/* lfn.c - Functions for handling VFAT long filenames

   Copyright (C) 1998 Roman Hodek <Roman.Hodek@informatik.uni-erlangen.de>
   Copyright (C) 2008-2014 Daniel Baumann <mail@daniel-baumann.ch>
   Copyright (C) 2015 Andreas Bombe <aeb@debian.org>

   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation, either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program. If not, see <http://www.gnu.org/licenses/>.

   The complete text of the GNU General Public License
   can be found in /usr/share/common-licenses/GPL-3 file.
*/

#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <limits.h>
#include <time.h>

#include "common.h"
#include "io.h"
#include "fsck.fat.h"
#include "lfn.h"
#include "file.h"

typedef struct {
    uint8_t id;			/* sequence number for slot */
    uint8_t name0_4[10];	/* first 5 characters in name */
    uint8_t attr;		/* attribute byte */
    uint8_t reserved;		/* always 0 */
    uint8_t alias_checksum;	/* checksum for 8.3 alias */
    uint8_t name5_10[12];	/* 6 more characters in name */
    uint16_t start;		/* starting cluster number, 0 in long slots */
    uint8_t name11_12[4];	/* last 2 characters in name */
} LFN_ENT;

#define LFN_ID_START	0x40
#define LFN_ID_SLOTMASK	0x1f

#define CHARS_PER_LFN	13

/* These modul-global vars represent the state of the LFN parser */
unsigned char *lfn_unicode = NULL;
unsigned char lfn_checksum;
int lfn_slot = -1;
off_t *lfn_offsets = NULL;
int lfn_parts = 0;

static unsigned char fat_uni2esc[64] = {
    '0', '1', '2', '3', '4', '5', '6', '7',
    '8', '9', 'A', 'B', 'C', 'D', 'E', 'F',
    'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N',
    'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V',
    'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd',
    'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l',
    'm', 'n', 'o', 'p', 'q', 'r', 's', 't',
    'u', 'v', 'w', 'x', 'y', 'z', '+', '-'
};

/* This defines which unicode chars are directly convertable to ISO-8859-1 */
#define UNICODE_CONVERTABLE(cl,ch)	(ch == 0 && (cl < 0x80 || cl >= 0xa0))

/* for maxlen param */
#define UNTIL_0		INT_MAX

/* Convert name parts collected so far (from previous slots) from unicode to
 * ASCII */
#define CNV_PARTS_SO_FAR()					\
	(cnv_unicode( lfn_unicode+(lfn_slot*CHARS_PER_LFN*2),	\
		      lfn_parts*CHARS_PER_LFN, 0 ))

#define BYTES_TO_WCHAR(cl,ch) ((wchar_t)((unsigned)(cl) + ((unsigned)(ch) << 8)))
static size_t mbslen(wchar_t x)
{
    wchar_t wstr[] = { x, 0 };
    return wcstombs(NULL, wstr, 0);
}

static size_t wctombs(char *dest, wchar_t x)
{
    wchar_t wstr[] = { x, 0 };
    size_t size = wcstombs(NULL, wstr, 0);
    if (size != (size_t) - 1)
	size = wcstombs(dest, wstr, size + 1);
    return size;
}

/* This function converts an unicode string to a normal ASCII string, assuming
 * ISO-8859-1 charset. Characters not in 8859-1 are converted to the same
 * escape notation as used by the kernel, i.e. the uuencode-like ":xxx" */
static char *cnv_unicode(const unsigned char *uni, int maxlen, int use_q)
{
    const unsigned char *up;
    unsigned char *out, *cp;
    int len, val;
    size_t x;

    for (len = 0, up = uni; (up - uni) / 2 < maxlen && (up[0] || up[1]);
	 up += 2) {
	if ((x = mbslen(BYTES_TO_WCHAR(up[0], up[1]))) != (size_t) - 1)
	    len += x;
	else if (UNICODE_CONVERTABLE(up[0], up[1]))
	    ++len;
	else
	    len += 4;
    }
    cp = out = use_q ? qalloc(&mem_queue, len + 1) : alloc(len + 1);

    for (up = uni; (up - uni) / 2 < maxlen && (up[0] || up[1]); up += 2) {
	if ((x =
	     wctombs((char *)cp, BYTES_TO_WCHAR(up[0], up[1]))) != (size_t) - 1)
	    cp += x;
	else if (UNICODE_CONVERTABLE(up[0], up[1]))
	    *cp++ = up[0];
	else {
	    /* here the same escape notation is used as in the Linux kernel */
	    *cp++ = ':';
	    val = (up[1] << 8) + up[0];
	    cp[2] = fat_uni2esc[val & 0x3f];
	    val >>= 6;
	    cp[1] = fat_uni2esc[val & 0x3f];
	    val >>= 6;
	    cp[0] = fat_uni2esc[val & 0x3f];
	    cp += 3;
	}
    }
    *cp = 0;

    return (char *)out;
}

static void copy_lfn_part(unsigned char *dst, LFN_ENT * lfn)
{
    memcpy(dst, lfn->name0_4, 10);
    memcpy(dst + 10, lfn->name5_10, 12);
    memcpy(dst + 22, lfn->name11_12, 4);
}

