import Foundation
import CryptoKit
import AppKit


enum MinificationType {
    case js
    case css
}

final class GenerationResultsHandler {

    /// The content folder where the input data is stored
    let contentFolder: URL

    /// The folder where the site is generated
    let outputFolder: URL

    private let fileUpdates: FileUpdateChecker

    /**
     All paths to page element folders, indexed by their unique id.

     This relation is used to generate relative links to pages using the ``Element.id`
     */
    private let pagePaths: [String: String]

    private let configuration: Configuration

    private var numberOfProcessedPages = 0

    private let numberOfTotalPages: Int

    init(in input: URL, to output: URL, configuration: Configuration, fileUpdates: FileUpdateChecker, pagePaths: [String: String], pageCount: Int) {
        self.contentFolder = input
        self.fileUpdates = fileUpdates
        self.outputFolder = output
        self.pagePaths = pagePaths
        self.configuration = configuration
        self.numberOfTotalPages = pageCount
    }

    // MARK: Internal storage

    /// Non-existent files. `key`: file path, `value`: source element
    private var missingFiles: [String : String] = [:]

    private(set) var files = FileData()

    /// Files which could not be read (`key`: file path relative to content)
    private var unreadableFiles: [String : (source: String, message: String)] = [:]

    /// Files which could not be written (`key`: file path relative to output folder)
    private var unwritableFiles: [String : (source: String, message: String)] = [:]

    /// The paths to all files which were changed (relative to output)
    private var generatedFiles: Set<String> = []

    /// The referenced pages which do not exist (`key`: page id, `value`: source element path)
    private var missingLinkedPages: [String : String] = [:]

    /// All pages without content which have been created (`key`: page path, `value`: source element path)
    private var emptyPages: [String : String] = [:]

    /// All pages which have `status` set to ``PageState.draft``
    private var draftPages: Set<String> = []

    /// Generic warnings for pages
    private var pageWarnings: [(message: String, source: String)] = []

    /// A cache to get the size of source images, so that files don't have to be loaded multiple times (`key` absolute source path, `value`: image size)
    private var imageSizeCache: [String : NSSize] = [:]

    private(set) var images = ImageData()

    // MARK: Generic warnings

    private func warning(_ message: String, destination: String, path: String) {
        let warning = "  \(destination): \(message) required by \(path)"
        images.warnings.append(warning)
    }

    func warning(_ message: String, source: String) {
        pageWarnings.append((message, source))
    }

    // MARK: Page data

    func getPagePath(for id: String, source: String) -> String? {
        guard let pagePath = pagePaths[id] else {
            missingLinkedPages[id] = source
            return nil
        }
        return pagePath
    }

    private func markPageAsEmpty(page: String, source: String) {
        emptyPages[page] = source
    }

    func markPageAsDraft(page: String) {
        draftPages.insert(page)
    }

    // MARK: File actions

    /**
     Add a file as required, so that it will be copied to the output directory.
     Special files may be minified.
     - Parameter file: The file path, relative to the content directory
     - Parameter source: The path of the source element requiring the file.
     */
    func require(file: String, source: String) {
        guard !isExternal(file: file) else {
            return
        }
        let url = contentFolder.appendingPathComponent(file)
        guard url.exists else {
            markFileAsMissing(at: file, requiredBy: source)
            return
        }
        guard url.isDirectory else {
            markForCopyOrMinification(file: file, source: source)
            return
        }
        do {
            try FileManager.default
                .contentsOfDirectory(atPath: url.path)
                .forEach {
                    // Recurse into subfolders
                    require(file: file + "/" + $0, source: source)
                }
        } catch {
            markFileAsUnreadable(at: file, requiredBy: source, message: "Failed to read folder: \(error)")
        }
    }

    private func markFileAsMissing(at path: String, requiredBy source: String) {
        missingFiles[path] = source
    }

    private func markFileAsUnreadable(at path: String, requiredBy source: String, message: String) {
        unreadableFiles[path] = (source, message)
    }

    private func markFileAsUnwritable(at path: String, requiredBy source: String, message: String) {
        unwritableFiles[path] = (source, message)
    }

    private func markFileAsGenerated(file: String) {
        generatedFiles.insert(file)
    }

    private func markForCopyOrMinification(file: String, source: String) {
        let ext = file.lastComponentAfter(".")
        if configuration.minifyCSSandJS, ext == "js" {
            files.toMinify[file] = (source, .js)
            return
        }
        if configuration.minifyCSSandJS, ext == "css" {
            files.toMinify[file] = (source, .css)
            return
        }
        files.toCopy[file] = source
    }

    /**
     Mark a file as explicitly missing (external).

     This is done for the `externalFiles` entries in metadata,
     to indicate that these files will be copied to the output folder manually.
     */
    func exclude(file: String, source: String) {
        files.external[file] = source
    }

    /**
     Mark a file as expected to be present in the output folder after generation.

