#!/usr/bin/env python3
import os, sys, re

#######################################################
def showMatchObject( MO):
    try:
        print( '\n.string = %r' % ( MO.string))
        groupCtr = -1
        while True:
            groupCtr += 1
            try:
                print( '.group( %d) = %r' % ( groupCtr, MO.group( groupCtr)))
            except:
                break
    except AttributeError:
        print( '\nMO = %r' % ( MO))
#######################################################

ipv4MatchStr = r'[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}'
ipv6MatchChars = r'A-Fa-f0-9:.'
LOGCHECK_HOST_IP_MS = ''.join(
    [
        r'(',                            ## below is "alternative match 1"
            r'(',
                r'(?<!',
                    r'::[Ff]{4}:',
                r')',
                ipv4MatchStr,
            r')',
        r'|',                           ## below is "alternative match 2"
            r'(',
                r'(?<=',
                    r'::[Ff]{4}:',
                r')',
                ipv4MatchStr,
            r')',
        ## r'|',                        ## below is "alternative match 3"
        ##     r'(',                    ## which is here commented out because
        ##         r'(?<=',             ## it *always* matches even though "alternative match 1"
        ##             r'[^',           ## is leftmost.
        ##                 ipv6MatchChars,
        ##             r']',
        ##         r')',
        ##         r'[',
        ##             ipv6MatchChars,
        ##         r']+',
        ##     r')',
        r')',
    ],
)
LOGCHECK_HOST_IP_RE = re.compile( LOGCHECK_HOST_IP_MS)

## The leftmost alternative ("alternative match 1") is matched
## unless the rightmost alternative ("alternative match 3") is uncommented.
showMatchObject(
    LOGCHECK_HOST_IP_RE.search(
        '[::ffff:208.123.4.22',
    ),
)

## These possibilities are the other ones I'm trying to account for in a single
## regexp.  They are provided here only as an explanation of what I'm up to,
## here, i.e., resolving a reporting problem related to logcheck and fail2ban.

## showMatchObject(
##     LOGCHECK_HOST_IP_RE.search(
##         '[208.123.4.22',
##     ),
## )
## showMatchObject(
##     LOGCHECK_HOST_IP_RE.search(
##         '[:abcd:098123.09123',
##     ),
## )