#!/usr/bin/python3

"""Like *ix head, but allows arbitrary line terminators."""

import os
import sys

sys.path.insert(0, '/usr/local/lib')
sys.path.insert(0, os.path.expanduser('~/lib'))

import readline0  # noqa: E402


def usage(retval):
    """Output a usage message."""
    sys.stderr.write('Usage: %s [-n lines] [-d delimiter] [-h]\n' % (sys.argv[0], ))
    sys.stderr.write('-n lines\tsays to output so many lines\n')
    sys.stderr.write('-d delimiter\tsays separate lines on "delimiter", not on a null byte\n')
    sys.stderr.write('-h\tsays to output this help message\n')
    sys.stderr.write('-v\tsays to operate verbosely\n')
    sys.exit(retval)


number_of_lines = -1
delimiter = b'\0'
verbose = False

while sys.argv[1:]:
    if sys.argv[1] == '-n' and sys.argv[2:]:
        number_of_lines = int(sys.argv[2])
        del sys.argv[1]
    elif sys.argv[1] == '-d' and sys.argv[2:]:
        delimiter = sys.argv[2]
        if len(delimiter) != 1:
            # Actually, multi-character delimiters might be fine. I've not tested that.
            sys.stderr.write('Sorry, your delimiter %s is invalid.  It must be a single character\n' % delimiter)
            usage(1)
        del sys.argv[1]
    elif sys.argv[1] == '-h':
        usage(0)
    elif sys.argv[1] == '-v':
        verbose = True
    else:
        usage(1)
    del sys.argv[1]

if number_of_lines < 0:
    sys.stderr.write('Sorry, you must give a non-negative number of lines with -n\n')
    usage(1)

for lineno, line in enumerate(readline0.readline0(file_=0, separator=delimiter)):
    if lineno >= number_of_lines:
        break
    if verbose:
        sys.stderr.write('Line number %d\n' % lineno)
        sys.stderr.write('type(line) == %s' % (type(line)), )
    os.write(1, line + delimiter)