//
//  OrderCodeScannerViewController.swift
//  suixinkan
//

import AVFoundation
import SnapKit
import UIKit

/// 订单扫码错误实体，描述相机不可用、权限拒绝和元数据异常。
enum OrderScannerError: LocalizedError {
    case cameraUnavailable
    case permissionDenied
    case invalidMetadata

    var errorDescription: String? {
        switch self {
        case .cameraUnavailable:
            "当前设备不可用相机，无法扫码。"
        case .permissionDenied:
            "未开启相机权限，请在系统设置中允许后重试。"
        case .invalidMetadata:
            "未识别到有效条码，请重试。"
        }
    }
}

/// 订单扫码页，包装 AVFoundation 扫码控制器并提供关闭与结果回调。
final class OrderCodeScannerViewController: UIViewController {

    var onScanResult: ((Result<String, Error>) -> Void)?

    private let scannerController = OrderScannerCaptureViewController()

    override func viewDidLoad() {
        super.viewDidLoad()
        view.backgroundColor = .black
        title = "扫码核销"
        navigationItem.leftBarButtonItem = UIBarButtonItem(title: "关闭", style: .plain, target: self, action: #selector(closeTapped))

        #if targetEnvironment(simulator)
        showUnavailablePlaceholder()
        #else
        if AppUITestLaunchState.isRunningUITests || AVCaptureDevice.default(for: .video) == nil {
            showUnavailablePlaceholder()
        } else {
            embedScanner()
        }
        #endif
    }

    private func embedScanner() {
        scannerController.onScanResult = { [weak self] result in
            self?.onScanResult?(result)
        }
        addChild(scannerController)
        view.addSubview(scannerController.view)
        scannerController.view.snp.makeConstraints { make in
            make.edges.equalToSuperview()
        }
        scannerController.didMove(toParent: self)

        let hintLabel = UILabel()
        hintLabel.text = "请将二维码/条码放入取景框"
        hintLabel.font = .systemFont(ofSize: AppMetrics.FontSize.footnote, weight: .medium)
        hintLabel.textColor = .white
        hintLabel.backgroundColor = UIColor.black.withAlphaComponent(0.55)
        hintLabel.layer.cornerRadius = 16
        hintLabel.clipsToBounds = true
        hintLabel.textAlignment = .center
        view.addSubview(hintLabel)
        hintLabel.snp.makeConstraints { make in
            make.centerX.equalToSuperview()
            make.bottom.equalTo(view.safeAreaLayoutGuide).inset(AppMetrics.Spacing.xxLarge)
            make.height.equalTo(32)
            make.width.greaterThanOrEqualTo(220)
        }
    }

    private func showUnavailablePlaceholder() {
        let stack = UIStackView()
        stack.axis = .vertical
        stack.spacing = AppMetrics.Spacing.small
        stack.alignment = .center

        let icon = UIImageView(image: UIImage(systemName: "camera.viewfinder"))
        icon.tintColor = .white
        icon.contentMode = .scaleAspectFit

        let titleLabel = UILabel()
        titleLabel.text = "当前环境不可用相机"
        titleLabel.font = .systemFont(ofSize: AppMetrics.FontSize.title3, weight: .semibold)
        titleLabel.textColor = .white

        let messageLabel = UILabel()
        messageLabel.text = "请在真机上使用扫码核销"
        messageLabel.font = .systemFont(ofSize: AppMetrics.FontSize.subheadline)
        messageLabel.textColor = UIColor.white.withAlphaComponent(0.72)

        stack.addArrangedSubview(icon)
        stack.addArrangedSubview(titleLabel)
        stack.addArrangedSubview(messageLabel)
        view.addSubview(stack)
        icon.snp.makeConstraints { make in
            make.width.height.equalTo(48)
        }
        stack.snp.makeConstraints { make in
            make.center.equalToSuperview()
        }
    }

    @objc private func closeTapped() {
        dismiss(animated: true)
    }
}

/// AVFoundation 扫码控制器，管理相机权限、预览层、识别类型和手电筒。
final class OrderScannerCaptureViewController: UIViewController, AVCaptureMetadataOutputObjectsDelegate {

    var onScanResult: ((Result<String, Error>) -> Void)?

    private let session = AVCaptureSession()
    private var previewLayer: AVCaptureVideoPreviewLayer?
    private var videoDevice: AVCaptureDevice?
    private var hasFinishedScan = false

    private let scanFrameView: UIView = {
        let view = UIView()
        view.layer.borderColor = UIColor.systemBlue.cgColor
        view.layer.borderWidth = 2
        view.layer.cornerRadius = 12
        view.backgroundColor = .clear
        return view
    }()

    private lazy var torchButton: UIButton = {
        let button = Self.makeScannerButton(title: "手电筒")
        button.addTarget(self, action: #selector(toggleTorch), for: .touchUpInside)
        return button
    }()

    private lazy var retryButton: UIButton = {
        let button = Self.makeScannerButton(title: "重新扫描")
        button.addTarget(self, action: #selector(restartScan), for: .touchUpInside)
        return button
    }()