     This is done for all links between pages, which only exist after the pages have been generated.
     */
    func expect(file: String, source: String) {
        files.expected[file] = source
    }

    /**
     Check if a file is marked as external.

     Also checks for sub-paths of the file, e.g if the folder `docs` is marked as external,
     then files like `docs/index.html` are also found to be external.
     - Note: All paths are either relative to root (no leading slash) or absolute paths of the domain (leading slash)
     */
    private func isExternal(file: String) -> Bool {
        // Deconstruct file path
        var path = ""
        for part in file.components(separatedBy: "/") {
            guard part != "" else {
                continue
            }
            if path == "" {
                path = part
            } else {
                path += "/" + part
            }
            if files.external[path] != nil {
                return true
            }
        }
        return false
    }

    func getContentOfRequiredFile(at path: String, source: String) -> String? {
        let url = contentFolder.appendingPathComponent(path)
        guard url.exists else {
            markFileAsMissing(at: path, requiredBy: source)
            return nil
        }
        return getContentOfFile(at: url, path: path, source: source)
    }

    /**
     Get the content of a file which may not exist.
     */
    func getContentOfOptionalFile(at path: String, source: String, createEmptyFileIfMissing: Bool = false) -> String? {
        let url = contentFolder.appendingPathComponent(path)
        guard url.exists else {
            if createEmptyFileIfMissing {
                writeIfChanged(.init(), file: path, source: source)
            }
            return nil
        }
        return getContentOfFile(at: url, path: path, source: source)
    }

    func getContentOfMdFile(at path: String, source: String) -> String? {
        guard let result = getContentOfOptionalFile(at: path, source: source, createEmptyFileIfMissing: configuration.createMdFilesIfMissing) else {
            markPageAsEmpty(page: path, source: source)
            return nil
        }
        return result
    }

    private func getContentOfFile(at url: URL, path: String, source: String) -> String? {
        do {
            return try String(contentsOf: url)
        } catch {
            markFileAsUnreadable(at: path, requiredBy: source, message: "\(error)")
            return nil
        }
    }

    @discardableResult
    func writeIfChanged(_ data: Data, file: String, source: String) -> Bool {
        let url = outputFolder.appendingPathComponent(file)

        defer {
            didCompletePage()
        }
        // Only write changed files
        if url.exists, let oldContent = try? Data(contentsOf: url), data == oldContent {
            return false
        }
        do {
            try data.createFolderAndWrite(to: url)
            markFileAsGenerated(file: file)
            return true
        } catch {
            markFileAsUnwritable(at: file, requiredBy: source, message: "Failed to write file: \(error)")
            return false
        }
    }

    // MARK: Images

    /**
     Request the creation of an image.
     - Returns: The final size of the image.
     */
    @discardableResult
    func requireSingleImage(source: String, destination: String, requiredBy path: String, width: Int, desiredHeight: Int? = nil) -> NSSize {
        requireImage(
            at: destination,
            generatedFrom: source,
            requiredBy: path,
            quality: 0.7,
            width: width,
            height: desiredHeight,
            alwaysGenerate: false)
    }

    /**
     Create images of different types.

     This function generates versions for the given image, including png/jpg, avif, and webp. Different pixel density versions (1x and 2x) are also generated.
     - Parameter destination: The path to the destination file
     */
    @discardableResult
    func requireMultiVersionImage(source: String, destination: String, requiredBy path: String, width: Int, desiredHeight: Int?) -> NSSize {
        // Add @2x version
        _ = requireScaledMultiImage(
            source: source,
            destination: destination.insert("@2x", beforeLast: "."),
            requiredBy: path,
            width: width * 2,
            desiredHeight: desiredHeight.unwrapped { $0 * 2 })

        // Add @1x version
        return requireScaledMultiImage(source: source, destination: destination, requiredBy: path, width: width, desiredHeight: desiredHeight)
    }

    func requireFullSizeMultiVersionImage(source: String, destination: String, requiredBy path: String) -> NSSize {
        requireMultiVersionImage(source: source, destination: destination, requiredBy: path, width: configuration.pageImageWidth, desiredHeight: nil)
    }

    @discardableResult
    private func requireScaledMultiImage(source: String, destination: String, requiredBy path: String, width: Int, desiredHeight: Int?) -> NSSize {
        let rawDestinationPath = destination.dropAfterLast(".")
        let avifPath = rawDestinationPath + ".avif"
        let webpPath = rawDestinationPath + ".webp"
        let needsGeneration = !outputFolder.appendingPathComponent(avifPath).exists || !outputFolder.appendingPathComponent(webpPath).exists

        let size = requireImage(at: destination, generatedFrom: source, requiredBy: path, quality: 1.0, width: width, height: desiredHeight, alwaysGenerate: needsGeneration)
        images.multiJobs[destination] = path
        return size
    }

    private func markImageAsMissing(path: String, source: String) {
        images.missing[source] = path
    }

    private func requireImage(at destination: String, generatedFrom source: String, requiredBy path: String, quality: Float, width: Int, height: Int?, alwaysGenerate: Bool) -> NSSize {
        let height = height.unwrapped(CGFloat.init)
        guard let imageSize = getImageSize(atPath: source, source: path) else {
            // Image marked as missing here
            return .zero
        }
        let scaledSize = imageSize.scaledDown(to: CGFloat(width))

