# DistUpgradeEdPatcher.py
#
# Copyright (c) 2011 Canonical
#
# Author: Michael Vogt <[email protected]>
#
# This program is free software; you can redistribute it and/or
# modify it under the terms of the GNU General Public License as
# published by the Free Software Foundation; either version 2 of the
# License, or (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
# USA

import hashlib
import re


class PatchError(Exception):
""" Error during the patch process """
pass

def patch(orig, edpatch, result_md5sum=None):
""" python implementation of enough "ed" to apply ed-style
patches. Note that this patches in memory so its *not*
suitable for big files
"""

# we only have two states, waiting for command or reading data
(STATE_EXPECT_COMMAND,
STATE_EXPECT_DATA) = range(2)

# this is inefficient for big files
orig_lines = open(orig, encoding="UTF-8").readlines()
start = end = 0

# we start in wait-for-commend state
state = STATE_EXPECT_COMMAND
for line in open(edpatch, encoding="UTF-8"):
if state == STATE_EXPECT_COMMAND:
# in commands get rid of whitespace,
line = line.strip()
# check if we have a substitute command
if line.startswith("s/"):
# strip away the "s/"
line = line[2:]
# chop off the flags at the end
subs, flags = line.rsplit("/", 1)
if flags:
raise PatchError("flags for s// not supported yet")
# get the actual substitution regexp and replacement and
# execute it
regexp, sep, repl = subs.partition("/")
new, count = re.subn(regexp, repl, orig_lines[start], count=1)
orig_lines[start] = new
continue
# otherwise the last char is the command
command = line[-1]
# read address
(start_str, sep, end_str) = line[:-1].partition(",")
# ed starts with 1 while python with 0
start = int(start_str)
start -= 1
# if we don't have end, set it to the next line
if end_str is "":
end = start+1
else:
end = int(end_str)
# interpret command
if command == "c":
del orig_lines[start:end]
state = STATE_EXPECT_DATA
start -= 1
elif command == "a":
# not allowed to have a range in append
state = STATE_EXPECT_DATA
elif command == "d":
del orig_lines[start:end]
else:
raise PatchError("unknown command: '%s'" % line)
elif state == STATE_EXPECT_DATA:
# this is the data end marker
if line == ".\n":
state = STATE_EXPECT_COMMAND
else:
# copy line verbatim and increase position
start += 1
orig_lines.insert(start, line)

# done with the patching, (optional) verify and write result
result = "".join(orig_lines)
if result_md5sum:
md5 = hashlib.md5()
md5.update(result.encode("UTF-8"))
if md5.hexdigest() != result_md5sum:
raise PatchError("the md5sum after patching is not correct")
open(orig, "w", encoding="UTF-8").write(result)
return True