import Foundation
import CoreBluetooth

final class DeviceManager: NSObject, CBCentralManagerDelegate {

    static let serviceUUID = CBUUID(string: "22071991-cccc-cccc-cccc-000000000001")
    
    static let characteristicUUID = CBUUID(string: "22071991-cccc-cccc-cccc-000000000002")
    
    private var manager: CBCentralManager! = nil
    
    private(set) var lastRSSI: Int = 0
    
    weak var delegate: DeviceManagerDelegate?

    var state: DeviceState = .disconnected {
        didSet {
            delegate?.deviceManager(didChangeState: state)
        }
    }
    
    override init() {
        super.init()
        self.manager = CBCentralManager(delegate: self, queue: nil)
    }

    @discardableResult
    func connect() -> Bool {
        switch state {
        case .bluetoothDisabled:
            log.info("Can't connect, bluetooth disabled")
            return false
        case .disconnected:
            break
        default:
            return true
        }
        guard !manager.isScanning else {
            state = .scanning
            return true
        }
        if !shouldConnectIfPossible {
            shouldConnectIfPossible = true
        }
        state = .scanning
        manager.scanForPeripherals(withServices: [DeviceManager.serviceUUID])
        return true
    }

    var shouldConnectIfPossible = true {
        didSet {
            updateConnectionOnChange()
            delegate?.deviceManager(shouldConnectToDevice: shouldConnectIfPossible)
        }
    }
    
    private func updateConnectionOnChange() {
        if shouldConnectIfPossible {
            ensureConnection()
        } else {
            disconnectIfNeeded()
        }
    }

    private func ensureConnection() {
        switch state {
        case .disconnected:
            connect()
        default:
            return
        }
    }

    private func disconnectIfNeeded() {
        switch state {
        case .bluetoothDisabled, .disconnected:
            return
        default:
            disconnect()
        }
    }
    
    func disconnect() {
        if shouldConnectIfPossible {
            shouldConnectIfPossible = false
        }
        switch state {
        case .bluetoothDisabled, .disconnected:
            return
        case .scanning:
            manager.stopScan()
            state = .disconnected
            return
        case .connecting(let device),
                .discoveringCharacteristic(let device),
                .discoveringServices(device: let device),
                .configured(let device, _):
            manager.cancelPeripheralConnection(device)
            manager.stopScan()
            state = .disconnected
            return
        }
    }

    @discardableResult
    func send(_ data: Data) -> Bool {
        guard case .configured(let device, let characteristic) = state else {
            return false
        }
        device.writeValue(data, for: characteristic, type: .withResponse)
        return self.read()
    }

    @discardableResult
    private func read() -> Bool {
        guard case .configured(let device, let characteristic) = state else {
            return false
        }
        device.readValue(for: characteristic)
        return true
    }

    func centralManager(_ central: CBCentralManager, didDiscover peripheral: CBPeripheral, advertisementData: [String : Any], rssi RSSI: NSNumber) {
        guard shouldConnectIfPossible else {
            return
        }
        peripheral.delegate = self
        manager.connect(peripheral)
        manager.stopScan()
        state = .connecting(device: peripheral)
    }
        
    func centralManagerDidUpdateState(_ central: CBCentralManager) {
        switch central.state {
        case .poweredOff:
            state = .bluetoothDisabled
        case .poweredOn:
            state = .disconnected
            connect()
        case .unsupported:
            state = .bluetoothDisabled
            log.info("Bluetooth is not supported")
        case .unknown:
            state = .bluetoothDisabled
            log.info("Bluetooth state is unknown")
        case .resetting:
            state = .bluetoothDisabled
            log.info("Bluetooth is resetting")
        case .unauthorized:
            state = .bluetoothDisabled
            log.info("Bluetooth is not authorized")
        @unknown default:
            state = .bluetoothDisabled
            log.warning("Unknown state \(central.state)")
        }
    }
        
