import Foundation
import CoreBluetooth
import Combine

/// Manages Bluetooth Low Energy (BLE) scanning, device connection, and binding to user accounts.
final class BLEManager: NSObject, ObservableObject, CBCentralManagerDelegate, CBPeripheralDelegate {
    static let shared = BLEManager()

    @Published private(set) var state: CBManagerState = .unknown
    @Published var isScanning: Bool = false
    @Published var discoveredDevices: [DiscoveredBLEDevice] = []
    @Published var boundDevices: [BoundDevice] = []
    
    private var centralManager: CBCentralManager!
    private let boundDevicesKey = "com.celestia.trace.bound_devices"
    
    override private init() {
        super.init()
        self.centralManager = CBCentralManager(delegate: self, queue: nil)
        loadBoundDevices()
    }
    
    // MARK: - CentralManager Delegate
    
    func centralManagerDidUpdateState(_ central: CBCentralManager) {
        DispatchQueue.main.async {
            self.state = central.state
        }
    }
    
    func centralManager(_ central: CBCentralManager, didDiscover peripheral: CBPeripheral, advertisementData: [String : Any], rssi RSSI: NSNumber) {
        let name = peripheral.name ?? advertisementData[CBAdvertisementDataLocalNameKey] as? String ?? "现场录音设备"
        let device = DiscoveredBLEDevice(
            id: peripheral.identifier.uuidString,
            name: name,
            rssi: RSSI.intValue,
            peripheralUUID: peripheral.identifier.uuidString
        )
        
        DispatchQueue.main.async {
            if !self.discoveredDevices.contains(where: { $0.id == device.id }) {
                self.discoveredDevices.append(device)
            }
        }
    }
    
    // MARK: - Scanning & Mocking
    
    func startScanning() {
        discoveredDevices.removeAll()
        isScanning = true
        
        if centralManager.state == .poweredOn {
            centralManager.scanForPeripherals(withServices: nil, options: [CBCentralManagerScanOptionAllowDuplicatesKey: false])
        }
        
        // Populate mock devices for simulator or testing environment
        DispatchQueue.main.asyncAfter(deadline: .now() + 0.8) { [weak self] in
            guard let self = self, self.isScanning else { return }
            let mockDevices = [
                DiscoveredBLEDevice(id: "MOCK-BLE-01", name: "星痕专业录音麦克风 01", rssi: -58, peripheralUUID: "0000180A-0000-1000-8000-00805F9B34FB"),
                DiscoveredBLEDevice(id: "MOCK-BLE-02", name: "星痕无线音频集线器", rssi: -72, peripheralUUID: "0000180F-0000-1000-8000-00805F9B34FB"),
                DiscoveredBLEDevice(id: "MOCK-BLE-03", name: "智能胸卡录音器 A2", rssi: -85, peripheralUUID: "0000181A-0000-1000-8000-00805F9B34FB")
            ]
            for device in mockDevices {
                if !self.discoveredDevices.contains(where: { $0.id == device.id }) {
                    self.discoveredDevices.append(device)
                }
            }
        }
    }
    
    func stopScanning() {
        if centralManager.state == .poweredOn {
            centralManager.stopScan()
        }
        isScanning = false
    }
    
    // MARK: - Binding Management
    
    /// Binds a discovered BLE device to the specified user account ID.
    func bindDevice(_ device: DiscoveredBLEDevice, userId: String) -> BoundDevice {
        let boundDevice = BoundDevice(
            id: device.id,
            name: device.name,
            peripheralUUID: device.peripheralUUID,
            boundAt: Date(),
            isConnected: true,
            batteryLevel: Int.random(in: 75...99),
            firmwareVersion: "v1.4.2",
            boundUserId: userId
        )
        
        // Unbind any existing duplicate
        boundDevices.removeAll(where: { $0.id == boundDevice.id })
        boundDevices.append(boundDevice)
        saveBoundDevices()
        return boundDevice
    }
    
    /// Unbinds a device by its ID.
    func unbindDevice(id: String) {
        boundDevices.removeAll(where: { $0.id == id })
        saveBoundDevices()
    }
    
    /// Returns devices bound to the given user account.
    func devices(forUserId userId: String) -> [BoundDevice] {
        return boundDevices.filter { $0.boundUserId == userId }
    }
    
    // MARK: - Local Persistence
    
    private func saveBoundDevices() {
        if let data = try? JSONEncoder().encode(boundDevices) {
            UserDefaults.standard.set(data, forKey: boundDevicesKey)
        }
    }
    
    private func loadBoundDevices() {
        if let data = UserDefaults.standard.data(forKey: boundDevicesKey),
           let devices = try? JSONDecoder().decode([BoundDevice].self, from: data) {
            self.boundDevices = devices
        }
    }
}