#!/usr/bin/env python
#
# Copyright (c) 2012, Matthias P. Braendli <matthias@mpb.li>
# 
# Permission to use, copy, modify, and/or distribute this software for any
# purpose with or without fee is hereby granted, provided that the above
# copyright notice and this permission notice appear in all copies.
#
# THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
# REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
# AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
# INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
# LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
# OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
# PERFORMANCE OF THIS SOFTWARE.

from math import sqrt
import wave
import sys
import struct
import subprocess
import traceback

DEBUG = False

class RunningStatistics():
    """Taken from http://www.johndcook.com/standard_deviation.html"""
    def __init__(self):
        self.m_n = 0
        self.m_oldM = 0.0
        self.m_newM = 0.0
        self.m_oldS = 0.0
        self.m_newS = 0.0

    def push(self, x):
        self.m_n += 1

        # See Knuth TAOCP vol 2, 3rd edition, page 232
        if self.m_n == 1:
            self.m_oldM = x
            self.m_newM = x
            self.m_oldS = 0.0
        else:
            self.m_newM = self.m_oldM + (x - self.m_oldM) / self.m_n
            self.m_newS = self.m_oldS + (x - self.m_oldM) * (x - self.m_newM)

            self.m_oldM = self.m_newM
            self.m_oldS = self.m_newS

    def mean(self):
        return self.m_newM

    def variance(self):
        if self.m_n > 1:
            return self.m_newS/(self.m_n - 1)
        else:
            return 0.0

    def standard_deviation(self):
        return sqrt(self.variance())

def run(rs):
    try:
        w = wave.open(proc.stdout)

        max_samps = min(w.getframerate() * MEASURE_TIME *
                w.getnchannels(), w.getnframes())

        if DEBUG:
            print("Number of frames: {0}".format(w.getnframes()))
            print("Sample width: {0}".format(w.getsampwidth()))
            print("Frame rate: {0}".format(w.getframerate()))
            print("Channels: {0}".format(w.getnchannels()))

            print("Max samps: {0}".format(max_samps))

        if w.getnchannels() == 1:
            if w.getsampwidth() == 2:
                STR = "<h"
            elif w.getsampwidth() == 4:
                STR = "<i"
            else:
                print("sample width not supported")
                sys.exit(3)

            for i in range(max_samps):
                framedata = w.readframes(1)
                data = struct.unpack(STR, framedata)
                rs.push(data)

        elif w.getnchannels() == 2:
            if w.getsampwidth() == 2:
                STR = "<hh"
            elif w.getsampwidth() == 4:
                STR = "<ii"
            else:
                print("sample width not supported")
                sys.exit(3)

            for i in range(max_samps):
                framedata = w.readframes(1)
                left, right = struct.unpack(STR, framedata)
                data = (left+right)/2
                rs.push(data)
        w.close()
    except Exception as e:
        print("AudioLevel Check: Exception!")
        traceback.print_exc()
        return 2
    return 0

MEASURE_TIME = 10 # seconds
THRESHOLD = 1000

def usage():
    print "Please specify url"

if len(sys.argv) != 2:
    usage()
    sys.exit(3)

url = sys.argv[1]


mpg123_args = [ 'mpg321', '-q', '-w', '-', url ]
args = ['mplayer', url, '-really-quiet',
        '-ao', 'pcm:file=/dev/stdout']

proc = subprocess.Popen(args, stdout=subprocess.PIPE, 
        stderr=subprocess.PIPE)

rs = RunningStatistics()
ret = run(rs)

#proc.stdout.close()
#proc.send_signal(13) # sigpipe
proc.terminate()
proc.communicate()
proc.wait()

if DEBUG:
    print("Mean {0}\nVariance {1} over {2} samples".format(
        rs.mean(), rs.standard_deviation(), rs.m_n))


if ret == 0:
    if rs.standard_deviation() < THRESHOLD:
        print("AudioLevel Check: Silence detected: std deviation {0}".format(
            rs.standard_deviation()))
        sys.exit(2)
    else:
        print("AudioLevel Check: Audio Level OK: std deviation {0}".format(
            rs.standard_deviation()))
        sys.exit(0)
else:
    sys.exit(ret)