#include "builtin.h"
#include "gettext.h"
#include "hex.h"
#include "config.h"
#include "commit.h"
#include "tree.h"
#include "blob.h"
#include "tag.h"
#include "refs.h"
#include "pack.h"
#include "cache-tree.h"
#include "fsck.h"
#include "parse-options.h"
#include "progress.h"
#include "packfile.h"
#include "object-file.h"
#include "object-name.h"
#include "odb.h"
#include "odb/streaming.h"
#include "path.h"
#include "read-cache-ll.h"
#include "replace-object.h"
#include "resolve-undo.h"
#include "run-command.h"
#include "sparse-index.h"
#include "worktree.h"
#include "pack-revindex.h"
#include "pack-bitmap.h"

#define REACHABLE 0x0001
#define SEEN      0x0002
#define HAS_OBJ   0x0004
/* This flag is set if something points to this object. */
#define USED      0x0008

static int show_root;
static int show_tags;
static int show_unreachable;
static int include_reflogs = 1;
static int check_full = 1;
static int connectivity_only;
static int check_strict;
static int keep_cache_objects;
static struct fsck_options fsck_walk_options;
static struct fsck_options fsck_obj_options;
static int errors_found;
static int write_lost_and_found;
static int verbose;
static int show_progress = -1;
static int show_dangling = 1;
static int name_objects;
static int check_references = 1;
static timestamp_t now;
#define ERROR_OBJECT 01
#define ERROR_REACHABLE 02
#define ERROR_PACK 04
#define ERROR_REFS 010
#define ERROR_COMMIT_GRAPH 020
#define ERROR_MULTI_PACK_INDEX 040
#define ERROR_PACK_REV_INDEX 0100
#define ERROR_BITMAP 0200

static const char *describe_object(const struct object_id *oid)
{
	return fsck_describe_object(&fsck_walk_options, oid);
}

static const char *printable_type(struct repository *repo,
				  const struct object_id *oid,
				  enum object_type type)
{
	const char *ret;

	if (type == OBJ_NONE)
		type = odb_read_object_info(repo->objects, oid, NULL);

	ret = type_name(type);
	if (!ret)
		ret = _("unknown");

	return ret;
}

static int objerror(struct repository *repo, struct object *obj, const char *err)
{
	errors_found |= ERROR_OBJECT;
	/* TRANSLATORS: e.g. error in tree 01bfda: <more explanation> */
	fprintf_ln(stderr, _("error in %s %s: %s"),
		   printable_type(repo, &obj->oid, obj->type),
		   describe_object(&obj->oid), err);
	return -1;
}

static int fsck_objects_error_func(struct fsck_options *o,
				   void *fsck_report,
				   enum fsck_msg_type msg_type,
				   enum fsck_msg_id msg_id UNUSED,
				   const char *message)
{
	struct fsck_object_report *report = fsck_report;
	const struct object_id *oid = report->oid;
	enum object_type object_type = report->object_type;

	switch (msg_type) {
	case FSCK_WARN:
		/* TRANSLATORS: e.g. warning in tree 01bfda: <more explanation> */
		fprintf_ln(stderr, _("warning in %s %s: %s"),
			   printable_type(o->repo, oid, object_type),
			   describe_object(oid), message);
		return 0;
	case FSCK_ERROR:
		/* TRANSLATORS: e.g. error in tree 01bfda: <more explanation> */
		fprintf_ln(stderr, _("error in %s %s: %s"),
			   printable_type(o->repo, oid, object_type),
			   describe_object(oid), message);
		return 1;
	default:
		BUG("%d (FSCK_IGNORE?) should never trigger this callback",
		    msg_type);
	}
}

static struct object_array pending;

static int mark_object(struct object *obj, enum object_type type,
		       void *data, struct fsck_options *options)
{
	struct object *parent = data;

	/*
	 * The only case data is NULL or type is OBJ_ANY is when
	 * mark_object_reachable() calls us.  All the callers of
	 * that function has non-NULL obj hence ...
	 */
	if (!obj) {
		/* ... these references to parent->fld are safe here */
		printf_ln(_("broken link from %7s %s"),
			  printable_type(options->repo, &parent->oid, parent->type),
			  describe_object(&parent->oid));
		printf_ln(_("broken link from %7s %s"),
			  (type == OBJ_ANY ? _("unknown") : type_name(type)),
			  _("unknown"));
		errors_found |= ERROR_REACHABLE;
		return 1;
	}

	if (type != OBJ_ANY && obj->type != type)
		/* ... and the reference to parent is safe here */
		objerror(options->repo, parent, _("wrong object type in link"));

	if (obj->flags & REACHABLE)
		return 0;
	obj->flags |= REACHABLE;

