import SwiftUI
import VisionKit

/// Wraps `VNDocumentCameraViewController` (the system document-scanning
/// camera UI) for SwiftUI. Only the first scanned page is used for v1 — good
/// enough for a single-receipt photo, and the backend already accepts a
/// single image per `/api/scan` call.
///
/// IMPORTANT: `VNDocumentCameraViewController.isSupported` is `false` on the
/// Simulator and on devices without a usable camera. Callers must check that
/// before presenting this view and fall back to the photo picker instead —
/// this type does not check it itself.
struct DocumentCameraView: UIViewControllerRepresentable {
    /// Called exactly once with the captured page, or `nil` if the user
    /// cancelled or the scan failed. Never left uncalled, so the caller never
    /// hangs waiting on a result.
    var onComplete: (UIImage?) -> Void

    func makeUIViewController(context: Context) -> VNDocumentCameraViewController {
        let controller = VNDocumentCameraViewController()
        controller.delegate = context.coordinator
        return controller
    }

    func updateUIViewController(_ uiViewController: VNDocumentCameraViewController, context: Context) {
        // No dynamic updates needed.
    }

    func makeCoordinator() -> Coordinator {
        Coordinator(onComplete: onComplete)
    }

    final class Coordinator: NSObject, VNDocumentCameraViewControllerDelegate {
        private let onComplete: (UIImage?) -> Void

        init(onComplete: @escaping (UIImage?) -> Void) {
            self.onComplete = onComplete
        }

        func documentCameraViewController(
            _ controller: VNDocumentCameraViewController,
            didFinishWith scan: VNDocumentCameraScan
        ) {
            let image = scan.pageCount > 0 ? scan.imageOfPage(at: 0) : nil
            controller.dismiss(animated: true) {
                self.onComplete(image)
            }
        }

        func documentCameraViewControllerDidCancel(_ controller: VNDocumentCameraViewController) {
            controller.dismiss(animated: true) {
                self.onComplete(nil)
            }
        }

        func documentCameraViewController(
            _ controller: VNDocumentCameraViewController,
            didFailWithError error: Error
        ) {
            controller.dismiss(animated: true) {
                self.onComplete(nil)
            }
        }
    }
}