#include "builtin.h"
#include "cache.h"
#include "parse-options.h"
#include "quote.h"
#include "pathspec.h"
#include "dir.h"
#include "utf8.h"
#include "submodule.h"
#include "submodule-config.h"
#include "string-list.h"
#include "run-command.h"
#include "remote.h"
#include "refs.h"
#include "connect.h"

static char *get_default_remote(void)
{
        char *dest = NULL, *ret;
        unsigned char sha1[20];
        struct strbuf sb = STRBUF_INIT;
        const char *refname = resolve_ref_unsafe("HEAD", 0, sha1, NULL);

        if (!refname)
                die(_("No such ref: %s"), "HEAD");

        /* detached HEAD */
        if (!strcmp(refname, "HEAD"))
                return xstrdup("origin");

        if (!skip_prefix(refname, "refs/heads/", &refname))
                die(_("Expecting a full ref name, got %s"), refname);

        strbuf_addf(&sb, "branch.%s.remote", refname);
        if (git_config_get_string(sb.buf, &dest))
                ret = xstrdup("origin");
        else
                ret = dest;

        strbuf_release(&sb);
        return ret;
}

static int starts_with_dot_slash(const char *str)
{
        return str[0] == '.' && is_dir_sep(str[1]);
}

static int starts_with_dot_dot_slash(const char *str)
{
        return str[0] == '.' && str[1] == '.' && is_dir_sep(str[2]);
}

/*
 * Returns 1 if it was the last chop before ':'.
 */
static int chop_last_dir(char **remoteurl, int is_relative)
{
        char *rfind = find_last_dir_sep(*remoteurl);
        if (rfind) {
                *rfind = '\0';
                return 0;
        }

        rfind = strrchr(*remoteurl, ':');
        if (rfind) {
                *rfind = '\0';
                return 1;
        }

        if (is_relative || !strcmp(".", *remoteurl))
                die(_("cannot strip one component off url '%s'"),
                        *remoteurl);

        free(*remoteurl);
        *remoteurl = xstrdup(".");
        return 0;
}

/*
 * The `url` argument is the URL that navigates to the submodule origin
 * repo. When relative, this URL is relative to the superproject origin
 * URL repo. The `up_path` argument, if specified, is the relative
 * path that navigates from the submodule working tree to the superproject
 * working tree. Returns the origin URL of the submodule.
 *
 * Return either an absolute URL or filesystem path (if the superproject
 * origin URL is an absolute URL or filesystem path, respectively) or a
 * relative file system path (if the superproject origin URL is a relative
 * file system path).
 *
 * When the output is a relative file system path, the path is either
 * relative to the submodule working tree, if up_path is specified, or to
 * the superproject working tree otherwise.
 *
 * NEEDSWORK: This works incorrectly on the domain and protocol part.
 * remote_url      url              outcome          expectation
 * http://a.com/b  ../c             http://a.com/c   as is
 * http://a.com/b  ../../c          http://c         error out
 * http://a.com/b  ../../../c       http:/c          error out
 * http://a.com/b  ../../../../c    http:c           error out
 * http://a.com/b  ../../../../../c    .:c           error out
 * NEEDSWORK: Given how chop_last_dir() works, this function is broken
 * when a local part has a colon in its path component, too.
 */
static char *relative_url(const char *remote_url,
                                const char *url,
                                const char *up_path)
{
        int is_relative = 0;
        int colonsep = 0;
        char *out;
        char *remoteurl = xstrdup(remote_url);
        struct strbuf sb = STRBUF_INIT;
        size_t len = strlen(remoteurl);

        if (is_dir_sep(remoteurl[len]))
                remoteurl[len] = '\0';

