import sounddevice as sd
import audioop
import time

frame_rate   = 44100
channels     = 2
sample_width = 2

class Mixer:
    def __init__(self):
        self.stream = sd.RawOutputStream(samplerate=frame_rate,
                        channels=channels,
                        dtype='int' + str(8*sample_width), # FIXME: ?
                        latency="high",
                        blocksize=5000,
                        callback=self.play_callback,
                        )
        self.open_files = []

    def add_file(self, music_file):
        if music_file not in self.open_files:
            self.open_files.append(music_file)
        self.start()

    def remove_file(self, music_file):
        self.open_files.remove(music_file)
        if len(self.open_files) == 0:
            self.stop()

    def stop(self):
        self.stream.stop()

    def start(self):
        self.stream.start()

    def play_callback(self, out_data, frame_count, time_info, status_flags):
        out_data_length = len(out_data)
        empty_data = b"\0" * out_data_length
        data = b"\0" * out_data_length

        for open_file in self.open_files:
            file_data = open_file.play_callback(out_data_length, frame_count)

            if data == empty_data:
                data = file_data
            elif file_data != empty_data:
                data = audioop.add(data, file_data, sample_width)

        out_data[:] = data