Building iOS VoIP Apps with Swift and CallKit: Complete Guide

import CallKit
import PushKit

class CallProvider: NSObject, CXProviderDelegate {
  let provider: CXProvider
  let callController = CXCallController()

  override init() {
    let config = CXProviderConfiguration()
    config.supportsVideo = false
    config.maximumCallsPerCallGroup = 1
    config.supportedHandleTypes = [.phoneNumber, .generic]
    self.provider = CXProvider(configuration: config)
    super.init()
    provider.setDelegate(self, queue: nil)
  }

  func reportIncomingCall(uuid: UUID, handle: String, displayName: String) {
    let update = CXCallUpdate()
    update.remoteHandle = CXHandle(type: .generic, value: handle)
    update.localizedCallerName = displayName
    provider.reportNewIncomingCall(with: uuid, update: update) { error in
      if let error = error { print("CallKit error: \(error)") }
    }
  }

  func provider(_ provider: CXProvider, perform action: CXAnswerCallAction) {
    // Answer the SIP call here via your PJSIP bridge
    SIPManager.shared.answerCall(callId: action.callUUID.uuidString)
    action.fulfill()
  }
}