# mpatch.py - Python implementation of mpatch.c

#

# Copyright 2009 Matt Mackall <mpm@selenic.com> and others

#

# This software may be used and distributed according to the terms of the

# GNU General Public License version 2 or any later version.

import struct

try:

    from cStringIO import StringIO

except ImportError:

    from StringIO import StringIO

# This attempts to apply a series of patches in time proportional to

# the total size of the patches, rather than patches * len(text). This

# means rather than shuffling strings around, we shuffle around

# pointers to fragments with fragment lists.

#

# When the fragment lists get too long, we collapse them. To do this

# efficiently, we do all our operations inside a buffer created by

# mmap and simply use memmove. This avoids creating a bunch of large

# temporary string buffers.

def patches(a, bins):

    plens = [len(x) for x in bins]

    pl = sum(plens)

    bl = len(a) + pl

    tl = bl + bl + pl # enough for the patches and two working texts

    b1, b2 = 0, bl

    m = StringIO()

    def move(dest, src, count):

        """move count bytes from src to dest

        The file pointer is left at the end of dest.

        """

        m.seek(src)

        buf = m.read(count)

        m.seek(dest)

        m.write(buf)

    # load our original text

    m.write(a)

    frags = [(len(a), b1)]

    # copy all the patches into our segment so we can memmove from them

    pos = b2 + bl

    m.seek(pos)

    for p in bins: m.write(p)

    def pull(dst, src, l): # pull l bytes from src

        while l:

            f = src.pop(0)

            if f[0] > l: # do we need to split?

                src.insert(0, (f[0] - l, f[1] + l))

                dst.append((l, f[1]))

                return

            dst.append(f)

            l -= f[0]

    def collect(buf, list):

        start = buf

        for l, p in list:

            move(buf, p, l)

            buf += l

        return (buf - start, start)

    for plen in plens:

        # if our list gets too long, execute it

        if len(frags) > 128:

            b2, b1 = b1, b2

            frags = [collect(b1, frags)]

        new = []

        end = pos + plen

        last = 0

        while pos < end:

            m.seek(pos)

            p1, p2, l = struct.unpack(">lll", m.read(12))

            pull(new, frags, p1 - last) # what didn't change

            pull([], frags, p2 - p1)    # what got deleted

            new.append((l, pos + 12))        # what got added

            pos += l + 12

            last = p2

        frags = new + frags                    # what was left at the end

    t = collect(b2, frags)

    m.seek(t[1])

    return m.read(t[0])

def patchedsize(orig, delta):

    outlen, last, bin = 0, 0, 0

    binend = len(delta)

    data = 12

    while data <= binend:

        decode = delta[bin:bin + 12]

        start, end, length = struct.unpack(">lll", decode)

        if start > end:

            break

        bin = data + length

        data = bin + 12

        outlen += start - last

        last = end

        outlen += length

    if bin != binend:

        raise Exception("patch cannot be decoded")

    outlen += orig - last

    return outlen