/* Convert name part in 'lfn' from unicode to ASCII */
static inline char *cnv_this_part(LFN_ENT *lfn)
{
	unsigned char part_uni[CHARS_PER_LFN * 2];
	copy_lfn_part(part_uni, lfn);
	return cnv_unicode(part_uni, CHARS_PER_LFN, 0);
}

static void clear_lfn_slots(int start, int end)
{
    int i;
    LFN_ENT empty;

    /* New dir entry is zeroed except first byte, which is set to 0xe5.
     * This is to avoid that some FAT-reading OSes (not Linux! ;) stop reading
     * a directory at the first zero entry...
     */
    memset(&empty, 0, sizeof(empty));
    empty.id = DELETED_FLAG;

    for (i = start; i <= end; ++i) {
	fs_write(lfn_offsets[i], sizeof(LFN_ENT), &empty);
    }
}

void lfn_fix_checksum(off_t from, off_t to, const char *short_name)
{
    int i;
    uint8_t sum;
    for (sum = 0, i = 0; i < 11; i++)
	sum = (((sum & 1) << 7) | ((sum & 0xfe) >> 1)) + short_name[i];

    for (; from < to; from += sizeof(LFN_ENT)) {
	fs_write(from + offsetof(LFN_ENT, alias_checksum), sizeof(sum), &sum);
    }
}

void lfn_reset(void)
{
    if (lfn_unicode)
	free(lfn_unicode);
    lfn_unicode = NULL;
    if (lfn_offsets)
	free(lfn_offsets);
    lfn_offsets = NULL;
    lfn_slot = -1;
}

/* This function is only called with de->attr == VFAT_LN_ATTR. It stores part
 * of the long name. */
void lfn_add_slot(DIR_ENT * de, off_t dir_offset)
{
    LFN_ENT *lfn = (LFN_ENT *) de;
    int slot = lfn->id & LFN_ID_SLOTMASK;
    unsigned offset;

    if (lfn_slot == 0)
	lfn_check_orphaned();

    if (de->attr != VFAT_LN_ATTR)
	die("lfn_add_slot called with non-LFN directory entry");