	if (is_promisor_object(options->repo, &obj->oid))
		/*
		 * Further recursion does not need to be performed on this
		 * object since it is a promisor object (so it does not need to
		 * be added to "pending").
		 */
		return 0;

	if (!(obj->flags & HAS_OBJ)) {
		if (parent && !odb_has_object(options->repo->objects, &obj->oid,
					      ODB_HAS_OBJECT_RECHECK_PACKED)) {
			printf_ln(_("broken link from %7s %s\n"
				    "              to %7s %s"),
				  printable_type(options->repo, &parent->oid, parent->type),
				  describe_object(&parent->oid),
				  printable_type(options->repo, &obj->oid, obj->type),
				  describe_object(&obj->oid));
			errors_found |= ERROR_REACHABLE;
		}
		return 1;
	}

	add_object_array(obj, NULL, &pending);
	return 0;
}

static void mark_object_reachable(struct object *obj)
{
	mark_object(obj, OBJ_ANY, NULL, &fsck_walk_options);
}

static int traverse_one_object(struct object *obj)
{
	int result = fsck_walk(obj, obj, &fsck_walk_options);

	if (obj->type == OBJ_TREE) {
		struct tree *tree = (struct tree *)obj;
		free_tree_buffer(tree);
	}
	return result;
}

static int traverse_reachable(struct repository *repo)
{
	struct progress *progress = NULL;
	unsigned int nr = 0;
	int result = 0;
	if (show_progress)
		progress = start_delayed_progress(repo,
						  _("Checking connectivity"), 0);
	while (pending.nr) {
		result |= traverse_one_object(object_array_pop(&pending));
		display_progress(progress, ++nr);
	}
	stop_progress(&progress);
	return !!result;
}

static int mark_used(struct object *obj, enum object_type type UNUSED,
		     void *data UNUSED, struct fsck_options *options UNUSED)
{
	if (!obj)
		return 1;
	obj->flags |= USED;
	return 0;
}

static int mark_unreachable_referents(const struct object_id *oid,
				      struct object_info *oi UNUSED,
				      void *data)
{
	struct repository *repo = data;
	struct fsck_options options;
	struct object *obj = lookup_object(data, oid);

	if (!obj || !(obj->flags & HAS_OBJ))
		return 0; /* not part of our original set */
	if (obj->flags & REACHABLE)
		return 0; /* reachable objects already traversed */

	/*
	 * Avoid passing OBJ_NONE to fsck_walk, which will parse the object
	 * (and we want to avoid parsing blobs).
	 */
	if (obj->type == OBJ_NONE) {
		enum object_type type = odb_read_object_info(repo->objects,
							     &obj->oid, NULL);
		if (type > 0)
			object_as_type(obj, type, 0);
	}

	fsck_options_init(&options, repo, FSCK_OPTIONS_DEFAULT);
	options.walk = mark_used;
	fsck_walk(obj, NULL, &options);
	if (obj->type == OBJ_TREE)
		free_tree_buffer((struct tree *)obj);

	return 0;
}

/*
 * Check a single reachable object
 */
static void check_reachable_object(struct repository *repo, struct object *obj)
{
	/*
	 * We obviously want the object to be parsed,
	 * except if it was in a pack-file and we didn't
	 * do a full fsck
	 */
	if (!(obj->flags & HAS_OBJ)) {
		if (is_promisor_object(repo, &obj->oid))
			return;
		if (has_object_pack(repo, &obj->oid))
			return; /* it is in pack - forget about it */
		printf_ln(_("missing %s %s"),
			  printable_type(repo, &obj->oid, obj->type),
			  describe_object(&obj->oid));
		errors_found |= ERROR_REACHABLE;
		return;
	}
}

/*
 * Check a single unreachable object
 */
static void check_unreachable_object(struct repository *repo, struct object *obj)
{
	/*
	 * Missing unreachable object? Ignore it. It's not like
	 * we miss it (since it can't be reached), nor do we want
	 * to complain about it being unreachable (since it does
	 * not exist).
	 */
	if (!(obj->flags & HAS_OBJ))
		return;

	/*
	 * Unreachable object that exists? Show it if asked to,
	 * since this is something that is prunable.
	 */
	if (show_unreachable) {
		printf_ln(_("unreachable %s %s"),
			  printable_type(repo, &obj->oid, obj->type),
			  describe_object(&obj->oid));
		return;
	}

