/*
 * 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 "common.h"
#include "commit.h"
#include "tree.h"
#include "git2/repository.h"
#include "git2/object.h"
#include "fileops.h"
#include "tree-cache.h"
#include "index.h"
#define DEFAULT_TREE_SIZE 16
#define MAX_FILEMODE_BYTES 6
static bool valid_filemode(const int filemode)
{
        return (filemode == GIT_FILEMODE_TREE
                || filemode == GIT_FILEMODE_BLOB
                || filemode == GIT_FILEMODE_BLOB_EXECUTABLE
                || filemode == GIT_FILEMODE_LINK
                || filemode == GIT_FILEMODE_COMMIT);
}
GIT_INLINE(git_filemode_t) normalize_filemode(git_filemode_t filemode)
{
        /* Tree bits set, but it's not a commit */
        if (GIT_MODE_TYPE(filemode) == GIT_FILEMODE_TREE)
                return GIT_FILEMODE_TREE;
        /* If any of the x bits are set */
        if (GIT_PERMS_IS_EXEC(filemode))
                return GIT_FILEMODE_BLOB_EXECUTABLE;
        /* 16XXXX means commit */
        if (GIT_MODE_TYPE(filemode) == GIT_FILEMODE_COMMIT)
                return GIT_FILEMODE_COMMIT;
        /* 12XXXX means commit */
        if (GIT_MODE_TYPE(filemode) == GIT_FILEMODE_LINK)
                return GIT_FILEMODE_LINK;
        /* Otherwise, return a blob */
        return GIT_FILEMODE_BLOB;
}
static int valid_entry_name(const char *filename)
{
        return *filename != '\0' &&
                strchr(filename, '/') == NULL &&
                (*filename != '.' ||
                 (strcmp(filename, ".") != 0 &&
                  strcmp(filename, "..") != 0 &&
                  strcmp(filename, DOT_GIT) != 0));
}
static int entry_sort_cmp(const void *a, const void *b)
{
        const git_tree_entry *e1 = (const git_tree_entry *)a;
        const git_tree_entry *e2 = (const git_tree_entry *)b;
        return git_path_cmp(
                e1->filename, e1->filename_len, git_tree_entry__is_tree(e1),
                e2->filename, e2->filename_len, git_tree_entry__is_tree(e2),
                git__strncmp);
}
int git_tree_entry_cmp(const git_tree_entry *e1, const git_tree_entry *e2)
{
        return entry_sort_cmp(e1, e2);
}
int git_tree_entry_icmp(const git_tree_entry *e1, const git_tree_entry *e2)
{
        return git_path_cmp(
                e1->filename, e1->filename_len, git_tree_entry__is_tree(e1),
                e2->filename, e2->filename_len, git_tree_entry__is_tree(e2),
                git__strncasecmp);
}
static git_tree_entry *alloc_entry(const char *filename)
{
        git_tree_entry *entry = NULL;
        size_t filename_len = strlen(filename);
        entry = git__malloc(sizeof(git_tree_entry) + filename_len + 1);
        if (!entry)
                return NULL;
        memset(entry, 0x0, sizeof(git_tree_entry));
        memcpy(entry->filename, filename, filename_len);
        entry->filename[filename_len] = 0;
        entry->filename_len = filename_len;
        return entry;
}
struct tree_key_search {
        const char *filename;
        size_t filename_len;
};
static int homing_search_cmp(const void *key, const void *array_member)
{
        const struct tree_key_search *ksearch = key;
        const git_tree_entry *entry = array_member;
        const size_t len1 = ksearch->filename_len;
        const size_t len2 = entry->filename_len;
        return memcmp(
                ksearch->filename,
                entry->filename,
                len1 < len2 ? len1 : len2
        );
}
/*
 * Search for an entry in a given tree.
 *
 * Note that this search is performed in two steps because
 * of the way tree entries are sorted internally in git:
 *
 * Entries in a tree are not sorted alphabetically; two entries
 * with the same root prefix will have different positions
 * depending on whether they are folders (subtrees) or normal files.
 *
 * Consequently, it is not possible to find an entry on the tree
 * with a binary search if you don't know whether the filename
 * you're looking for is a folder or a normal file.
 *
 * To work around this, we first perform a homing binary search
 * on the tree, using the minimal length root prefix of our filename.
