/*

 bdiff.c - efficient binary diff extension for Mercurial

 Copyright 2005, 2006 Matt Mackall <mpm@selenic.com>

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

 the GNU General Public License, incorporated herein by reference.

 Based roughly on Python difflib

*/

#define PY_SSIZE_T_CLEAN

#include <Python.h>

#include <stdlib.h>

#include <string.h>

#include <limits.h>

#include "compat.h"

#include "util.h"

#include "bitmanipulation.h"

	int hash, n, e;

	ssize_t len;

	const char *l;

};

struct pos {

	int pos, len;

};

	int a1, a2, b1, b2;

};

{

	unsigned hash;

	int i;

	const char *p, *b = a;

	const char * const plast = a + len - 1;

	/* count the lines */

	i = 1; /* extra line for sentinel */

	for (p = a; p < a + len; p++)

		if (*p == '\n' || p == plast)

			i++;

	if (!l)

		return -1;

	/* build the line array and calculate hashes */

	hash = 0;

	for (p = a; p < a + len; p++) {

		/* Leonid Yuriev's hash */

		hash = (hash * 1664525) + (unsigned char)*p + 1013904223;

		if (*p == '\n' || p == plast) {

			l->hash = hash;

			hash = 0;

			l->len = p - b + 1;

			l->l = b;

			l->n = INT_MAX;

			l++;

			b = p + 1;

		}

	}

	/* set up a sentinel */

	l->hash = 0;

	l->len = 0;

	l->l = a + len;

	return i - 1;

}

{

	return a->hash != b->hash || a->len != b->len || memcmp(a->l, b->l, a->len);

}

{

	int i, j, buckets = 1, t, scale;

	struct pos *h = NULL;

	/* build a hash table of the next highest power of 2 */

	while (buckets < bn + 1)

		buckets *= 2;

	/* try to allocate a large hash table to avoid collisions */

	for (scale = 4; scale; scale /= 2) {

		h = (struct pos *)malloc(scale * buckets * sizeof(struct pos));

		if (h)

			break;

	}

	if (!h)

		return 0;

	buckets = buckets * scale - 1;

	/* clear the hash table */

	for (i = 0; i <= buckets; i++) {

		h[i].pos = -1;

		h[i].len = 0;

	}

	/* add lines to the hash table chains */

	for (i = 0; i < bn; i++) {

		/* find the equivalence class */

		for (j = b[i].hash & buckets; h[j].pos != -1;

		     j = (j + 1) & buckets)

			if (!cmp(b + i, b + h[j].pos))

				break;

		/* add to the head of the equivalence class */

		b[i].n = h[j].pos;

		b[i].e = j;

		h[j].pos = i;

		h[j].len++; /* keep track of popularity */

	}

	/* compute popularity threshold */

	t = (bn >= 31000) ? bn / 1000 : 1000000 / (bn + 1);

	/* match items in a to their equivalence class in b */

	for (i = 0; i < an; i++) {

		/* find the equivalence class */

		for (j = a[i].hash & buckets; h[j].pos != -1;

		     j = (j + 1) & buckets)

			if (!cmp(a + i, b + h[j].pos))

				break;

		a[i].e = j; /* use equivalence class for quick compare */

		if (h[j].len <= t)

			a[i].n = h[j].pos; /* point to head of match list */

		else

			a[i].n = -1; /* too popular */

	}

	/* discard hash tables */

	free(h);

	return 1;

}

			 int a1, int a2, int b1, int b2, int *omi, int *omj)

{

	int mi = a1, mj = b1, mk = 0, i, j, k, half;

	/* window our search on large regions to better bound

	   worst-case performance. by choosing a window at the end, we

	   reduce skipping overhead on the b chains. */

	if (a2 - a1 > 30000)

		a1 = a2 - 30000;

	half = (a1 + a2) / 2;

	for (i = a1; i < a2; i++) {

		/* skip all lines in b after the current block */

		for (j = a[i].n; j >= b2; j = b[j].n)