	/*
	 * "!USED" means that nothing at all points to it, including
	 * other unreachable objects. In other words, it's the "tip"
	 * of some set of unreachable objects, usually a commit that
	 * got dropped.
	 *
	 * Such starting points are more interesting than some random
	 * set of unreachable objects, so we show them even if the user
	 * hasn't asked for _all_ unreachable objects. If you have
	 * deleted a branch by mistake, this is a prime candidate to
	 * start looking at, for example.
	 */
	if (!(obj->flags & USED)) {
		if (show_dangling)
			printf_ln(_("dangling %s %s"),
				  printable_type(repo, &obj->oid, obj->type),
				  describe_object(&obj->oid));
		if (write_lost_and_found) {
			char *filename = repo_git_path(repo, "lost-found/%s/%s",
				obj->type == OBJ_COMMIT ? "commit" : "other",
				describe_object(&obj->oid));
			FILE *f;

			if (safe_create_leading_directories_const(repo, filename)) {
				error(_("could not create lost-found"));
				free(filename);
				return;
			}
			f = xfopen(filename, "w");
			if (obj->type == OBJ_BLOB) {
				if (odb_stream_blob_to_fd(repo->objects, fileno(f),
							  &obj->oid, NULL, 1))
					die_errno(_("could not write '%s'"), filename);
			} else
				fprintf(f, "%s\n", describe_object(&obj->oid));
			if (fclose(f))
				die_errno(_("could not finish '%s'"),
					  filename);
			free(filename);
		}
		return;
	}

	/*
	 * Otherwise? It's there, it's unreachable, and some other unreachable
	 * object points to it. Ignore it - it's not interesting, and we showed
	 * all the interesting cases above.
	 */
}

static void check_object(struct repository *repo, struct object *obj)
{
	if (verbose)
		fprintf_ln(stderr, _("Checking %s"), describe_object(&obj->oid));

	if (obj->flags & REACHABLE)
		check_reachable_object(repo, obj);
	else
		check_unreachable_object(repo, obj);
}

static void check_connectivity(struct repository *repo)
{
	int i, max;

	/* Traverse the pending reachable objects */
	traverse_reachable(repo);

	/*
	 * With --connectivity-only, we won't have actually opened and marked
	 * unreachable objects with USED. Do that now to make --dangling, etc
	 * accurate.
	 */
	if (connectivity_only && (show_dangling || write_lost_and_found)) {
		/*
		 * Even though we already have a "struct object" for each of
		 * these in memory, we must not iterate over the internal
		 * object hash as we do below. Our loop would potentially
		 * resize the hash, making our iteration invalid.
		 *
		 * Instead, we'll just go back to the source list of objects,
		 * and ignore any that weren't present in our earlier
		 * traversal.
		 */
		odb_for_each_object(repo->objects, NULL,
				    mark_unreachable_referents, repo, 0);
	}

	/* Look up all the requirements, warn about missing objects.. */
	max = get_max_object_index(repo);
	if (verbose)
		fprintf_ln(stderr, _("Checking connectivity (%d objects)"), max);

	for (i = 0; i < max; i++) {
		struct object *obj = get_indexed_object(repo, i);

		if (obj)
			check_object(repo, obj);
	}
}

static int fsck_obj(struct repository *repo,
		    struct object *obj, void *buffer, unsigned long size)
{
	int err;

	if (obj->flags & SEEN)
		return 0;
	obj->flags |= SEEN;

	if (verbose)
		fprintf_ln(stderr, _("Checking %s %s"),
			   printable_type(repo, &obj->oid, obj->type),
			   describe_object(&obj->oid));

	if (fsck_walk(obj, NULL, &fsck_obj_options))
		objerror(repo, obj, _("broken links"));
	err = fsck_object(obj, buffer, size, &fsck_obj_options);
	if (err)
		goto out;

	if (obj->type == OBJ_COMMIT) {
		struct commit *commit = (struct commit *) obj;

		if (!commit->parents && show_root)
			printf_ln(_("root %s"),
				  describe_object(&commit->object.oid));
	}

	if (obj->type == OBJ_TAG) {
		struct tag *tag = (struct tag *) obj;

		if (show_tags && tag->tagged) {
			printf_ln(_("tagged %s %s (%s) in %s"),
				  printable_type(repo, &tag->tagged->oid, tag->tagged->type),
				  describe_object(&tag->tagged->oid),
				  tag->tag,
				  describe_object(&tag->object.oid));
		}
	}

out:
	if (obj->type == OBJ_TREE)
		free_tree_buffer((struct tree *)obj);
	return err;
}

static int fsck_obj_buffer(const struct object_id *oid, enum object_type type,
			   unsigned long size, void *buffer, int *eaten, void *cb_data)
{
	struct repository *repo = cb_data;
	struct object *obj;

