/*

 * Copyright (C) the libgit2 contributors. All rights reserved.

 *

 * This file is part of libgit2, distributed under the GNU GPL v2 with

 * a Linking Exception. For full terms see the included COPYING file.

 */

#include "git2/sys/hashsig.h"

#include "fileops.h"

#include "util.h"

typedef uint32_t hashsig_t;

typedef uint64_t hashsig_state;

#define HASHSIG_SCALE 100

#define HASHSIG_MAX_RUN 80

#define HASHSIG_HASH_START	0x012345678ABCDEF0LL

#define HASHSIG_HASH_SHIFT  5

#define HASHSIG_HASH_MIX(S,CH) \

	(S) = ((S) << HASHSIG_HASH_SHIFT) - (S) + (hashsig_state)(CH)

#define HASHSIG_HEAP_SIZE ((1 << 7) - 1)

#define HASHSIG_HEAP_MIN_SIZE 4

typedef int (*hashsig_cmp)(const void *a, const void *b, void *);

typedef struct {

	int size, asize;

	hashsig_cmp cmp;

	hashsig_t values[HASHSIG_HEAP_SIZE];

} hashsig_heap;

struct git_hashsig {

	hashsig_heap mins;

	hashsig_heap maxs;

	size_t lines;

	git_hashsig_option_t opt;

};

#define HEAP_LCHILD_OF(I) (((I)<<1)+1)

#define HEAP_RCHILD_OF(I) (((I)<<1)+2)

#define HEAP_PARENT_OF(I) (((I)-1)>>1)

static void hashsig_heap_init(hashsig_heap *h, hashsig_cmp cmp)

{

	h->size  = 0;

	h->asize = HASHSIG_HEAP_SIZE;

	h->cmp   = cmp;

}

static int hashsig_cmp_max(const void *a, const void *b, void *payload)

{

	hashsig_t av = *(const hashsig_t *)a, bv = *(const hashsig_t *)b;

	GIT_UNUSED(payload);

	return (av < bv) ? -1 : (av > bv) ? 1 : 0;

}

static int hashsig_cmp_min(const void *a, const void *b, void *payload)

{

	hashsig_t av = *(const hashsig_t *)a, bv = *(const hashsig_t *)b;

	GIT_UNUSED(payload);

	return (av > bv) ? -1 : (av < bv) ? 1 : 0;

}

static void hashsig_heap_up(hashsig_heap *h, int el)

{

	int parent_el = HEAP_PARENT_OF(el);

	while (el > 0 && h->cmp(&h->values[parent_el], &h->values[el], NULL) > 0) {

		hashsig_t t = h->values[el];

		h->values[el] = h->values[parent_el];

		h->values[parent_el] = t;

		el = parent_el;

		parent_el = HEAP_PARENT_OF(el);

	}

}

static void hashsig_heap_down(hashsig_heap *h, int el)

{

	hashsig_t v, lv, rv;

	/* 'el < h->size / 2' tests if el is bottom row of heap */

	while (el < h->size / 2) {

		int lel = HEAP_LCHILD_OF(el), rel = HEAP_RCHILD_OF(el), swapel;

		v  = h->values[el];

		lv = h->values[lel];

		rv = h->values[rel];

		if (h->cmp(&v, &lv, NULL) < 0 && h->cmp(&v, &rv, NULL) < 0)

			break;

		swapel = (h->cmp(&lv, &rv, NULL) < 0) ? lel : rel;

		h->values[el] = h->values[swapel];

		h->values[swapel] = v;

		el = swapel;

	}

}

static void hashsig_heap_sort(hashsig_heap *h)

{

	/* only need to do this at the end for signature comparison */

	git__qsort_r(h->values, h->size, sizeof(hashsig_t), h->cmp, NULL);

}

static void hashsig_heap_insert(hashsig_heap *h, hashsig_t val)

{

	/* if heap is not full, insert new element */

	if (h->size < h->asize) {

		h->values[h->size++] = val;

		hashsig_heap_up(h, h->size - 1);

	}

	/* if heap is full, pop top if new element should replace it */

	else if (h->cmp(&val, &h->values[0], NULL) > 0) {

		h->size--;

		h->values[0] = h->values[h->size];

		hashsig_heap_down(h, 0);

	}

}

typedef struct {

	int use_ignores;

	uint8_t ignore_ch[256];

} hashsig_in_progress;

static void hashsig_in_progress_init(

	hashsig_in_progress *prog, git_hashsig *sig)

{

	int i;

	/* no more than one can be set */

	assert(!(sig->opt & GIT_HASHSIG_IGNORE_WHITESPACE) ||

		   !(sig->opt & GIT_HASHSIG_SMART_WHITESPACE));

	if (sig->opt & GIT_HASHSIG_IGNORE_WHITESPACE) {

		for (i = 0; i < 256; ++i)

			prog->ignore_ch[i] = git__isspace_nonlf(i);

		prog->use_ignores = 1;

	} else if (sig->opt & GIT_HASHSIG_SMART_WHITESPACE) {

		for (i = 0; i < 256; ++i)

			prog->ignore_ch[i] = git__isspace(i);

		prog->use_ignores = 1;

	} else {

		memset(prog, 0, sizeof(*prog));

	}

}

static int hashsig_add_hashes(

	git_hashsig *sig,

	const uint8_t *data,

	size_t size,

	hashsig_in_progress *prog)

