import UserNotifications

/// Rich (image) push — see docs/api/push-notifications-integration-guide.md §4.3.
/// Only fires when Atomenta's push payload sets `"mutable-content": 1`, which
/// it does by default on any push carrying an image (real wire key is
/// `"image"`, not the guide's `"imageUrl"` — verified against
/// `PushNotificationService.dispatchApns`/`dispatchApnsMany` in Atomenta).
/// `@unchecked Sendable`: the extension process only ever runs one
/// `didReceive`/`serviceExtensionTimeWillExpire` cycle at a time — there's no
/// real concurrent access to `contentHandler`/`bestAttemptContent` to guard
/// against, just a background download completion handing back to this
/// instance.
final class NotificationService: UNNotificationServiceExtension, @unchecked Sendable {
    private var contentHandler: ((UNNotificationContent) -> Void)?
    private var bestAttemptContent: UNMutableNotificationContent?

    override func didReceive(_ request: UNNotificationRequest, withContentHandler contentHandler: @escaping (UNNotificationContent) -> Void) {
        self.contentHandler = contentHandler
        let mutableContent = (request.content.mutableCopy() as? UNMutableNotificationContent) ?? UNMutableNotificationContent()
        bestAttemptContent = mutableContent

        guard let imageURLString = request.content.userInfo["image"] as? String,
              let imageURL = URL(string: imageURLString) else {
            deliver()
            return
        }

        URLSession.shared.downloadTask(with: imageURL) { [weak self] location, _, _ in
            if let location, let attachment = Self.attachment(fromDownloadedFile: location) {
                self?.bestAttemptContent?.attachments = [attachment]
            }
            self?.deliver()
        }.resume()
    }

    /// The system calls this if `didReceive` doesn't finish within its time
    /// budget — must still deliver the best content built so far, since
    /// `contentHandler` is contractually required to run exactly once.
    override func serviceExtensionTimeWillExpire() {
        deliver()
    }

    private func deliver() {
        guard let bestAttemptContent else { return }
        contentHandler?(bestAttemptContent)
        contentHandler = nil
    }

    private static func attachment(fromDownloadedFile location: URL) -> UNNotificationAttachment? {
        let tmpURL = FileManager.default.temporaryDirectory
            .appendingPathComponent(UUID().uuidString)
            .appendingPathExtension("jpg")
        do {
            try FileManager.default.moveItem(at: location, to: tmpURL)
            return try UNNotificationAttachment(identifier: "image", url: tmpURL)
        } catch {
            return nil
        }
    }
}