~bzr-pqm/bzr/bzr.dev

# (C) 2005 Matt Mackall

# (C) 2005 Canonical Ltd

# based on code by Matt Mackall, hacked by Martin Pool

# mm's code works line-by-line; this just works on byte strings.

# Possibly slower; possibly gives better results for code not

# regularly separated by newlines and anyhow a bit simpler.

# 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

# TODO: maybe work on files not strings?

# FIXME: doesn't work properly on files without trailing newlines

import difflib

import struct

import sys

import unittest

from cStringIO import StringIO

def linesplit(a):

    """Split into two lists: content and line positions.

    This returns (al, ap).

    al[i] is the string content of line i of the file, including its

    newline (if any).

    ap[i] is the byte position in the file where that line starts.

    ap[-1] is the byte position of the end of the file (i.e. the

    length of the file.)

    This transformation allows us to do a line-based diff and then map

    back to byte positions.

    """

    al, ap = [], []

    last = 0

    n = a.find("\n") + 1

    while n > 0:

        ap.append(last)

        al.append(a[last:n])

        last = n

        n = a.find("\n", n) + 1

    if last < len(a):

        al.append(a[last:])

        ap.append(last)

    # position at the end

    ap.append(len(a))

    return (al, ap)

def diff(a, b):

    # TODO: Use different splits, perhaps rsync-like, for binary files?

    (al, ap) = linesplit(a)

    (bl, bp) = linesplit(b)

    d = difflib.SequenceMatcher(None, al, bl)

    ## sys.stderr.write('  ~ real_quick_ratio: %.4f\n' % d.real_quick_ratio())

    for o, m, n, s, t in d.get_opcodes():

        if o == 'equal': continue

        # a[m:n] should be replaced by b[s:t]

        if s == t:

            yield ap[m], ap[n], ''

        else:

            yield ap[m], ap[n], ''.join(bl[s:t])

def tobinary(ops):

    b = StringIO()

    for f in ops:

        b.write(struct.pack(">III", f[0], f[1], len(f[2])))

        b.write(f[2])

    return b.getvalue()

def bdiff(a, b):

    return tobinary(diff(a, b))

def patch(t, ops):

    last = 0

    b = StringIO()

    for m, n, r in ops:

        b.write(t[last:m])

        if r:

            b.write(r)

        last = n

    b.write(t[last:])

    return b.getvalue()

def frombinary(b):

    bin = StringIO(b)

    while True:

        p = bin.read(12)

        if not p:

            break

        m, n, l = struct.unpack(">III", p)

        if l == 0:

            r = ''

        else:

            r = bin.read(l)

            if len(r) != l:

                raise Exception("truncated patch data")

        yield m, n, r

def bpatch(t, b):

    return patch(t, frombinary(b))

class TestDiffPatch(unittest.TestCase):

    def doDiffPatch(self, old, new):

        diff = bdiff(old, new)

        result = bpatch(old, diff)

        self.assertEquals(new, result)

    def testSimpleDiff(self):

        """Simply add a line at the end"""

        self.doDiffPatch('a\nb\n', 'a\nb\nc\n')

    def testTrailingLine(self):

        """Test diff that adds an unterminated line.

        (Old versions didn't do this properly.)"""

        self.doDiffPatch('a\nb\nc\n',

                         'a\nb\nc\nd')

if __name__ == '__main__':

    unittest.main()