    if (lfn->id & LFN_ID_START && slot != 0) {
	if (lfn_slot != -1) {
	    int can_clear = 0;
	    /* There is already a LFN "in progess", so it is an error that a
	     * new start entry is here. */
	    /* Causes: 1) if slot# == expected: start bit set mysteriously, 2)
	     *         old LFN overwritten by new one */
	    /* Fixes: 1) delete previous LFN 2) if slot# == expected and
	     *        checksum ok: clear start bit */
	    /* XXX: Should delay that until next LFN known (then can better
	     * display the name) */
	    printf("A new long file name starts within an old one.\n");
	    if (slot == lfn_slot && lfn->alias_checksum == lfn_checksum) {
		char *part1 = cnv_this_part(lfn);
		char *part2 = CNV_PARTS_SO_FAR();
		printf("  It could be that the LFN start bit is wrong here\n"
		       "  if \"%s\" seems to match \"%s\".\n", part1, part2);
		free(part1);
		free(part2);
		can_clear = 1;
	    }
	    switch (get_choice(2, "  Not auto-correcting this.",
			       can_clear ? 3 : 2,
			       1, "Delete previous LFN",
			       2, "Leave it as it is",
			       3, "Clear start bit and concatenate LFNs")) {
	    case 1:
		clear_lfn_slots(0, lfn_parts - 1);
		lfn_reset();
		break;
	    case 2:
		break;
	    case 3:
		lfn->id &= ~LFN_ID_START;
		fs_write(dir_offset + offsetof(LFN_ENT, id),
			 sizeof(lfn->id), &lfn->id);
		break;
	    }
	}
	lfn_slot = slot;
	lfn_checksum = lfn->alias_checksum;
	lfn_unicode = alloc((lfn_slot * CHARS_PER_LFN + 1) * 2);
	lfn_offsets = alloc(lfn_slot * sizeof(off_t));
	lfn_parts = 0;
    } else if (lfn_slot == -1 && slot != 0) {
	/* No LFN in progress, but slot found; start bit missing */
	/* Causes: 1) start bit got lost, 2) Previous slot with start bit got
	 *         lost */
	/* Fixes: 1) delete LFN, 2) set start bit */
	char *part = cnv_this_part(lfn);
	printf("Long filename fragment \"%s\" found outside a LFN "
	       "sequence.\n  (Maybe the start bit is missing on the "
	       "last fragment)\n", part);
	free(part);
	switch (get_choice(2, "  Not auto-correcting this.",
			   3,
			   1, "Delete fragment",
			   2, "Leave it as it is",
			   3, "Set start bit")) {
	case 1:
	    if (!lfn_offsets)
		lfn_offsets = alloc(sizeof(off_t));
	    lfn_offsets[0] = dir_offset;
	    clear_lfn_slots(0, 0);
	    lfn_reset();
	    return;
	case 2:
	    lfn_reset();
	    return;
	case 3:
	    lfn->id |= LFN_ID_START;
	    fs_write(dir_offset + offsetof(LFN_ENT, id),
		     sizeof(lfn->id), &lfn->id);
	    lfn_slot = slot;
	    lfn_checksum = lfn->alias_checksum;
	    lfn_unicode = alloc((lfn_slot * CHARS_PER_LFN + 1) * 2);
	    lfn_offsets = alloc(lfn_slot * sizeof(off_t));
	    lfn_parts = 0;
	    break;
	}
    } else if (slot != lfn_slot) {
	/* wrong sequence number */
	/* Causes: 1) seq-no destroyed */
	/* Fixes: 1) delete LFN, 2) fix number (maybe only if following parts
	 *        are ok?, maybe only if checksum is ok?) (Attention: space
	 *        for name was allocated before!) */
	int can_fix = 0;
	printf("Unexpected long filename sequence number "
	       "(%d vs. expected %d).\n", slot, lfn_slot);
	if (lfn->alias_checksum == lfn_checksum && lfn_slot > 0) {
	    char *part1 = cnv_this_part(lfn);
	    char *part2 = CNV_PARTS_SO_FAR();
	    printf("  It could be that just the number is wrong\n"
		   "  if \"%s\" seems to match \"%s\".\n", part1, part2);
	    free(part1);
	    free(part2);
	    can_fix = 1;
	}
	switch (get_choice(2, "  Not auto-correcting this.",
			   can_fix ? 3 : 2,
			   1, "Delete LFN",
			   2, "Leave it as it is (and ignore LFN so far)",
			   3, "Correct sequence number")) {
	case 1:
	    if (!lfn_offsets) {
		lfn_offsets = alloc(sizeof(off_t));
		lfn_parts = 0;
	    }
	    lfn_offsets[lfn_parts++] = dir_offset;
	    clear_lfn_slots(0, lfn_parts - 1);
	    lfn_reset();
	    return;
	case 2:
	    lfn_reset();
	    return;
	case 3:
	    lfn->id = (lfn->id & ~LFN_ID_SLOTMASK) | lfn_slot;
	    fs_write(dir_offset + offsetof(LFN_ENT, id),
		     sizeof(lfn->id), &lfn->id);
	    break;
	}
    }

    if (lfn->alias_checksum != lfn_checksum) {
	/* checksum mismatch */
	/* Causes: 1) checksum field here destroyed */
	/* Fixes: 1) delete LFN, 2) fix checksum */
	printf("Checksum in long filename part wrong "
	       "(%02x vs. expected %02x).\n",
	       lfn->alias_checksum, lfn_checksum);
	switch (get_choice(2, "  Not auto-correcting this.",
			   3,
			   1, "Delete LFN",
			   2, "Leave it as it is",
			   3, "Correct checksum")) {
	case 1:
	    lfn_offsets[lfn_parts++] = dir_offset;
	    clear_lfn_slots(0, lfn_parts - 1);
	    lfn_reset();
	    return;
	case 2:
	    break;
	case 3:
	    lfn->alias_checksum = lfn_checksum;
	    fs_write(dir_offset + offsetof(LFN_ENT, alias_checksum),
		     sizeof(lfn->alias_checksum), &lfn->alias_checksum);
	    break;
	}
    }

    if (lfn_slot != -1) {
	lfn_slot--;
	offset = lfn_slot * CHARS_PER_LFN * 2;
	copy_lfn_part(lfn_unicode + offset, lfn);
	if (lfn->id & LFN_ID_START)
	    lfn_unicode[offset + 26] = lfn_unicode[offset + 27] = 0;
	lfn_offsets[lfn_parts++] = dir_offset;
    }

    if (lfn->reserved != 0) {
	printf("Reserved field in VFAT long filename slot is not 0 "
	       "(but 0x%02x).\n", lfn->reserved);
	if (get_choice(1, "Auto-setting to 0.",
		       2,
		       1, "Fix",
		       2, "Leave it") == 1) {
	    lfn->reserved = 0;
	    fs_write(dir_offset + offsetof(LFN_ENT, reserved),
		     sizeof(lfn->reserved), &lfn->reserved);
	}
    }
    if (lfn->start != htole16(0)) {
	printf("Start cluster field in VFAT long filename slot is not 0 "
	       "(but 0x%04x).\n", lfn->start);
	if (get_choice(1, "Auto-setting to 0.",
		       2,
		       1, "Fix",
		       2, "Leave it") == 1) {
	    lfn->start = htole16(0);
	    fs_write(dir_offset + offsetof(LFN_ENT, start),
		     sizeof(lfn->start), &lfn->start);
	}
    }
}