    func centralManager(_ central: CBCentralManager, didConnect peripheral: CBPeripheral) {
        log.info("Connected to " +  peripheral.name!)
        peripheral.discoverServices([DeviceManager.serviceUUID])
        state = .discoveringServices(device: peripheral)
    }
        
    func centralManager(_ central: CBCentralManager, didDisconnectPeripheral peripheral: CBPeripheral, error: Error?) {
        log.info("Disconnected from " +  peripheral.name!)
        state = .disconnected
        // Attempt to reconnect
        if shouldConnectIfPossible {
            connect()
        }
    }
    
    func centralManager(_ central: CBCentralManager, didFailToConnect peripheral: CBPeripheral, error: Error?) {
        log.warning("Failed to connect device '\(peripheral.name ?? "NO_NAME")'")
        if let error = error {
            log.warning(error.localizedDescription)
        }
        state = manager.isScanning ? .scanning : .disconnected
        // Attempt to reconnect
        if shouldConnectIfPossible {
            connect()
        }
    }
}

extension DeviceManager: CBPeripheralDelegate {
    
    func peripheral(_ peripheral: CBPeripheral, didDiscoverServices error: Error?) {
        guard let services = peripheral.services, !services.isEmpty else {
            log.error("No services found for device '\(peripheral.name ?? "NO_NAME")'")
            manager.cancelPeripheralConnection(peripheral)
            return
        }
        guard let service = services.first(where: { $0.uuid.uuidString == DeviceManager.serviceUUID.uuidString }) else {
            log.error("Required service not found for '\(peripheral.name ?? "NO_NAME")': \(services.map { $0.uuid.uuidString})")
            manager.cancelPeripheralConnection(peripheral)
            return
        }
        peripheral.discoverCharacteristics([DeviceManager.characteristicUUID], for: service)
        state = .discoveringCharacteristic(device: peripheral)
    }
    
    func peripheral(_ peripheral: CBPeripheral, didDiscoverCharacteristicsFor service: CBService, error: Error?) {
        if let error = error {
            log.error("Failed to discover characteristics: \(error)")
            manager.cancelPeripheralConnection(peripheral)
            return
        }
        guard let characteristics = service.characteristics, !characteristics.isEmpty else {
            log.error("No characteristics found for device")
            manager.cancelPeripheralConnection(peripheral)
            return
        }
        for characteristic in characteristics {
            guard characteristic.uuid == DeviceManager.characteristicUUID else {
                log.warning("Unused characteristic \(characteristic.uuid.uuidString)")
                continue
            }
            state = .configured(device: peripheral, characteristic: characteristic)
            peripheral.setNotifyValue(true, for: characteristic)
        }
    }
    
    func peripheral(_ peripheral: CBPeripheral, didWriteValueFor characteristic: CBCharacteristic, error: Error?) {
        if let error = error {
            log.error("Peripheral failed to write value for \(characteristic.uuid.uuidString): \(error)")
        }
    }
    
    func peripheral(_ peripheral: CBPeripheral, didReadRSSI RSSI: NSNumber, error: Error?) {
        if let error = error {
            log.warning("Failed to get RSSI: \(error)")
            return
        }
        lastRSSI = RSSI.intValue
        log.info("RSSI: \(lastRSSI)")
    }
    
    func peripheral(_ peripheral: CBPeripheral, didUpdateValueFor characteristic: CBCharacteristic, error: Error?) {
        if let error = error {
            log.error("Failed to read value update: \(error)")
            return
        }
        guard case .configured(device: _, characteristic: let storedCharacteristic) = state else {
            log.warning("Received data while not properly configured")
            return
        }
        guard characteristic.uuid == storedCharacteristic.uuid else {
            log.warning("Read unknown characteristic \(characteristic.uuid.uuidString)")
            return
        }
        guard let data = characteristic.value else {
            log.warning("No data")
            return
        }
        delegate?.deviceManager(didReceive: data)
    }
}