        if (!url_is_local_not_ssh(remoteurl) || is_absolute_path(remoteurl))
                is_relative = 0;
        else {
                is_relative = 1;
                /*
                 * Prepend a './' to ensure all relative
                 * remoteurls start with './' or '../'
                 */
                if (!starts_with_dot_slash(remoteurl) &&
                    !starts_with_dot_dot_slash(remoteurl)) {
                        strbuf_reset(&sb);
                        strbuf_addf(&sb, "./%s", remoteurl);
                        free(remoteurl);
                        remoteurl = strbuf_detach(&sb, NULL);
                }
        }
        /*
         * When the url starts with '../', remove that and the
         * last directory in remoteurl.
         */
        while (url) {
                if (starts_with_dot_dot_slash(url)) {
                        url += 3;
                        colonsep |= chop_last_dir(&remoteurl, is_relative);
                } else if (starts_with_dot_slash(url))
                        url += 2;
                else
                        break;
        }
        strbuf_reset(&sb);
        strbuf_addf(&sb, "%s%s%s", remoteurl, colonsep ? ":" : "/", url);
        free(remoteurl);

        if (starts_with_dot_slash(sb.buf))
                out = xstrdup(sb.buf + 2);
        else
                out = xstrdup(sb.buf);
        strbuf_reset(&sb);

        if (!up_path || !is_relative)
                return out;

        strbuf_addf(&sb, "%s%s", up_path, out);
        free(out);
        return strbuf_detach(&sb, NULL);
}

static int resolve_relative_url(int argc, const char **argv, const char *prefix)
{
        char *remoteurl = NULL;
        char *remote = get_default_remote();
        const char *up_path = NULL;
        char *res;
        const char *url;
        struct strbuf sb = STRBUF_INIT;

        if (argc != 2 && argc != 3)
                die("resolve-relative-url only accepts one or two arguments");

        url = argv[1];
        strbuf_addf(&sb, "remote.%s.url", remote);
        free(remote);

        if (git_config_get_string(sb.buf, &remoteurl))
                /* the repository is its own authoritative upstream */
                remoteurl = xgetcwd();

        if (argc == 3)
                up_path = argv[2];

        res = relative_url(remoteurl, url, up_path);
        puts(res);
        free(res);
        free(remoteurl);
        return 0;
}

static int resolve_relative_url_test(int argc, const char **argv, const char *prefix)
{
        char *remoteurl, *res;
        const char *up_path, *url;

        if (argc != 4)
                die("resolve-relative-url-test only accepts three arguments: <up_path> <remoteurl> <url>");

        up_path = argv[1];
        remoteurl = xstrdup(argv[2]);
        url = argv[3];

        if (!strcmp(up_path, "(null)"))
                up_path = NULL;

        res = relative_url(remoteurl, url, up_path);
        puts(res);
        free(res);
        free(remoteurl);
        return 0;
}

struct module_list {
        const struct cache_entry **entries;
        int alloc, nr;
};
#define MODULE_LIST_INIT { NULL, 0, 0 }

static int module_list_compute(int argc, const char **argv,
                               const char *prefix,
                               struct pathspec *pathspec,
                               struct module_list *list)
{
        int i, result = 0;
        char *ps_matched = NULL;
        parse_pathspec(pathspec, 0,
                       PATHSPEC_PREFER_FULL |
                       PATHSPEC_STRIP_SUBMODULE_SLASH_CHEAP,
                       prefix, argv);

        if (pathspec->nr)
                ps_matched = xcalloc(pathspec->nr, 1);

        if (read_cache() < 0)
                die(_("index file corrupt"));

        for (i = 0; i < active_nr; i++) {
                const struct cache_entry *ce = active_cache[i];

                if (!match_pathspec(pathspec, ce->name, ce_namelen(ce),
                                    0, ps_matched, 1) ||
                    !S_ISGITLINK(ce->ce_mode))
                        continue;

                ALLOC_GROW(list->entries, list->nr + 1, list->alloc);
                list->entries[list->nr++] = ce;
                while (i + 1 < active_nr &&
                       !strcmp(ce->name, active_cache[i + 1]->name))
                        /*
                         * Skip entries with the same name in different stages
                         * to make sure an entry is returned only once.
                         */
                        i++;
        }

        if (ps_matched && report_path_error(ps_matched, pathspec, prefix))
                result = -1;

        free(ps_matched);

        return result;
}

static int module_list(int argc, const char **argv, const char *prefix)
{
        int i;
        struct pathspec pathspec;
        struct module_list list = MODULE_LIST_INIT;