	/*
	 * Note, buffer may be NULL if type is OBJ_BLOB. See
	 * verify_packfile(), data_valid variable for details.
	 */
	obj = parse_object_buffer(repo, oid, type, size, buffer, eaten);
	if (!obj) {
		errors_found |= ERROR_OBJECT;
		return error(_("%s: object corrupt or missing"),
			     oid_to_hex(oid));
	}
	obj->flags &= ~(REACHABLE | SEEN);
	obj->flags |= HAS_OBJ;
	return fsck_obj(repo, obj, buffer, size);
}

static int default_refs;

static void fsck_handle_reflog_oid(struct repository *repo,
				   const char *refname, struct object_id *oid,
				   timestamp_t timestamp)
{
	struct object *obj;

	if (!is_null_oid(oid)) {
		obj = lookup_object(repo, oid);
		if (obj && (obj->flags & HAS_OBJ)) {
			if (timestamp)
				fsck_put_object_name(&fsck_walk_options, oid,
						     "%s@{%"PRItime"}",
						     refname, timestamp);
			obj->flags |= USED;
			mark_object_reachable(obj);
		} else if (!is_promisor_object(repo, oid)) {
			error(_("%s: invalid reflog entry %s"),
			      refname, oid_to_hex(oid));
			errors_found |= ERROR_REACHABLE;
		}
	}
}

static int fsck_handle_reflog_ent(const char *refname,
				  struct object_id *ooid, struct object_id *noid,
				  const char *email UNUSED,
				  timestamp_t timestamp, int tz UNUSED,
				  const char *message UNUSED, void *cb_data)
{
	struct repository *repo = cb_data;

	if (now && timestamp > now)
		return 0;

	if (verbose)
		fprintf_ln(stderr, _("Checking reflog %s->%s"),
			   oid_to_hex(ooid), oid_to_hex(noid));

	fsck_handle_reflog_oid(repo, refname, ooid, 0);
	fsck_handle_reflog_oid(repo, refname, noid, timestamp);
	return 0;
}

static int fsck_handle_reflog(const char *logname, void *cb_data)
{
	struct strbuf refname = STRBUF_INIT;
	struct worktree *wt = cb_data;

	strbuf_worktree_ref(wt, &refname, logname);
	refs_for_each_reflog_ent(get_main_ref_store(wt->repo),
				 refname.buf, fsck_handle_reflog_ent,
				 wt->repo);
	strbuf_release(&refname);
	return 0;
}

struct ref_snapshot {
	char *refname;
	struct object_id oid;
	/* TODO: Maybe supplement with latest reflog entry info too? */
};

struct snapshot {
	size_t nr;
	size_t alloc;
	struct ref_snapshot *ref;
	/* TODO: Consider also snapshotting the index of each worktree. */
};

struct snapshot_ref_data {
	struct repository *repo;
	struct snapshot *snap;
};

static int snapshot_ref(const struct reference *ref, void *cb_data)
{
	struct snapshot_ref_data *data = cb_data;
	struct snapshot *snap = data->snap;
	struct object *obj;

	obj = parse_object(data->repo, ref->oid);
	if (!obj) {
		if (is_promisor_object(data->repo, ref->oid)) {
			/*
			 * Increment default_refs anyway, because this is a
			 * valid ref.
			 */
			 default_refs++;
			 return 0;
		}
		error(_("%s: invalid sha1 pointer %s"),
		      ref->name, oid_to_hex(ref->oid));
		errors_found |= ERROR_REACHABLE;
		/* We'll continue with the rest despite the error.. */
		return 0;
	}
	if (obj->type != OBJ_COMMIT && is_branch(ref->name)) {
		error(_("%s: not a commit"), ref->name);
		errors_found |= ERROR_REFS;
	}
	default_refs++;

	ALLOC_GROW(snap->ref, snap->nr + 1, snap->alloc);
	snap->ref[snap->nr].refname = xstrdup(ref->name);
	oidcpy(&snap->ref[snap->nr].oid, ref->oid);
	snap->nr++;

	return 0;
}

static int fsck_handle_ref(const struct reference *ref, void *cb_data)
{
	struct repository *repo = cb_data;
	struct object *obj;

	obj = parse_object(repo, ref->oid);
	obj->flags |= USED;
	fsck_put_object_name(&fsck_walk_options,
			     ref->oid, "%s", ref->name);
	mark_object_reachable(obj);

	return 0;
}

static void snapshot_refs(struct repository *repo,
			  struct snapshot *snap, int argc, const char **argv)
{
	struct refs_for_each_ref_options opts = {
		.flags = REFS_FOR_EACH_INCLUDE_BROKEN,
	};
	struct snapshot_ref_data data = {
		.repo = repo,
		.snap = snap,
	};
	struct worktree **worktrees, **p;
	const char *head_points_at;
	struct object_id head_oid;