 * Once the comparisons for this homing search start becoming
 * ambiguous because of folder vs file sorting, we look linearly
 * around the area for our target file.
 */
static int tree_key_search(
        size_t *at_pos, git_vector *entries, const char *filename, size_t filename_len)
{
        struct tree_key_search ksearch;
        const git_tree_entry *entry;
        size_t homing, i;
        ksearch.filename = filename;
        ksearch.filename_len = filename_len;
        /* Initial homing search; find an entry on the tree with
         * the same prefix as the filename we're looking for */
        if (git_vector_bsearch2(&homing, entries, &homing_search_cmp, &ksearch) < 0)
                return GIT_ENOTFOUND; /* just a signal error; not passed back to user */
        /* We found a common prefix. Look forward as long as
         * there are entries that share the common prefix */
        for (i = homing; i < entries->length; ++i) {
                entry = entries->contents[i];
                if (homing_search_cmp(&ksearch, entry) < 0)
                        break;
                if (entry->filename_len == filename_len &&
                        memcmp(filename, entry->filename, filename_len) == 0) {
                        if (at_pos)
                                *at_pos = i;
                        return 0;
                }
        }
        /* If we haven't found our filename yet, look backwards
         * too as long as we have entries with the same prefix */
        if (homing > 0) {
                i = homing - 1;
                do {
                        entry = entries->contents[i];
                        if (homing_search_cmp(&ksearch, entry) > 0)
                                break;
                        if (entry->filename_len == filename_len &&
                                memcmp(filename, entry->filename, filename_len) == 0) {
                                if (at_pos)
                                        *at_pos = i;
                                return 0;
                        }
                } while (i-- > 0);
        }
        /* The filename doesn't exist at all */
        return GIT_ENOTFOUND;
}
void git_tree_entry_free(git_tree_entry *entry)
{
        if (entry == NULL)
                return;
        git__free(entry);
}
git_tree_entry *git_tree_entry_dup(const git_tree_entry *entry)
{
        size_t total_size;
        git_tree_entry *copy;
        assert(entry);
        total_size = sizeof(git_tree_entry) + entry->filename_len + 1;
        copy = git__malloc(total_size);
        if (!copy)
                return NULL;
        memcpy(copy, entry, total_size);
        return copy;
}
void git_tree__free(void *_tree)
{
        git_tree *tree = _tree;
        size_t i;
        git_tree_entry *e;
        git_vector_foreach(&tree->entries, i, e)
                git_tree_entry_free(e);
        git_vector_free(&tree->entries);
        git__free(tree);
}
git_filemode_t git_tree_entry_filemode(const git_tree_entry *entry)
{
        return (git_filemode_t)entry->attr;
}
const char *git_tree_entry_name(const git_tree_entry *entry)
{
        assert(entry);
        return entry->filename;
}
const git_oid *git_tree_entry_id(const git_tree_entry *entry)
{
        assert(entry);
        return &entry->oid;
}
git_otype git_tree_entry_type(const git_tree_entry *entry)
{
        assert(entry);
        if (S_ISGITLINK(entry->attr))
                return GIT_OBJ_COMMIT;
        else if (S_ISDIR(entry->attr))
                return GIT_OBJ_TREE;
        else
                return GIT_OBJ_BLOB;
}
int git_tree_entry_to_object(
        git_object **object_out,
        git_repository *repo,
        const git_tree_entry *entry)
{
        assert(entry && object_out);
        return git_object_lookup(object_out, repo, &entry->oid, GIT_OBJ_ANY);
}
static const git_tree_entry *entry_fromname(
        const git_tree *tree, const char *name, size_t name_len)
{
        size_t idx;
        assert(tree->entries.sorted); /* be safe when we cast away constness */
        if (tree_key_search(&idx, (git_vector *)&tree->entries, name, name_len) < 0)
                return NULL;
        return git_vector_get(&tree->entries, idx);
}
const git_tree_entry *git_tree_entry_byname(
        const git_tree *tree, const char *filename)
{
        assert(tree && filename);
        return entry_fromname(tree, filename, strlen(filename));
}
const git_tree_entry *git_tree_entry_byindex(
        const git_tree *tree, size_t idx)
{
        assert(tree);
        return git_vector_get(&tree->entries, idx);
}
const git_tree_entry *git_tree_entry_byoid(
        const git_tree *tree, const git_oid *oid)
{
        size_t i;
        const git_tree_entry *e;
        assert(tree);
        git_vector_foreach(&tree->entries, i, e) {
                if (memcmp(&e->oid.id, &oid->id, sizeof(oid->id)) == 0)
                        return e;
        }
        return NULL;
}
int git_tree__prefix_position(const git_tree *tree, const char *path)
{
        const git_vector *entries = &tree->entries;
        struct tree_key_search ksearch;
        size_t at_pos;
        if (!path)
