#!/usr/bin/python

import difflib, struct, mmap

devzero = file("/dev/zero")

def unidiff(a, ad, b, bd, fn):

    if not a and not b: return ""

    a = a.splitlines(1)

    b = b.splitlines(1)

    l = list(difflib.unified_diff(a, b, "a/" + fn, "b/" + fn, ad, bd))

    return "".join(l)

def textdiff(a, b):

    return diff(a.splitlines(1), b.splitlines(1))

def sortdiff(a, b):

    la = lb = 0

    while 1:

        if la >= len(a) or lb >= len(b): break

        if b[lb] < a[la]:

            si = lb

            while lb < len(b) and b[lb] < a[la] : lb += 1

            yield "insert", la, la, si, lb

        elif a[la] < b[lb]:

            si = la

            while la < len(a) and a[la] < b[lb]: la += 1

            yield "delete", si, la, lb, lb

        else:

            la += 1

            lb += 1

    if lb < len(b):

        yield "insert", la, la, lb, len(b)

    if la < len(a):

        yield "delete", la, len(a), lb, lb

def diff(a, b, sorted=0):

    bin = []

    p = [0]

    for i in a: p.append(p[-1] + len(i))

    if sorted:

        d = sortdiff(a, b)

    else:

        d = difflib.SequenceMatcher(None, a, b).get_opcodes()

    for o, m, n, s, t in d:

        if o == 'equal': continue

        s = "".join(b[s:t])

        bin.append(struct.pack(">lll", p[m], p[n], len(s)) + s)

    return "".join(bin)

# 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):

    if not bins: return a

    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

    if not tl: return a

    m = mmap.mmap(devzero.fileno(), tl, mmap.MAP_PRIVATE)

    # 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:

            m.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:

            p1, p2, l = struct.unpack(">lll", m[pos:pos + 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)

    return m[t[1]:t[1] + t[0]]

def patch(a, bin):

    return patches(a, [bin])

try:

    import mpatch

    patches = mpatch.patches

except:

    pass