        struct option module_list_options[] = {
                OPT_STRING(0, "prefix", &prefix,
                           N_("path"),
                           N_("alternative anchor for relative paths")),
                OPT_END()
        };

        const char *const git_submodule_helper_usage[] = {
                N_("git submodule--helper list [--prefix=<path>] [<path>...]"),
                NULL
        };

        argc = parse_options(argc, argv, prefix, module_list_options,
                             git_submodule_helper_usage, 0);

        if (module_list_compute(argc, argv, prefix, &pathspec, &list) < 0)
                return 1;

        for (i = 0; i < list.nr; i++) {
                const struct cache_entry *ce = list.entries[i];

                if (ce_stage(ce))
                        printf("%06o %s U\t", ce->ce_mode, sha1_to_hex(null_sha1));
                else
                        printf("%06o %s %d\t", ce->ce_mode,
                               oid_to_hex(&ce->oid), ce_stage(ce));

                utf8_fprintf(stdout, "%s\n", ce->name);
        }
        return 0;
}

static void init_submodule(const char *path, const char *prefix, int quiet)
{
        const struct submodule *sub;
        struct strbuf sb = STRBUF_INIT;
        char *upd = NULL, *url = NULL, *displaypath;

        /* Only loads from .gitmodules, no overlay with .git/config */
        gitmodules_config();

        if (prefix) {
                strbuf_addf(&sb, "%s%s", prefix, path);
                displaypath = strbuf_detach(&sb, NULL);
        } else
                displaypath = xstrdup(path);

        sub = submodule_from_path(null_sha1, path);

        if (!sub)
                die(_("No url found for submodule path '%s' in .gitmodules"),
                        displaypath);

        /*
         * Copy url setting when it is not set yet.
         * To look up the url in .git/config, we must not fall back to
         * .gitmodules, so look it up directly.
         */
        strbuf_reset(&sb);
        strbuf_addf(&sb, "submodule.%s.url", sub->name);
        if (git_config_get_string(sb.buf, &url)) {
                url = xstrdup(sub->url);

                if (!url)
                        die(_("No url found for submodule path '%s' in .gitmodules"),
                                displaypath);

                /* Possibly a url relative to parent */
                if (starts_with_dot_dot_slash(url) ||
                    starts_with_dot_slash(url)) {
                        char *remoteurl, *relurl;
                        char *remote = get_default_remote();
                        struct strbuf remotesb = STRBUF_INIT;
                        strbuf_addf(&remotesb, "remote.%s.url", remote);
                        free(remote);

                        if (git_config_get_string(remotesb.buf, &remoteurl))
                                /*
                                 * The repository is its own
                                 * authoritative upstream
                                 */
                                remoteurl = xgetcwd();
                        relurl = relative_url(remoteurl, url, NULL);
                        strbuf_release(&remotesb);
                        free(remoteurl);
                        free(url);
                        url = relurl;
                }

                if (git_config_set_gently(sb.buf, url))
                        die(_("Failed to register url for submodule path '%s'"),
                            displaypath);
                if (!quiet)
                        fprintf(stderr,
                                _("Submodule '%s' (%s) registered for path '%s'\n"),
                                sub->name, url, displaypath);
        }

        /* Copy "update" setting when it is not set yet */
        strbuf_reset(&sb);
        strbuf_addf(&sb, "submodule.%s.update", sub->name);
        if (git_config_get_string(sb.buf, &upd) &&
            sub->update_strategy.type != SM_UPDATE_UNSPECIFIED) {
                if (sub->update_strategy.type == SM_UPDATE_COMMAND) {
                        fprintf(stderr, _("warning: command update mode suggested for submodule '%s'\n"),
                                sub->name);
                        upd = xstrdup("none");
                } else
                        upd = xstrdup(submodule_strategy_to_string(&sub->update_strategy));

                if (git_config_set_gently(sb.buf, upd))
                        die(_("Failed to register update mode for submodule path '%s'"), displaypath);
        }
        strbuf_release(&sb);
        free(displaypath);
        free(url);
        free(upd);
}

