# Filename: grep.py
# Author: Ian N. Schenck
# Version: 8/23/2005
#
# This script accepts regular expressions, as well as an "invert"
# option, and applies the regular expression using grep.  This wrapper
# provides security and pipeline.
#
# Grep is launched based on these inputs:
# -i		Input file
# -o		Output file
# -pattern	RegEx pattern
# -v	        true or false (output NON-matching lines)

import sys
import os
import re
import string
import commands
from subprocess import Popen, PIPE
from tempfile import NamedTemporaryFile

# This function is exceedingly useful, perhaps package for reuse?
def getopts(argv):
    opts = {}
    while argv:
	if argv[0][0] == '-':
	    opts[argv[0]] = argv[1]
	    argv = argv[2:]
	else:
	    argv = argv[1:]
    return opts

def main():
    args = sys.argv[1:]

    try:
        opts = getopts(args)
    except IndexError:
        print "Usage:"
        print " -i		Input file"
        print " -o		Output file"
        print " -pattern	RegEx pattern"
        print " -v		true or false (Invert match)"
        return 0

    outputfile = opts.get("-o")
    if outputfile == None:
        print "No output file specified."
        return -1
    
    inputfile = opts.get("-i")
    if inputfile == None:
        print "No input file specified."
        return -2

    invert = opts.get("-v")
    if invert == None:
        print "Match style (Invert or normal) not specified."
        return -3

    pattern = opts.get("-pattern")
    if pattern == None:
        print "RegEx pattern not specified."
        return -4

    # All inputs have been specified at this point, now validate.

    # replace if input has been escaped, remove sq
    # characters that are allowed but need to be escaped
    mapped_chars =  {   '>' :'__gt__',
                        '<' :'__lt__',
                        '\'':'__sq__',
                        '"' :'__dq__',
                        '[' :'__ob__',
                        ']' :'__cb__',
                        '{' :'__oc__',
                        '}' :'__cc__'
                    }
    
    # with new sanitizing we only need to replace for single quote,
    # but this needs to remain for backwards compatibility
    for key, value in mapped_chars.items():
        pattern = pattern.replace(value, key)

    # match filename and invert flag
    fileRegEx = re.compile("^[A-Za-z0-9./\-_]+$")
    invertRegEx = re.compile("(true)|(false)")

    # verify that filename and inversion flag are in the correct format
    if not fileRegEx.match(outputfile):
        print "Illegal output filename."
        return -5
    if not fileRegEx.match(inputfile):
        print "Illegal input filename."
        return -6
    if not invertRegEx.match(invert):
        print "Illegal invert option."
        return -7

    # invert grep search?
    if invert == "true":
        invertflag = "-v"
        print "Not matching pattern: %s" % pattern
    else:
        invertflag = ""
        print "Matching pattern: %s" % pattern

    # set version flag
    versionflag  = "-P"
    
    # MacOS 10.8.2 does not support -P option for perl-regex anymore
    versionmatch = Popen("grep -V | grep 'BSD'", shell=True, stdout=PIPE).communicate()[0];
    if versionmatch:
        versionflag = "-E"

    # create temp file holding pattern
    # by using a file to hold the pattern, we don't have worry about sanitizing grep commandline and can include single quotes in pattern
    pattern_file_name = NamedTemporaryFile().name
    open( pattern_file_name, 'w' ).write( pattern )
    
    # generate grep command
    commandline = "grep %s %s -f %s %s > %s" % ( versionflag, invertflag, pattern_file_name, inputfile, outputfile )
    
    # run grep
    errorcode, stdout = commands.getstatusoutput(commandline)
    
    # remove temp pattern file
    os.unlink( pattern_file_name )
    
    # return error code
    return errorcode

if __name__ == "__main__":
    main()