import Foundation

/**
 A class that handles the storage of the website data.

 BaseFolder
 - pages: Contains the markdown files of the localized pages, file name is the url
 - images: Contains the raw images
 - files: Contains additional files
 - videos: Contains raw video files
 - posts: Contains the markdown files for localized posts, file name is the post id
 -
 */
final class Storage {

    private(set) var baseFolder: URL

    private let encoder = JSONEncoder()

    private let decoder = JSONDecoder()

    private let fm = FileManager.default

    /**
     Create the storage.
     */
    init(baseFolder: URL) {
        self.baseFolder = baseFolder
        encoder.outputFormatting = [.prettyPrinted, .sortedKeys]
    }

    // MARK: Helper

    private func subFolder(_ name: String) -> URL {
        baseFolder.appending(path: name, directoryHint: .isDirectory)
    }

    private func files(in folder: URL) throws -> [URL] {
        do {
            return try fm.contentsOfDirectory(at: folder, includingPropertiesForKeys: [.isDirectoryKey])
                .filter { !$0.hasDirectoryPath }
        } catch {
            print("Failed to get files in folder \(folder.path): \(error)")
            throw error
        }
    }

    private func fileNames(in folder: URL) throws -> [String] {
        try fm.contentsOfDirectory(atPath: folder.path())
            .filter { !$0.hasPrefix(".") }
            .sorted()
    }

    private func files(in folder: URL, type: String) throws -> [URL] {
        try files(in: folder).filter { $0.pathExtension == type }
    }

    // MARK: Folders

    func update(baseFolder: URL, moveContent: Bool) throws {
        let oldFolder = self.baseFolder
        self.baseFolder = baseFolder
        try createFolderStructure()
        guard moveContent else {
            return
        }
        // TODO: Move all files
    }

    private func create(folder: URL) throws {
        guard !FileManager.default.fileExists(atPath: folder.path) else {
            return
        }
        try FileManager.default.createDirectory(at: folder, withIntermediateDirectories: true)
    }

    func createFolderStructure() throws {
        try create(folder: pagesFolder)
        try create(folder: imagesFolder)
        try create(folder: filesFolder)
        try create(folder: videosFolder)
        try create(folder: postsFolder)
        try create(folder: tagsFolder)
    }

    // MARK: Pages

    /// The folder path where the markdown and metadata files of the pages are stored (by their id/url component)
    private var pagesFolder: URL { subFolder("pages") }

    private func pageFileUrl(pageId: String) -> URL {
        pagesFolder.appending(path: pageId, directoryHint: .notDirectory)
    }

    private func pageContentUrl(pageId: String, language: ContentLanguage) -> URL {
        pagesFolder.appending(path: "\(pageId)-\(language.rawValue).md", directoryHint: .notDirectory)
    }

    private func pageMetadataUrl(pageId: String) -> URL {
        pagesFolder.appending(path: pageId + ".json", directoryHint: .notDirectory)
    }

    @discardableResult
    func save(pageContent: String, for pageId: String, language: ContentLanguage) -> Bool {
        let contentUrl = pageContentUrl(pageId: pageId, language: language)
        return write(content: pageContent, to: contentUrl, type: "page", id: pageId)
    }

    @discardableResult
    func save(pageMetadata: PageFile, for pageId: String) -> Bool {
        let contentUrl = pageMetadataUrl(pageId: pageId)
        return write(pageMetadata, type: "page", id: pageId, to: contentUrl)
    }

    @discardableResult
    func copyPageContent(from url: URL, for pageId: String, language: ContentLanguage) -> Bool {
        let contentUrl = pageContentUrl(pageId: pageId, language: language)
        return copy(file: url, to: contentUrl, type: "page content", id: pageId)
    }

    func loadAllPages() throws -> [String : PageFile] {
        try loadAll(in: pagesFolder)
    }

    func pageContent(for pageId: String, language: ContentLanguage) -> String {
        let contentUrl = pageContentUrl(pageId: pageId, language: language)
        guard fm.fileExists(atPath: contentUrl.path()) else {
            print("No file at \(contentUrl.path())")
            return "New file"
        }
        do {
            return try String(contentsOf: contentUrl, encoding: .utf8)
        } catch {
            print("Failed to load page content for \(pageId) (\(language)): \(error)")
            return error.localizedDescription
        }
    }

    // MARK: Posts

    /// The folder path where the markdown files of the posts are stored (by their unique id/url component)
    private var postsFolder: URL { subFolder("posts") }

    private func postFileUrl(postId: String) -> URL {
        postsFolder.appending(path: postId, directoryHint: .notDirectory).appendingPathExtension("json")
    }