{

	const uint8_t *scan = data, *end = data + size;

	hashsig_state state = HASHSIG_HASH_START;

	int use_ignores = prog->use_ignores, len;

	uint8_t ch;

	while (scan < end) {

		state = HASHSIG_HASH_START;

		for (len = 0; scan < end && len < HASHSIG_MAX_RUN; ) {

			ch = *scan;

			if (use_ignores)

				for (; scan < end && git__isspace_nonlf(ch); ch = *scan)

					++scan;

			else if (sig->opt &

					 (GIT_HASHSIG_IGNORE_WHITESPACE | GIT_HASHSIG_SMART_WHITESPACE))

				for (; scan < end && ch == '\r'; ch = *scan)

					++scan;

			/* peek at next character to decide what to do next */

			if (sig->opt & GIT_HASHSIG_SMART_WHITESPACE)

				use_ignores = (ch == '\n');

			if (scan >= end)

				break;

			++scan;

			/* check run terminator */

			if (ch == '\n' || ch == '\0') {

				sig->lines++;

				break;

			}

			++len;

			HASHSIG_HASH_MIX(state, ch);

		}

		if (len > 0) {

			hashsig_heap_insert(&sig->mins, (hashsig_t)state);

			hashsig_heap_insert(&sig->maxs, (hashsig_t)state);

			while (scan < end && (*scan == '\n' || !*scan))

				++scan;

		}

	}

	prog->use_ignores = use_ignores;

	return 0;

}

static int hashsig_finalize_hashes(git_hashsig *sig)

{

	if (sig->mins.size < HASHSIG_HEAP_MIN_SIZE &&

		!(sig->opt & GIT_HASHSIG_ALLOW_SMALL_FILES)) {

		giterr_set(GITERR_INVALID,

			"file too small for similarity signature calculation");

		return GIT_EBUFS;

	}

	hashsig_heap_sort(&sig->mins);

	hashsig_heap_sort(&sig->maxs);

	return 0;

}

static git_hashsig *hashsig_alloc(git_hashsig_option_t opts)

{

	git_hashsig *sig = git__calloc(1, sizeof(git_hashsig));

	if (!sig)

		return NULL;

	hashsig_heap_init(&sig->mins, hashsig_cmp_min);

	hashsig_heap_init(&sig->maxs, hashsig_cmp_max);

	sig->opt = opts;

	return sig;

}

int git_hashsig_create(

	git_hashsig **out,

	const char *buf,

	size_t buflen,

	git_hashsig_option_t opts)

{

	int error;

	hashsig_in_progress prog;

	git_hashsig *sig = hashsig_alloc(opts);

	GITERR_CHECK_ALLOC(sig);

	hashsig_in_progress_init(&prog, sig);

	error = hashsig_add_hashes(sig, (const uint8_t *)buf, buflen, &prog;;

	if (!error)

		error = hashsig_finalize_hashes(sig);

	if (!error)

		*out = sig;

	else

		git_hashsig_free(sig);

	return error;

}

int git_hashsig_create_fromfile(

	git_hashsig **out,

	const char *path,

	git_hashsig_option_t opts)

{

	uint8_t buf[0x1000];

	ssize_t buflen = 0;

	int error = 0, fd;

	hashsig_in_progress prog;

	git_hashsig *sig = hashsig_alloc(opts);

	GITERR_CHECK_ALLOC(sig);

	if ((fd = git_futils_open_ro(path)) < 0) {

		git__free(sig);

		return fd;

	}

	hashsig_in_progress_init(&prog, sig);

	while (!error) {

		if ((buflen = p_read(fd, buf, sizeof(buf))) <= 0) {

			if ((error = (int)buflen) < 0)

				giterr_set(GITERR_OS,

					"read error on '%s' calculating similarity hashes", path);

			break;

		}

		error = hashsig_add_hashes(sig, buf, buflen, &prog;;

	}

	p_close(fd);

	if (!error)

		error = hashsig_finalize_hashes(sig);

	if (!error)

		*out = sig;

	else

		git_hashsig_free(sig);

	return error;

}

void git_hashsig_free(git_hashsig *sig)

{

	git__free(sig);

}

static int hashsig_heap_compare(const hashsig_heap *a, const hashsig_heap *b)

{

	int matches = 0, i, j, cmp;

	assert(a->cmp == b->cmp);

	/* hash heaps are sorted - just look for overlap vs total */

	for (i = 0, j = 0; i < a->size && j < b->size; ) {

		cmp = a->cmp(&a->values[i], &b->values[j], NULL);

		if (cmp < 0)

			++i;

		else if (cmp > 0)

			++j;

		else {

			++i; ++j; ++matches;

		}

	}

	return HASHSIG_SCALE * (matches * 2) / (a->size + b->size);

}

int git_hashsig_compare(const git_hashsig *a, const git_hashsig *b)

{

	/* if we have no elements in either file then each file is either

	 * empty or blank.  if we're ignoring whitespace then the files are

	 * similar, otherwise they're dissimilar.

	 */

	if (a->mins.size == 0 && b->mins.size == 0) {

		if ((!a->lines && !b->lines) ||

			(a->opt & GIT_HASHSIG_IGNORE_WHITESPACE))

			return HASHSIG_SCALE;

		else

			return 0;

	}

	/* if we have fewer than the maximum number of elements, then just use

	 * one array since the two arrays will be the same

	 */

	if (a->mins.size < HASHSIG_HEAP_SIZE)

		return hashsig_heap_compare(&a->mins, &b->mins);

	else

		return (hashsig_heap_compare(&a->mins, &b->mins) +

				hashsig_heap_compare(&a->maxs, &b->maxs)) / 2;

}