import Foundation

final class FileGenerator {

    let input: URL

    let outputFolder: URL

    let runFolder: URL

    private let files: FileData

    /// All files copied to the destination.
    private var copiedFiles: Set<String> = []

    /// 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)] = [:]

    private var failedMinifications: [(file: String, source: String, message: String)] = []

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

    private var minifiedFiles: [String] = []

    private let numberOfFilesToCopy: Int

    private var numberOfCopiedFiles = 0

    private let numberOfFilesToMinify: Int

    private var numberOfMinifiedFiles = 0

    private var numberOfExistingFiles = 0

    private var tempFile: URL {
        runFolder.appendingPathComponent("temp")
    }

    init(input: URL, output: URL, runFolder: URL, files: FileData) {
        self.input = input
        self.outputFolder = output
        self.runFolder = runFolder
        self.files = files

        numberOfFilesToCopy = files.toCopy.count
        numberOfFilesToMinify = files.toMinify.count
    }

    func generate() {
        copy(files: files.toCopy)
        print("          Copied files: \(copiedFiles.count)/\(numberOfFilesToCopy)       ")
        minify(files: files.toMinify)
        print("        Minified files: \(minifiedFiles.count)/\(numberOfFilesToMinify)     ")
        checkExpected(files: files.expected)
        print("        Expected files: \(numberOfExistingFiles)/\(files.expected.count)")
        print("        External files: \(files.external.count)")
        print("")
    }

    private func didCopyFile() {
        numberOfCopiedFiles += 1
        print("          Copied files: \(numberOfCopiedFiles)/\(numberOfFilesToCopy)   \r", terminator: "")
        fflush(stdout)
    }

    private func didMinifyFile() {
        numberOfMinifiedFiles += 1
        print("        Minified files: \(numberOfMinifiedFiles)/\(numberOfFilesToMinify)    \r", terminator: "")
        fflush(stdout)
    }

    // MARK: File copies

    private func copy(files: [String : String]) {
        for (file, source) in files {
            copyFileIfChanged(file: file, source: source)
        }
    }

    private func copyFileIfChanged(file: String, source: String) {
        let cleanPath = cleanRelativeURL(file)
        let destinationUrl = outputFolder.appendingPathComponent(cleanPath)

        defer { didCopyFile() }
        guard copyIfChanged(cleanPath, to: destinationUrl, source: source) else {
            return
        }
        copiedFiles.insert(cleanPath)
    }

    private func copyIfChanged(_ file: String, to destination: URL, source: String) -> Bool {
        let url = input.appendingPathComponent(file)
        do {
            let data = try Data(contentsOf: url)
            return writeIfChanged(data, file: file, source: source)
        } catch {
            markFileAsUnreadable(at: file, requiredBy: source, message: "\(error)")
            return false
        }
    }

    @discardableResult
    func writeIfChanged(_ data: Data, file: String, source: String) -> Bool {
        let url = outputFolder.appendingPathComponent(file)
        // Only write changed files
        if url.exists, let oldContent = try? Data(contentsOf: url), data == oldContent {
            return false
        }
        do {
            try data.createFolderAndWrite(to: url)
            return true
        } catch {
            markFileAsUnwritable(at: file, requiredBy: source, message: "Failed to write file: \(error)")
            return false
        }
    }

    // MARK: File minification

    private func minify(files: [String : (source: String, type: MinificationType)]) {
        for (file, other) in files {
            minify(file: file, source: other.source, type: other.type)
        }
    }

    private func minify(file: String, source: String, type: MinificationType) {
        let url = input.appendingPathComponent(file)
        let command: String
        switch type {
        case .js:
            command = "uglifyjs \(url.path) > \(tempFile.path)"
        case .css:
            command = "cleancss \(url.path) -o \(tempFile.path)"
        }

        defer {
            didMinifyFile()
            try? tempFile.delete()
        }

        let output: String
        do {
            output = try safeShell(command)
        } catch {
            failedMinifications.append((file, source, "Failed to minify with error: \(error)"))
            return
        }
        guard tempFile.exists else {
            failedMinifications.append((file, source, output))
            return
        }
        let data: Data
        do {
            data = try Data(contentsOf: tempFile)
        } catch {
            markFileAsUnreadable(at: file, requiredBy: source, message: "\(error)")
            return
        }
        if writeIfChanged(data, file: file, source: source) {
            minifiedFiles.append(file)
        }
    }


    private func cleanRelativeURL(_ raw: String) -> String {
        let raw = raw.dropAfterLast("#") // Clean links to page content
        guard raw.contains("..") else {
            return raw
        }
        var result: [String] = []
        for component in raw.components(separatedBy: "/") {
            if component == ".." {
                _ = result.popLast()
            } else {
                result.append(component)
            }
        }
        return result.joined(separator: "/")
    }

    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)
    }

    // MARK: File expectationts

    private func checkExpected(files: [String: String]) {
        for (file, source) in files {
            guard !isExternal(file: file) else {
                numberOfExistingFiles += 1
                continue
            }
            let cleanPath = cleanRelativeURL(file)
            let destinationUrl = outputFolder.appendingPathComponent(cleanPath)
            guard destinationUrl.exists else {
                markFileAsMissing(at: cleanPath, requiredBy: source)
                continue
            }
            numberOfExistingFiles += 1
        }
    }

    private func markFileAsMissing(at path: String, requiredBy source: String) {
        missingFiles[path] = 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 writeResults(to file: URL) {
        guard !unreadableFiles.isEmpty || !unwritableFiles.isEmpty || !failedMinifications.isEmpty || !missingFiles.isEmpty || !copiedFiles.isEmpty || !minifiedFiles.isEmpty || !files.expected.isEmpty || !files.external.isEmpty else {
            do {
                try FileManager.default.removeItem(at: file)
            } catch {
                print("    Failed to delete file log: \(error)")
            }
            return
        }
        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("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("Failed minifications", failedMinifications) { "\($0.file) (required by \($0.source)): \($0.message)" }
        add("Missing files", missingFiles) { "\($0.key) (required by \($0.value))" }
        add("Copied files", copiedFiles) { $0 }
        add("Minified files", minifiedFiles) { $0 }
        add("Expected files", files.expected) { "\($0.key) (required by \($0.value))" }
        add("External files", files.external) { "\($0.key) (required by \($0.value))" }

        let data = lines.joined(separator: "\n").data(using: .utf8)!
        do {
            try data.createFolderAndWrite(to: file)
        } catch {
            print("    Failed to save file log: \(error)")
        }
    }
}