/*

 pathencode.c - efficient path name encoding

 Copyright 2012 Facebook

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

 the GNU General Public License, incorporated herein by reference.

*/

/*

 * An implementation of the name encoding scheme used by the fncache

 * store.  The common case is of a path < 120 bytes long, which is

 * handled either in a single pass with no allocations or two passes

 * with a single allocation.  For longer paths, multiple passes are

 * required.

 */

#include <Python.h>

#include <assert.h>

#include <ctype.h>

#include <stdlib.h>

#include <string.h>

#include "util.h"

/* state machine for the fast path */

enum path_state {

	START,   /* first byte of a path component */

	A,       /* "AUX" */

	AU,

	THIRD,   /* third of a 3-byte sequence, e.g. "AUX", "NUL" */

	C,       /* "CON" or "COMn" */

	CO,

	COMLPT,  /* "COM" or "LPT" */

	COMLPTn,

	L,

	LP,

	N,

	NU,

	P,       /* "PRN" */

	PR,

	LDOT,    /* leading '.' */

	DOT,     /* '.' in a non-leading position */

	H,       /* ".h" */

	HGDI,    /* ".hg", ".d", or ".i" */

	SPACE,

	DEFAULT, /* byte of a path component after the first */

};

/* state machine for dir-encoding */

enum dir_state {

	DDOT,

	DH,

	DHGDI,

	DDEFAULT,

};

static inline int inset(const uint32_t bitset[], char c)

{

	return bitset[((uint8_t)c) >> 5] & (1 << (((uint8_t)c) & 31));

}

static inline void charcopy(char *dest, Py_ssize_t *destlen, size_t destsize,

                            char c)

{

	if (dest) {

		assert(*destlen < destsize);

		dest[*destlen] = c;

	}

	(*destlen)++;

}

static inline void memcopy(char *dest, Py_ssize_t *destlen, size_t destsize,

                           const void *src, Py_ssize_t len)

{

	if (dest) {

		assert(*destlen + len < destsize);

		memcpy((void *)&dest[*destlen], src, len);

	}

	*destlen += len;

}

static inline void hexencode(char *dest, Py_ssize_t *destlen, size_t destsize,

			     uint8_t c)

{

	static const char hexdigit[] = "0123456789abcdef";

	charcopy(dest, destlen, destsize, hexdigit[c >> 4]);

	charcopy(dest, destlen, destsize, hexdigit[c & 15]);

}

/* 3-byte escape: tilde followed by two hex digits */

static inline void escape3(char *dest, Py_ssize_t *destlen, size_t destsize,

			   char c)

{

	charcopy(dest, destlen, destsize, '~');

	hexencode(dest, destlen, destsize, c);

}

static Py_ssize_t _encodedir(char *dest, size_t destsize,

                             const char *src, Py_ssize_t len)

{

	enum dir_state state = DDEFAULT;

	Py_ssize_t i = 0, destlen = 0;

	while (i < len) {

		switch (state) {

		case DDOT:

			switch (src[i]) {

			case 'd':

			case 'i':

				state = DHGDI;

				charcopy(dest, &destlen, destsize, src[i++]);

				break;

			case 'h':

				state = DH;

				charcopy(dest, &destlen, destsize, src[i++]);

				break;

			default:

				state = DDEFAULT;

				break;

			}

			break;

		case DH:

			if (src[i] == 'g') {

				state = DHGDI;

				charcopy(dest, &destlen, destsize, src[i++]);

			}

			else state = DDEFAULT;

			break;

		case DHGDI:

			if (src[i] == '/') {

				memcopy(dest, &destlen, destsize, ".hg", 3);

				charcopy(dest, &destlen, destsize, src[i++]);

			}

			state = DDEFAULT;

			break;

		case DDEFAULT:

			if (src[i] == '.')

				state = DDOT;

			charcopy(dest, &destlen, destsize, src[i++]);

			break;

		}

	}

	return destlen;

}

PyObject *encodedir(PyObject *self, PyObject *args)

{

	Py_ssize_t len, newlen;

	PyObject *pathobj, *newobj;

	char *path;

	if (!PyArg_ParseTuple(args, "O:encodedir", &pathobj))

		return NULL;

	if (PyString_AsStringAndSize(pathobj, &path, &len) == -1) {

		PyErr_SetString(PyExc_TypeError, "expected a string");

		return NULL;

	}

	newlen = len ? _encodedir(NULL, 0, path, len + 1) : 1;

	if (newlen == len + 1) {

		Py_INCREF(pathobj);

		return pathobj;

	}

	newobj = PyString_FromStringAndSize(NULL, newlen);

	if (newobj) {

		PyString_GET_SIZE(newobj)--;

		_encodedir(PyString_AS_STRING(newobj), newlen, path,

			   len + 1);

	}

	return newobj;

}

static Py_ssize_t _encode(const uint32_t twobytes[8], const uint32_t onebyte[8],

			  char *dest, Py_ssize_t destlen, size_t destsize,

			  const char *src, Py_ssize_t len,

			  int encodedir)

{

	enum path_state state = START;

	Py_ssize_t i = 0;

	/*

	 * Python strings end with a zero byte, which we use as a

	 * terminal token as they are not valid inside path names.

