import AVFoundation
import Combine
import SwiftUI
#if os(iOS)
import UIKit
#elseif os(macOS)
import AppKit
#endif

struct QRScannerSheet: View {
    let seededPayload: String
    let title: String
    let description: String
    let navigationTitleText: String
    let onCodeScanned: (String) -> Void

    @Environment(\.dismiss) private var dismiss
    @Environment(\.horizontalSizeClass) private var horizontalSizeClass
    @State private var manualFallback = ""

    init(
        seededPayload: String,
        title: String = "Scan QR",
        description: String = "Use the camera to scan an idp.global QR challenge.",
        navigationTitle: String = "Scan QR",
        onCodeScanned: @escaping (String) -> Void
    ) {
        self.seededPayload = seededPayload
        self.title = title
        self.description = description
        self.navigationTitleText = navigationTitle
        self.onCodeScanned = onCodeScanned
    }

    var body: some View {
        NavigationStack {
            AppScrollScreen(compactLayout: compactLayout) {
                AppSectionCard(title: title, compactLayout: compactLayout) {
                    Text(description)
                        .font(.subheadline)
                        .foregroundStyle(.secondary)

                    LiveQRScannerView(onCodeScanned: onCodeScanned)
                        .frame(minHeight: 340)
                }

                AppSectionCard(title: "Manual fallback", compactLayout: compactLayout) {
                    AppTextEditorField(text: $manualFallback, minHeight: 120)

                    if compactLayout {
                        VStack(spacing: 12) {
                            useFallbackButton
                            useSeededButton
                        }
                    } else {
                        HStack(spacing: 12) {
                            useFallbackButton
                            useSeededButton
                        }
                    }
                }
            }
            .navigationTitle(navigationTitleText)
            .toolbar {
                ToolbarItem(placement: .cancellationAction) {
                    Button("Close") {
                        dismiss()
                    }
                }
            }
            .onAppear {
                manualFallback = seededPayload
            }
        }
    }

    private var compactLayout: Bool {
        #if os(iOS)
        horizontalSizeClass == .compact
        #else
        false
        #endif
    }

    private var useFallbackButton: some View {
        Button {
            let chosen = manualFallback.trimmingCharacters(in: .whitespacesAndNewlines)
            onCodeScanned(chosen.isEmpty ? seededPayload : chosen)
            dismiss()
        } label: {
            Label("Use payload", systemImage: "arrow.up.forward.square")
                .frame(maxWidth: .infinity)
        }
        .buttonStyle(.borderedProminent)
    }

    private var useSeededButton: some View {
        Button {
            manualFallback = seededPayload
        } label: {
            Label("Reset sample", systemImage: "wand.and.rays")
                .frame(maxWidth: .infinity)
        }
        .buttonStyle(.bordered)
    }
}

private struct LiveQRScannerView: View {
    let onCodeScanned: (String) -> Void

    @StateObject private var scanner = QRScannerViewModel()

    var body: some View {
        ZStack(alignment: .bottomLeading) {
            Group {
                if scanner.isPreviewAvailable {
                    ScannerPreview(session: scanner.captureSession)
                        .clipShape(RoundedRectangle(cornerRadius: 30, style: .continuous))
                } else {
                    RoundedRectangle(cornerRadius: 30, style: .continuous)
                        .fill(Color.black.opacity(0.86))

                    VStack(alignment: .leading, spacing: 12) {
                        Image(systemName: "video.slash.fill")
                            .font(.system(size: 28, weight: .semibold))
                            .foregroundStyle(.white)
                        Text("Live camera preview unavailable")
                            .font(.title3.weight(.semibold))
                            .foregroundStyle(.white)
                        Text(scanner.statusMessage)
                            .foregroundStyle(.white.opacity(0.78))
                    }
                    .padding(24)
                }
            }

            RoundedRectangle(cornerRadius: 30, style: .continuous)
                .strokeBorder(.white.opacity(0.22), lineWidth: 1.5)

            VStack(alignment: .leading, spacing: 8) {
                Text("Camera Scanner")
                    .font(.headline.weight(.semibold))
                    .foregroundStyle(.white)
                Text(scanner.statusMessage)
                    .foregroundStyle(.white.opacity(0.84))
            }
            .padding(22)

            ScanFrameOverlay()
                .padding(40)
        }
        .task {
            scanner.onCodeScanned = { payload in
                onCodeScanned(payload)
            }
            await scanner.start()
        }
        .onDisappear {
            scanner.stop()
        }
    }
}

private struct ScanFrameOverlay: View {
    var body: some View {
        GeometryReader { geometry in
            let size = min(geometry.size.width, geometry.size.height) * 0.5

            RoundedRectangle(cornerRadius: 28, style: .continuous)
                .strokeBorder(.white.opacity(0.82), style: StrokeStyle(lineWidth: 3, dash: [10, 8]))
                .frame(width: size, height: size)
                .position(x: geometry.size.width / 2, y: geometry.size.height / 2)
        }
        .allowsHitTesting(false)
    }
}

private final class QRScannerViewModel: NSObject, ObservableObject, AVCaptureMetadataOutputObjectsDelegate {
    @Published var isPreviewAvailable = false
    @Published var statusMessage = "Point the camera at the QR code from the idp.global web portal."

    let captureSession = AVCaptureSession()

    var onCodeScanned: ((String) -> Void)?

