Read a WAV file and convert it to an array of amplitudes in Swift

I have followed a very good tutorial on udacity.com to explore the basis of audio applications with Swift. I would like to extend its current functionalities, starting with displaying the waveform of the WAV file. For that purpose, I would need to retrieve the amplitude versus sample from the WAV file. How could I proceed in swift, given that I have a recorded file already?

Thank you!