#!/usr/bin/env python
# -*- coding: utf-8 -*-
"""
  lcz -- estimate line-count of gzip file
  Intended for log files with regular line lengths and content.

  Usage: lcz FILE

"""
import gzip
import sys
import textwrap
import zlib

SAMPLE_SIZE = 51200
z = zlib.decompressobj(-zlib.MAX_WBITS)

try:
    with gzip.open(sys.argv[1], 'r') as f:
        f._init_read()
        f._read_gzip_header()
        zchunk = f.fileobj.read(SAMPLE_SIZE)
        f.fileobj.seek(0, 2)
        file_size = f.fileobj.tell()
except IndexError:
    sys.exit(textwrap.dedent(__doc__).strip())
except IOError as e:
    sys.exit(textwrap.dedent(__doc__).strip() + '\n' + str(e))
else:
    chunk = z.decompress(zchunk)
    zbytes_per_line = float(SAMPLE_SIZE) / chunk.count('\n')
    print(file_size / zbytes_per_line)