#!/usr/bin/python
# Increment a counter file with safe locking.
# You can use this as an "xfilter" with mailfilter to count messages that match
# particular rules.
# Adam Sampson <ats@offog.org>

import sys, os, fcntl

def main(args):
	if len(args) != 1:
		print "Usage: increment-counter counter-file"
		sys.exit(1)
	fn = args[0]

	fd = os.open(fn, os.O_RDWR | os.O_CREAT)
	fcntl.lockf(fd, fcntl.LOCK_EX)
	s = os.read(fd, 4096)
	try:
		n = int(s)
	except ValueError:
		print >>sys.stderr, "Couldn't read value from counter file " + fn + ", assuming 0"
		n = 0
	fnn = fn + ".new"
	f = open(fnn, "w")
	f.write(str(n + 1))
	f.close()
	os.rename(fnn, fn)
	os.close(fd)

	while 1:
		s = sys.stdin.read(4096)
		if s == "":
			break
		sys.stdout.write(s)

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