#! /usr/bin/env python3

"""Reverse grep.

Usage: rgrep [-i] pattern file
"""

import sys
import re
import getopt


def main():
 bufsize = 64 * 1024
 reflags = 0
 opts, args = getopt.getopt(sys.argv[1:], "i")
 for o, a in opts:
 if o == '-i':
 reflags = reflags | re.IGNORECASE
 if len(args) < 2:
 usage("not enough arguments")
 if len(args) > 2:
 usage("exactly one file argument required")
 pattern, filename = args
 try:
 prog = re.compile(pattern, reflags)
 except re.error as msg:
 usage("error in regular expression: %s" % msg)
 try:
 f = open(filename)
 except IOError as msg:
 usage("can't open %r: %s" % (filename, msg), 1)
 f.seek(0, 2)
 pos = f.tell()
 leftover = None
 while pos > 0:
 size = min(pos, bufsize)
 pos = pos - size
 f.seek(pos)
 buffer = f.read(size)
 lines = buffer.split("\n")
 del buffer
 if leftover is None:
 if not lines[-1]:
 del lines[-1]
 else:
 lines[-1] = lines[-1] + leftover
 if pos > 0:
 leftover = lines[0]
 del lines[0]
 else:
 leftover = None
 for line in reversed(lines):
 if prog.search(line):
 print(line)


def usage(msg, code=2):
 sys.stdout = sys.stderr
 print(msg)
 print(__doc__)
 sys.exit(code)


if __name__ == '__main__':
 main()