/* ssdeep
 * Copyright (C) 2002 Andrew Tridgell <tridge@samba.org>
 * Copyright (C) 2006 ManTech International Corporation
 * Copyright (C) 2013 Helmut Grohne <helmut@subdivi.de>
 *
 * 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 2 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, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 *
 * Earlier versions of this code were named fuzzy.c and can be found at:
 *     http://www.samba.org/ftp/unpacked/junkcode/spamsum/
 *     http://ssdeep.sf.net/
 */

#include <assert.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#if defined(__GNUC__) && __GNUC__ >= 3
#define likely(x)       __builtin_expect(!!(x), 1)
#define unlikely(x)     __builtin_expect(!!(x), 0)
#else
#define likely(x) x
#define unlikely(x) x
#endif

#define SPAMSUM_LENGTH 64
#define FUZZY_MAX_RESULT (SPAMSUM_LENGTH + (SPAMSUM_LENGTH/2 + 20))
#define ROLLING_WINDOW 7
#define MIN_BLOCKSIZE 3
#define HASH_PRIME 0x01000193
#define HASH_INIT 0x28021967

struct roll_state {
	unsigned char window[ROLLING_WINDOW];
	uint32_t h1, h2, h3;
	uint32_t n;
};

static void roll_init(/*@out@*/ struct roll_state *self) {
	memset(self, 0, sizeof(struct roll_state));
}

/*
 * a rolling hash, based on the Adler checksum. By using a rolling hash
 * we can perform auto resynchronisation after inserts/deletes

 * internally, h1 is the sum of the bytes in the window and h2
 * is the sum of the bytes times the index

 * h3 is a shift/xor based rolling hash, and is mostly needed to ensure that
 * we can cope with large blocksize values
 */
static void roll_hash(struct roll_state *self, unsigned char c) {
	self->h2 -= self->h1;
 	self->h2 += ROLLING_WINDOW * (uint32_t)c;

	self->h1 += (uint32_t)c;
	self->h1 -= (uint32_t)self->window[self->n % ROLLING_WINDOW];

	self->window[self->n % ROLLING_WINDOW] = c;
	self->n++;

	/* The original spamsum AND'ed this value with 0xFFFFFFFF which
	 * in theory should have no effect. This AND has been removed
	 * for performance (jk) */
	self->h3 <<= 5;
 	self->h3 ^= c;
}

static uint32_t roll_sum(const struct roll_state *self) {
	return self->h1 + self->h2 + self->h3;
}

/* A simple non-rolling hash, based on the FNV hash. */
static uint32_t sum_hash(unsigned char c, uint32_t h) {
	return (h * HASH_PRIME) ^ c;
}

/* A blockhash contains a signature state for a specific (implicit) blocksize.
 * The blocksize is given by the start_blocksize from ssdeep_context times two
 * to the power of the position of the element in the blockhashes member of
 * ssdeep_context (head position = 0). The h and halfh members are the FNV
 * hashes, where halfh stops to be reset after digest is SPAMSUM_LENGTH/2 long.
 * The halfh hash is needed be able to truncate digest for the second output
 * hash to stay compatible with ssdeep output. */
struct blockhash_context {
	uint32_t h, halfh;
	char digest[SPAMSUM_LENGTH];
	unsigned int dlen;
	/*@null@*/ struct blockhash_context *next;
};

struct ssdeep_context {
	unsigned int start_blocksize;
	struct blockhash_context *blockhashes;
	size_t total_size;
	struct roll_state roll;
};

static int ssdeep_init(/*@out@*/ struct ssdeep_context *self) {
	self->blockhashes = malloc(sizeof(struct blockhash_context));
	if(NULL == self->blockhashes)
		return -1;
	self->start_blocksize = MIN_BLOCKSIZE;
	self->blockhashes->h = HASH_INIT;
	self->blockhashes->halfh = HASH_INIT;
	self->blockhashes->dlen = 0;
	self->blockhashes->next = NULL;
	self->total_size = 0;
	roll_init(&self->roll);
	return 0;
}