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

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

    override func viewWillDisappear(_ animated: Bool) {
        super.viewWillDisappear(animated)
        updateTorch(enabled: false)
        stopSession()
    }

    private func checkPermissionAndStart() {
        switch AVCaptureDevice.authorizationStatus(for: .video) {
        case .authorized:
            startSession()
        case .notDetermined:
            AVCaptureDevice.requestAccess(for: .video) { [weak self] granted in
                DispatchQueue.main.async {
                    guard let self else { return }
                    if granted {
                        self.startSession()
                    } else {
                        self.onScanResult?(.failure(OrderScannerError.permissionDenied))
                    }
                }
            }
        case .denied, .restricted:
            onScanResult?(.failure(OrderScannerError.permissionDenied))
        @unknown default:
            onScanResult?(.failure(OrderScannerError.permissionDenied))
        }
    }

    private func startSession() {
        hasFinishedScan = false
        guard !session.isRunning else { return }
        do {
            try configureSession()
        } catch {
            onScanResult?(.failure(error))
            return
        }
        DispatchQueue.global(qos: .userInitiated).async { [weak self] in
            self?.session.startRunning()
        }
    }

    private func stopSession() {
        guard session.isRunning else { return }
        session.stopRunning()
    }

    private static func makeScannerButton(title: String) -> UIButton {
        var config = UIButton.Configuration.filled()
        config.title = title
        config.baseForegroundColor = .white
        config.baseBackgroundColor = UIColor.black.withAlphaComponent(0.42)
        config.cornerStyle = .capsule
        return UIButton(configuration: config)
    }

    private func configureSession() throws {
        if previewLayer != nil { return }
        guard let videoDevice = AVCaptureDevice.default(for: .video) else {
            throw OrderScannerError.cameraUnavailable
        }
        self.videoDevice = videoDevice

        let videoInput = try AVCaptureDeviceInput(device: videoDevice)
        guard session.canAddInput(videoInput) else { throw OrderScannerError.cameraUnavailable }
        session.addInput(videoInput)

        let metadataOutput = AVCaptureMetadataOutput()
        guard session.canAddOutput(metadataOutput) else { throw OrderScannerError.invalidMetadata }
        session.addOutput(metadataOutput)

        metadataOutput.setMetadataObjectsDelegate(self, queue: .main)
        let desiredTypes: [AVMetadataObject.ObjectType] = [.qr, .ean8, .ean13, .pdf417, .code39, .code93, .code128, .dataMatrix, .aztec, .itf14, .upce]
        let supportedTypes = desiredTypes.filter { metadataOutput.availableMetadataObjectTypes.contains($0) }
        guard !supportedTypes.isEmpty else { throw OrderScannerError.invalidMetadata }
        metadataOutput.metadataObjectTypes = supportedTypes

        let preview = AVCaptureVideoPreviewLayer(session: session)
        preview.videoGravity = .resizeAspectFill
        preview.frame = view.layer.bounds
        view.layer.insertSublayer(preview, at: 0)
        previewLayer = preview
        torchButton.isEnabled = videoDevice.hasTorch
    }

    func metadataOutput(_ output: AVCaptureMetadataOutput, didOutput metadataObjects: [AVMetadataObject], from connection: AVCaptureConnection) {
        guard !hasFinishedScan else { return }
        guard let metadataObject = metadataObjects.first as? AVMetadataMachineReadableCodeObject,
              let code = metadataObject.stringValue,
              !code.isEmpty else { return }
        hasFinishedScan = true
        stopSession()
        UINotificationFeedbackGenerator().notificationOccurred(.success)
        onScanResult?(.success(code))
    }

    private func setupControls() {
        view.addSubview(scanFrameView)
        view.addSubview(torchButton)
        view.addSubview(retryButton)

        scanFrameView.snp.makeConstraints { make in
            make.centerX.equalToSuperview()
            make.centerY.equalToSuperview().offset(-40)
            make.width.height.equalTo(240)
        }
        torchButton.snp.makeConstraints { make in
            make.leading.equalTo(view.safeAreaLayoutGuide).inset(16)
            make.bottom.equalTo(view.safeAreaLayoutGuide).inset(18)
        }
        retryButton.snp.makeConstraints { make in
            make.trailing.equalTo(view.safeAreaLayoutGuide).inset(16)
            make.bottom.equalTo(view.safeAreaLayoutGuide).inset(18)
        }
    }

    @objc private func toggleTorch() {
        updateTorch(enabled: !(videoDevice?.isTorchActive ?? false))
    }

    private func updateTorch(enabled: Bool) {
        guard let device = videoDevice, device.hasTorch else { return }
        do {
            try device.lockForConfiguration()
            if enabled {
                try device.setTorchModeOn(level: AVCaptureDevice.maxAvailableTorchLevel)
            } else {
                device.torchMode = .off
            }
            device.unlockForConfiguration()
            torchButton.configuration?.title = enabled ? "关闭手电" : "手电筒"
        } catch {
            torchButton.configuration?.title = "手电筒不可用"
        }
    }

    @objc private func restartScan() {
        hasFinishedScan = false
        updateTorch(enabled: false)
        startSession()
    }
}