import Foundation
import Ink
import Splash

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

final class PageContentParser {

    private let pageLinkMarker = "page:"

    private let tagLinkMarker = "tag:"

    private static let codeHighlightFooter = "<script>hljs.highlightAll();</script>"

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

    let results = PageGenerationResults()

    private let content: Content

    let language: ContentLanguage

    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) {
        for request in results.imagesToGenerate {
            generator.generateImageSet(
                for: request.image.id,
                maxWidth: CGFloat(request.size),
                maxHeight: CGFloat(request.size))
        }
    }

    func reset() {
        results.reset()
    }

    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 {
            results.requiredHeaders.insert(.codeHightlighting)
            results.requiredFooters.insert(PageContentParser.codeHighlightFooter)
            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) {
            return handlePageLink(file: file, html: html, markdown: markdown)
        }
        if file.hasPrefix(tagLinkMarker) {
            return handleTagLink(file: file, html: html, markdown: markdown)
        }
        #warning("Check existence of linked file")
        return html
    }

    private func handlePageLink(file: String, html: String, markdown: Substring) -> String {
        // 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.absoluteUrlToPage(page, language: language)
        return html.replacingOccurrences(of: textToChange, with: pagePath)
    }

    private func handleTagLink(file: String, html: String, markdown: Substring) -> String {
        // Retain links pointing to elements within a page
        let textToChange = file.dropAfterFirst("#")
        let tagId = textToChange.replacingOccurrences(of: tagLinkMarker, with: "")
        guard let tag = content.tag(tagId) else {
            results.missingTags.insert(tagId)
            // Remove link since the tag can't be found
            return markdown.between("[", and: "]")
        }
        results.linkedTags.insert(tag)
        let tagPath = content.absoluteUrlToTag(tag, language: language)
        return html.replacingOccurrences(of: textToChange, with: tagPath)
    }

    private func handleHTML(html: String, markdown: Substring) -> String {
        #warning("Check HTML code in markdown for required resources")
        // Things to check: <img src=  <a href= <source>
        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 percentDecoded(_ string: String) -> String {
        guard let decoded = string.removingPercentEncoding else {
            print("Invalid string: \(string)")
            return string
        }
        return decoded
    }

    private func processMarkdownImage(html: String, markdown: Substring) -> String {
        //
        let argumentList = percentDecoded(markdown.between(first: "](", andLast: ")"))
        let arguments = argumentList.components(separatedBy: ";")


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

        guard let command = ShorthandMarkdownKey(rawValue: rawCommand) else {
            // Treat unknown commands as normal links
            results.unknownCommands.append(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 .gitLink:
            return handleGitButtons(arguments)
        case .pageLink:
            return handlePageLink(arguments)
        case .includedHtml:
            return handleExternalHtml(arguments)
        case .box:
            return handleSimpleBox(arguments)
        case .model:
            return handleModel(arguments)
        case .svg:
            return handleSvg(arguments)
        default:
            results.unknownCommands.append(command.rawValue)
            return ""
        }
    }

    /**
     Format: `[image](<imageId>;<caption?>]`
     */
    private func handleImage(_ arguments: [String]) -> String {
        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.absoluteUrlToFile(image)

        guard !image.type.isSvg else {
            return SvgImage(imagePath: path, altText: altText).content
        }

        let thumbnail = FeedEntryData.Image(
            rawImagePath: path,
            width: thumbnailWidth,
            height: thumbnailWidth,
            altText: altText)
        results.imagesToGenerate.insert(.init(size: thumbnailWidth, image: image))

        let largeImage = FeedEntryData.Image(
            rawImagePath: path,
            width: largeImageWidth,
            height: largeImageWidth,
            altText: altText)
        results.imagesToGenerate.insert(.init(size: largeImageWidth, image: image))

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

    /**
     Format: `![hiking-stats](<time>;<elevation-up>;<elevation-down>;<distance>;<calories>)`
     */
    private func handleHikingStatistics(_ arguments: [String]) -> String {
        #warning("Make statistics more generic using key-value pairs")
        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
    }

    /**
     Format: `![download](<<fileId>,<text>,<download-filename?>;...)`
     */
    private func handleDownloadButtons(_ arguments: [String]) -> String {
        let buttons = arguments.compactMap(convertButton)
        return ContentButtons(items: buttons).content
    }

    private func convertButton(definition button: String) -> ContentButtons.Item? {
        let parts = button.components(separatedBy: ",")
        guard (2...3).contains(parts.count) else {
            results.invalidCommandArguments.append((.downloadButtons, parts))
            return nil
        }
        let fileId = parts[0].trimmed
        let title = parts[1].trimmed
        let downloadName = parts.count > 2 ? parts[2].trimmed : nil

        guard let file = content.file(id: fileId) else {
            results.missingFiles.insert(fileId)
            return nil
        }
        results.files.insert(file)
        let filePath = content.absoluteUrlToFile(file)
        return ContentButtons.Item(icon: .download, filePath: filePath, text: title, downloadFileName: downloadName)
    }