			;

		/* loop through all lines match a[i] in b */

		for (; j >= b1; j = b[j].n) {

			/* does this extend an earlier match? */

			for (k = 1; j - k >= b1 && i - k >= a1; k++) {

				/* reached an earlier match? */

				if (pos[j - k].pos == i - k) {

					k += pos[j - k].len;

					break;

				}

				/* previous line mismatch? */

				if (a[i - k].e != b[j - k].e)

					break;

			}

			pos[j].pos = i;

			pos[j].len = k;

			/* best match so far? we prefer matches closer

			   to the middle to balance recursion */

			if (k > mk || (k == mk && (i <= mi || i < half))) {

				mi = i;

				mj = j;

				mk = k;

			}

		}

	}

	if (mk) {

		mi = mi - mk + 1;

		mj = mj - mk + 1;

	}

	/* expand match to include subsequent popular lines */

	while (mi + mk < a2 && mj + mk < b2 &&

	       a[mi + mk].e == b[mj + mk].e)

		mk++;

	*omi = mi;

	*omj = mj;

	return mk;

}

{

	int i, j, k;

	while (1) {

		/* find the longest match in this chunk */

		k = longest_match(a, b, pos, a1, a2, b1, b2, &i, &j);

		if (!k)

			return l;

		/* and recurse on the remaining chunks on either side */

		l = recurse(a, b, pos, a1, i, b1, j, l);

		if (!l)

			return NULL;

		if (!l->next)

			return NULL;

		l = l->next;

		l->a1 = i;

		l->a2 = i + k;

		l->b1 = j;

		l->b2 = j + k;

		l->next = NULL;

		/* tail-recursion didn't happen, so do equivalent iteration */

		a1 = i + k;

		b1 = j + k;

	}

}

{

	struct pos *pos;

	int t, count = 0;

	/* allocate and fill arrays */

	t = equatelines(a, an, b, bn);

	pos = (struct pos *)calloc(bn ? bn : 1, sizeof(struct pos));

	if (pos && t) {

		/* generate the matching block list */

		curr = recurse(a, b, pos, 0, an, 0, bn, base);

		if (!curr)

			return -1;

		/* sentinel end hunk */

		if (!curr->next)

			return -1;

		curr = curr->next;

		curr->a1 = curr->a2 = an;

		curr->b1 = curr->b2 = bn;

		curr->next = NULL;

	}

	free(pos);

	/* normalize the hunk list, try to push each hunk towards the end */

	for (curr = base->next; curr; curr = curr->next) {

		if (!next)

			break;

		if (curr->a2 == next->a1 || curr->b2 == next->b1)

			while (curr->a2 < an && curr->b2 < bn

			       && next->a1 < next->a2

			       && next->b1 < next->b2

			       && !cmp(a + curr->a2, b + curr->b2)) {

				curr->a2++;

				next->a1++;

				curr->b2++;

				next->b1++;

			}

	}

	for (curr = base->next; curr; curr = curr->next)

		count++;

	return count;

}

{

	for (; l; l = n) {

		n = l->next;

		free(l);

	}

}

static PyObject *blocks(PyObject *self, PyObject *args)

{

	PyObject *sa, *sb, *rl = NULL, *m;

	int an, bn, count, pos = 0;

	l.next = NULL;

	if (!PyArg_ParseTuple(args, "SS:bdiff", &sa, &sb))

		return NULL;

	if (!a || !b)

		goto nomem;

	if (count < 0)

		goto nomem;

	rl = PyList_New(count);

	if (!rl)

		goto nomem;

	for (h = l.next; h; h = h->next) {

		m = Py_BuildValue("iiii", h->a1, h->a2, h->b1, h->b2);

		PyList_SetItem(rl, pos, m);

		pos++;

	}

nomem:

	free(a);

	free(b);

	return rl ? rl : PyErr_NoMemory();

}

static PyObject *bdiff(PyObject *self, PyObject *args)

{

	char *sa, *sb, *rb;

