Bluetooth Channel Sounding for Accessory Finding

import SwiftUI
import CoreBluetooth

// MARK: - Channel Sounding Manager

class ChannelSoundingManager: NSObject, ObservableObject {
    @Published var distanceMeters: Double? = nil
    @Published var statusMessage: String = "Idle"

    private var centralManager: CBCentralManager!
    private var targetPeripheral: CBPeripheral?

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

    func startSession(with peripheral: CBPeripheral) {
        guard CBCentralManager.supportsFeatures(.channelSounding) else {
            statusMessage = "Channel Sounding not supported on this device."
            return
        }
        targetPeripheral = peripheral
        peripheral.delegate = self
        peripheral.startChannelSoundingSession()
        statusMessage = "Session active — measuring distance…"
    }

    func stopSession() {
        targetPeripheral?.cancelChannelSoundingSession()
    }
}

// MARK: - CBCentralManagerDelegate

extension ChannelSoundingManager: CBCentralManagerDelegate {
    func centralManagerDidUpdateState(_ central: CBCentralManager) {
        statusMessage = central.state == .poweredOn ? "Bluetooth ready" : "Bluetooth unavailable"
    }
}

// MARK: - CBPeripheralDelegate (Channel Sounding)

extension ChannelSoundingManager: CBPeripheralDelegate {
    func peripheral(_ peripheral: CBPeripheral,
                    didReceive results: CBChannelSoundingResults) {
        if let distance = results.distance {
            distanceMeters = distance
            statusMessage = String(format: "Distance: %.2f m", distance)
        } else {
            statusMessage = "Measurement unavailable"
        }
    }

    func peripheral(_ peripheral: CBPeripheral,
                    didCompleteChannelSoundingSession error: Error?) {
        statusMessage = error == nil ? "Session ended." : "Session error: \(error!.localizedDescription)"
        distanceMeters = nil
    }
}

// MARK: - SwiftUI View

struct ChannelSoundingView: View {
    @StateObject private var manager = ChannelSoundingManager()

    var body: some View {
        VStack(spacing: 24) {
            Text("Bluetooth Channel Sounding")
                .font(.title2.bold())

            if let dist = manager.distanceMeters {
                Text(String(format: "%.2f m", dist))
                    .font(.system(size: 64, weight: .semibold, design: .rounded))
                    .foregroundStyle(.blue)
            } else {
                Text("--")
                    .font(.system(size: 64, weight: .light, design: .rounded))
                    .foregroundStyle(.secondary)
            }

            Text(manager.statusMessage)
                .font(.subheadline)
                .foregroundStyle(.secondary)
                .multilineTextAlignment(.center)

            Button("Stop Session") { manager.stopSession() }
                .buttonStyle(.borderedProminent)
                .tint(.red)
        }
        .padding()
    }
}

#Preview {
    ChannelSoundingView()
}