import Foundation

private struct StreamResolutionError: LocalizedError {
    let message: String
    var errorDescription: String? { message }
}

enum StreamURL: Sendable {
    case youtube(URL)
    case miruro(mediaID: String, episode: Int)

    static func parse(_ text: String) throws -> StreamURL {
        let text = text.trimmingCharacters(in: .whitespacesAndNewlines)
        if let url = try? YouTubeResolver.validateURL(text) { return .youtube(url) }
        let invalid = StreamResolutionError(message: "Enter a YouTube video URL or a Miruro episode URL from barelystarted.miruro.tv.")
        guard !text.unicodeScalars.contains(where: {
            CharacterSet.whitespacesAndNewlines.contains($0) || CharacterSet.controlCharacters.contains($0)
        }), let components = URLComponents(string: text),
              components.scheme?.lowercased() == "https",
              components.host?.lowercased() == "barelystarted.miruro.tv",
              components.user == nil, components.password == nil,
              components.port == nil || components.port == 443,
              components.fragment == nil,
              components.percentEncodedPath == components.path,
              components.url != nil else { throw invalid }
        let path = components.path.split(separator: "/", omittingEmptySubsequences: false)
        guard path.count == 4, path[0].isEmpty, path[1] == "watch",
              !path[3].isEmpty, path[3].utf8.count <= 512,
              path[3].utf8.allSatisfy({ isSegmentByte($0) }),
              let query = components.queryItems, query.count == 1, query[0].name == "ep",
              let number = query[0].value, let episode = Int(number),
              components.percentEncodedQuery == "ep=\(episode)",
              ResolvedSource.validIdentity(mediaID: String(path[2]), episode: episode) else { throw invalid }
        return .miruro(mediaID: String(path[2]), episode: episode)
    }

    private static func isSegmentByte(_ byte: UInt8) -> Bool {
        (65...90).contains(byte) || (97...122).contains(byte) ||
            (48...57).contains(byte) || byte == 45 || byte == 95
    }
}

enum MiruroResolver {
    static let bodyLimit = 2 * 1024 * 1024

    static func resolve(mediaID: String, episode: Int) async throws -> ResolvedSource {
        try Task.checkCancellation()
        guard ResolvedSource.validIdentity(mediaID: mediaID, episode: episode) else {
            throw StreamResolutionError(message: "Invalid Miruro episode identity.")
        }
        var components = URLComponents(string: "https://barelystarted.miruro.tv/api/sources")!
        components.queryItems = [URLQueryItem(name: "id", value: mediaID), URLQueryItem(name: "n", value: String(episode))]
        var request = URLRequest(url: components.url!)
        request.timeoutInterval = 25
        request.setValue("application/json", forHTTPHeaderField: "Accept")
        let configuration = URLSessionConfiguration.ephemeral
        configuration.timeoutIntervalForRequest = 25
        configuration.timeoutIntervalForResource = 25
        configuration.httpShouldSetCookies = false
        configuration.httpCookieStorage = nil
        configuration.urlCache = nil
        let session = URLSession(configuration: configuration, delegate: MiruroRedirectPolicy(), delegateQueue: nil)
        defer { session.invalidateAndCancel() }
        do {
            let (bytes, response) = try await session.bytes(for: request)
            try validateResponse(response)
            var data = Data()
            if response.expectedContentLength > 0 { data.reserveCapacity(Int(response.expectedContentLength)) }
            for try await byte in bytes {
                try Task.checkCancellation()
                guard data.count < bodyLimit else {
                    throw StreamResolutionError(message: "Miruro source response exceeded 2 MiB.")
                }
                data.append(byte)
            }
            try Task.checkCancellation()
            return try decode(data, mediaID: mediaID, episode: episode)
        } catch {
            if Task.isCancelled || error is CancellationError || (error as? URLError)?.code == .cancelled {
                throw CancellationError()
            }
            if let error = error as? StreamResolutionError { throw error }
            throw StreamResolutionError(message: "Miruro request failed or timed out. No retry was attempted.")
        }
    }

    static func validateResponse(_ response: URLResponse) throws {
        guard let response = response as? HTTPURLResponse else {
            throw StreamResolutionError(message: "Miruro returned an invalid HTTP response.")
        }
        guard response.statusCode == 200 else {
            throw StreamResolutionError(message: "Miruro HTTP \(response.statusCode). No retry was attempted.")
        }
        guard response.mimeType?.lowercased() == "application/json" else {
            throw StreamResolutionError(message: "Miruro returned an unexpected content type; protection pages are not supported.")
        }
        guard response.expectedContentLength <= Int64(bodyLimit) else {
            throw StreamResolutionError(message: "Miruro source response exceeded 2 MiB.")
        }
    }