                return 0;
        ksearch.filename = path;
        ksearch.filename_len = strlen(path);
        assert(tree->entries.sorted); /* be safe when we cast away constness */
        /* Find tree entry with appropriate prefix */
        git_vector_bsearch2(
                &at_pos, (git_vector *)entries, &homing_search_cmp, &ksearch);
        for (; at_pos < entries->length; ++at_pos) {
                const git_tree_entry *entry = entries->contents[at_pos];
                if (homing_search_cmp(&ksearch, entry) < 0)
                        break;
        }
        for (; at_pos > 0; --at_pos) {
                const git_tree_entry *entry = entries->contents[at_pos - 1];
                if (homing_search_cmp(&ksearch, entry) > 0)
                        break;
        }
        return (int)at_pos;
}
size_t git_tree_entrycount(const git_tree *tree)
{
        assert(tree);
        return tree->entries.length;
}
unsigned int git_treebuilder_entrycount(git_treebuilder *bld)
{
        assert(bld);
        return (unsigned int)bld->entrycount;
}
static int tree_error(const char *str, const char *path)
{
        if (path)
                giterr_set(GITERR_TREE, "%s - %s", str, path);
        else
                giterr_set(GITERR_TREE, "%s", str);
        return -1;
}
int git_tree__parse(void *_tree, git_odb_object *odb_obj)
{
        git_tree *tree = _tree;
        const char *buffer = git_odb_object_data(odb_obj);
        const char *buffer_end = buffer + git_odb_object_size(odb_obj);
        if (git_vector_init(&tree->entries, DEFAULT_TREE_SIZE, entry_sort_cmp) < 0)
                return -1;
        while (buffer < buffer_end) {
                git_tree_entry *entry;
                int attr;
                if (git__strtol32(&attr, buffer, &buffer, 8) < 0 || !buffer)
                        return tree_error("Failed to parse tree. Can't parse filemode", NULL);
                attr = normalize_filemode(attr); /* make sure to normalize the filemode */
                if (*buffer++ != ' ')
                        return tree_error("Failed to parse tree. Object is corrupted", NULL);
                if (memchr(buffer, 0, buffer_end - buffer) == NULL)
                        return tree_error("Failed to parse tree. Object is corrupted", NULL);
                /** Allocate the entry and store it in the entries vector */
                {
                        entry = alloc_entry(buffer);
                        GITERR_CHECK_ALLOC(entry);
                        if (git_vector_insert(&tree->entries, entry) < 0) {
                                git__free(entry);
                                return -1;
                        }
                        entry->attr = attr;
                }
                while (buffer < buffer_end && *buffer != 0)
                        buffer++;
                buffer++;
                git_oid_fromraw(&entry->oid, (const unsigned char *)buffer);
                buffer += GIT_OID_RAWSZ;
        }
        git_vector_sort(&tree->entries);
        return 0;
}
static size_t find_next_dir(const char *dirname, git_index *index, size_t start)
{
        size_t dirlen, i, entries = git_index_entrycount(index);
        dirlen = strlen(dirname);
        for (i = start; i < entries; ++i) {
                const git_index_entry *entry = git_index_get_byindex(index, i);
                if (strlen(entry->path) < dirlen ||
                    memcmp(entry->path, dirname, dirlen) ||
                        (dirlen > 0 && entry->path[dirlen] != '/')) {
                        break;
                }
        }
        return i;
}
static int append_entry(
        git_treebuilder *bld,
        const char *filename,
        const git_oid *id,
        git_filemode_t filemode)
{
        git_tree_entry *entry;
        if (!valid_entry_name(filename))
                return tree_error("Failed to insert entry. Invalid name for a tree entry", filename);
        entry = alloc_entry(filename);
        GITERR_CHECK_ALLOC(entry);
        git_oid_cpy(&entry->oid, id);
        entry->attr = (uint16_t)filemode;
        if (git_vector_insert(&bld->entries, entry) < 0) {
                git__free(entry);
                return -1;
        }
        bld->entrycount++;
        return 0;
}
static int write_tree(
        git_oid *oid,
        git_repository *repo,
        git_index *index,
        const char *dirname,
        size_t start)
{
        git_treebuilder *bld = NULL;
        size_t i, entries = git_index_entrycount(index);
        int error;
        size_t dirname_len = strlen(dirname);
        const git_tree_cache *cache;
        cache = git_tree_cache_get(index->tree, dirname);
        if (cache != NULL && cache->entries >= 0){
                git_oid_cpy(oid, &cache->oid);
                return (int)find_next_dir(dirname, index, start);
        }
        if ((error = git_treebuilder_create(&bld, NULL)) < 0 || bld == NULL)
                return -1;
        /*
         * This loop is unfortunate, but necessary. The index doesn't have
         * any directores, so we need to handle that manually, and we
         * need to keep track of the current position.
