#!/usr/bin/python3
#
# This is a helper tool for editing configuration files during the setup
# process. The tool is given new values for settings as command-line
# arguments. It comments-out existing setting values in the configuration
# file and adds new values either after their former location or at the
# end.
#
# The configuration file has settings that look like:
#
# NAME=VALUE
#
# If the -s option is given, then space becomes the delimiter, i.e.:
#
# NAME VALUE
#
# If the -w option is given, then setting lines continue onto following
# lines while the lines start with whitespace, e.g.:
#
# NAME VAL
#   UE

import sys
import re

# sanity check
if len(sys.argv) < 3:
    print("usage: python3 editconf.py /etc/file.conf [-s] [-w] [-t] NAME=VAL [NAME=VAL ...]")
    sys.exit(1)

# parse command line arguments
filename = sys.argv[1]
settings = sys.argv[2:]

delimiter = "="
delimiter_re = r"\s*=\s*"
comment_char = "#"
folded_lines = False
testing = False
while settings[0][0] == "-" and settings[0] != "--":
    opt = settings.pop(0)
    if opt == "-s":
        # Space is the delimiter
        delimiter = " "
        delimiter_re = r"\s+"
    elif opt == "-w":
        # Line folding is possible in this file.
        folded_lines = True
    elif opt == "-c":
        # Specifies a different comment character.
        comment_char = settings.pop(0)
    elif opt == "-t":
        testing = True
    else:
        print("Invalid option.")
        sys.exit(1)

# create the new config file in memory

found = set()
buf = ""
input_lines = list(open(filename))

while len(input_lines) > 0:
    line = input_lines.pop(0)

    # If this configuration file uses folded lines, append any folded lines
    # into our input buffer.
    if folded_lines and line[0] not in (comment_char, " ", ""):
        while len(input_lines) > 0 and input_lines[0][0] in " \t":
            line += input_lines.pop(0)

    # See if this line is for any settings passed on the command line.
    for i in range(len(settings)):
        # Check that this line contain this setting from the command-line arguments.
        name, val = settings[i].split("=", 1)
        m = re.match(
            "(\s*)" +
            "(" + re.escape(comment_char) + "\s*)?" +
            re.escape(name) + delimiter_re + "(.*?)\s*$",
            line, re.S)
        if not m:
            continue
        indent, is_comment, existing_val = m.groups()

        # If this is already the setting, do nothing.
        if is_comment is None and existing_val == val:
            # It may be that we've already inserted this setting higher
            # in the file so check for that first.
            if i in found:
                break
            buf += line
            found.add(i)
            break

        # comment-out the existing line (also comment any folded lines)
        if is_comment is None:
            buf += comment_char + line.rstrip().replace("\n", "\n" + comment_char) + "\n"
        else:
            # the line is already commented, pass it through
            buf += line

        # if this option oddly appears more than once, don't add the setting again
        if i in found:
            break

        # add the new setting
        buf += indent + name + delimiter + val + "\n"

        # note that we've applied this option
        found.add(i)

        break
    else:
        # If did not match any setting names, pass this line through.
        buf += line

# Put any settings we didn't see at the end of the file.
for i in range(len(settings)):
    if i not in found:
        name, val = settings[i].split("=", 1)
        buf += name + delimiter + val + "\n"

if not testing:
    # Write out the new file.
    with open(filename, "w") as f:
        f.write(buf)
else:
    # Just print the new file to stdout.
    print(buf)