/*
mpatch.c - efficient binary patching for Mercurial

This implements a patch algorithm that's O(m + nlog n) where m is the
size of the output and n is the number of patches.

Given a list of binary patches, it unpacks each into a hunk list,
then combines the hunk lists with a treewise recursion to form a
single hunk list. This hunk list is then applied to the original
text.

The text (or binary) fragments are copied directly from their source
Python objects into a preallocated output string to avoid the
allocation of intermediate Python objects. Working memory is about 2x
the total number of hunks.

Copyright 2005, 2006 Matt Mackall <[email protected]>

This software may be used and distributed according to the terms
of the GNU General Public License, incorporated herein by reference.
*/

#include <Python.h>
#include <stdlib.h>
#include <string.h>

/* Definitions to get compatibility with python 2.4 and earlier which
  does not have Py_ssize_t. See also PEP 353.
  Note: msvc (8 or earlier) does not have ssize_t, so we use Py_ssize_t.
*/
#if PY_VERSION_HEX < 0x02050000 && !defined(PY_SSIZE_T_MIN)
typedef int Py_ssize_t;
#define PY_SSIZE_T_MAX INT_MAX
#define PY_SSIZE_T_MIN INT_MIN
#endif

#ifdef _WIN32
# ifdef _MSC_VER
/* msvc 6.0 has problems */
#  define inline __inline
typedef unsigned long uint32_t;
# else
#  include <stdint.h>
# endif
static uint32_t ntohl(uint32_t x)
{
       return ((x & 0x000000ffUL) << 24) |
               ((x & 0x0000ff00UL) <<  8) |
               ((x & 0x00ff0000UL) >>  8) |
               ((x & 0xff000000UL) >> 24);
}
#else
/* not windows */
# include <sys/types.h>
# if defined __BEOS__ && !defined __HAIKU__
#  include <ByteOrder.h>
# else
#  include <arpa/inet.h>
# endif
# include <inttypes.h>
#endif

static char mpatch_doc[] = "Efficient binary patching.";
static PyObject *mpatch_Error;

struct frag {
       int start, end, len;
       const char *data;
};

struct flist {
       struct frag *base, *head, *tail;
};

static struct flist *lalloc(int size)
{
       struct flist *a = NULL;

       if (size < 1)
               size = 1;

       a = (struct flist *)malloc(sizeof(struct flist));
       if (a) {
               a->base = (struct frag *)malloc(sizeof(struct frag) * size);
               if (a->base) {
                       a->head = a->tail = a->base;
                       return a;
               }
               free(a);
               a = NULL;
       }
       if (!PyErr_Occurred())
               PyErr_NoMemory();
       return NULL;
}

static void lfree(struct flist *a)
{
       if (a) {
               free(a->base);
               free(a);
       }
}

static int lsize(struct flist *a)
{
       return a->tail - a->head;
}

/* move hunks in source that are less cut to dest, compensating
  for changes in offset. the last hunk may be split if necessary.
*/
static int gather(struct flist *dest, struct flist *src, int cut, int offset)
{
       struct frag *d = dest->tail, *s = src->head;
       int postend, c, l;

       while (s != src->tail) {
               if (s->start + offset >= cut)
                       break; /* we've gone far enough */

               postend = offset + s->start + s->len;
               if (postend <= cut) {
                       /* save this hunk */
                       offset += s->start + s->len - s->end;
                       *d++ = *s++;
               }
               else {
                       /* break up this hunk */
                       c = cut - offset;
                       if (s->end < c)
                               c = s->end;
                       l = cut - offset - s->start;
                       if (s->len < l)
                               l = s->len;

                       offset += s->start + l - c;

                       d->start = s->start;
                       d->end = c;
                       d->len = l;
                       d->data = s->data;
                       d++;
                       s->start = c;
                       s->len = s->len - l;
                       s->data = s->data + l;

                       break;
               }
       }

       dest->tail = d;
       src->head = s;
       return offset;
}

/* like gather, but with no output list */
static int discard(struct flist *src, int cut, int offset)
{
       struct frag *s = src->head;
       int postend, c, l;

       while (s != src->tail) {
               if (s->start + offset >= cut)
                       break;

               postend = offset + s->start + s->len;
               if (postend <= cut) {
                       offset += s->start + s->len - s->end;
                       s++;
               }
               else {
                       c = cut - offset;
                       if (s->end < c)
                               c = s->end;
                       l = cut - offset - s->start;
                       if (s->len < l)
                               l = s->len;

                       offset += s->start + l - c;
                       s->start = c;
                       s->len = s->len - l;
                       s->data = s->data + l;

                       break;
               }
       }

       src->head = s;
       return offset;
}

/* combine hunk lists a and b, while adjusting b for offset changes in a/
  this deletes a and b and returns the resultant list. */
static struct flist *combine(struct flist *a, struct flist *b)
{
       struct flist *c = NULL;
       struct frag *bh, *ct;
       int offset = 0, post;

       if (a && b)
               c = lalloc((lsize(a) + lsize(b)) * 2);

       if (c) {

               for (bh = b->head; bh != b->tail; bh++) {
                       /* save old hunks */
                       offset = gather(c, a, bh->start, offset);

                       /* discard replaced hunks */
                       post = discard(a, bh->end, offset);

                       /* insert new hunk */
                       ct = c->tail;
                       ct->start = bh->start - offset;
                       ct->end = bh->end - post;
                       ct->len = bh->len;
                       ct->data = bh->data;
                       c->tail++;
                       offset = post;
               }

