#! /usr/bin/env python

"""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, msg:

        usage("error in regular expression: %s" % str(msg))

    try:

        f = open(filename)

    except IOError, msg:

        usage("can't open %s: %s" % (repr(filename), str(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

        lines.reverse()

        for line in 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()