	for (int i = 0; i < argc; i++) {
		const char *arg = argv[i];
		struct object_id oid;
		if (!repo_get_oid(repo, arg, &oid)) {
			struct reference ref = {
				.name = arg,
				.oid = &oid,
			};

			snapshot_ref(&ref, &data);
			continue;
		}
		error(_("invalid parameter: expected sha1, got '%s'"), arg);
		errors_found |= ERROR_OBJECT;
	}

	if (argc) {
		include_reflogs = 0;
		return;
	}

	refs_for_each_ref_ext(get_main_ref_store(repo),
			      snapshot_ref, &data, &opts);

	worktrees = get_worktrees();
	for (p = worktrees; *p; p++) {
		struct worktree *wt = *p;
		struct strbuf refname = STRBUF_INIT;

		strbuf_worktree_ref(wt, &refname, "HEAD");

		head_points_at = refs_resolve_ref_unsafe(get_main_ref_store(repo),
							 refname.buf, 0, &head_oid, NULL);

		if (head_points_at && !is_null_oid(&head_oid)) {
			struct reference ref = {
				.name = refname.buf,
				.oid = &head_oid,
			};

			snapshot_ref(&ref, &data);
		}
		strbuf_release(&refname);

		/*
		 * TODO: Could use refs_for_each_reflog(...) to find
		 * latest entry instead of using a global 'now' for that
		 * purpose.
		 */
	}
	free_worktrees(worktrees);

	/* Ignore reflogs newer than now */
	now = time(NULL);
}


static void free_snapshot_refs(struct snapshot *snap)
{
	for (size_t i = 0; i < snap->nr; i++)
		free(snap->ref[i].refname);
	free(snap->ref);
}

static void process_refs(struct repository *repo, struct snapshot *snap)
{
	struct worktree **worktrees, **p;

	for (size_t i = 0; i < snap->nr; i++) {
		struct reference ref = {
			.name = snap->ref[i].refname,
			.oid = &snap->ref[i].oid,
		};
		fsck_handle_ref(&ref, repo);
	}

	if (include_reflogs) {
		worktrees = get_worktrees();
		for (p = worktrees; *p; p++) {
			struct worktree *wt = *p;

			refs_for_each_reflog(get_worktree_ref_store(wt),
					     fsck_handle_reflog, wt);
		}
		free_worktrees(worktrees);
	}

	/*
	 * Not having any default heads isn't really fatal, but
	 * it does mean that "--unreachable" no longer makes any
	 * sense (since in this case everything will obviously
	 * be unreachable by definition.
	 *
	 * Showing dangling objects is valid, though (as those
	 * dangling objects are likely lost heads).
	 *
	 * So we just print a warning about it, and clear the
	 * "show_unreachable" flag.
	 */
	if (!default_refs) {
		fprintf_ln(stderr, _("notice: No default references"));
		show_unreachable = 0;
	}
}

struct for_each_loose_cb {
	struct repository *repo;
	struct progress *progress;
};

static int fsck_loose(const struct object_id *oid, const char *path,
		      void *cb_data)
{
	struct for_each_loose_cb *data = cb_data;
	struct object *obj;
	enum object_type type = OBJ_NONE;
	size_t size;
	void *contents = NULL;
	int eaten;
	struct object_info oi = OBJECT_INFO_INIT;
	struct object_id real_oid = *null_oid(data->repo->hash_algo);
	int err = 0;

	oi.sizep = &size;
	oi.typep = &type;

	if (read_loose_object(data->repo, path, oid, &real_oid, &contents, &oi) < 0) {
		if (contents && !oideq(&real_oid, oid))
			err = error(_("%s: hash-path mismatch, found at: %s"),
				    oid_to_hex(&real_oid), path);
		else
			err = error(_("%s: object corrupt or missing: %s"),
				    oid_to_hex(oid), path);
	}
	if (err < 0) {
		errors_found |= ERROR_OBJECT;
		free(contents);
		return 0; /* keep checking other objects */
	}

	if (!contents && type != OBJ_BLOB)
		BUG("read_loose_object streamed a non-blob");

	obj = parse_object_buffer(data->repo, oid, type, size,
				  contents, &eaten);

	if (!obj) {
		errors_found |= ERROR_OBJECT;
		error(_("%s: object could not be parsed: %s"),
		      oid_to_hex(oid), path);
		if (!eaten)
			free(contents);
		return 0; /* keep checking other objects */
	}

	obj->flags &= ~(REACHABLE | SEEN);
	obj->flags |= HAS_OBJ;
	if (fsck_obj(data->repo, obj, contents, size))
		errors_found |= ERROR_OBJECT;