    private let queue = DispatchQueue(label: "global.idp.qrscanner")
    private var isConfigured = false
    private var hasDeliveredCode = false

    func start() async {
        #if os(iOS) && targetEnvironment(simulator)
        await MainActor.run {
            isPreviewAvailable = false
            statusMessage = "The iOS simulator has no live camera feed. Use the seeded payload below."
        }
        #else
        #endif

        #if !(os(iOS) && targetEnvironment(simulator))
        let authorization = AVCaptureDevice.authorizationStatus(for: .video)
        switch authorization {
        case .authorized:
            await configureIfNeeded()
            startRunning()
        case .notDetermined:
            let granted = await requestCameraAccess()
            await MainActor.run {
                self.statusMessage = granted
                    ? "Point the camera at the QR code from the idp.global web portal."
                    : "Camera access was denied. Use the fallback payload below."
            }
            guard granted else { return }
            await configureIfNeeded()
            startRunning()
        case .denied, .restricted:
            await MainActor.run {
                isPreviewAvailable = false
                statusMessage = "Camera access is unavailable. Use the fallback payload below."
            }
        @unknown default:
            await MainActor.run {
                isPreviewAvailable = false
                statusMessage = "Camera access could not be initialized on this device."
            }
        }
        #endif
    }

    func stop() {
        queue.async {
            if self.captureSession.isRunning {
                self.captureSession.stopRunning()
            }
        }
    }

    func metadataOutput(
        _ output: AVCaptureMetadataOutput,
        didOutput metadataObjects: [AVMetadataObject],
        from connection: AVCaptureConnection
    ) {
        guard !hasDeliveredCode,
              let readable = metadataObjects.first as? AVMetadataMachineReadableCodeObject,
              readable.type == .qr,
              let payload = readable.stringValue else {
            return
        }

        hasDeliveredCode = true
        stop()

        #if os(iOS)
        UINotificationFeedbackGenerator().notificationOccurred(.success)
        #endif

        DispatchQueue.main.async { [onCodeScanned] in
            onCodeScanned?(payload)
        }
    }

    private func requestCameraAccess() async -> Bool {
        await withCheckedContinuation { continuation in
            AVCaptureDevice.requestAccess(for: .video) { granted in
                continuation.resume(returning: granted)
            }
        }
    }

    private func configureIfNeeded() async {
        guard !isConfigured else {
            await MainActor.run {
                self.isPreviewAvailable = true
            }
            return
        }

        await withCheckedContinuation { (continuation: CheckedContinuation<Void, Never>) in
            queue.async {
                self.captureSession.beginConfiguration()
                defer {
                    self.captureSession.commitConfiguration()
                    continuation.resume()
                }

                guard let device = AVCaptureDevice.default(for: .video),
                      let input = try? AVCaptureDeviceInput(device: device),
                      self.captureSession.canAddInput(input) else {
                    DispatchQueue.main.async {
                        self.isPreviewAvailable = false
                        self.statusMessage = "No compatible camera was found. Use the fallback payload below."
                    }
                    return
                }

                self.captureSession.addInput(input)

                let output = AVCaptureMetadataOutput()
                guard self.captureSession.canAddOutput(output) else {
                    DispatchQueue.main.async {
                        self.isPreviewAvailable = false
                        self.statusMessage = "Unable to configure QR metadata scanning on this device."
                    }
                    return
                }

                self.captureSession.addOutput(output)
                output.setMetadataObjectsDelegate(self, queue: DispatchQueue.main)
                output.metadataObjectTypes = [.qr]
                self.isConfigured = true

                DispatchQueue.main.async {
                    self.isPreviewAvailable = true
                    self.statusMessage = "Point the camera at the QR code from the idp.global web portal."
                }
            }
        }
    }

    private func startRunning() {
        queue.async {
            guard !self.captureSession.isRunning else { return }
            self.hasDeliveredCode = false
            self.captureSession.startRunning()
        }
    }
}

extension QRScannerViewModel: @unchecked Sendable {}

#if os(iOS)
private struct ScannerPreview: UIViewRepresentable {
    let session: AVCaptureSession

    func makeUIView(context: Context) -> ScannerPreviewUIView {
        let view = ScannerPreviewUIView()
        view.previewLayer.session = session
        view.previewLayer.videoGravity = .resizeAspectFill
        return view
    }

    func updateUIView(_ uiView: ScannerPreviewUIView, context: Context) {
        uiView.previewLayer.session = session
    }
}

private final class ScannerPreviewUIView: UIView {
    override class var layerClass: AnyClass {
        AVCaptureVideoPreviewLayer.self
    }

    var previewLayer: AVCaptureVideoPreviewLayer {
        layer as! AVCaptureVideoPreviewLayer
    }
}
#elseif os(macOS)
private struct ScannerPreview: NSViewRepresentable {
    let session: AVCaptureSession

    func makeNSView(context: Context) -> ScannerPreviewNSView {
        let view = ScannerPreviewNSView()
        view.attach(session: session)
        return view
    }

    func updateNSView(_ nsView: ScannerPreviewNSView, context: Context) {
        nsView.attach(session: session)
    }
}

private final class ScannerPreviewNSView: NSView {
    private var previewLayer: AVCaptureVideoPreviewLayer?

    override init(frame frameRect: NSRect) {
        super.init(frame: frameRect)
        wantsLayer = true
    }

    required init?(coder: NSCoder) {
        super.init(coder: coder)
        wantsLayer = true
    }

    func attach(session: AVCaptureSession) {
        let layer = previewLayer ?? AVCaptureVideoPreviewLayer(session: session)
        layer.session = session
        layer.videoGravity = .resizeAspectFill
        self.layer = layer
        previewLayer = layer
    }
}
#endif