import Foundation

struct YouTubeChapter: Decodable, Identifiable, Sendable {
    let start: Double
    let end: Double?
    let title: String?
    var id: Int { Int(start * 1000) }

    enum CodingKeys: String, CodingKey { case title; case start = "start_time"; case end = "end_time" }
}

struct YouTubeVideoInfo: Decodable, Sendable {
    let id: String
    let webpageURL: String?
    let title: String
    let uploader: String?
    let channel: String?
    let duration: Double?
    let chapters: [YouTubeChapter]?

    enum CodingKeys: String, CodingKey {
        case id, title, uploader, channel, duration, chapters
        case webpageURL = "webpage_url"
    }

    var artist: String { channel?.isEmpty == false ? channel! : (uploader ?? "") }
    var usableChapters: [YouTubeChapter] {
        guard let chapters else { return [] }
        return chapters.filter { $0.start.isFinite && $0.start >= 0 && ($0.end ?? duration ?? 0) > $0.start }
    }
}

struct PreparedYouTubeImport: Sendable {
    let directory: URL
    let files: [URL]
}

enum YouTubeImportService {
    static func inspect(_ rawURL: String) throws -> YouTubeVideoInfo {
        guard let url = validatedURL(rawURL) else { throw YouTubeImportError.invalidURL }
        guard let ytDLP = MediaToolLocator.executable(named: "yt-dlp") else {
            throw MediaToolError.missing("yt-dlp")
        }
        guard MediaToolLocator.executable(named: "deno") != nil else { throw MediaToolError.missing("Deno") }
        let arguments = ["--dump-single-json", "--skip-download", "--no-playlist", "--no-warnings", "--quiet", "--no-cache-dir"]
            + MediaToolLocator.javascriptRuntimeArguments() + [url.absoluteString]
        let data = try MediaProcess.run(ytDLP, arguments: arguments)
        do { return try JSONDecoder().decode(YouTubeVideoInfo.self, from: data) }
        catch { throw YouTubeImportError.invalidVideoInfo(error.localizedDescription) }
    }

    static func prepare(_ video: YouTubeVideoInfo, splitByChapters: Bool) throws -> PreparedYouTubeImport {
        guard let sourceURL = validatedURL(video.webpageURL ?? "https://www.youtube.com/watch?v=\(video.id)") else { throw YouTubeImportError.invalidURL }
        guard let ytDLP = MediaToolLocator.executable(named: "yt-dlp") else { throw MediaToolError.missing("yt-dlp") }
        guard let ffmpeg = MediaToolLocator.executable(named: "ffmpeg") else { throw MediaToolError.missing("FFmpeg") }
        guard MediaToolLocator.executable(named: "deno") != nil else { throw MediaToolError.missing("Deno") }
        let chapters = video.usableChapters
        guard !splitByChapters || !chapters.isEmpty else { throw YouTubeImportError.noChapters }

        let directory = FileManager.default.temporaryDirectory.appendingPathComponent("tonuino-youtube-\(UUID().uuidString)", isDirectory: true)
        try FileManager.default.createDirectory(at: directory, withIntermediateDirectories: false)
        do {
            let outputTemplate = directory.appendingPathComponent("source.%(ext)s").path
            let downloadArguments = ["--format", "bestaudio/best", "--output", outputTemplate, "--no-playlist", "--no-warnings", "--no-progress", "--quiet", "--no-cache-dir"]
                + MediaToolLocator.javascriptRuntimeArguments() + [sourceURL.absoluteString]
            _ = try MediaProcess.run(ytDLP, arguments: downloadArguments)

            let sourceFiles = try FileManager.default.contentsOfDirectory(at: directory, includingPropertiesForKeys: nil, options: [.skipsHiddenFiles])
                .filter { $0.lastPathComponent.hasPrefix("source.") && !$0.pathExtension.lowercased().hasSuffix("part") }
            guard let audioURL = sourceFiles.first else { throw YouTubeImportError.downloadOutputMissing }

            let outputs: [URL]
            if splitByChapters {
                outputs = try chapters.enumerated().map { index, chapter in
                    let end = chapter.end ?? video.duration ?? 0
                    let length = end - chapter.start
                    guard length > 0 else { throw YouTubeImportError.invalidChapter }
                    let output = directory.appendingPathComponent(String(format: "chapter-%03d.mp3", index + 1))
                    let displayTitle = chapter.title?.trimmingCharacters(in: .whitespacesAndNewlines).nonEmpty ?? "Kapitel \(index + 1)"
                    let args = [
                        "-nostdin", "-hide_banner", "-loglevel", "error", "-y",
                        "-ss", String(format: "%.3f", chapter.start), "-i", audioURL.path, "-t", String(format: "%.3f", length),
                        "-map", "0:a:0", "-vn", "-codec:a", "libmp3lame", "-q:a", "2", "-id3v2_version", "3",
                        "-metadata", "title=\(displayTitle)", "-metadata", "artist=\(video.artist)", "-metadata", "album=\(video.title)",
                        "-metadata", "track=\(index + 1)/\(chapters.count)", output.path
                    ]
                    _ = try MediaProcess.run(ffmpeg, arguments: args)
                    return output
                }
            } else {
                let output = directory.appendingPathComponent("audio.mp3")
                let args = [
                    "-nostdin", "-hide_banner", "-loglevel", "error", "-y", "-i", audioURL.path,
                    "-map", "0:a:0", "-vn", "-codec:a", "libmp3lame", "-q:a", "2", "-id3v2_version", "3",
                    "-metadata", "title=\(video.title)", "-metadata", "artist=\(video.artist)", "-metadata", "album=\(video.title)", output.path
                ]
                _ = try MediaProcess.run(ffmpeg, arguments: args)
                outputs = [output]
            }
            return PreparedYouTubeImport(directory: directory, files: outputs)
        } catch {
            try? FileManager.default.removeItem(at: directory)
            throw error
        }
    }

    private static func validatedURL(_ raw: String) -> URL? {
        guard let components = URLComponents(string: raw.trimmingCharacters(in: .whitespacesAndNewlines)),
              components.scheme?.lowercased() == "https",
              let host = components.host?.lowercased(),
              ["youtube.com", "www.youtube.com", "m.youtube.com", "music.youtube.com", "youtu.be", "www.youtube-nocookie.com"].contains(host),
              let url = components.url else { return nil }
        return url
    }
}

private extension String {
    var nonEmpty: String? { isEmpty ? nil : self }
}

enum YouTubeImportError: LocalizedError {
    case invalidURL, invalidVideoInfo(String), noChapters, invalidChapter, downloadOutputMissing

    var errorDescription: String? {
        switch self {
        case .invalidURL: "Bitte eine HTTPS-URL zu einem einzelnen YouTube-Video eingeben. Playlists werden nicht importiert."
        case .invalidVideoInfo(let detail): "Videoinformationen konnten nicht gelesen werden: \(detail)"
        case .noChapters: "Dieses Video enthält keine verwendbaren Kapitel. Importiere es als eine Datei."
        case .invalidChapter: "Mindestens ein Kapitel hat eine ungültige Zeitspanne."
        case .downloadOutputMissing: "yt-dlp hat keine Audiodatei erzeugt."
        }
    }
}