#!/usr/bin/env python3
"""Report the real playback duration of Ogg Vorbis files, without decoding audio.

Reads the sample rate out of the Vorbis identification header and the total
sample count from the granule position of the final OggS page, then divides.

This is how you tell a sound file that is genuinely shorter from a sound that
merely stops early: the file either contains fewer samples or it does not.

Usage:
    ogg_duration.py <file.ogg> [file.ogg ...]
"""

import struct
import sys


def info(path):
    with open(path, "rb") as fh:
        data = fh.read()

    mark = data.find(b"\x01vorbis")
    if mark < 0:
        return None
    # packet type(1) + 'vorbis'(6) + version(4) + channels(1) -> rate(4)
    if len(data) < mark + 16:
        return None
    rate = struct.unpack_from("<I", data, mark + 12)[0]
    channels = data[mark + 11]

    granule = 0
    pos = 0
    while True:
        pos = data.find(b"OggS", pos)
        if pos < 0:
            break
        if pos + 27 <= len(data):
            granule = struct.unpack_from("<q", data, pos + 6)[0]
            seg_count = data[pos + 26]
            table_end = pos + 27 + seg_count
            body = sum(data[pos + 27:table_end])
            pos = table_end + body
        else:
            pos += 4

    seconds = granule / float(rate) if rate else 0.0
    return {
        "bytes": len(data),
        "rate": rate,
        "channels": channels,
        "samples": granule,
        "seconds": seconds,
    }


def main(argv):
    for path in argv:
        got = info(path)
        if got is None:
            print("{:<52} not a Vorbis stream".format(path[-52:]))
            continue
        print("{:<52} {:>7.3f}s  {:>6} Hz  {:>2}ch  {:>8} samples  {:>6} B".format(
            path[-52:], got["seconds"], got["rate"], got["channels"],
            got["samples"], got["bytes"]))
    return 0


if __name__ == "__main__":
    raise SystemExit(main(sys.argv[1:]))