static int module_init(int argc, const char **argv, const char *prefix)
{
        struct pathspec pathspec;
        struct module_list list = MODULE_LIST_INIT;
        int quiet = 0;
        int i;

        struct option module_init_options[] = {
                OPT_STRING(0, "prefix", &prefix,
                           N_("path"),
                           N_("alternative anchor for relative paths")),
                OPT__QUIET(&quiet, N_("Suppress output for initializing a submodule")),
                OPT_END()
        };

        const char *const git_submodule_helper_usage[] = {
                N_("git submodule--helper init [<path>]"),
                NULL
        };

        argc = parse_options(argc, argv, prefix, module_init_options,
                             git_submodule_helper_usage, 0);

        if (module_list_compute(argc, argv, prefix, &pathspec, &list) < 0)
                return 1;

        for (i = 0; i < list.nr; i++)
                init_submodule(list.entries[i]->name, prefix, quiet);

        return 0;
}

static int module_name(int argc, const char **argv, const char *prefix)
{
        const struct submodule *sub;

        if (argc != 2)
                usage(_("git submodule--helper name <path>"));

        gitmodules_config();
        sub = submodule_from_path(null_sha1, argv[1]);

        if (!sub)
                die(_("no submodule mapping found in .gitmodules for path '%s'"),
                    argv[1]);

        printf("%s\n", sub->name);

        return 0;
}

static int clone_submodule(const char *path, const char *gitdir, const char *url,
                           const char *depth, struct string_list *reference, int quiet)
{
        struct child_process cp = CHILD_PROCESS_INIT;

        argv_array_push(&cp.args, "clone");
        argv_array_push(&cp.args, "--no-checkout");
        if (quiet)
                argv_array_push(&cp.args, "--quiet");
        if (depth && *depth)
                argv_array_pushl(&cp.args, "--depth", depth, NULL);
        if (reference->nr) {
                struct string_list_item *item;
                for_each_string_list_item(item, reference)
                        argv_array_pushl(&cp.args, "--reference",
                                         item->string, NULL);
        }
        if (gitdir && *gitdir)
                argv_array_pushl(&cp.args, "--separate-git-dir", gitdir, NULL);

        argv_array_push(&cp.args, url);
        argv_array_push(&cp.args, path);

        cp.git_cmd = 1;
        prepare_submodule_repo_env(&cp.env_array);
        cp.no_stdin = 1;

        return run_command(&cp);
}

struct submodule_alternate_setup {
        const char *submodule_name;
        enum SUBMODULE_ALTERNATE_ERROR_MODE {
                SUBMODULE_ALTERNATE_ERROR_DIE,
                SUBMODULE_ALTERNATE_ERROR_INFO,
                SUBMODULE_ALTERNATE_ERROR_IGNORE
        } error_mode;
        struct string_list *reference;
};
#define SUBMODULE_ALTERNATE_SETUP_INIT { NULL, \
        SUBMODULE_ALTERNATE_ERROR_IGNORE, NULL }

static int add_possible_reference_from_superproject(
                struct alternate_object_database *alt, void *sas_cb)
{
        struct submodule_alternate_setup *sas = sas_cb;

        /* directory name, minus trailing slash */
        size_t namelen = alt->name - alt->base - 1;
        struct strbuf name = STRBUF_INIT;
        strbuf_add(&name, alt->base, namelen);

        /*
         * If the alternate object store is another repository, try the
         * standard layout with .git/modules/<name>/objects
         */
        if (ends_with(name.buf, ".git/objects")) {
                char *sm_alternate;
                struct strbuf sb = STRBUF_INIT;
                struct strbuf err = STRBUF_INIT;
                strbuf_add(&sb, name.buf, name.len - strlen("objects"));
                /*
                 * We need to end the new path with '/' to mark it as a dir,
                 * otherwise a submodule name containing '/' will be broken
                 * as the last part of a missing submodule reference would
                 * be taken as a file name.
                 */
                strbuf_addf(&sb, "modules/%s/", sas->submodule_name);

