jacobsapps

@main
struct FakeTwitterApp: App {
    @UIApplicationDelegateAdaptor(FakeTwitterAppDelegate.self) private var appDelegate

    private let modelContainer: ModelContainer
    private let level4Engine: UploadJobEngine

    init() {
        let schema = Schema([PersistedUploadJob.self])
        let configuration = ModelConfiguration(schema: schema, isStoredInMemoryOnly: false)

jacobsapps

private func processQueueIfNeeded() async {
    guard !isProcessing else { return }
    isProcessing = true
    defer { isProcessing = false }

    while let nextJob = fetchNextOutstandingJobSnapshot() {
        do {
            try withJob(nextJob.id) { _, job in
                job.state = .uploading
                job.attempts += 1

jacobsapps

func postTweet(
    text: String,
    strategy _: RetryStrategy,
    retryOptions _: RetryOptions
) async throws {
    await engine.enqueue(text: text)
}

func enqueue(text: String) async {
    let context = ModelContext(container)

jacobsapps

enum UploadJobState: String, Codable {
    case pending
    case uploading
    case succeeded
    case failed
}

@Model
final class PersistedUploadJob {
    @Attribute(.unique) var id: UUID

jacobsapps

final class FakeTwitterAppDelegate: NSObject, UIApplicationDelegate {
    func application(
        _ application: UIApplication,
        handleEventsForBackgroundURLSession identifier: String,
        completionHandler: @escaping () -> Void
    ) {
        guard identifier == BackgroundSessionCoordinator.backgroundSessionIdentifier else {
            completionHandler()
            return
        }

jacobsapps

func uploadChunks(videoURL: URL, sessionId: String, fileSize: Int64) async throws {
    var offset: Int64 = 0
    let chunkSize: Int64 = 512 * 1024

    while offset < fileSize {
        let handle = try FileHandle(forReadingFrom: videoURL)
        defer { try? handle.close() }
        try handle.seek(toOffset: UInt64(offset))
        let chunkData = try handle.read(upToCount: Int(min(chunkSize, fileSize - offset))) ?? Data()

jacobsapps

private lazy var session: URLSession = {
    let configuration = URLSessionConfiguration.background(withIdentifier: Self.backgroundSessionIdentifier)
    configuration.isDiscretionary = false
    configuration.sessionSendsLaunchEvents = true
    configuration.waitsForConnectivity = true
    configuration.timeoutIntervalForRequest = 120
    return URLSession(configuration: configuration, delegate: self, delegateQueue: .main)
}()

jacobsapps

func resumableUpload(videoURL: URL, sessionId: String, fileSize: Int64) async throws {
    var offset = max(
        startResponse.nextOffset,
        await offsetStore.offset(for: sessionId)
    )

    while offset < fileSize {
        do {
            let chunkFile = try temporaryChunkFile(
                sourceVideoURL: videoURL, offset: offset, length: Int(chunkSize)

jacobsapps

private func makeChunkRequest(sessionId: String, offset: Int64, totalBytes: Int64) -> URLRequest {
    var request = URLRequest(url: url("level3/uploads/\(sessionId)/chunk"))
    request.httpMethod = "PUT"
    request.setValue("application/octet-stream", forHTTPHeaderField: "Content-Type")
    request.setValue("\(offset)", forHTTPHeaderField: "Upload-Offset")
    request.setValue("\(totalBytes)", forHTTPHeaderField: "Upload-Length")
    return request
}

jacobsapps

private func makeIdempotencyKey(enabled: Bool) -> String? {
    guard enabled else { return nil }
    let key = UUID().uuidString
    return key
}

private func makePostRequest(text: String, idempotencyKey: String?) throws -> URLRequest {
    var request = makeRequest(path: "level2/tweets", method: "POST")
    request.setValue("application/json", forHTTPHeaderField: "Content-Type")
    if let idempotencyKey {