(for: language)

        let path = content.pathToImage(image)

        let thumbnail = FeedEntryData.Image(
            rawImagePath: path,
            width: thumbnailWidth,
            height: thumbnailWidth,
            altText: altText)

        let largeImage = FeedEntryData.Image(
            rawImagePath: path,
            width: largeImageWidth,
            height: largeImageWidth,
            altText: altText)

        return PageImage(
            imageId: imageId.replacingOccurrences(of: ".", with: "-"),
            thumbnail: thumbnail,
            largeImage: largeImage,
            caption: caption).content
    }

    private func handleHikingStatistics(_ arguments: [String]) -> String {
        guard (1...5).contains(arguments.count) else {
            results.invalidCommandArguments.append((.hikingStatistics, arguments))
            return ""
        }

        let time = arguments[0].trimmed
        let elevationUp = arguments.count > 1 ? arguments[1].trimmed : nil
        let elevationDown = arguments.count > 2 ? arguments[2].trimmed : nil
        let distance = arguments.count > 3 ? arguments[3].trimmed : nil
        let calories = arguments.count > 4 ? arguments[4].trimmed : nil

        return HikingStatistics(
            time: time,
            elevationUp: elevationUp,
            elevationDown: elevationDown,
            distance: distance,
            calories: calories)
        .content
    }

    private func handleDownloadButtons(_ arguments: [String]) -> String {
        // ![download](<<fileId>,<text>,<download-filename?>;...)
        let buttons: [ContentButtons.Item] = arguments.compactMap { button in
            let parts = button.components(separatedBy: ",")
            guard (2...3).contains(parts.count) else {
                results.invalidCommandArguments.append((.downloadButtons, parts))
                return nil
            }
            let file = parts[0].trimmed
            let title = parts[1].trimmed
            let downloadName = parts.count > 2 ? parts[2].trimmed : nil

            // Ensure that file is available
            guard let filePath = content.pathToFile(file) else {
                results.missingFiles.insert(file)
                return nil
            }
            return ContentButtons.Item(icon: .download, filePath: filePath, text: title, downloadFileName: downloadName)
        }
        return ContentButtons(items: buttons).content
    }

    private func handleVideo(_ arguments: [String]) -> String {
        // ![video](<fileId>;<option1...>]
        guard arguments.count >= 1 else {
            results.invalidCommandArguments.append((.video, arguments))
            return ""
        }
        let fileId = arguments[0].trimmed

        let options = arguments.dropFirst().compactMap(convertVideoOption)

        guard let file = content.file(id: fileId) else {
            results.missingFiles.insert(fileId)
            return ""
        }
        results.files.insert(file)

        guard let videoType = file.type.videoType?.htmlType else {
            results.warnings.append("Unknown video file type for \(fileId)")
            return ""
        }

        let filePath = content.pathToFile(file)
        return ContentPageVideo(
            filePath: filePath,
            videoType: videoType,
            options: options)
        .content
    }

    private func convertVideoOption(_ videoOption: String) -> VideoOption? {
        guard let optionText = videoOption.trimmed.nonEmpty else {
            return nil
        }
        guard let option = VideoOption(rawValue: optionText) else {
            results.invalidCommandArguments.append((.video, [optionText]))
            return nil
        }
        if case let .poster(imageId) = option {
            if let image = content.image(imageId) {
                results.files.insert(image)
                let link = content.pathToImage(image)
                let width = 2*thumbnailWidth
                let fullLink = WebsiteImage.imagePath(source: link, width: width, height: width)
                return .poster(image: fullLink)
            } else {
                results.missingFiles.insert(imageId)
                return nil // Image file not present, so skip the option
            }
        }
        if case let .src(videoId) = option {
            if let video = content.video(videoId) {
                results.files.insert(video)
                let link = content.pathToVideo(video)
                // TODO: Set correct video path?
                return .src(link)
            } else {
                results.missingFiles.insert(videoId)
                return nil // Video file not present, so skip the option
            }
        }
        return option
    }

    /*

    private func handleGif(file: String, altText: String) -> String {
        let imagePath = page.pathRelativeToRootForContainedInputFile(file)
        results.require(file: imagePath, source: page.path)

        guard let size = results.getImageSize(atPath: imagePath, source: page.path) else {
            return ""
        }
        let width = Int(size.width)
        let height = Int(size.height)
        return factory.html.image(file: file, width: width, height: height, altText: altText)
    }

    private func handleSvg(file: String, area: String?) -> String {
        let imagePath = page.pathRelativeToRootForContainedInputFile(file)
        results.require(file: imagePath, source: page.path)

        guard let size = results.getImageSize(atPath: imagePath, source: page.path) else {
            return "" // Missing image warning already produced
        }
        let width = Int(size.width)
        let height = Int(size.height)

