/// CoreBluetooth BLE MIDI connection manager.
/// Scans for "EIS4", connects, subscribes to MIDI notifications,
/// parses incoming BLE MIDI packets into EisMessage values.

import CoreBluetooth
import Foundation

@Observable
final class BLEManager: NSObject {

    static let midiServiceUUID = CBUUID(string: "03B80E5A-EDE8-4B33-A751-6CE34EC4C700")
    static let midiCharUUID    = CBUUID(string: "7772E5DB-3868-4112-A1A9-F2669D106BF3")

    enum ConnectionState: String {
        case disconnected = "Disconnected"
        case scanning     = "Scanning..."
        case connecting   = "Connecting..."
        case connected    = "Connected"
    }

    var state: ConnectionState = .disconnected
    var lastMessage: EisMessage?

    private var centralManager: CBCentralManager!
    private var peripheral: CBPeripheral?
    private var midiCharacteristic: CBCharacteristic?
    private var onMessage: ((EisMessage) -> Void)?

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

    func setMessageHandler(_ handler: @escaping (EisMessage) -> Void) {
        onMessage = handler
    }

    func startScanning() {
        guard centralManager.state == .poweredOn else { return }
        state = .scanning
        centralManager.scanForPeripherals(
            withServices: [Self.midiServiceUUID],
            options: nil
        )
    }

    func disconnect() {
        if let p = peripheral {
            centralManager.cancelPeripheralConnection(p)
        }
        peripheral = nil
        midiCharacteristic = nil
        state = .disconnected
    }

    func sendCommand(_ sysex: [UInt8]) {
        guard let char = midiCharacteristic, let p = peripheral else { return }
        let packet = Self.wrapBLEMIDI(sysex)
        p.writeValue(packet, for: char, type: .withoutResponse)
    }

    // MARK: - BLE MIDI packet handling

    /// Wrap raw SysEx into a BLE MIDI packet.
    /// Input:  [F0, 7D, CMD, ...payload, F7]
    /// Output: [0x80, 0x80, F0, 7D, CMD, ...payload, 0x80, F7]
    static func wrapBLEMIDI(_ sysex: [UInt8]) -> Data {
        var pkt: [UInt8] = [0x80, 0x80]
        pkt.append(contentsOf: sysex.dropLast())
        pkt.append(0x80)
        pkt.append(0xF7)
        return Data(pkt)
    }

    /// Extract SysEx payload from BLE MIDI notification.
    /// Returns bytes between F0 and F7 exclusive, stripping timestamps.
    /// Result: [7D, RSP_ID, ...data]
    static func extractSysEx(from data: Data) -> [UInt8]? {
        let bytes = Array(data)
        guard bytes.count >= 5 else { return nil }

        var i = 1 // skip header
        while i < bytes.count {
            let b = bytes[i]
            if b == 0xF0 { break }
            if b & 0x80 != 0 && b != 0xF7 { i += 1; continue }
            i += 1
        }
        guard i < bytes.count, bytes[i] == 0xF0 else { return nil }
        i += 1

        var payload: [UInt8] = []
        while i < bytes.count && bytes[i] != 0xF7 {
            if bytes[i] & 0x80 != 0 { i += 1; continue }
            payload.append(bytes[i])
            i += 1
        }
        guard !payload.isEmpty else { return nil }
        return payload
    }
}

// MARK: - CBCentralManagerDelegate

extension BLEManager: CBCentralManagerDelegate {

    func centralManagerDidUpdateState(_ central: CBCentralManager) {
        if central.state == .poweredOn {
            startScanning()
        }
    }

    func centralManager(
        _ central: CBCentralManager,
        didDiscover peripheral: CBPeripheral,
        advertisementData: [String: Any],
        rssi RSSI: NSNumber
    ) {
        guard peripheral.name == "EIS4" else { return }
        central.stopScan()
        self.peripheral = peripheral
        state = .connecting
        central.connect(peripheral, options: nil)
    }

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

    func centralManager(
        _ central: CBCentralManager,
        didDisconnectPeripheral peripheral: CBPeripheral,
        error: Error?
    ) {
        self.peripheral = nil
        self.midiCharacteristic = nil
        state = .disconnected
        startScanning()
    }
}

// MARK: - CBPeripheralDelegate

extension BLEManager: CBPeripheralDelegate {

    func peripheral(_ peripheral: CBPeripheral, didDiscoverServices error: Error?) {
        guard let service = peripheral.services?.first(where: {
            $0.uuid == Self.midiServiceUUID
        }) else { return }
        peripheral.discoverCharacteristics([Self.midiCharUUID], for: service)
    }

    func peripheral(
        _ peripheral: CBPeripheral,
        didDiscoverCharacteristicsFor service: CBService,
        error: Error?
    ) {
        guard let char = service.characteristics?.first(where: {
            $0.uuid == Self.midiCharUUID
        }) else { return }
        midiCharacteristic = char
        peripheral.setNotifyValue(true, for: char)
    }

    func peripheral(
        _ peripheral: CBPeripheral,
        didUpdateNotificationStateFor characteristic: CBCharacteristic,
        error: Error?
    ) {
        if characteristic.isNotifying {
            state = .connected
            sendCommand(buildSysexGetConfig())
        }
    }

    func peripheral(
        _ peripheral: CBPeripheral,
        didUpdateValueFor characteristic: CBCharacteristic,
        error: Error?
    ) {
        guard let data = characteristic.value,
              let sysex = Self.extractSysEx(from: data),
              let msg = parseSysex(sysex) else { return }
        lastMessage = msg
        onMessage?(msg)
    }
}