static const char *b64 =
	"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

static int ssdeep_engine_step(struct ssdeep_context *self, unsigned char c) {
	size_t h;
	unsigned int bs;
	struct blockhash_context *bh;
	/* At each character we update the rolling hash and the normal hashes.
	 * When the rolling hash hits a reset value then we emit a normal hash
	 * as a element of the signature and reset the normal hash. */
	roll_hash(&self->roll, c);
	h = roll_sum(&self->roll);

	for(bh = self->blockhashes; NULL != bh; bh = bh->next) {
		bh->h = sum_hash(c, bh->h);
		bh->halfh = sum_hash(c, bh->halfh);
	}

	bs = self->start_blocksize;
	bh = self->blockhashes;
	while(bh != NULL) {
		/* With growing blocksize almost no runs fail the next test. */
		if(likely(h % bs != bs - 1))
			/* Once this condition is false for one bs, it is
			 * automatically false for all further bs. I.e. if
			 * h === -1 (mod 2*bs) then h === -1 (mod bs). */
			break;
		/* We don't need bs until next iteration. Update now, so we
		 * don't forget about it. */
		bs *= 2;
		/* We have hit a reset point. We now emit hashes which are
		 * based on all characters in the piece of the message between
		 * the last reset point and this one */
		if(unlikely(0 == bh->dlen)) { /* Can only happen 30 times. */
			/* First step for this blocksize. Clone next. */
			assert(NULL == bh->next);
			bh->next = malloc(sizeof(
					struct blockhash_context));
			if(NULL == bh->next)
				return -1;
			bh->next->h = bh->h;
			bh->next->dlen = 0;
			bh->next->next = NULL;
		}
		if(bh->dlen < SPAMSUM_LENGTH - 1) {
			/* We can have a problem with the tail overflowing. The
			 * easiest way to cope with this is to only reset the
			 * normal hash if we have room for more characters in
			 * our signature. This has the effect of combining the
			 * last few pieces of the message into a single piece
			 * */
			bh->digest[bh->dlen++] = b64[bh->h % 64];
			bh->h = HASH_INIT;
			if(bh->dlen < SPAMSUM_LENGTH / 2)
				bh->halfh = HASH_INIT;
		} else if(NULL != bh->next &&
				(size_t)self->start_blocksize * SPAMSUM_LENGTH <
					self->total_size &&
				bh->next->dlen >= SPAMSUM_LENGTH / 2 &&
				bh == self->blockhashes) {
			/* Operating on the currently smallest blocksize and
			 * the next blocksize is already large enough. */
			self->start_blocksize *= 2;
			bh = bh->next;
			free(self->blockhashes);
			self->blockhashes = bh;
			continue;
		}
		bh = bh->next;
	}
	++self->total_size;
	return 0;
}

static int ssdeep_engine(struct ssdeep_context *self,
		const unsigned char *buffer, size_t buffer_size) {
	for( ;buffer_size > 0; ++buffer, --buffer_size)
		if(ssdeep_engine_step(self, *buffer) < 0)
			return -1;
	return 0;
}

static void ssdeep_digest(const struct ssdeep_context *self,
		/*@out@*/ char *result) {
	unsigned int bs = self->start_blocksize;
	uint32_t h = roll_sum(&self->roll);
	int i, remain = FUZZY_MAX_RESULT - 1;
	const struct blockhash_context *bh = self->blockhashes, *bhp;
	/* Verify that our elimination was not overeager. */
	assert(bs == MIN_BLOCKSIZE ||
			(size_t)bs / 2 * SPAMSUM_LENGTH < self->total_size);

	/* Initial blocksize guess. */
	while((size_t)bs * SPAMSUM_LENGTH < self->total_size) {
		bs *= 2;
		assert(bh->next != NULL);
		bh = bh->next;
	}
	/* Adapt blocksize guess to actual digest length. */
	while(bs > self->start_blocksize && bh->dlen < SPAMSUM_LENGTH / 2) {
		bs /= 2;
		/* Slow version of bh = bh->prev; */
		for(bhp = self->blockhashes; bhp->next != bh; bhp = bhp->next)
			;
		bh = bhp;
	}
	assert(bh != NULL);
	assert(!(bs > MIN_BLOCKSIZE && bh->dlen < SPAMSUM_LENGTH / 2));

