Solution.kt

mport android.media.AudioFormat
import android.media.AudioRecord
import android.media.MediaRecorder

class AudioRecorder {

    private val minBufferSize: Int = AudioRecord.getMinBufferSize(SAMPLE_RATE_HZ, AUDIO_RECORDING_FORMAT, AUDIO_ENCODING)
    private var audioRecord: AudioRecord? = null

    fun startRecording() {
        if (audioRecord != null) {
            throw RuntimeException("Starting record with non null audioRecord, Did you forget to clean something up?")
        }
        
        audioRecord = AudioRecord(MediaRecorder.AudioSource.DEFAULT,
                SAMPLE_RATE_HZ,
                AUDIO_RECORDING_FORMAT,
                AUDIO_ENCODING,
                minBufferSize)

        audioRecord?.startRecording()
        val data = ShortArray(minBufferSize)

        while (isRecording) {
            val numberOfShortsRead = audioRecord?.read(data, 0, data.size) ?: AUDIO_RECORD_IS_NULL_ERROR
            // write to buffer if its safe
            if (numberOfShortsRead >= 0) {
                // TODO so something with data
            } else {
                // TODO handle error including AUDIO_RECORD_IS_NULL_ERROR
            }
        }
        audioRecord?.release()
        audioRecord = null // docs say we have to null this after release
    }

    fun stopRecording() {
        if (audioRecord?.state == AudioRecord.STATE_INITIALIZED) {
            audioRecord?.stop()
            audioRecord?.release()
            audioRecord = null // docs say we have to null this after release
        }
    }

    private val isRecording: Boolean
        get() = audioRecord?.recordingState == AudioRecord.RECORDSTATE_RECORDING

    companion object {
        private const val AUDIO_RECORDING_FORMAT = AudioFormat.CHANNEL_IN_MONO
        private const val SAMPLE_RATE_HZ = 16000
        private const val AUDIO_ENCODING = AudioFormat.ENCODING_PCM_16BIT
        private const val AUDIO_RECORD_IS_NULL_ERROR = -999
    }
}