	if (!eaten)
		free(contents);
	return 0; /* keep checking other objects, even if we saw an error */
}

static int fsck_cruft(const char *basename, const char *path,
		      void *data UNUSED)
{
	if (!starts_with(basename, "tmp_obj_"))
		fprintf_ln(stderr, _("bad sha1 file: %s"), path);
	return 0;
}

static int fsck_subdir(unsigned int nr, const char *path UNUSED, void *data)
{
	struct for_each_loose_cb *cb_data = data;
	struct progress *progress = cb_data->progress;
	display_progress(progress, nr + 1);
	return 0;
}

static void fsck_source(struct repository *repo, struct odb_source *source)
{
	struct progress *progress = NULL;
	struct for_each_loose_cb cb_data = {
		.repo = source->odb->repo,
		.progress = progress,
	};

	if (verbose)
		fprintf_ln(stderr, _("Checking object directory"));

	if (show_progress)
		progress = start_progress(repo,
					  _("Checking object directories"), 256);

	for_each_loose_file_in_source(source, fsck_loose,
				      fsck_cruft, fsck_subdir, &cb_data);
	display_progress(progress, 256);
	stop_progress(&progress);
}

static int fsck_cache_tree(struct repository *repo, struct cache_tree *it, const char *index_path)
{
	int i;
	int err = 0;

	if (verbose)
		fprintf_ln(stderr, _("Checking cache tree of %s"), index_path);

	if (0 <= it->entry_count) {
		struct object *obj = parse_object(repo, &it->oid);
		if (!obj) {
			error(_("%s: invalid sha1 pointer in cache-tree of %s"),
			      oid_to_hex(&it->oid), index_path);
			errors_found |= ERROR_REFS;
			return 1;
		}
		obj->flags |= USED;
		fsck_put_object_name(&fsck_walk_options, &it->oid, ":");
		mark_object_reachable(obj);
		if (obj->type != OBJ_TREE)
			err |= objerror(repo, obj, _("non-tree in cache-tree"));
	}
	for (i = 0; i < it->subtree_nr; i++)
		err |= fsck_cache_tree(repo, it->down[i]->cache_tree, index_path);
	return err;
}

static int fsck_resolve_undo(struct index_state *istate,
			     const char *index_path)
{
	struct string_list_item *item;
	struct string_list *resolve_undo = istate->resolve_undo;

	if (!resolve_undo)
		return 0;

	for_each_string_list_item(item, resolve_undo) {
		const char *path = item->string;
		struct resolve_undo_info *ru = item->util;
		int i;

		if (!ru)
			continue;
		for (i = 0; i < 3; i++) {
			struct object *obj;

			if (!ru->mode[i] || !S_ISREG(ru->mode[i]))
				continue;

			obj = parse_object(istate->repo, &ru->oid[i]);
			if (!obj) {
				error(_("%s: invalid sha1 pointer in resolve-undo of %s"),
				      oid_to_hex(&ru->oid[i]),
				      index_path);
				errors_found |= ERROR_REFS;
				continue;
			}
			obj->flags |= USED;
			fsck_put_object_name(&fsck_walk_options, &ru->oid[i],
					     ":(%d):%s", i, path);
			mark_object_reachable(obj);
		}
	}
	return 0;
}

static void fsck_index(struct index_state *istate, const char *index_path,
		       int is_current_worktree)
{
	unsigned int i;

	/* TODO: audit for interaction with sparse-index. */
	ensure_full_index(istate);
	for (i = 0; i < istate->cache_nr; i++) {
		unsigned int mode;
		struct blob *blob;
		struct object *obj;

		mode = istate->cache[i]->ce_mode;
		if (S_ISGITLINK(mode))
			continue;
		blob = lookup_blob(istate->repo,
				   &istate->cache[i]->oid);
		if (!blob)
			continue;
		obj = &blob->object;
		obj->flags |= USED;
		fsck_put_object_name(&fsck_walk_options, &obj->oid,
				     "%s:%s",
				     is_current_worktree ? "" : index_path,
				     istate->cache[i]->name);
		mark_object_reachable(obj);
	}
	if (istate->cache_tree)
		fsck_cache_tree(istate->repo, istate->cache_tree, index_path);
	fsck_resolve_undo(istate, index_path);
}

static int mark_object_for_connectivity(const struct object_id *oid,
					struct object_info *oi UNUSED,
					void *cb_data)
{
	struct repository *repo = cb_data;
	struct object *obj = lookup_unknown_object(repo, oid);
	obj->flags |= HAS_OBJ;
	return 0;
}

