import AVFoundation
import SwiftUI

/// Camera-based QR scanner for pairing codes.
struct QRScannerView: UIViewControllerRepresentable {
    let onScan: (String) -> Void

    func makeUIViewController(context: Context) -> ScannerViewController {
        let controller = ScannerViewController()
        controller.onScan = onScan
        return controller
    }

    func updateUIViewController(_ controller: ScannerViewController, context: Context) {}
}

final class ScannerViewController: UIViewController, @preconcurrency AVCaptureMetadataOutputObjectsDelegate {
    var onScan: ((String) -> Void)?

    private let session = AVCaptureSession()
    private var previewLayer: AVCaptureVideoPreviewLayer?
    private var didScan = false

    override func viewDidLoad() {
        super.viewDidLoad()
        view.backgroundColor = .black

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

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

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

    override func viewDidLayoutSubviews() {
        super.viewDidLayoutSubviews()
        previewLayer?.frame = view.bounds
    }

    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        didScan = false
        let session = session
        DispatchQueue.global(qos: .userInitiated).async {
            if !session.isRunning {
                session.startRunning()
            }
        }
    }

    override func viewWillDisappear(_ animated: Bool) {
        super.viewWillDisappear(animated)
        let session = session
        DispatchQueue.global(qos: .userInitiated).async {
            if session.isRunning {
                session.stopRunning()
            }
        }
    }

    func metadataOutput(
        _ output: AVCaptureMetadataOutput,
        didOutput metadataObjects: [AVMetadataObject],
        from connection: AVCaptureConnection
    ) {
        guard !didScan,
            let object = metadataObjects.first as? AVMetadataMachineReadableCodeObject,
            object.type == .qr,
            let value = object.stringValue
        else { return }
        didScan = true
        UINotificationFeedbackGenerator().notificationOccurred(.success)
        onScan?(value)
    }

    private func showUnavailableLabel() {
        let label = UILabel()
        label.text = "Camera unavailable"
        label.textColor = .white
        label.textAlignment = .center
        label.frame = view.bounds
        label.autoresizingMask = [.flexibleWidth, .flexibleHeight]
        view.addSubview(label)
    }
}