    /**
     Format: `![video](<fileId>;<option1...>]`
     */
    private func handleVideo(_ arguments: [String]) -> String {
        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.invalidCommandArguments.append((.video, arguments))
            return ""
        }

        let filePath = content.absoluteUrlToFile(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.absoluteUrlToFile(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.absoluteUrlToFile(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 handleExternalButtons(_ arguments: [String]) -> String {
        // ![external](<<url>;<text>...>
        handleButtons(icon: .externalLink, arguments: arguments)
    }

    private func handleGitButtons(_ arguments: [String]) -> String {
        // ![git](<<url>;<text>...>
        handleButtons(icon: .gitLink, arguments: arguments)
    }

    private func handleButtons(icon: PageIcon, arguments: [String]) -> String {
        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: icon,
                filePath: url,
                text: title)
        }
        return ContentButtons(items: buttons).content
    }

    /**
     Format: `![html](<fileId>)`
     */
    private func handleExternalHtml(_ arguments: [String]) -> String {
        guard arguments.count == 1 else {
            results.invalidCommandArguments.append((.includedHtml, arguments))
            return ""
        }
        let fileId = arguments[0]
        guard let file = content.file(id: fileId) else {
            results.missingFiles.insert(fileId)
            return ""
        }
        return file.textContent()
    }

    /**
     Format: `![box](<title>;<body>)`
     */
    private func handleSimpleBox(_ arguments: [String]) -> String {
        guard arguments.count > 1 else {
            results.invalidCommandArguments.append((.box, arguments))
            return ""
        }
        let title = arguments[0]
        let text = arguments.dropFirst().joined(separator: ";")
        return ContentBox(title: title, text: text).content
    }

    /**
     Format: `![page](<pageId>)`
     */
    private func handlePageLink(_ arguments: [String]) -> String {
        guard arguments.count == 1 else {
            results.invalidCommandArguments.append((.pageLink, arguments))
            return ""
        }
        let pageId = arguments[0]

        guard let page = content.page(pageId) else {
            results.missingPages.insert(pageId)
            return ""
        }
        guard !page.isDraft else {
            // Prevent linking to unpublished content
            return ""
        }

        let localized = page.localized(in: language)
        let url = content.absoluteUrlToPage(page, language: language)
        let title = localized.linkPreviewTitle ?? localized.title
        let description = localized.linkPreviewDescription ?? ""

        let image = localized.linkPreviewImage.map { image in
            let size = content.settings.pages.pageLinkImageSize
            results.files.insert(image)
            results.imagesToGenerate.insert(.init(size: size, image: image))

            return RelatedPageLink.Image(
                url: content.absoluteUrlToFile(image),
                description: image.getDescription(for: language),
                size: size)
        }

        return RelatedPageLink(
            title: title,
            description: description,
            url: url,
            image: image)
            .content
    }

    /**
     Format: `![model](<file>)`
     */
    private func handleModel(_ arguments: [String]) -> String {
        guard arguments.count == 1 else {
            results.invalidCommandArguments.append((.model, arguments))
            return ""
        }
        let fileId = arguments[0]
        guard fileId.hasSuffix(".glb") else {
            results.invalidCommandArguments.append((.model, ["\(fileId) is not a .glb file"]))
            return ""
        }

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

        let path = content.absoluteUrlToFile(file)
        let description = file.getDescription(for: language)
        return ModelViewer(file: path, description: description).content
    }

    private func handleSvg(_ arguments: [String]) -> String {
        guard arguments.count == 5 else {
            results.invalidCommandArguments.append((.svg, arguments))
            return ""
        }

        guard let x = Int(arguments[1]),
              let y = Int(arguments[2]),
              let partWidth = Int(arguments[3]),
              let partHeight = Int(arguments[4]) else {
            results.invalidCommandArguments.append((.svg, arguments))
            return ""
        }

        let imageId = arguments[0]

        guard let image = content.image(imageId) else {
            results.missingFiles.insert(imageId)
            return ""
        }
        guard case .image(let imageType) = image.type,
              imageType == .svg else {
            results.invalidCommandArguments.append((.svg, arguments))
            return ""
        }

        let path = content.absoluteUrlToFile(image)

        return PartialSvgImage(
            imagePath: path,
            altText: image.getDescription(for: language),
            x: x,
            y: y,
            width: partWidth,
            height: partHeight)
        .content
    }

}

/*
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)
}
*/