/*
 * diff-delta code taken from git.git. See diff-delta.c for details.
 *
 */
#ifndef INCLUDE_git_delta_h__
#define INCLUDE_git_delta_h__

#include "common.h"

/* opaque object for delta index */
struct git_delta_index;

/*
 * create_delta_index: compute index data from given buffer
 *
 * This returns a pointer to a struct delta_index that should be passed to
 * subsequent create_delta() calls, or to free_delta_index().  A NULL pointer
 * is returned on failure.  The given buffer must not be freed nor altered
 * before free_delta_index() is called.  The returned pointer must be freed
 * using free_delta_index().
 */
extern struct git_delta_index *
git_delta_create_index(const void *buf, unsigned long bufsize);

/*
 * free_delta_index: free the index created by create_delta_index()
 *
 * Given pointer must be what create_delta_index() returned, or NULL.
 */
extern void git_delta_free_index(struct git_delta_index *index);

/*
 * sizeof_delta_index: returns memory usage of delta index
 *
 * Given pointer must be what create_delta_index() returned, or NULL.
 */
extern unsigned long git_delta_sizeof_index(struct git_delta_index *index);

/*
 * create_delta: create a delta from given index for the given buffer
 *
 * This function may be called multiple times with different buffers using
 * the same delta_index pointer.  If max_delta_size is non-zero and the
 * resulting delta is to be larger than max_delta_size then NULL is returned.
 * On success, a non-NULL pointer to the buffer with the delta data is
 * returned and *delta_size is updated with its size.  The returned buffer
 * must be freed by the caller.
 */
extern void *git_delta_create(
	const struct git_delta_index *index,
	const void *buf,
	unsigned long bufsize,
	unsigned long *delta_size,
	unsigned long max_delta_size);

/*
 * diff_delta: create a delta from source buffer to target buffer
 *
 * If max_delta_size is non-zero and the resulting delta is to be larger
 * than max_delta_size then NULL is returned.  On success, a non-NULL
 * pointer to the buffer with the delta data is returned and *delta_size is
 * updated with its size.  The returned buffer must be freed by the caller.
 */
GIT_INLINE(void *) git_delta(
	const void *src_buf, unsigned long src_bufsize,
	const void *trg_buf, unsigned long trg_bufsize,
	unsigned long *delta_size,
	unsigned long max_delta_size)
{
	struct git_delta_index *index = git_delta_create_index(src_buf, src_bufsize);
	if (index) {
		void *delta = git_delta_create(
			index, trg_buf, trg_bufsize, delta_size, max_delta_size);
		git_delta_free_index(index);
		return delta;
	}
	return NULL;
}

/*
 * patch_delta: recreate target buffer given source buffer and delta data
 *
 * On success, a non-NULL pointer to the target buffer is returned and
 * *trg_bufsize is updated with its size.  On failure a NULL pointer is
 * returned.  The returned buffer must be freed by the caller.
 */
extern void *git_delta_patch(
	const void *src_buf, unsigned long src_size,
	const void *delta_buf, unsigned long delta_size,
	unsigned long *dst_size);

/* the smallest possible delta size is 4 bytes */
#define GIT_DELTA_SIZE_MIN	4

/*
 * This must be called twice on the delta data buffer, first to get the
 * expected source buffer size, and again to get the target buffer size.
 */
GIT_INLINE(unsigned long) git_delta_get_hdr_size(
	const unsigned char **datap, const unsigned char *top)
{
	const unsigned char *data = *datap;
	unsigned long cmd, size = 0;
	int i = 0;
	do {
		cmd = *data++;
		size |= (cmd & 0x7f) << i;
		i += 7;
	} while (cmd & 0x80 && data < top);
	*datap = data;
	return size;
}

#endif