AVAudioPlayerNode - State of playback and start/finish notifications

Question

I have an AVAudioPlayerNode object that is linked with an AVAudioEngine. I used the schedule method to load them in the queue. How can I know the state of the playback and when a single file start and finish to play?

This is the code I use for scheduling :

playerNode.scheduleFile(file, at: audioTime) {
    // Completion
}