	i = snprintf(result, (size_t)remain, "%u:", bs);
	/* In theory snprintf can fail. It is unclear how though, so we assume
	 * that it doesn't for simplicity. */
	assert(i > 0);
	assert(i < remain);
	remain -= i;
	result += i;
	i = (int)bh->dlen;
	if(i > remain)
		i = remain;
	memcpy(result, bh->digest, (size_t)i);
	result += i;
	remain -= i;
	if(remain > 0 && h != 0) {
		*result++ = b64[bh->h % 64];
		--remain;
	}
	if(remain > 0) {
		*result++ = ':';
		--remain;
	}
	if(NULL != bh->next) {
		bh = bh->next;
		i = (int)bh->dlen;
		if(i > SPAMSUM_LENGTH / 2 - 1)
			i = SPAMSUM_LENGTH / 2 - 1;
		if(i > remain)
			i = remain;
		memcpy(result, bh->digest, (size_t)i);
		result += i;
		remain -= i;
		if(remain > 0 && h != 0) {
			*result++ = b64[bh->halfh % 64];
			--remain;
		}
	} else if(remain > 0 && h != 0) {
		assert(bh->dlen == 0);
		*result++ = b64[bh->h % 64];
		--remain;
	}
	*result = '\0';
}

static void ssdeep_clear(struct ssdeep_context *self) {
	struct blockhash_context *bh, *bhn;
	bh = self->blockhashes;
	while(bh) {
		bhn = bh->next;
		free(bh);
		bh = bhn;
	}
}

int fuzzy_hash_buf(const unsigned char *buf, uint32_t buf_len,
		/*@out@*/ char *result) {
	struct ssdeep_context ctx[1];
	if(ssdeep_init(ctx) < 0)
		return -1;
	if(ssdeep_engine(ctx, buf, buf_len) < 0) {
		ssdeep_clear(ctx);
		return -1;
	}
	ssdeep_digest(ctx, result);
	ssdeep_clear(ctx);
	return 0;
}

int fuzzy_hash_stream(FILE *handle, /*@out@*/ char *result) {
	struct ssdeep_context ctx[1];
	unsigned char buffer[4096];
	size_t n;
	if(ssdeep_init(ctx) < 0)
		return -1;
	for(;;) {
		n = fread(buffer, 1, 4096, handle);
		if(0 == n)
			break;
		if(ssdeep_engine(ctx, buffer, n) < 0)
			goto errout;
	}
	if(ferror(handle) != 0)
		goto errout;
	ssdeep_digest(ctx, result);
	ssdeep_clear(ctx);
	return 0;
errout:
	ssdeep_clear(ctx);
	return -1;
}

#ifdef S_SPLINT_S
typedef size_t off_t;
#endif

int fuzzy_hash_file(FILE *handle, /*@out@*/ char *result) {
	off_t fpos;
	int status;
	fpos = ftello(handle);
	if(fseek(handle, 0, SEEK_SET) < 0)
		return -1;
	status = fuzzy_hash_stream(handle, result);
	if(status == 0)
		if(fseeko(handle, fpos, SEEK_SET) < 0)
			return -1;
	return status;
}

int fuzzy_hash_filename(const char *filename, /*@out@*/ char *result) {
	int status;
	FILE *handle = fopen(filename, "rb");
	if(NULL == handle)
		return -1;
	status = fuzzy_hash_file(handle, result);
	/* We cannot do anything about an fclose failure. */
	(void)fclose(handle);
	return status;
}

#ifdef S_SPLINT_S
extern /*@only@*/ /*@null@*/ char *realpath(const char *,
		/*@null@*/ const char *);
#endif

int main(int argc, char **argv) {
	char digest[FUZZY_MAX_RESULT], *p;
	int i;
	puts("ssdeep,1.1--blocksize:hash:hash,filename");
	for(i = 1; i < argc; ++i) {
		p = realpath(argv[i], NULL);
		if(p == NULL)
			return 1;
		if(fuzzy_hash_filename(argv[i], digest) < 0) {
			free(p);
			return 1;
		}
		printf("%s,\"%s\"\n", digest, p);
		free(p);
	}
	return 0;
}