import Foundation
import Ink

struct PageContentGenerator {

    private let files: FileProcessor

    init(files: FileProcessor) {
        self.files = files
    }

    func generate(page: Page, language: String, at url: URL) throws -> String {
        var errorToThrow: Error? = nil

        let content = try wrap(.missingPage(page: url.path, language: language)) {
            try String(contentsOf: url)
        }

        var hasCodeContent = false

        let imageModifier = Modifier(target: .images) { html, markdown in
            let result = processMarkdownImage(markdown: markdown, html: html, page: page)
            switch result {
            case .success(let content):
                return content
            case .failure(let error):
                errorToThrow = error
                return ""
            }
        }
        let codeModifier = Modifier(target: .codeBlocks) { html, markdown in
            if markdown.starts(with: "```swift") {
                #warning("Syntax highlight swift code")
                return html
            }
            hasCodeContent = true
            return html
        }
        let parser = MarkdownParser(modifiers: [imageModifier, codeModifier])

        #warning("Check links in markdown for (missing) files to copy")
        if hasCodeContent {
            #warning("Automatically add hljs hightlighting if code samples are found")
        }

        let result = parser.html(from: content)
        if let error = errorToThrow {
            throw error
        }
        return result
    }

    private func processMarkdownImage(markdown: Substring, html: String, page: Page) -> Result<String, Error> {
        let fileAndTitle = markdown
            .components(separatedBy: "(").last!
            .components(separatedBy: ")").first!

        let file = fileAndTitle.components(separatedBy: " \"").first! // Remove title
        let rightSubtitle: String?
        if fileAndTitle.contains(" \"") {
            rightSubtitle = fileAndTitle.dropBeforeFirst("\"").dropAfterLast("\"")
        } else {
            rightSubtitle = nil
        }
        let leftSubtitle = markdown
            .components(separatedBy: "]").first!
            .components(separatedBy: "[").last!.nonEmpty

        #warning("Specify page image width in configuration")
        let pageImageWidth = 748
        let size: NSSize
        let imagePath = page.pathRelativeToRootForContainedInputFile(file)
        do {
            size = try files.requireImage(
                source: imagePath,
                destination: imagePath,
                width: pageImageWidth,
                desiredHeight: nil,
                createDoubleVersion: true)
        } catch {
            return .failure(error)
        }
        let file2x = file.insert("@2x", beforeLast: ".")
        #warning("Move HTML code to single location")
        let result = articelImage(
            image: file,
            image2x: file2x,
            width: size.width,
            height: size.height,
            rightSubtitle: rightSubtitle,
            leftSubtitle: leftSubtitle)
        return .success(result)
    }

    private func articelImage(image: String, image2x: String, width: CGFloat, height: CGFloat, rightSubtitle: String?, leftSubtitle: String?) -> String {
        let subtitleCode = subtitle(left: leftSubtitle, right: rightSubtitle)
        return fullImageCode(image: image, image2x: image2x, width: width, height: height, subtitle: subtitleCode)
    }

    private func articleImageWithoutSubtitle(image: String, image2x: String, width: CGFloat, height: CGFloat) -> String {
        """
        <span class="image">
            <img src="\(image)" srcset="\(image2x) 2x" width="\(Int(width))" height="\(Int(height))" loading="lazy"/>
        </span>
        """
    }

    private func subtitle(left: String?, right: String?) -> String {
        guard left != nil || right != nil else {
            return ""
        }
        let leftCode = left.unwrapped { "<span class=\"left\">\($0)</span>" } ?? ""
        let rightCode = right.unwrapped { "<span class=\"right\">\($0)</span>" } ?? ""
        return """
        <div class="subtitle">
            \(leftCode)
            \(rightCode)
        </div>
        """
    }

    private func fullImageCode(image: String, image2x: String, width: CGFloat, height: CGFloat, subtitle: String) -> String {
        """
        <span class="image">
            <img src="\(image)" srcset="\(image2x) 2x" width="\(Int(width))" height="\(Int(height))" loading="lazy"/>
            \(subtitle)
        </span>
        """
    }
}