import CoreBluetooth

final class BluetoothManager: NSObject, CBCentralManagerDelegate {
    private var centralManager: CBCentralManager!
    private var discoveredPeripheral: CBPeripheral?

    override init() {
        super.init()
        centralManager = CBCentralManager(delegate: self, queue: nil)
    }

    func centralManagerDidUpdateState(_ central: CBCentralManager) {
        guard central.state == .poweredOn else { return }
        startScanning()
    }
}

let heartRateServiceUUID = CBUUID(string: "180D")

func startScanning() {
    centralManager.scanForPeripherals(
        withServices: [heartRateServiceUUID],
        options: [CBCentralManagerScanOptionAllowDuplicatesKey: false]
    )
}

func centralManager(
    _ central: CBCentralManager,
    didDiscover peripheral: CBPeripheral,
    advertisementData: [String: Any],
    rssi RSSI: NSNumber
) {
    guard RSSI.intValue > -70 else { return } // Filter weak signals

    // IMPORTANT: Retain the peripheral -- it will be deallocated otherwise
    discoveredPeripheral = peripheral
    centralManager.stopScan()
    centralManager.connect(peripheral, options: nil)
}

func centralManager(
    _ central: CBCentralManager,
    didConnect peripheral: CBPeripheral
) {
    peripheral.delegate = self
    peripheral.discoverServices([heartRateServiceUUID])
}

func centralManager(
    _ central: CBCentralManager,
    didDisconnectPeripheral peripheral: CBPeripheral,
    timestamp: CFAbsoluteTime,
    isReconnecting: Bool,
    error: Error?
) {
    if isReconnecting {
        // System is automatically reconnecting
        return
    }
    // Handle disconnection -- optionally reconnect
    discoveredPeripheral = nil
}

extension BluetoothManager: CBPeripheralDelegate {
    func peripheral(
        _ peripheral: CBPeripheral,
        didDiscoverServices error: Error?
    ) {
        guard let services = peripheral.services else { return }
        for service in services {
            peripheral.discoverCharacteristics(nil, for: service)
        }
    }

    func peripheral(
        _ peripheral: CBPeripheral,
        didDiscoverCharacteristicsFor service: CBService,
        error: Error?
    ) {
        guard let characteristics = service.characteristics else { return }
        for characteristic in characteristics {
            if characteristic.properties.contains(.notify) {
                peripheral.setNotifyValue(true, for: characteristic)
            }
            if characteristic.properties.contains(.read) {
                peripheral.readValue(for: characteristic)
            }
        }
    }
}

func peripheral(
    _ peripheral: CBPeripheral,
    didUpdateValueFor characteristic: CBCharacteristic,
    error: Error?
) {
    guard let data = characteristic.value else { return }

    switch characteristic.uuid {
    case CBUUID(string: "2A37"):
        if let heartRate = parseHeartRate(data) {
            print("Heart rate: \(heartRate) bpm")
        }
    case CBUUID(string: "2A19"):
        let batteryLevel = data.first.map { Int($0) } ?? 0
        print("Battery: \(batteryLevel)%")
    default:
        break
    }
}

private func parseHeartRate(_ data: Data) -> Int? {
    guard data.count >= 2 else { return nil }
    let flags = data[0]
    let is16Bit = (flags & 0x01) != 0
    if is16Bit {
        guard data.count >= 3 else { return nil }
        return Int(data[1]) | (Int(data[2]) << 8)
    } else {
        return Int(data[1])
    }
}

func writeValue(_ data: Data, to characteristic: CBCharacteristic,
                on peripheral: CBPeripheral,
                preferResponse: Bool = true) {
    let type: CBCharacteristicWriteType
    if preferResponse, characteristic.properties.contains(.write) {
        type = .withResponse
    } else if characteristic.properties.contains(.writeWithoutResponse),
              peripheral.canSendWriteWithoutResponse {
        type = .withoutResponse
    } else if characteristic.properties.contains(.write) {
        type = .withResponse
    } else {
        return
    }

    guard data.count <= peripheral.maximumWriteValueLength(for: type) else { return }
    peripheral.writeValue(data, for: characteristic, type: type)
}

