#!/usr/bin/python
# -*- coding: utf-8 -*-
"""Test inotify watching a file in Python using ctypes.
"""
import ctypes
import os
import posix
import struct
import sys
import time

SEEK_END = 2
IN_MODIFY = 2                       # hopefully!
inotify_event = "=iiii"             # should be OK for LP64 and ILP32 
inotify_event_size = struct.calcsize(inotify_event)

if __name__ == '__main__':
    verbose = (sys.argv[1] == '-v')
    if verbose:
        sys.argv.pop(1)

    fn = sys.argv[1]
    fh = open(fn)
    fh.seek(0, 2)
    libc = ctypes.CDLL('libc.so.6', use_errno=True)
    inotify_fd = libc.inotify_init()
    inotify_fh = os.fdopen(inotify_fd)
    watch_id = libc.inotify_add_watch(inotify_fd, fn, IN_MODIFY)
    if watch_id < 0:
        raise OSError(ctypes.get_errno())
    data = fh.read()
    sys.stdout.write(data)
    sys.stdout.flush()
    while True:
        # An unreasonably large buffer
        events = posix.read(inotify_fd, 32768)
        while events:
            first_event = events[:inotify_event_size]
            event_header = struct.unpack(inotify_event, first_event)
            n = event_header[3]
            if verbose:
                sys.stderr.write(
                    "wd=%d, mask=0x%x, cookie=%d, len=%d, name=%r\n"
                    % (event_header + (events[inotify_event_size:
                                              inotify_event_size+n],)))
            assert inotify_event_size + n <= len(events)
            events = events[inotify_event_size+n:]

            time.sleep(.005)   # In case lots of data is being written
            data = fh.read()
            sys.stdout.write(data)
            sys.stdout.flush()