        // Check desired height, then we can forget about it
        if let height = height {
            let expectedHeight = scaledSize.width / CGFloat(width) * height
            if abs(expectedHeight - scaledSize.height) > 2 {
                warning("Expected a height of \(expectedHeight) (is \(scaledSize.height))", destination: destination, path: path)
            }
        }

        let job = ImageJob(
            destination: destination,
            width: width,
            path: path,
            quality: quality,
            alwaysGenerate: alwaysGenerate)
        insert(job: job, source: source)

        return scaledSize
    }

    private func getImageSize(atPath path: String, source: String) -> NSSize? {
        if let size = imageSizeCache[path] {
            return size
        }
        let url = contentFolder.appendingPathComponent(path)
        guard url.exists else {
            markImageAsMissing(path: path, source: source)
            return nil
        }
        guard let data = getImageData(at: url, path: path, source: source) else {
            return nil
        }

        guard let image = NSImage(data: data) else {
            images.unreadable[path] = source
            return nil
        }

        let size = image.size
        imageSizeCache[path] = size
        return size
    }

    private func getImageData(at url: URL, path: String, source: String) -> Data? {
        do {
            let data = try Data(contentsOf: url)
            fileUpdates.didLoad(data, at: path)
            return data
        } catch {
            markFileAsUnreadable(at: path, requiredBy: source, message: "\(error)")
            return nil
        }
    }

    private func insert(job: ImageJob, source: String) {
        guard let existingSource = images.jobs[source] else {
            images.jobs[source] = [job]
            return
        }

        guard let existingJob = existingSource.first(where: { $0.destination == job.destination }) else {
            images.jobs[source] = existingSource + [job]
            return
        }

        guard existingJob.width != job.width else {
            return
        }
        warning("Different width \(existingJob.width) as \(job.path) (width \(job.width))",
                destination: job.destination, path: existingJob.path)
    }

    // MARK: Visual output

    func didCompletePage() {
        numberOfProcessedPages += 1
        print("       Processed pages: \(numberOfProcessedPages)/\(numberOfTotalPages)    \r", terminator: "")
        fflush(stdout)
    }

    func printOverview() {
        var notes: [String] = []
        func addIfNotZero(_ count: Int, _ name: String) {
            guard count > 0 else {
                return
            }
            notes.append("\(count) \(name)")
        }
        func addIfNotZero<S>(_ sequence: Array<S>, _ name: String) {
            addIfNotZero(sequence.count, name)
        }
        addIfNotZero(missingFiles.count, "missing files")
        addIfNotZero(unreadableFiles.count, "unreadable files")
        addIfNotZero(unwritableFiles.count, "unwritable files")
        addIfNotZero(missingLinkedPages.count, "missing linked pages")
        addIfNotZero(pageWarnings.count, "warnings")

        print("         Updated pages: \(generatedFiles.count)/\(numberOfProcessedPages)     ")
        print("                Drafts: \(draftPages.count)")
        print("           Empty pages: \(emptyPages.count)")
        if !notes.isEmpty {
            print("                 Notes: " + notes.joined(separator: ", "))
        }
        print("")
    }

    func writeResults(to file: URL) {
        var lines: [String] = []
        func add<S>(_ name: String, _ property: S, convert: (S.Element) -> String) where S: Sequence {
            let elements = property.map { "  " + convert($0) }.sorted()
            guard !elements.isEmpty else {
                return
            }
            lines.append("\(name):")
            lines.append(contentsOf: elements)
        }
        add("Missing files", missingFiles) { "\($0.key) (required by \($0.value))" }
        add("Unreadable files", unreadableFiles) { "\($0.key) (required by \($0.value.source)): \($0.value.message)" }
        add("Unwritable files", unwritableFiles) { "\($0.key) (required by \($0.value.source)): \($0.value.message)" }
        add("Missing linked pages", missingLinkedPages) { "\($0.key) (linked by \($0.value))" }
        add("Warnings", pageWarnings) { "\($0.source): \($0.message)" }
        add("Drafts", draftPages) { $0 }
        add("Empty pages", emptyPages) { "\($0.key) (from \($0.value))" }
        add("Generated files", generatedFiles) { $0 }
        let data = lines.joined(separator: "\n").data(using: .utf8)!
        do {
            try data.createFolderAndWrite(to: file)
        } catch {
            print("    Failed to save log: \(error)")
        }
    }
}