         */
        for (i = start; i < entries; ++i) {
                const git_index_entry *entry = git_index_get_byindex(index, i);
                const char *filename, *next_slash;
        /*
         * If we've left our (sub)tree, exit the loop and return. The
         * first check is an early out (and security for the
         * third). The second check is a simple prefix comparison. The
         * third check catches situations where there is a directory
         * win32/sys and a file win32mmap.c. Without it, the following
         * code believes there is a file win32/mmap.c
         */
                if (strlen(entry->path) < dirname_len ||
                    memcmp(entry->path, dirname, dirname_len) ||
                    (dirname_len > 0 && entry->path[dirname_len] != '/')) {
                        break;
                }
                filename = entry->path + dirname_len;
                if (*filename == '/')
                        filename++;
                next_slash = strchr(filename, '/');
                if (next_slash) {
                        git_oid sub_oid;
                        int written;
                        char *subdir, *last_comp;
                        subdir = git__strndup(entry->path, next_slash - entry->path);
                        GITERR_CHECK_ALLOC(subdir);
                        /* Write out the subtree */
                        written = write_tree(&sub_oid, repo, index, subdir, i);
                        if (written < 0) {
                                git__free(subdir);
                                goto on_error;
                        } else {
                                i = written - 1; /* -1 because of the loop increment */
                        }
                        /*
                         * We need to figure out what we want toinsert
                         * into this tree. If we're traversing
                         * deps/zlib/, then we only want to write
                         * 'zlib' into the tree.
                         */
                        last_comp = strrchr(subdir, '/');
                        if (last_comp) {
                                last_comp++; /* Get rid of the '/' */
                        } else {
                                last_comp = subdir;
                        }
                        error = append_entry(bld, last_comp, &sub_oid, S_IFDIR);
                        git__free(subdir);
                        if (error < 0)
                                goto on_error;
                } else {
                        error = append_entry(bld, filename, &entry->oid, entry->mode);
                        if (error < 0)
                                goto on_error;
                }
        }
        if (git_treebuilder_write(oid, repo, bld) < 0)
                goto on_error;
        git_treebuilder_free(bld);
        return (int)i;
on_error:
        git_treebuilder_free(bld);
        return -1;
}
int git_tree__write_index(
        git_oid *oid, git_index *index, git_repository *repo)
{
        int ret;
        bool old_ignore_case = false;
        assert(oid && index && repo);
        if (git_index_has_conflicts(index)) {
                giterr_set(GITERR_INDEX,
                        "Cannot create a tree from a not fully merged index.");
                return GIT_EUNMERGED;
        }
        if (index->tree != NULL && index->tree->entries >= 0) {
                git_oid_cpy(oid, &index->tree->oid);
                return 0;
        }
        /* The tree cache didn't help us; we'll have to write
         * out a tree. If the index is ignore_case, we must
         * make it case-sensitive for the duration of the tree-write
         * operation. */
        if (index->ignore_case) {
                old_ignore_case = true;
                git_index__set_ignore_case(index, false);
        }
        ret = write_tree(oid, repo, index, "", 0);
        if (old_ignore_case)
                git_index__set_ignore_case(index, true);
        return ret < 0 ? ret : 0;
}
int git_treebuilder_create(git_treebuilder **builder_p, const git_tree *source)
{
        git_treebuilder *bld;
        size_t i, source_entries = DEFAULT_TREE_SIZE;
        assert(builder_p);
        bld = git__calloc(1, sizeof(git_treebuilder));
        GITERR_CHECK_ALLOC(bld);
        if (source != NULL)
                source_entries = source->entries.length;
        if (git_vector_init(&bld->entries, source_entries, entry_sort_cmp) < 0)
                goto on_error;
        if (source != NULL) {
                git_tree_entry *entry_src;
                git_vector_foreach(&source->entries, i, entry_src) {
                        if (append_entry(
                                bld, entry_src->filename,
                                &entry_src->oid,
                                entry_src->attr) < 0)
                                goto on_error;
