#!/usr/bin/env python
### Use inotify to tail logfile (argv[1]), mimicking tail -F (follow if rotated). 
###
### Usage: ./tail-F_inotify.py /path/to/file
###
### @author: "Charlie Schluting" <charlie@schluting.com>
### Copyright: the only free-as-in-freedom one: MIT license
###

import sys, os, pyinotify
from optparse import OptionParser

parser = OptionParser()
parser.add_option("--debug", help="print debug messages", action="store_true", dest="debug")
(options, args) = parser.parse_args()

myfile = args[0] 
if options.debug:
    print "I am totally opening " + myfile 

wm = pyinotify.WatchManager()
    
# watched events on the directory, and parse $path for file_of_interest:
dirmask = pyinotify.IN_MODIFY | pyinotify.IN_DELETE | pyinotify.IN_MOVE_SELF | pyinotify.IN_CREATE
    
# open file, skip to end..
global fh 
fh = open(myfile, 'r')
fh.seek(0,2)
    
# the event handlers:
class PTmp(pyinotify.ProcessEvent):
    def process_IN_MODIFY(self, event):
        if myfile not in os.path.join(event.path, event.name):
            return
        else:
    	    print fh.readline().rstrip()
    
    def process_IN_MOVE_SELF(self, event):
        if options.debug:
            print "The file moved! Continuing to read from that, until a new one is created.."

    def process_IN_CREATE(self, event):
        if myfile in os.path.join(event.path, event.name):
            # yay, I exist, umm.. again!
            global fh
            fh.close
            fh = open(myfile, 'r')
            # catch up, in case lines were written during the time we were re-opening:
            if options.debug:
                print "My file was created! I'm now catching up with lines in the newly created file." 
            for line in fh.readlines():
                print line.rstrip()
            # then skip to the end, and wait for more IN_MODIFY events
            fh.seek(0,2)
        return

notifier = pyinotify.Notifier(wm, PTmp())

# watch the directory, so we can get IN_CREATE events and re-open the file when logrotate comes along.
# if you just watch the file, pyinotify errors when it moves, saying "can't track, can't trust it.. watch 
#  the directory".
index = myfile.rfind('/')
wm.add_watch(myfile[:index], dirmask)

while True:
    try:
        notifier.process_events()
        if notifier.check_events():
            notifier.read_events()
    except KeyboardInterrupt:
        break

# cleanup: stop the inotify, and close the file handle:
notifier.stop()
fh.close()

sys.exit(0)