/* This function is always called when de->attr != VFAT_LN_ATTR is found, to
 * retrieve the previously constructed LFN. */
char *lfn_get(DIR_ENT * de, off_t * lfn_offset)
{
    char *lfn;
    uint8_t sum;
    int i;

    *lfn_offset = 0;
    if (de->attr == VFAT_LN_ATTR)
	die("lfn_get called with LFN directory entry");

#if 0
    if (de->lcase)
	printf("lcase=%02x\n", de->lcase);
#endif

    if (lfn_slot == -1)
	/* no long name for this file */
	return NULL;

    if (lfn_slot != 0) {
	/* The long name isn't finished yet. */
	/* Causes: 1) LFN slot overwritten by non-VFAT aware tool */
	/* Fixes: 1) delete LFN 2) move overwriting entry to somewhere else
	 * and let user enter missing part of LFN (hard to do :-()
	 * 3) renumber entries and truncate name */
	char *long_name = CNV_PARTS_SO_FAR();
	char *short_name = file_name(de->name);
	char *fix_num_string;
	int choice;

	printf("Unfinished long file name \"%s\".\n"
	       "  (Start may have been overwritten by %s)\n",
	       long_name, short_name);
	free(long_name);

	xasprintf(&fix_num_string,
		   "Fix numbering (truncates long name and attaches "
		   "it to short name %s)", short_name);
	choice = get_choice(2, "  Not auto-correcting this.",
			    3,
			    1, "Delete LFN",
			    2, "Leave it as it is",
			    3, fix_num_string);
	free(fix_num_string);

	switch (choice) {
	case 1:
	    clear_lfn_slots(0, lfn_parts - 1);
	    lfn_reset();
	    return NULL;
	case 2:
	    lfn_reset();
	    return NULL;
	case 3:
	    for (i = 0; i < lfn_parts; ++i) {
		uint8_t id = (lfn_parts - i) | (i == 0 ? LFN_ID_START : 0);
		fs_write(lfn_offsets[i] + offsetof(LFN_ENT, id),
			 sizeof(id), &id);
	    }
	    memmove(lfn_unicode, lfn_unicode + lfn_slot * CHARS_PER_LFN * 2,
		    lfn_parts * CHARS_PER_LFN * 2);
	    break;
	}
    }

    for (sum = 0, i = 0; i < MSDOS_NAME; i++)
	sum = (((sum & 1) << 7) | ((sum & 0xfe) >> 1)) + de->name[i];
    if (sum != lfn_checksum) {
	/* checksum doesn't match, long name doesn't apply to this alias */
	/* Causes: 1) alias renamed */
	/* Fixes: 1) Fix checksum in LFN entries */
	char *long_name = CNV_PARTS_SO_FAR();
	char *short_name = file_name(de->name);
	char *fix_check_string;
	int choice;

	printf("Wrong checksum for long file name \"%s\".\n"
	       "  (Short name %s may have changed without updating the long name)\n",
	       long_name, short_name);
	free(long_name);

	xasprintf(&fix_check_string,
		  "Fix checksum (attaches to short name %s)", short_name);
	choice = get_choice(9, "  Not auto-correcting this.",
			    3,
			    1, "Delete LFN",
			    2, "Leave it as it is",
			    3, fix_check_string);
	free(fix_check_string);

	switch (choice) {
	case 1:
	    clear_lfn_slots(0, lfn_parts - 1);
	    lfn_reset();
	    return NULL;
	case 2:
	    lfn_reset();
	    return NULL;
	case 3:
	    for (i = 0; i < lfn_parts; ++i) {
		fs_write(lfn_offsets[i] + offsetof(LFN_ENT, alias_checksum),
			 sizeof(sum), &sum);
	    }
	    break;
	}
    }

    *lfn_offset = lfn_offsets[0];
    lfn = cnv_unicode(lfn_unicode, UNTIL_0, 1);
    lfn_reset();
    return (lfn);
}

void lfn_check_orphaned(void)
{
    char *long_name;

    if (lfn_slot == -1)
	return;

    long_name = CNV_PARTS_SO_FAR();
    printf("Orphaned long file name part \"%s\"\n", long_name);
    free(long_name);
    if (get_choice(1, "  Auto-deleting.",
		   2,
		   1, "Delete",
		   2, "Leave it") == 1) {
	clear_lfn_slots(0, lfn_parts - 1);
    }
    lfn_reset();
}