	PyObject *result = NULL;

	int an, bn, count;

	Py_ssize_t len = 0, la, lb;

	PyThreadState *_save;

	l.next = NULL;

	if (!PyArg_ParseTuple(args, "s#s#:bdiff", &sa, &la, &sb, &lb))

		return NULL;

	if (la > UINT_MAX || lb > UINT_MAX) {

		PyErr_SetString(PyExc_ValueError, "bdiff inputs too large");

		return NULL;

	}

	_save = PyEval_SaveThread();

	if (!al || !bl)

		goto nomem;

	if (count < 0)

		goto nomem;

	/* calculate length of output */

	la = lb = 0;

	for (h = l.next; h; h = h->next) {

		if (h->a1 != la || h->b1 != lb)

			len += 12 + bl[h->b1].l - bl[lb].l;

		la = h->a2;

		lb = h->b2;

	}

	PyEval_RestoreThread(_save);

	_save = NULL;

	result = PyBytes_FromStringAndSize(NULL, len);

	if (!result)

		goto nomem;

	/* build binary patch */

	rb = PyBytes_AsString(result);

	la = lb = 0;

	for (h = l.next; h; h = h->next) {

		if (h->a1 != la || h->b1 != lb) {

			len = bl[h->b1].l - bl[lb].l;

			putbe32((uint32_t)(al[la].l - al->l), rb);

			putbe32((uint32_t)(al[h->a1].l - al->l), rb + 4);

			putbe32((uint32_t)len, rb + 8);

			memcpy(rb + 12, bl[lb].l, len);

			rb += 12 + len;

		}

		la = h->a2;

		lb = h->b2;

	}

nomem:

	if (_save)

		PyEval_RestoreThread(_save);

	free(al);

	free(bl);

	return result ? result : PyErr_NoMemory();

}

/*

 * If allws != 0, remove all whitespace (' ', \t and \r). Otherwise,

 * reduce whitespace sequences to a single space and trim remaining whitespace

 * from end of lines.

 */

static PyObject *fixws(PyObject *self, PyObject *args)

{

	PyObject *s, *result = NULL;

	char allws, c;

	const char *r;

	Py_ssize_t i, rlen, wlen = 0;

	char *w;

	if (!PyArg_ParseTuple(args, "Sb:fixws", &s, &allws))

		return NULL;

	r = PyBytes_AsString(s);

	rlen = PyBytes_Size(s);

	w = (char *)malloc(rlen ? rlen : 1);

	if (!w)

		goto nomem;

	for (i = 0; i != rlen; i++) {

		c = r[i];

		if (c == ' ' || c == '\t' || c == '\r') {

			if (!allws && (wlen == 0 || w[wlen - 1] != ' '))

				w[wlen++] = ' ';

		} else if (c == '\n' && !allws

			  && wlen > 0 && w[wlen - 1] == ' ') {

			w[wlen - 1] = '\n';

		} else {

			w[wlen++] = c;

		}

	}

	result = PyBytes_FromStringAndSize(w, wlen);

nomem:

	free(w);

	return result ? result : PyErr_NoMemory();

}

static char mdiff_doc[] = "Efficient binary diff.";

static PyMethodDef methods[] = {

	{"bdiff", bdiff, METH_VARARGS, "calculate a binary diff\n"},

	{"blocks", blocks, METH_VARARGS, "find a list of matching lines\n"},

	{"fixws", fixws, METH_VARARGS, "normalize diff whitespaces\n"},

	{NULL, NULL}

};

#ifdef IS_PY3K

static struct PyModuleDef bdiff_module = {

	PyModuleDef_HEAD_INIT,

	"bdiff",

	mdiff_doc,

	-1,

	methods

};

PyMODINIT_FUNC PyInit_bdiff(void)

{

	return PyModule_Create(&bdiff_module);

}

#else

PyMODINIT_FUNC initbdiff(void)

{

	Py_InitModule3("bdiff", methods, mdiff_doc);

}

#endif