terebi/Sources/App/CastMediaServer.swift

import Foundation

struct CastMediaInput: Sendable {
    let videoURL: String
    let videoHeaders: String
    let audioURL: String?
    let audioHeaders: String?
    let local: Bool
    let restricted: Bool
    let live: Bool
    let duration: Double
    let subtitles: [ResolvedSubtitle]
}

struct CastMediaDescription: Sendable {
    let url: URL
    let contentType: String
    let duration: Double
    let live: Bool
    let tracks: [CastTextTrack]
}

struct CastTextTrack: Sendable {
    let id: Int
    let url: URL
    let language: String
    let label: String
}

private struct CastDeliveryError: LocalizedError {
    let errorDescription: String? = "Could not deliver cast media. Check the connection and media compatibility. Private details are redacted."
}

// A start task retains this owner until native probing returns. Cancellation never
// frees a handle in use; destruction and worker joins always run off the main actor.
private final class CastMediaLifetime: @unchecked Sendable {
    let handle: OpaquePointer
    init(input: CastMediaInput) throws {
        var error = [CChar](repeating: 0, count: 512)
        let result = input.videoURL.withCString { video in
            input.videoHeaders.withCString { headers in
                (input.audioURL ?? "").withCString { audio in
                    (input.audioHeaders ?? "").withCString { audioHeaders in
                        var source = CastMediaSource(video_url: video, video_headers: headers,
                            audio_url: audio, audio_headers: audioHeaders, local: input.local,
                            restricted: input.restricted, live: input.live, duration: input.duration)
                        return cast_media_create(&source, &error)
                    }
                }
            }
        }
        guard let result else { throw CastDeliveryError() }
        handle = result
    }
    func cancel() { cast_media_cancel(handle) }
    func start(host: String) throws -> (String, Double) {
        var url = [CChar](repeating: 0, count: 512)
        var error = [CChar](repeating: 0, count: 512)
        var duration = 0.0
        guard host.withCString({ cast_media_start(handle, $0, &url, &duration, &error) }) else {
            throw CastDeliveryError()
        }
        return (url.withUnsafeBufferPointer { String(cString: $0.baseAddress!) }, duration)
    }
    func subtitle(id: Int, data: Data) throws -> URL {
        var url = [CChar](repeating: 0, count: 512)
        let success = data.withUnsafeBytes {
            cast_media_subtitle(handle, Int32(id), $0.baseAddress, $0.count, &url)
        }
        guard success, let result = URL(string: url.withUnsafeBufferPointer { String(cString: $0.baseAddress!) }) else { throw CastDeliveryError() }
        return result
    }
    deinit {
        // Capture an explicitly Sendable owner instead of crossing an actor with a pointer.
        let cleanup = CastMediaCleanup(handle: handle)
        DispatchQueue.global(qos: .utility).async { cast_media_destroy(cleanup.handle) }
    }
}
private struct CastMediaCleanup: @unchecked Sendable { let handle: OpaquePointer }

@MainActor final class CastMediaServer {
    private var lifetime: CastMediaLifetime?
    private var operation: Task<CastMediaDescription, Error>?

    init() {}

    func start(input: CastMediaInput, receiverHost: String) async throws -> CastMediaDescription {
        stop()
        guard input.subtitles.count <= 32 else { throw CastDeliveryError() }
        let owner = try CastMediaLifetime(input: input)
        lifetime = owner
        let task = Task.detached(priority: .userInitiated) {
            do {
                let (text, duration) = try owner.start(host: receiverHost)
                try Task.checkCancellation()
                guard let url = URL(string: text) else { throw CastDeliveryError() }
                var tracks: [CastTextTrack] = []
                for (index, subtitle) in input.subtitles.enumerated() {
                    try Task.checkCancellation()
                    let data = try await WebVTTDocument.loadData(url: subtitle.url, headers: subtitle.headers)
                    guard let text = String(data: data, encoding: .utf8) else { throw CastDeliveryError() }
                    _ = try WebVTTDocument.parse(text)
                    let trackURL = try owner.subtitle(id: index + 1, data: data)
                    tracks.append(CastTextTrack(id: index + 1, url: trackURL,
                        language: subtitle.language, label: subtitle.label))
                }
                try Task.checkCancellation()
                return CastMediaDescription(url: url, contentType: "application/vnd.apple.mpegurl",
                    duration: duration, live: input.live, tracks: tracks)
            } catch {
                owner.cancel()
                if Task.isCancelled { throw CancellationError() }
                throw CastDeliveryError()
            }
        }
        operation = task
        do {
            let result = try await withTaskCancellationHandler {
                try await task.value
            } onCancel: {
                owner.cancel()
                task.cancel()
            }
            guard lifetime === owner else { throw CancellationError() }
            operation = nil
            return result
        } catch {
            if lifetime === owner { stop() }
            if error is CancellationError { throw error }
            throw CastDeliveryError()
        }
    }

    func stop() {
        operation?.cancel()
        operation = nil
        lifetime?.cancel()
        lifetime = nil
    }

    deinit {
        operation?.cancel()
        lifetime?.cancel()
    }
}