// Confirmation callback for .withResponse writes.
func peripheral(
    _ peripheral: CBPeripheral,
    didWriteValueFor characteristic: CBCharacteristic,
    error: Error?
) {
    if let error {
        print("Write failed: \(error.localizedDescription)")
    }
}

// Resume queued .withoutResponse writes here.
func peripheralIsReady(toSendWriteWithoutResponse peripheral: CBPeripheral) {}

// Subscribe
peripheral.setNotifyValue(true, for: characteristic)

// Unsubscribe
peripheral.setNotifyValue(false, for: characteristic)

// Confirmation
func peripheral(
    _ peripheral: CBPeripheral,
    didUpdateNotificationStateFor characteristic: CBCharacteristic,
    error: Error?
) {
    if characteristic.isNotifying {
        print("Now receiving notifications for \(characteristic.uuid)")
    }
}

final class BLEPeripheralManager: NSObject, CBPeripheralManagerDelegate {
    private var peripheralManager: CBPeripheralManager!
    private let serviceUUID = CBUUID(string: "12345678-1234-1234-1234-123456789ABC")
    private let charUUID = CBUUID(string: "12345678-1234-1234-1234-123456789ABD")

    override init() {
        super.init()
        peripheralManager = CBPeripheralManager(delegate: self, queue: nil)
    }

    func peripheralManagerDidUpdateState(_ peripheral: CBPeripheralManager) {
        guard peripheral.state == .poweredOn else { return }
        setupService()
    }

    private func setupService() {
        let characteristic = CBMutableCharacteristic(
            type: charUUID,
            properties: [.read, .notify],
            value: nil,
            permissions: [.readable]
        )

        let service = CBMutableService(type: serviceUUID, primary: true)
        service.characteristics = [characteristic]
        peripheralManager.add(service)
    }

    func peripheralManager(
        _ peripheral: CBPeripheralManager,
        didAdd service: CBService,
        error: Error?
    ) {
        guard error == nil else { return }
        peripheralManager.startAdvertising([
            CBAdvertisementDataServiceUUIDsKey: [serviceUUID],
            CBAdvertisementDataLocalNameKey: "MyDevice"
        ])
    }
}

// 1. Create with a restoration identifier
centralManager = CBCentralManager(
    delegate: self,
    queue: nil,
    options: [CBCentralManagerOptionRestoreIdentifierKey: "myCentral"]
)

// 2. Implement the restoration delegate method
func centralManager(
    _ central: CBCentralManager,
    willRestoreState dict: [String: Any]
) {
    if let peripherals = dict[CBCentralManagerRestoredStatePeripheralsKey]
        as? [CBPeripheral] {
        for peripheral in peripherals {
            // Re-assign delegate and retain
            peripheral.delegate = self
            discoveredPeripheral = peripheral
        }
    }
    let restoredServices = dict[CBCentralManagerRestoredStateScanServicesKey]
        as? [CBUUID]
    let restoredOptions = dict[CBCentralManagerRestoredStateScanOptionsKey]
        as? [String: Any]
    // Resume scanning with restoredServices/restoredOptions if still needed.
}

peripheralManager = CBPeripheralManager(
    delegate: self,
    queue: nil,
    options: [CBPeripheralManagerOptionRestoreIdentifierKey: "myPeripheral"]
)

func peripheralManager(
    _ peripheral: CBPeripheralManager,
    willRestoreState dict: [String: Any]
) {
    let services = dict[CBPeripheralManagerRestoredStateServicesKey]
        as? [CBMutableService]
    let advertisement = dict[CBPeripheralManagerRestoredStateAdvertisementDataKey]
        as? [String: Any]
    // Reconnect app state to restored services/advertisement as needed.
}