static int check_pack_rev_indexes(struct repository *r, int show_progress)
{
	struct progress *progress = NULL;
	struct packed_git *p;
	uint32_t pack_count = 0;
	int res = 0;

	if (show_progress) {
		repo_for_each_pack(r, p)
			pack_count++;
		progress = start_delayed_progress(r,
						  "Verifying reverse pack-indexes", pack_count);
		pack_count = 0;
	}

	repo_for_each_pack(r, p) {
		int load_error = load_pack_revindex_from_disk(p);

		if (load_error < 0) {
			error(_("unable to load rev-index for pack '%s'"), p->pack_name);
			res = ERROR_PACK_REV_INDEX;
		} else if (!load_error &&
			   !load_pack_revindex(r, p) &&
			   verify_pack_revindex(p)) {
			error(_("invalid rev-index for pack '%s'"), p->pack_name);
			res = ERROR_PACK_REV_INDEX;
		}
		display_progress(progress, ++pack_count);
	}
	stop_progress(&progress);

	return res;
}

static void fsck_refs(struct repository *r)
{
	struct child_process refs_verify = CHILD_PROCESS_INIT;
	struct progress *progress = NULL;

	if (show_progress)
		progress = start_progress(r, _("Checking ref database"), 1);

	if (verbose)
		fprintf_ln(stderr, _("Checking ref database"));

	child_process_init(&refs_verify);
	refs_verify.git_cmd = 1;
	strvec_pushl(&refs_verify.args, "refs", "verify", NULL);
	if (verbose)
		strvec_push(&refs_verify.args, "--verbose");
	if (check_strict)
		strvec_push(&refs_verify.args, "--strict");

	if (run_command(&refs_verify))
		errors_found |= ERROR_REFS;

	display_progress(progress, 1);
	stop_progress(&progress);
}

static char const * const fsck_usage[] = {
	N_("git fsck [--tags] [--root] [--unreachable] [--cache] [--no-reflogs]\n"
	   "         [--[no-]full] [--strict] [--verbose] [--lost-found]\n"
	   "         [--[no-]dangling] [--[no-]progress] [--connectivity-only]\n"
	   "         [--[no-]name-objects] [--[no-]references] [<object>...]"),
	NULL
};

static struct option fsck_opts[] = {
	OPT__VERBOSE(&verbose, N_("be verbose")),
	OPT_BOOL(0, "unreachable", &show_unreachable, N_("show unreachable objects")),
	OPT_BOOL(0, "dangling", &show_dangling, N_("show dangling objects")),
	OPT_BOOL(0, "tags", &show_tags, N_("report tags")),
	OPT_BOOL(0, "root", &show_root, N_("report root nodes")),
	OPT_BOOL(0, "cache", &keep_cache_objects, N_("make index objects head nodes")),
	OPT_BOOL(0, "reflogs", &include_reflogs, N_("make reflogs head nodes (default)")),
	OPT_BOOL(0, "full", &check_full, N_("also consider packs and alternate objects")),
	OPT_BOOL(0, "connectivity-only", &connectivity_only, N_("check only connectivity")),
	OPT_BOOL(0, "strict", &check_strict, N_("enable more strict checking")),
	OPT_BOOL(0, "lost-found", &write_lost_and_found,
				N_("write dangling objects in .git/lost-found")),
	OPT_BOOL(0, "progress", &show_progress, N_("show progress")),
	OPT_BOOL(0, "name-objects", &name_objects, N_("show verbose names for reachable objects")),
	OPT_BOOL(0, "references", &check_references, N_("check reference database consistency")),
	OPT_END(),
};

int cmd_fsck(int argc,
	     const char **argv,
	     const char *prefix,
	     struct repository *repo)
{
	struct odb_source *source;
	struct snapshot snap = {
		.nr = 0,
		.alloc = 0,
		.ref = NULL
	};

	/* fsck knows how to handle missing promisor objects */
	fetch_if_missing = 0;

	errors_found = 0;
	disable_replace_refs();
	save_commit_buffer = 0;

	argc = parse_options(argc, argv, prefix, fsck_opts, fsck_usage, 0);

	fsck_options_init(&fsck_walk_options, repo, FSCK_OPTIONS_DEFAULT);
	fsck_walk_options.walk = mark_object;

	fsck_options_init(&fsck_obj_options, repo, FSCK_OPTIONS_DEFAULT);
	fsck_obj_options.walk = mark_used;
	fsck_obj_options.error_func = fsck_objects_error_func;
	if (check_strict)
		fsck_obj_options.strict = 1;

	if (show_progress == -1)
		show_progress = isatty(2);
	if (verbose)
		show_progress = 0;

	if (write_lost_and_found) {
		check_full = 1;
		include_reflogs = 0;
	}

	if (name_objects)
		fsck_enable_object_names(&fsck_walk_options);

	repo_config(repo, git_fsck_config, &fsck_obj_options);
	prepare_repo_settings(repo);

	if (check_references)
		fsck_refs(repo);