                }
        }
        *builder_p = bld;
        return 0;
on_error:
        git_treebuilder_free(bld);
        return -1;
}
int git_treebuilder_insert(
        const git_tree_entry **entry_out,
        git_treebuilder *bld,
        const char *filename,
        const git_oid *id,
        git_filemode_t filemode)
{
        git_tree_entry *entry;
        size_t pos;
        assert(bld && id && filename);
        if (!valid_filemode(filemode))
                return tree_error("Failed to insert entry. Invalid filemode for file", filename);
        if (!valid_entry_name(filename))
                return tree_error("Failed to insert entry. Invalid name for a tree entry", filename);
        if (!tree_key_search(&pos, &bld->entries, filename, strlen(filename))) {
                entry = git_vector_get(&bld->entries, pos);
                if (entry->removed) {
                        entry->removed = 0;
                        bld->entrycount++;
                }
        } else {
                entry = alloc_entry(filename);
                GITERR_CHECK_ALLOC(entry);
                if (git_vector_insert(&bld->entries, entry) < 0) {
                        git__free(entry);
                        return -1;
                }
                bld->entrycount++;
        }
        git_oid_cpy(&entry->oid, id);
        entry->attr = filemode;
        if (entry_out)
                *entry_out = entry;
        return 0;
}
static git_tree_entry *treebuilder_get(git_treebuilder *bld, const char *filename)
{
        size_t idx;
        git_tree_entry *entry;
        assert(bld && filename);
        if (tree_key_search(&idx, &bld->entries, filename, strlen(filename)) < 0)
                return NULL;
        entry = git_vector_get(&bld->entries, idx);
        if (entry->removed)
                return NULL;
        return entry;
}
const git_tree_entry *git_treebuilder_get(git_treebuilder *bld, const char *filename)
{
        return treebuilder_get(bld, filename);
}
int git_treebuilder_remove(git_treebuilder *bld, const char *filename)
{
        git_tree_entry *remove_ptr = treebuilder_get(bld, filename);
        if (remove_ptr == NULL || remove_ptr->removed)
                return tree_error("Failed to remove entry. File isn't in the tree", filename);
        remove_ptr->removed = 1;
        bld->entrycount--;
        return 0;
}
int git_treebuilder_write(git_oid *oid, git_repository *repo, git_treebuilder *bld)
{
        int error = 0;
        size_t i;
        git_buf tree = GIT_BUF_INIT;
        git_odb *odb;
        assert(bld);
        git_vector_sort(&bld->entries);
        /* Grow the buffer beforehand to an estimated size */
        error = git_buf_grow(&tree, bld->entries.length * 72);
        for (i = 0; i < bld->entries.length && !error; ++i) {
                git_tree_entry *entry = git_vector_get(&bld->entries, i);
                if (entry->removed)
                        continue;
                git_buf_printf(&tree, "%o ", entry->attr);
                git_buf_put(&tree, entry->filename, entry->filename_len + 1);
                git_buf_put(&tree, (char *)entry->oid.id, GIT_OID_RAWSZ);
                if (git_buf_oom(&tree))
                        error = -1;
        }
        if (!error &&
                !(error = git_repository_odb__weakptr(&odb, repo)))
                error = git_odb_write(oid, odb, tree.ptr, tree.size, GIT_OBJ_TREE);
        git_buf_free(&tree);
        return error;
}
void git_treebuilder_filter(
        git_treebuilder *bld,
        git_treebuilder_filter_cb filter,
        void *payload)
{
        size_t i;
        git_tree_entry *entry;
        assert(bld && filter);
        git_vector_foreach(&bld->entries, i, entry) {
                if (!entry->removed && filter(entry, payload)) {
                        entry->removed = 1;
                        bld->entrycount--;
                }
        }
}
void git_treebuilder_clear(git_treebuilder *bld)
{
        size_t i;
        git_tree_entry *e;
        assert(bld);
        git_vector_foreach(&bld->entries, i, e)
                git_tree_entry_free(e);
        git_vector_clear(&bld->entries);
        bld->entrycount = 0;
}
void git_treebuilder_free(git_treebuilder *bld)
{
        if (bld == NULL)
                return;
        git_treebuilder_clear(bld);
        git_vector_free(&bld->entries);
        git__free(bld);
}
static size_t subpath_len(const char *path)
{
        const char *slash_pos = strchr(path, '/');
        if (slash_pos == NULL)
                return strlen(path);
        return slash_pos - path;
}
int git_tree_entry_bypath(
        git_tree_entry **entry_out,
        const git_tree *root,
        const char *path)
{
        int error = 0;
        git_tree *subtree;
        const git_tree_entry *entry;
        size_t filename_len;
        /* Find how long is the current path component (i.e.
