import Foundation
import CoreBluetooth

/// Provisioner for KBeacon / KBPro hardware
/// Protocol: FFE0 service, FFE1 write, FFE2 notify
/// Auth via CMD_AUTH (0x01), config via CMD_WRITE_PARAMS (0x03), save via CMD_SAVE (0x04)
final class KBeaconProvisioner: NSObject, BeaconProvisioner {

    // MARK: - Protocol Commands
    private enum CMD: UInt8 {
        case auth       = 0x01
        case readParams = 0x02
        case writeParams = 0x03
        case save       = 0x04
    }

    // MARK: - Parameter IDs
    private enum ParamID: UInt8 {
        case uuid        = 0x10
        case major       = 0x11
        case minor       = 0x12
        case txPower     = 0x13
        case advInterval = 0x14
    }

    // MARK: - Known passwords (tried in order, matching Android)
    private static let passwords: [Data] = [
        "kd1234".data(using: .utf8)!,
        Data(repeating: 0, count: 16),
        Data([0x31,0x32,0x33,0x34,0x35,0x36,0x37,0x38,0x39,0x30,0x31,0x32,0x33,0x34,0x35,0x36]),
        "0000000000000000".data(using: .utf8)!,
        "1234567890123456".data(using: .utf8)!
    ]

    // MARK: - State

    private let peripheral: CBPeripheral
    private let centralManager: CBCentralManager
    private var writeChar: CBCharacteristic?
    private var notifyChar: CBCharacteristic?

    private var connectionContinuation: CheckedContinuation<Void, Error>?
    private var serviceContinuation: CheckedContinuation<Void, Error>?
    private var writeContinuation: CheckedContinuation<Data, Error>?

    private(set) var isConnected = false
    var diagnosticLog: ProvisionLog?
    var bleManager: BLEManager?

    // MARK: - Init

    init(peripheral: CBPeripheral, centralManager: CBCentralManager) {
        self.peripheral = peripheral
        self.centralManager = centralManager
        super.init()
        self.peripheral.delegate = self
    }

    // MARK: - BeaconProvisioner

    func connect() async throws {
        // Connect with retry
        for attempt in 1...GATTConstants.maxRetries {
            do {
                try await connectOnce()
                try await discoverServices()
                try await authenticate()
                isConnected = true
                return
            } catch {
                disconnect()
                if attempt < GATTConstants.maxRetries {
                    try await Task.sleep(nanoseconds: UInt64(GATTConstants.retryDelay * 1_000_000_000))
                } else {
                    throw error
                }
            }
        }
    }

    func writeConfig(_ config: BeaconConfig) async throws {
        guard isConnected, let writeChar else {
            throw ProvisionError.notConnected
        }

        // Build parameter payload
        var params = Data()

        // UUID (16 bytes)
        params.append(ParamID.uuid.rawValue)
        let uuidBytes = config.uuid.hexToBytes
        params.append(contentsOf: uuidBytes)

        // Major (2 bytes BE)
        params.append(ParamID.major.rawValue)
        params.append(UInt8(config.major >> 8))
        params.append(UInt8(config.major & 0xFF))

        // Minor (2 bytes BE)
        params.append(ParamID.minor.rawValue)
        params.append(UInt8(config.minor >> 8))
        params.append(UInt8(config.minor & 0xFF))

        // TX Power
        params.append(ParamID.txPower.rawValue)
        params.append(config.txPower)

        // Adv Interval
        params.append(ParamID.advInterval.rawValue)
        params.append(UInt8(config.advInterval >> 8))
        params.append(UInt8(config.advInterval & 0xFF))

        // Send CMD_WRITE_PARAMS
        let writeCmd = Data([CMD.writeParams.rawValue]) + params
        let writeResp = try await sendCommand(writeCmd)
        guard writeResp.first == CMD.writeParams.rawValue else {
            throw ProvisionError.writeFailed("Unexpected write response")
        }

        // Send CMD_SAVE to flash
        let saveResp = try await sendCommand(Data([CMD.save.rawValue]))
        guard saveResp.first == CMD.save.rawValue else {
            throw ProvisionError.saveFailed
        }
    }

    func disconnect() {
        if peripheral.state == .connected || peripheral.state == .connecting {
            centralManager.cancelPeripheralConnection(peripheral)
        }
        isConnected = false
    }

    // MARK: - Private: Connection

    private func connectOnce() async throws {
        try await withCheckedThrowingContinuation { (cont: CheckedContinuation<Void, Error>) in
            connectionContinuation = cont