                sm_alternate = compute_alternate_path(sb.buf, &err);
                if (sm_alternate) {
                        string_list_append(sas->reference, xstrdup(sb.buf));
                        free(sm_alternate);
                } else {
                        switch (sas->error_mode) {
                        case SUBMODULE_ALTERNATE_ERROR_DIE:
                                die(_("submodule '%s' cannot add alternate: %s"),
                                    sas->submodule_name, err.buf);
                        case SUBMODULE_ALTERNATE_ERROR_INFO:
                                fprintf(stderr, _("submodule '%s' cannot add alternate: %s"),
                                        sas->submodule_name, err.buf);
                        case SUBMODULE_ALTERNATE_ERROR_IGNORE:
                                ; /* nothing */
                        }
                }
                strbuf_release(&sb);
        }

        strbuf_release(&name);
        return 0;
}

static void prepare_possible_alternates(const char *sm_name,
                struct string_list *reference)
{
        char *sm_alternate = NULL, *error_strategy = NULL;
        struct submodule_alternate_setup sas = SUBMODULE_ALTERNATE_SETUP_INIT;

        git_config_get_string("submodule.alternateLocation", &sm_alternate);
        if (!sm_alternate)
                return;

        git_config_get_string("submodule.alternateErrorStrategy", &error_strategy);

        if (!error_strategy)
                error_strategy = xstrdup("die");

        sas.submodule_name = sm_name;
        sas.reference = reference;
        if (!strcmp(error_strategy, "die"))
                sas.error_mode = SUBMODULE_ALTERNATE_ERROR_DIE;
        else if (!strcmp(error_strategy, "info"))
                sas.error_mode = SUBMODULE_ALTERNATE_ERROR_INFO;
        else if (!strcmp(error_strategy, "ignore"))
                sas.error_mode = SUBMODULE_ALTERNATE_ERROR_IGNORE;
        else
                die(_("Value '%s' for submodule.alternateErrorStrategy is not recognized"), error_strategy);

        if (!strcmp(sm_alternate, "superproject"))
                foreach_alt_odb(add_possible_reference_from_superproject, &sas);
        else if (!strcmp(sm_alternate, "no"))
                ; /* do nothing */
        else
                die(_("Value '%s' for submodule.alternateLocation is not recognized"), sm_alternate);

        free(sm_alternate);
        free(error_strategy);
}

static int module_clone(int argc, const char **argv, const char *prefix)
{
        const char *name = NULL, *url = NULL, *depth = NULL;
        int quiet = 0;
        FILE *submodule_dot_git;
        char *p, *path = NULL, *sm_gitdir;
        struct strbuf rel_path = STRBUF_INIT;
        struct strbuf sb = STRBUF_INIT;
        struct string_list reference = STRING_LIST_INIT_NODUP;

        struct option module_clone_options[] = {
                OPT_STRING(0, "prefix", &prefix,
                           N_("path"),
                           N_("alternative anchor for relative paths")),
                OPT_STRING(0, "path", &path,
                           N_("path"),
                           N_("where the new submodule will be cloned to")),
                OPT_STRING(0, "name", &name,
                           N_("string"),
                           N_("name of the new submodule")),
                OPT_STRING(0, "url", &url,
                           N_("string"),
                           N_("url where to clone the submodule from")),
                OPT_STRING_LIST(0, "reference", &reference,
                           N_("repo"),
                           N_("reference repository")),
                OPT_STRING(0, "depth", &depth,
                           N_("string"),
                           N_("depth for shallow clones")),
                OPT__QUIET(&quiet, "Suppress output for cloning a submodule"),
                OPT_END()
        };

        const char *const git_submodule_helper_usage[] = {
                N_("git submodule--helper clone [--prefix=<path>] [--quiet] "
                   "[--reference <repository>] [--name <name>] [--depth <depth>] "
                   "--url <url> --path <path>"),
                NULL
        };

        argc = parse_options(argc, argv, prefix, module_clone_options,
                             git_submodule_helper_usage, 0);

        if (argc || !url || !path || !*path)
                usage_with_options(git_submodule_helper_usage,
                                   module_clone_options);

        strbuf_addf(&sb, "%s/modules/%s", get_git_dir(), name);
        sm_gitdir = xstrdup(absolute_path(sb.buf));
        strbuf_reset(&sb);