    @discardableResult
    func save(post: PostFile, for postId: String) -> Bool {
        let contentUrl = postFileUrl(postId: postId)
        return write(post, type: "post", id: postId, to: contentUrl)
    }

    func loadAllPosts() throws -> [String : PostFile] {
        try loadAll(in: postsFolder)
    }

    private func post(at url: URL) throws -> PostFile {
        try read(at: url)
    }

    private func postContent(for postId: String) throws -> PostFile {
        let url = postFileUrl(postId: postId)
        return try post(at: url)
    }

    // MARK: Tags

    /// The folder path where the source images are stored (by their unique name)
    private var tagsFolder: URL { subFolder("tags") }

    private func tagFileUrl(tagId: String) -> URL {
        tagsFolder.appending(path: tagId, directoryHint: .notDirectory)
    }

    private func tagMetadataUrl(tagId: String) -> URL {
        tagFileUrl(tagId: tagId).appendingPathExtension("json")
    }

    @discardableResult
    func save(tagMetadata: TagFile, for tagId: String) -> Bool {
        let contentUrl = tagMetadataUrl(tagId: tagId)
        return write(tagMetadata, type: "tag", id: tagId, to: contentUrl)
    }

    func loadAllTags() throws -> [String : TagFile] {
        try loadAll(in: tagsFolder)
    }

    // MARK: Images

    /// The folder path where the source images are stored (by their unique name)
    private var imagesFolder: URL { subFolder("images") }

    private func imageUrl(image: String) -> URL {
        imagesFolder.appending(path: image, directoryHint: .notDirectory)
    }

    @discardableResult
    func copyImage(at url: URL, imageId: String) -> Bool {
        let contentUrl = imageUrl(image: imageId)
        return copy(file: url, to: contentUrl, type: "image", id: imageId)
    }

    // MARK: Files

    /// The folder path where other files are stored (by their unique name)
    private var filesFolder: URL { subFolder("files") }

    private func fileUrl(file: String) -> URL {
        filesFolder.appending(path: file, directoryHint: .notDirectory)
    }

    @discardableResult
    func copyFile(at url: URL, fileId: String) -> Bool {
        let contentUrl = fileUrl(file: fileId)
        return copy(file: url, to: contentUrl, type: "file", id: fileId)
    }

    func loadAllFiles() throws -> [String : URL] {
        try files(in: filesFolder).reduce(into: [:]) { files, url in
            files[url.lastPathComponent] = url
        }
    }

    // MARK: Videos

    /// The folder path where source videos are stored (by their unique name)
    private var videosFolder: URL { subFolder("videos") }

    private func videoUrl(video: String) -> URL {
        videosFolder.appending(path: video, directoryHint: .notDirectory)
    }

    @discardableResult
    func copyVideo(at url: URL, videoId: String) -> Bool {
        let contentUrl = videoUrl(video: videoId)
        return copy(file: url, to: contentUrl, type: "video", id: videoId)
    }

    func loadAllVideos() throws -> [String] {
        try fileNames(in: videosFolder)
    }

    // MARK: Writing files

    private func write<T>(_ value: T, type: String, id: String, to file: URL) -> Bool where T: Encodable {
        let content: Data
        do {
            content = try encoder.encode(value)
        } catch {
            print("Failed to encode content of \(type) '\(id)': \(error)")
            return false
        }
        do {
            try content.write(to: file, options: .atomic)
            return true
        } catch {
            print("Failed to save content for \(type) '\(id)': \(error)")
            return false
        }
    }

    private func copy(file: URL, to destination: URL, type: String, id: String) -> Bool {
        do {
            try fm.copyItem(at: file, to: destination)
            return true
        } catch {
            print("Failed to copy content file for \(type) '\(id)': \(error)")
            return false
        }
    }

    private func write(content: String, to file: URL, type: String, id: String) -> Bool {
        do {
            try content.write(to: file, atomically: true, encoding: .utf8)
            return true
        } catch {
            print("Failed to save content for \(type) '\(id)': \(error)")
            return false
        }
    }

    private func read<T>(at url: URL) throws -> T where T: Decodable {
        let data = try Data(contentsOf: url)
        return try decoder.decode(T.self, from: data)
    }

    private func loadAll<T>(in folder: URL) throws -> [String : T] where T: Decodable {
        try files(in: folder, type: "json").reduce(into: [:]) { items, url in
            let id = url.deletingPathExtension().lastPathComponent
            let item: T = try read(at: url)
            items[id] = item
        }
    }

}