	/*
	 * Take a snapshot of the refs before walking objects to avoid looking
	 * at a set of refs that may be changed by the user while we are walking
	 * objects. We can still walk over new objects that are added during the
	 * execution of fsck but won't miss any objects that were reachable.
	 */
	snapshot_refs(repo, &snap, argc, argv);

	/* Ensure we get a "fresh" view of the odb */
	odb_reprepare(repo->objects);

	if (connectivity_only) {
		odb_for_each_object(repo->objects, NULL,
				    mark_object_for_connectivity, repo, 0);
	} else {
		odb_prepare_alternates(repo->objects);
		for (source = repo->objects->sources; source; source = source->next)
			fsck_source(repo, source);

		if (check_full) {
			struct packed_git *p;
			uint32_t total = 0, count = 0;
			struct progress *progress = NULL;

			if (show_progress) {
				repo_for_each_pack(repo, p) {
					if (open_pack_index(p))
						continue;
					total += p->num_objects;
				}

				progress = start_progress(repo,
							  _("Checking objects"), total);
			}

			repo_for_each_pack(repo, p) {
				/* verify gives error messages itself */
				if (verify_pack(repo,
						p, fsck_obj_buffer, repo,
						progress, count))
					errors_found |= ERROR_PACK;
				count += p->num_objects;
			}
			stop_progress(&progress);
		}

		if (fsck_finish(&fsck_obj_options))
			errors_found |= ERROR_OBJECT;
	}

	/* Process the snapshotted refs and the reflogs. */
	process_refs(repo, &snap);

	/* If not given any explicit objects, process index files too. */
	if (!argc)
		keep_cache_objects = 1;
	if (keep_cache_objects) {
		/*
		 * TODO: Consider first walking these indexes in snapshot_refs,
		 * to snapshot where the index entries used to point, and then
		 * check those snapshotted locations here.
		 */
		struct worktree **worktrees, **p;

		verify_index_checksum = 1;
		verify_ce_order = 1;

		worktrees = get_worktrees();
		for (p = worktrees; *p; p++) {
			struct worktree *wt = *p;
			struct index_state istate =
				INDEX_STATE_INIT(repo);
			char *path, *wt_gitdir;

			/*
			 * Make a copy since the buffer is reusable
			 * and may get overwritten by other calls
			 * while we're examining the index.
			 */
			path = xstrdup(worktree_git_path(wt, "index"));
			wt_gitdir = get_worktree_git_dir(wt);

			read_index_from(&istate, path, wt_gitdir);
			fsck_index(&istate, path, wt->is_current);

			discard_index(&istate);
			free(wt_gitdir);
			free(path);
		}
		free_worktrees(worktrees);
	}

	errors_found |= check_pack_rev_indexes(repo, show_progress);
	if (verify_bitmap_files(repo))
		errors_found |= ERROR_BITMAP;

	check_connectivity(repo);

	if (repo->settings.core_commit_graph) {
		struct child_process commit_graph_verify = CHILD_PROCESS_INIT;

		odb_prepare_alternates(repo->objects);
		for (source = repo->objects->sources; source; source = source->next) {
			child_process_init(&commit_graph_verify);
			commit_graph_verify.git_cmd = 1;
			strvec_pushl(&commit_graph_verify.args, "commit-graph",
				     "verify", "--object-dir", source->path, NULL);
			if (show_progress)
				strvec_push(&commit_graph_verify.args, "--progress");
			else
				strvec_push(&commit_graph_verify.args, "--no-progress");
			if (run_command(&commit_graph_verify))
				errors_found |= ERROR_COMMIT_GRAPH;
		}
	}

	if (repo->settings.core_multi_pack_index) {
		struct child_process midx_verify = CHILD_PROCESS_INIT;

		odb_prepare_alternates(repo->objects);
		for (source = repo->objects->sources; source; source = source->next) {
			child_process_init(&midx_verify);
			midx_verify.git_cmd = 1;
			strvec_pushl(&midx_verify.args, "multi-pack-index",
				     "verify", "--object-dir", source->path, NULL);
			if (show_progress)
				strvec_push(&midx_verify.args, "--progress");
			else
				strvec_push(&midx_verify.args, "--no-progress");
			if (run_command(&midx_verify))
				errors_found |= ERROR_MULTI_PACK_INDEX;
		}
	}

	free_snapshot_refs(&snap);
	return errors_found;
}