         * the filename between two slashes */
        filename_len = subpath_len(path);
        if (filename_len == 0) {
                giterr_set(GITERR_TREE, "Invalid tree path given");
                return GIT_ENOTFOUND;
        }
        entry = entry_fromname(root, path, filename_len);
        if (entry == NULL) {
                giterr_set(GITERR_TREE,
                        "The path '%s' does not exist in the given tree", path);
                return GIT_ENOTFOUND;
        }
        switch (path[filename_len]) {
        case '/':
                /* If there are more components in the path...
                 * then this entry *must* be a tree */
                if (!git_tree_entry__is_tree(entry)) {
                        giterr_set(GITERR_TREE,
                                "The path '%s' does not exist in the given tree", path);
                        return GIT_ENOTFOUND;
                }
                /* If there's only a slash left in the path, we 
                 * return the current entry; otherwise, we keep
                 * walking down the path */
                if (path[filename_len + 1] != '\0')
                        break;
        case '\0':
                /* If there are no more components in the path, return
                 * this entry */
                *entry_out = git_tree_entry_dup(entry);
                return 0;
        }
        if (git_tree_lookup(&subtree, root->object.repo, &entry->oid) < 0)
                return -1;
        error = git_tree_entry_bypath(
                entry_out,
                subtree,
                path + filename_len + 1
        );
        git_tree_free(subtree);
        return error;
}
static int tree_walk(
        const git_tree *tree,
        git_treewalk_cb callback,
        git_buf *path,
        void *payload,
        bool preorder)
{
        int error = 0;
        size_t i;
        const git_tree_entry *entry;
        git_vector_foreach(&tree->entries, i, entry) {
                if (preorder) {
                        error = callback(path->ptr, entry, payload);
                        if (error > 0) {
                                error = 0;
                                continue;
                        }
                        if (error < 0) {
                                giterr_clear();
                                return GIT_EUSER;
                        }
                }
                if (git_tree_entry__is_tree(entry)) {
                        git_tree *subtree;
                        size_t path_len = git_buf_len(path);
                        if ((error = git_tree_lookup(
                                &subtree, tree->object.repo, &entry->oid)) < 0)
                                break;
                        /* append the next entry to the path */
                        git_buf_puts(path, entry->filename);
                        git_buf_putc(path, '/');
                        if (git_buf_oom(path))
                                return -1;
                        error = tree_walk(subtree, callback, path, payload, preorder);
                        git_tree_free(subtree);
                        if (error != 0)
                                break;
                        git_buf_truncate(path, path_len);
                }
                if (!preorder && callback(path->ptr, entry, payload) < 0) {
                        giterr_clear();
                        error = GIT_EUSER;
                        break;
                }
        }
        return error;
}
int git_tree_walk(
        const git_tree *tree,
        git_treewalk_mode mode,
        git_treewalk_cb callback,
        void *payload)
{
        int error = 0;
        git_buf root_path = GIT_BUF_INIT;
        if (mode != GIT_TREEWALK_POST && mode != GIT_TREEWALK_PRE) {
                giterr_set(GITERR_INVALID, "Invalid walking mode for tree walk");
                return -1;
        }
        error = tree_walk(
                tree, callback, &root_path, payload, (mode == GIT_TREEWALK_PRE));
        git_buf_free(&root_path);
        return error;
}