#!/usr/bin/python
import os
import sys
import getopt

opts_short = ['h', 'n', 'o:', 'v', 'V']
opts_long = ['help', 'no-update', 'output=', 'verbose', 'version']
opts_desc = ['Displays this information', 'Does not update the pointer to where it left off', 'Where to send the new lines (defaults to stdout)', 'Displays debugging information on stderr', 'Prints version and exits']

def print_usage():
	sys.stderr.write("""Usage:
  lnl [options] (logfile)

Available options are:
""")
	for i in range(0, len(opts_short)):
		argstr = "-%s, --%s"
		if opts_short[i][-1] == ':':
			argstr = "-%s, --%s <arg>" % (opts_short[i][0], opts_long[i][:-1])
		else:
			argstr = "-%s, --%s" % (opts_short[i], opts_long[i])
		argstr = ("%s                          " % (argstr,))[:24]
		desc = opts_desc[i]
		sys.stderr.write("\n  %s %s" % (argstr, desc))

	sys.stderr.write('\n')

opts, args = getopt.getopt(sys.argv[1:], ''.join(opts_short), opts_long)

output_f = sys.stdout
verbose = False
update_pos = True

for o, a in opts:
	if o in ('-V', '--version'):
		print_version()
		sys.exit(0)
	elif o in ('-h', '--help'):
		print_usage()
		sys.exit(0)
	elif o in ('-o', '--output'):
		output_f = a
	elif o in ('-v', '--verbose'):
		verbose = True
	elif o in ('-n', '--no-update'):
		update_pos = False

if len(args) != 1:
	print_usage()
	sys.exit(0)

args = args[0]
prefdir = None
def make_prefs_dir():
	global prefdir
	homedir = os.environ['HOME']
	pwd = open('/etc/passwd', 'r')
	for pwdl in pwd:
		try:
			uname, upass, uid, gid, fullname, home, shell = pwdl.split(':')
		except ValueError:
			continue
		if os.getuid() == int(uid):
			homedir = home
			break
			
	
	prefdir = os.path.join(homedir, '.lognewlines')
	if not os.path.exists(prefdir):
		os.mkdir(prefdir)
	

if type(output_f) == str:
	output_f = open(output_f, 'wb')

make_prefs_dir()
fn = os.path.realpath(os.path.abspath(args))
fnn = os.path.split(fn)[1]
preffn = os.path.join(prefdir, fnn)
newpf = []
line_no = 0
read_pos = 0

if os.path.exists(preffn):
	pf = open(preffn, 'r')
	for p in pf:
		line_no += 1
		try:
			path, pos = p.split(':')
		except:
			sys.stderr.write("Invalid pref file entry: file %s, line %d\n" % (fnn, line_no))
			continue
		
		if path == fn:
			read_pos = int(pos)
			newpf += [None]
		else:
			newpf += [p]		


lf = open(fn, 'rb')
lf.seek(0, 2)
size = lf.tell()
lf.seek(0)
if size < read_pos:
	""" file has been restarted from scratch! """
	while lf.tell() < size:
		output_f.write(lf.read(1024))
	
elif size == read_pos:
	""" no changes! """
	sys.exit(0)
else:
	""" more to read! """
	lf.seek(read_pos)
	while lf.tell() < size:
		output_f.write(lf.read(1024))

""" rewrite pref file """
try:
	i = newpf.index(None)
except ValueError:
	i = len(newpf)
	newpf += [None]

newpf[i] = "%s:%d\n" % (fn, size)

pf = open(preffn, 'w')
pf.write(''.join(newpf))