        var altText = "image " + file.lastComponentAfter("/")
        guard let area = area else {
            return factory.html.image(file: file, width: width, height: height, altText: altText)
        }
        let parts = area.components(separatedBy: ",").map { $0.trimmed }
        switch parts.count {
        case 1:
            return factory.html.image(file: file, width: width, height: height, altText: parts[0])
        case 4:
            break
        case 5:
            altText = parts[4]
        default:
            results.warning("Invalid area string for svg image", source: page.path)
            return factory.html.image(file: file, width: width, height: height, altText: altText)
        }
        guard let x = Int(parts[0]),
              let y = Int(parts[1]),
              let partWidth = Int(parts[2]),
              let partHeight = Int(parts[3]) else {
            results.warning("Invalid area string for svg image", source: page.path)
            return factory.html.image(file: file, width: width, height: height, altText: altText)
        }
        let part = SVGSelection(x, y, partWidth, partHeight)
        return factory.html.svgImage(file: file, part: part, altText: altText)
    }

    private func handleFile(file: String, fileExtension: String) -> String {
        results.warning("Unhandled file \(file) with extension \(fileExtension)", source: page.path)
        return ""
    }
*/
    private func handleExternalButtons(_ arguments: [String]) -> String {
        // ![external](<<url>;<text>...>
        guard arguments.count >= 1 else {
            results.invalidCommandArguments.append((.externalLink, arguments))
            return ""
        }
        let buttons: [ContentButtons.Item] = arguments.compactMap { button in
            let parts = button.components(separatedBy: ",")
            guard parts.count == 2 else {
                results.invalidCommandArguments.append((.externalLink, parts))
                return nil
            }
            let rawUrl = parts[0].trimmed
            guard let url = rawUrl.addingPercentEncoding(withAllowedCharacters: .urlQueryAllowed) else {
                results.invalidCommandArguments.append((.externalLink, parts))
                return nil
            }
            let title = parts[1].trimmed

            return .init(
                icon: .externalLink,
                filePath: url,
                text: title)
        }
        return ContentButtons(items: buttons).content
    }
/*
    private func handleExternalHTML(file: String) -> String {
        let path = page.pathRelativeToRootForContainedInputFile(file)
        return results.getContentOfRequiredFile(at: path, source: page.path) ?? ""
    }

    private func handleSimpleBox(content: String) -> String {
        let parts = content.components(separatedBy: ";")
        guard parts.count > 1 else {
            results.warning("Invalid box specification", page: page)
            return ""
        }
        let title = parts[0]
        let text = parts.dropFirst().joined(separator: ";")
        return factory.makePlaceholder(title: title, text: text)
    }

    private func handlePageLink(pageId: String) -> String {
        guard let linkedPage = siteRoot.find(pageId) else {
            // Checking the page path will add it to the missing pages
            _ = results.getPagePath(for: pageId, source: page.path, language: language)
            // Remove link since the page can't be found
            return ""
        }
        guard linkedPage.state == .standard else {
            // Prevent linking to unpublished content
            return ""
        }
        var content = [PageLinkTemplate.Key: String]()

        content[.title] = linkedPage.title(for: language)
        content[.altText] = ""

        let fullThumbnailPath = linkedPage.thumbnailFilePath(for: language).destination
        // Note: Here we assume that the thumbnail was already used elsewhere, so already generated
        let relativeImageUrl = page.relativePathToOtherSiteElement(file: fullThumbnailPath)
        let metadata = linkedPage.localized(for: language)

        if linkedPage.state.hasThumbnailLink {
            let fullPageUrl = linkedPage.fullPageUrl(for: language)
            let relativePageUrl = page.relativePathToOtherSiteElement(file: fullPageUrl)
            content[.url] = "href=\"\(relativePageUrl)\""
        }

        content[.image] = relativeImageUrl.dropAfterLast(".")
        if let suffix = metadata.thumbnailSuffix {
            content[.title] = factory.html.make(title: metadata.title, suffix: suffix)
        } else {
            content[.title] = metadata.title
        }

        let path = linkedPage.makePath(language: language, from: siteRoot)
        content[.path] = factory.pageLink.makePath(components: path)

        content[.description] = metadata.relatedContentText
        if let parent = linkedPage.findParent(from: siteRoot), parent.thumbnailStyle == .large {
            content[.className] = " related-page-link-large"
        }

        // We assume that the thumbnail images are already required by overview pages.
        return factory.pageLink.generate(content)
    }

    private func handle3dModel(content: String) -> String {
        let parts = content.components(separatedBy: ";")
        guard parts.count > 1 else {
            results.warning("Invalid 3d model specification", page: page)
            return ""
        }
        let file = parts[0]
        guard file.hasSuffix(".glb") else {
            results.warning("Invalid 3d model file \(file) (must be .glb)", page: page)
            return ""
        }

        // Ensure that file is available
        let filePath = page.pathRelativeToRootForContainedInputFile(file)
        results.require(file: filePath, source: page.path)

        // Add required file to head
        headers.insert(.modelViewer)

        let description = parts.dropFirst().joined(separator: ";")
        return """
        <model-viewer alt="\(description)" src="\(file)" ar shadow-intensity="1" camera-controls touch-action="pan-y"></model-viewer>
        """
    }
    */
}