            // Register for connection callbacks via BLEManager (the CBCentralManagerDelegate)
            bleManager?.onPeripheralConnected = { [weak self] connectedPeripheral in
                guard connectedPeripheral.identifier == self?.peripheral.identifier else { return }
                if let c = self?.connectionContinuation {
                    self?.connectionContinuation = nil
                    c.resume()
                }
            }
            bleManager?.onPeripheralFailedToConnect = { [weak self] failedPeripheral, error in
                guard failedPeripheral.identifier == self?.peripheral.identifier else { return }
                if let c = self?.connectionContinuation {
                    self?.connectionContinuation = nil
                    c.resume(throwing: error ?? ProvisionError.connectionTimeout)
                }
            }

            centralManager.connect(peripheral, options: nil)

            // Timeout
            DispatchQueue.main.asyncAfter(deadline: .now() + GATTConstants.connectionTimeout) { [weak self] in
                if let c = self?.connectionContinuation {
                    self?.connectionContinuation = nil
                    c.resume(throwing: ProvisionError.connectionTimeout)
                }
            }
        }
    }

    private func discoverServices() async throws {
        try await withCheckedThrowingContinuation { (cont: CheckedContinuation<Void, Error>) in
            serviceContinuation = cont
            peripheral.discoverServices([GATTConstants.ffe0Service])

            DispatchQueue.main.asyncAfter(deadline: .now() + GATTConstants.operationTimeout) { [weak self] in
                if let c = self?.serviceContinuation {
                    self?.serviceContinuation = nil
                    c.resume(throwing: ProvisionError.serviceDiscoveryTimeout)
                }
            }
        }
    }

    private func authenticate() async throws {
        for password in Self.passwords {
            let cmd = Data([CMD.auth.rawValue]) + password
            do {
                let resp = try await sendCommand(cmd)
                if resp.first == CMD.auth.rawValue && resp.count > 1 && resp[1] == 0x00 {
                    return // Auth success
                }
            } catch {
                continue
            }
        }
        throw ProvisionError.authFailed
    }

    private func sendCommand(_ data: Data) async throws -> Data {
        guard let writeChar else { throw ProvisionError.notConnected }

        return try await withCheckedThrowingContinuation { (cont: CheckedContinuation<Data, Error>) in
            writeContinuation = cont
            peripheral.writeValue(data, for: writeChar, type: .withResponse)

            DispatchQueue.main.asyncAfter(deadline: .now() + GATTConstants.operationTimeout) { [weak self] in
                if let c = self?.writeContinuation {
                    self?.writeContinuation = nil
                    c.resume(throwing: ProvisionError.operationTimeout)
                }
            }
        }
    }
}

// MARK: - CBPeripheralDelegate

extension KBeaconProvisioner: CBPeripheralDelegate {

    func peripheral(_ peripheral: CBPeripheral, didDiscoverServices error: Error?) {
        if let error {
            serviceContinuation?.resume(throwing: error)
            serviceContinuation = nil
            return
        }

        guard let service = peripheral.services?.first(where: { $0.uuid == GATTConstants.ffe0Service }) else {
            serviceContinuation?.resume(throwing: ProvisionError.serviceNotFound)
            serviceContinuation = nil
            return
        }

        peripheral.discoverCharacteristics([GATTConstants.ffe1Char, GATTConstants.ffe2Char], for: service)
    }

    func peripheral(_ peripheral: CBPeripheral, didDiscoverCharacteristicsFor service: CBService, error: Error?) {
        if let error {
            serviceContinuation?.resume(throwing: error)
            serviceContinuation = nil
            return
        }

        for char in service.characteristics ?? [] {
            switch char.uuid {
            case GATTConstants.ffe1Char:
                writeChar = char
            case GATTConstants.ffe2Char:
                notifyChar = char
                peripheral.setNotifyValue(true, for: char)
            default:
                break
            }
        }

        if writeChar != nil {
            serviceContinuation?.resume()
            serviceContinuation = nil
        } else {
            serviceContinuation?.resume(throwing: ProvisionError.characteristicNotFound)
            serviceContinuation = nil
        }
    }

    func peripheral(_ peripheral: CBPeripheral, didUpdateValueFor characteristic: CBCharacteristic, error: Error?) {
        guard characteristic.uuid == GATTConstants.ffe2Char,
              let data = characteristic.value else { return }

        if let cont = writeContinuation {
            writeContinuation = nil
            cont.resume(returning: data)
        }
    }

    func peripheral(_ peripheral: CBPeripheral, didWriteValueFor characteristic: CBCharacteristic, error: Error?) {
        // Write acknowledgment — actual response comes via notify on FFE2
        if let error {
            if let cont = writeContinuation {
                writeContinuation = nil
                cont.resume(throwing: error)
            }
        }
    }
}