import numpy as np
from scipy.io import wavfile
import ctypes
replaygain = ctypes.CDLL('libreplaygain.so')


def calculate_replaygain(samples, frame_rate=44100):
    """
    pass in a generator that produces audio samples
    returns the maximum sample.

    https://github.com/vontrapp/replaygain
    """
    replaygain.gain_init_analysis(frame_rate)
    block_size = 10000
    channel_count = samples.shape[1]
    i = 0
    samples = samples.astype(np.float64)

    while i * block_size < samples.shape[0]:
        channel_left = samples[i*block_size:(i+1)*block_size,0]
        channel_right = samples[i*block_size:(i+1)*block_size,1]

        samples_p_left = channel_left.ctypes.data_as(ctypes.POINTER(ctypes.c_double))
        samples_p_right = channel_right.ctypes.data_as(ctypes.POINTER(ctypes.c_double))

        replaygain.gain_analyze_samples(samples_p_left, samples_p_right, channel_left.shape[0], channel_count)
        i += 1
    
    return replaygain.gain_get_chapter()


if __name__ == '__main__':
    frame_rate, samples = wavfile.read('directions.wav')
    samples = samples.astype(np.float64) / 2**15
    gain = calculate_replaygain(samples, frame_rate=frame_rate)
    print "Recommended gain: %f dB" % gain
    gain = calculate_replaygain(np.random.random((441000, 2)) * 2 - 1, frame_rate=44100)
    print "Recommended gain: %f dB" % gain