               /* hold on to tail from a */
               memcpy(c->tail, a->head, sizeof(struct frag) * lsize(a));
               c->tail += lsize(a);
       }

       lfree(a);
       lfree(b);
       return c;
}

/* decode a binary patch into a hunk list */
static struct flist *decode(const char *bin, int len)
{
       struct flist *l;
       struct frag *lt;
       const char *data = bin + 12, *end = bin + len;
       char decode[12]; /* for dealing with alignment issues */

       /* assume worst case size, we won't have many of these lists */
       l = lalloc(len / 12 + 1);
       if (!l)
               return NULL;

       lt = l->tail;

       while (data <= end) {
               memcpy(decode, bin, 12);
               lt->start = ntohl(*(uint32_t *)decode);
               lt->end = ntohl(*(uint32_t *)(decode + 4));
               lt->len = ntohl(*(uint32_t *)(decode + 8));
               if (lt->start > lt->end || lt->len < 0)
                       break; /* sanity check */
               bin = data + lt->len;
               if (bin < data)
                       break; /* big data + big (bogus) len can wrap around */
               lt->data = data;
               data = bin + 12;
               lt++;
       }

       if (bin != end) {
               if (!PyErr_Occurred())
                       PyErr_SetString(mpatch_Error, "patch cannot be decoded");
               lfree(l);
               return NULL;
       }

       l->tail = lt;
       return l;
}

/* calculate the size of resultant text */
static int calcsize(int len, struct flist *l)
{
       int outlen = 0, last = 0;
       struct frag *f = l->head;

       while (f != l->tail) {
               if (f->start < last || f->end > len) {
                       if (!PyErr_Occurred())
                               PyErr_SetString(mpatch_Error,
                                               "invalid patch");
                       return -1;
               }
               outlen += f->start - last;
               last = f->end;
               outlen += f->len;
               f++;
       }

       outlen += len - last;
       return outlen;
}

static int apply(char *buf, const char *orig, int len, struct flist *l)
{
       struct frag *f = l->head;
       int last = 0;
       char *p = buf;

       while (f != l->tail) {
               if (f->start < last || f->end > len) {
                       if (!PyErr_Occurred())
                               PyErr_SetString(mpatch_Error,
                                               "invalid patch");
                       return 0;
               }
               memcpy(p, orig + last, f->start - last);
               p += f->start - last;
               memcpy(p, f->data, f->len);
               last = f->end;
               p += f->len;
               f++;
       }
       memcpy(p, orig + last, len - last);
       return 1;
}

/* recursively generate a patch of all bins between start and end */
static struct flist *fold(PyObject *bins, int start, int end)
{
       int len;
       Py_ssize_t blen;
       const char *buffer;

       if (start + 1 == end) {
               /* trivial case, output a decoded list */
               PyObject *tmp = PyList_GetItem(bins, start);
               if (!tmp)
                       return NULL;
               if (PyObject_AsCharBuffer(tmp, &buffer, &blen))
                       return NULL;
               return decode(buffer, blen);
       }

       /* divide and conquer, memory management is elsewhere */
       len = (end - start) / 2;
       return combine(fold(bins, start, start + len),
                      fold(bins, start + len, end));
}

static PyObject *
patches(PyObject *self, PyObject *args)
{
       PyObject *text, *bins, *result;
       struct flist *patch;
       const char *in;
       char *out;
       int len, outlen;
       Py_ssize_t inlen;

       if (!PyArg_ParseTuple(args, "OO:mpatch", &text, &bins))
               return NULL;

       len = PyList_Size(bins);
       if (!len) {
               /* nothing to do */
               Py_INCREF(text);
               return text;
       }

       if (PyObject_AsCharBuffer(text, &in, &inlen))
               return NULL;

       patch = fold(bins, 0, len);
       if (!patch)
               return NULL;

       outlen = calcsize(inlen, patch);
       if (outlen < 0) {
               result = NULL;
               goto cleanup;
       }
       result = PyString_FromStringAndSize(NULL, outlen);
       if (!result) {
               result = NULL;
               goto cleanup;
       }
       out = PyString_AsString(result);
       if (!apply(out, in, inlen, patch)) {
               Py_DECREF(result);
               result = NULL;
       }
cleanup:
       lfree(patch);
       return result;
}

/* calculate size of a patched file directly */
static PyObject *
patchedsize(PyObject *self, PyObject *args)
{
       long orig, start, end, len, outlen = 0, last = 0;
       int patchlen;
       char *bin, *binend, *data;
       char decode[12]; /* for dealing with alignment issues */

       if (!PyArg_ParseTuple(args, "ls#", &orig, &bin, &patchlen))
               return NULL;

       binend = bin + patchlen;
       data = bin + 12;

       while (data <= binend) {
               memcpy(decode, bin, 12);
               start = ntohl(*(uint32_t *)decode);
               end = ntohl(*(uint32_t *)(decode + 4));
               len = ntohl(*(uint32_t *)(decode + 8));
               if (start > end)
                       break; /* sanity check */
               bin = data + len;
               if (bin < data)
                       break; /* big data + big (bogus) len can wrap around */
               data = bin + 12;
               outlen += start - last;
               last = end;
               outlen += len;
       }

       if (bin != binend) {
               if (!PyErr_Occurred())
                       PyErr_SetString(mpatch_Error, "patch cannot be decoded");
               return NULL;
       }

       outlen += orig - last;
       return Py_BuildValue("l", outlen);
}

static PyMethodDef methods[] = {
       {"patches", patches, METH_VARARGS, "apply a series of patches\n"},
       {"patchedsize", patchedsize, METH_VARARGS, "calculed patched size\n"},
       {NULL, NULL}
};

PyMODINIT_FUNC
initmpatch(void)
{
       Py_InitModule3("mpatch", methods, mpatch_doc);
       mpatch_Error = PyErr_NewException("mpatch.mpatchError", NULL, NULL);
}

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