	 */

	while (i < len) {

		switch (state) {

		case START:

			switch (src[i]) {

			case '/':

				charcopy(dest, &destlen, destsize, src[i++]);

				break;

			case '.':

				state = LDOT;

				escape3(dest, &destlen, destsize, src[i++]);

				break;

			case ' ':

				state = DEFAULT;

				escape3(dest, &destlen, destsize, src[i++]);

				break;

			case 'a':

				state = A;

				charcopy(dest, &destlen, destsize, src[i++]);

				break;

			case 'c':

				state = C;

				charcopy(dest, &destlen, destsize, src[i++]);

				break;

			case 'l':

				state = L;

				charcopy(dest, &destlen, destsize, src[i++]);

				break;

			case 'n':

				state = N;

				charcopy(dest, &destlen, destsize, src[i++]);

				break;

			case 'p':

				state = P;

				charcopy(dest, &destlen, destsize, src[i++]);

				break;

			default:

				state = DEFAULT;

				break;

			}

			break;

		case A:

			if (src[i] == 'u') {

				state = AU;

				charcopy(dest, &destlen, destsize, src[i++]);

			}

			else state = DEFAULT;

			break;

		case AU:

			if (src[i] == 'x') {

				state = THIRD;

				i++;

			}

			else state = DEFAULT;

			break;

		case THIRD:

			state = DEFAULT;

			switch (src[i]) {

			case '.':

			case '/':

			case '\0':

				escape3(dest, &destlen, destsize, src[i - 1]);

				break;

			default:

				i--;

				break;

			}

			break;

		case C:

			if (src[i] == 'o') {

				state = CO;

				charcopy(dest, &destlen, destsize, src[i++]);

			}

			else state = DEFAULT;

			break;

		case CO:

			if (src[i] == 'm') {

				state = COMLPT;

				i++;

			}

			else if (src[i] == 'n') {

				state = THIRD;

				i++;

			}

			else state = DEFAULT;

			break;

		case COMLPT:

			switch (src[i]) {

			case '1': case '2': case '3': case '4': case '5':

			case '6': case '7': case '8': case '9':

				state = COMLPTn;

				i++;

				break;

			default:

				state = DEFAULT;

				charcopy(dest, &destlen, destsize, src[i - 1]);

				break;

			}

			break;

		case COMLPTn:

			state = DEFAULT;

			switch (src[i]) {

			case '.':

			case '/':

			case '\0':

				escape3(dest, &destlen, destsize, src[i - 2]);

				charcopy(dest, &destlen, destsize, src[i - 1]);

				break;

			default:

				memcopy(dest, &destlen, destsize,

					&src[i - 2], 2);

				break;

			}

			break;

		case L:

			if (src[i] == 'p') {

				state = LP;

				charcopy(dest, &destlen, destsize, src[i++]);

			}

			else state = DEFAULT;

			break;

		case LP:

			if (src[i] == 't') {

				state = COMLPT;

				i++;

			}

			else state = DEFAULT;

			break;

		case N:

			if (src[i] == 'u') {

				state = NU;

				charcopy(dest, &destlen, destsize, src[i++]);

			}

			else state = DEFAULT;

			break;

		case NU:

			if (src[i] == 'l') {

				state = THIRD;

				i++;

			}

			else state = DEFAULT;

			break;

		case P:

			if (src[i] == 'r') {

				state = PR;

				charcopy(dest, &destlen, destsize, src[i++]);

			}

			else state = DEFAULT;

			break;

		case PR:

			if (src[i] == 'n') {

				state = THIRD;

				i++;

			}

			else state = DEFAULT;

			break;

		case LDOT:

			switch (src[i]) {

			case 'd':

			case 'i':

				state = HGDI;

				charcopy(dest, &destlen, destsize, src[i++]);

				break;

			case 'h':

				state = H;

				charcopy(dest, &destlen, destsize, src[i++]);

				break;

			default:

				state = DEFAULT;

				break;

			}

			break;

		case DOT:

			switch (src[i]) {

			case '/':

			case '\0':

				state = START;

				memcopy(dest, &destlen, destsize, "~2e", 3);

				charcopy(dest, &destlen, destsize, src[i++]);

				break;

			case 'd':

			case 'i':

				state = HGDI;

				charcopy(dest, &destlen, destsize, '.');

				charcopy(dest, &destlen, destsize, src[i++]);

				break;

			case 'h':

				state = H;

				memcopy(dest, &destlen, destsize, ".h", 2);

				i++;

				break;

			default:

				state = DEFAULT;

				charcopy(dest, &destlen, destsize, '.');

				break;

			}

			break;

		case H:

			if (src[i] == 'g') {