nucleic-remote-ios/NucleicRemote/NucleicRemote/Views/PairingScannerView.swift

import SwiftUI
import AVFoundation
import NucleicProtocol

/// Camera QR scanner (UX_IOS §7). Decodes the Mac's `nucleic://pair?d=…` QR into a
/// `PairingPayload` and hands it back exactly once.
struct PairingScannerView: View {
    let onScanned: (PairingPayload) -> Void
    @Environment(\.dismiss) private var dismiss
    @State private var error: String?

    var body: some View {
        NavigationStack {
            ZStack {
                QRScannerRepresentable { value in handle(value) }
                    .ignoresSafeArea()
                VStack {
                    Spacer()
                    RoundedRectangle(cornerRadius: 16)
                        .stroke(.white.opacity(0.8), lineWidth: 3)
                        .frame(width: 240, height: 240)
                    Spacer()
                    if let error {
                        Text(error).foregroundStyle(.white)
                            .padding().background(.red.opacity(0.8), in: Capsule())
                    } else {
                        Text("Point at the QR code on your Mac")
                            .foregroundStyle(.white)
                            .padding().background(.black.opacity(0.5), in: Capsule())
                    }
                    Spacer().frame(height: 40)
                }
            }
            .navigationTitle("Scan to pair")
            .navigationBarTitleDisplayMode(.inline)
            .toolbar { ToolbarItem(placement: .cancellationAction) { Button("Cancel") { dismiss() } } }
        }
    }

    private func handle(_ value: String) {
        guard let payload = try? PairingPayload(qrString: value) else {
            error = "That isn't a Nucleic pairing code"; return
        }
        onScanned(payload)
    }
}

/// UIKit bridge for the AVCaptureSession metadata scan.
struct QRScannerRepresentable: UIViewControllerRepresentable {
    let onFound: (String) -> Void

    func makeUIViewController(context: Context) -> QRScannerController {
        let controller = QRScannerController()
        controller.onFound = onFound
        return controller
    }
    func updateUIViewController(_ controller: QRScannerController, context: Context) {}
}

final class QRScannerController: UIViewController, AVCaptureMetadataOutputObjectsDelegate {
    var onFound: ((String) -> Void)?
    private let session = AVCaptureSession()
    private var didFind = false

    override func viewDidLoad() {
        super.viewDidLoad()
        guard let device = AVCaptureDevice.default(for: .video),
              let input = try? AVCaptureDeviceInput(device: device),
              session.canAddInput(input) else { return }
        session.addInput(input)

        let output = AVCaptureMetadataOutput()
        guard session.canAddOutput(output) else { return }
        session.addOutput(output)
        output.setMetadataObjectsDelegate(self, queue: .main)
        output.metadataObjectTypes = [.qr]

        let preview = AVCaptureVideoPreviewLayer(session: session)
        preview.videoGravity = .resizeAspectFill
        preview.frame = view.layer.bounds
        view.layer.addSublayer(preview)

        Task.detached { [session] in session.startRunning() }
    }

    override func viewDidDisappear(_ animated: Bool) {
        super.viewDidDisappear(animated)
        session.stopRunning()
    }

    func metadataOutput(
        _ output: AVCaptureMetadataOutput,
        didOutput metadataObjects: [AVMetadataObject],
        from connection: AVCaptureConnection
    ) {
        guard !didFind,
              let object = metadataObjects.first as? AVMetadataMachineReadableCodeObject,
              let value = object.stringValue else { return }
        didFind = true
        onFound?(value)
    }
}