    // Match Tubular's direct ssub/Sun projection, without provider or server retry.
    static func decode(_ data: Data, mediaID: String, episode: Int) throws -> ResolvedSource {
        do {
            guard data.count <= bodyLimit,
                  ResolvedSource.validIdentity(mediaID: mediaID, episode: episode) else { throw InvalidProjection() }
            let response = try JSONDecoder().decode(Sources.self, from: data)
            guard response.episodeNumber == episode else { throw InvalidProjection() }
            let config = response.config.sun
            guard config.player == "native", !config.proxy,
                  config.hls?.segments?.enabled != true, config.hls?.query?.enabled != true else {
                throw StreamResolutionError(message: "Miruro Sun requires unsupported proxy or HLS rewriting.")
            }
            guard let provider = response.tracks.first(where: { $0.track == "ssub" })?
                .providers.first(where: { $0.provider == "sun" }),
                  let server = provider.servers.first(where: { !$0.streams.isEmpty }),
                  let stream = server.streams.first else {
                throw StreamResolutionError(message: "Direct Miruro Sun soft-subtitle source is unavailable.")
            }
            guard ["hls", "m3u8", "application/vnd.apple.mpegurl", "application/x-mpegurl"].contains(stream.format),
                  !stream.hasEmbed else { throw InvalidProjection() }
            let headers = server.headers ?? [:]
            var subtitles: [ResolvedSubtitle] = []
            for subtitle in provider.subtitles where subtitle.format == "vtt" {
                guard subtitles.count < 32 else { throw InvalidProjection() }
                subtitles.append(ResolvedSubtitle(url: subtitle.file, format: subtitle.format, language: subtitle.language,
                    label: subtitle.label, isDefault: subtitle.default, headers: headers))
            }
            return try ResolvedSource.validated(.init(version: 1, url: stream.url, headers: headers,
                identity: .init(provider: "miruro", media_id: mediaID, episode: episode),
                title: nil, subtitles: subtitles))
        } catch {
            if let error = error as? StreamResolutionError { throw error }
            throw StreamResolutionError(message: "Miruro returned invalid or unsupported source metadata.")
        }
    }

    private struct InvalidProjection: Error {}
    private struct Sources: Decodable {
        let episodeNumber: Int
        let tracks: [Track]
        let config: Config
    }
    private struct Config: Decodable { let sun: ProviderConfig }
    private struct ProviderConfig: Decodable {
        let player: String
        let proxy: Bool
        let hls: HLS?
    }
    private struct HLS: Decodable {
        struct Rule: Decodable { let enabled: Bool? }
        let segments: Rule?
        let query: Rule?
    }
    private struct Track: Decodable {
        let track: String
        let providers: [Provider]
    }
    private struct Provider: Decodable {
        let provider: String
        let servers: [Server]
        let subtitles: [Subtitle]
    }
    private struct Server: Decodable {
        let headers: [String: String]?
        let streams: [Stream]
    }
    private struct Stream: Decodable {
        let url: String
        let format: String
        let hasEmbed: Bool
        enum CodingKeys: String, CodingKey { case url, format, embed }
        init(from decoder: Decoder) throws {
            let values = try decoder.container(keyedBy: CodingKeys.self)
            url = try values.decode(String.self, forKey: .url)
            format = try values.decode(String.self, forKey: .format)
            if values.contains(.embed) {
                hasEmbed = try !values.decodeNil(forKey: .embed)
            } else {
                hasEmbed = false
            }
        }
    }
    private struct Subtitle: Decodable {
        let file: String
        let format: String
        let language: String
        let label: String
        let `default`: Bool
    }
}

private final class MiruroRedirectPolicy: NSObject, URLSessionTaskDelegate, @unchecked Sendable {
    func urlSession(_ session: URLSession, task: URLSessionTask,
                    willPerformHTTPRedirection response: HTTPURLResponse, newRequest request: URLRequest,
                    completionHandler: @escaping (URLRequest?) -> Void) {
        completionHandler(nil)
    }
}