        if (!is_absolute_path(path)) {
                strbuf_addf(&sb, "%s/%s", get_git_work_tree(), path);
                path = strbuf_detach(&sb, NULL);
        } else
                path = xstrdup(path);

        if (!file_exists(sm_gitdir)) {
                if (safe_create_leading_directories_const(sm_gitdir) < 0)
                        die(_("could not create directory '%s'"), sm_gitdir);

                prepare_possible_alternates(name, &reference);

                if (clone_submodule(path, sm_gitdir, url, depth, &reference, quiet))
                        die(_("clone of '%s' into submodule path '%s' failed"),
                            url, path);
        } else {
                if (safe_create_leading_directories_const(path) < 0)
                        die(_("could not create directory '%s'"), path);
                strbuf_addf(&sb, "%s/index", sm_gitdir);
                unlink_or_warn(sb.buf);
                strbuf_reset(&sb);
        }

        /* Write a .git file in the submodule to redirect to the superproject. */
        strbuf_addf(&sb, "%s/.git", path);
        if (safe_create_leading_directories_const(sb.buf) < 0)
                die(_("could not create leading directories of '%s'"), sb.buf);
        submodule_dot_git = fopen(sb.buf, "w");
        if (!submodule_dot_git)
                die_errno(_("cannot open file '%s'"), sb.buf);

        fprintf_or_die(submodule_dot_git, "gitdir: %s\n",
                       relative_path(sm_gitdir, path, &rel_path));
        if (fclose(submodule_dot_git))
                die(_("could not close file %s"), sb.buf);
        strbuf_reset(&sb);
        strbuf_reset(&rel_path);

        /* Redirect the worktree of the submodule in the superproject's config */
        p = git_pathdup_submodule(path, "config");
        if (!p)
                die(_("could not get submodule directory for '%s'"), path);
        git_config_set_in_file(p, "core.worktree",
                               relative_path(path, sm_gitdir, &rel_path));
        strbuf_release(&sb);
        strbuf_release(&rel_path);
        free(sm_gitdir);
        free(path);
        free(p);
        return 0;
}

struct submodule_update_clone {
        /* index into 'list', the list of submodules to look into for cloning */
        int current;
        struct module_list list;
        unsigned warn_if_uninitialized : 1;

        /* update parameter passed via commandline */
        struct submodule_update_strategy update;

        /* configuration parameters which are passed on to the children */
        int quiet;
        int recommend_shallow;
        struct string_list references;
        const char *depth;
        const char *recursive_prefix;
        const char *prefix;

        /* Machine-readable status lines to be consumed by git-submodule.sh */
        struct string_list projectlines;

        /* If we want to stop as fast as possible and return an error */
        unsigned quickstop : 1;

        /* failed clones to be retried again */
        const struct cache_entry **failed_clones;
        int failed_clones_nr, failed_clones_alloc;
};
#define SUBMODULE_UPDATE_CLONE_INIT {0, MODULE_LIST_INIT, 0, \
        SUBMODULE_UPDATE_STRATEGY_INIT, 0, -1, STRING_LIST_INIT_DUP, \
        NULL, NULL, NULL, \
        STRING_LIST_INIT_DUP, 0, NULL, 0, 0}


static void next_submodule_warn_missing(struct submodule_update_clone *suc,
                struct strbuf *out, const char *displaypath)
{
        /*
         * Only mention uninitialized submodules when their
         * paths have been specified.
         */
        if (suc->warn_if_uninitialized) {
                strbuf_addf(out,
                        _("Submodule path '%s' not initialized"),
                        displaypath);
                strbuf_addch(out, '\n');
                strbuf_addstr(out,
                        _("Maybe you want to use 'update --init'?"));
                strbuf_addch(out, '\n');
        }
}

/**
 * Determine whether 'ce' needs to be cloned. If so, prepare the 'child' to
 * run the clone. Returns 1 if 'ce' needs to be cloned, 0 otherwise.
 */
static int prepare_to_clone_next_submodule(const struct cache_entry *ce,
                                           struct child_process *child,
                                           struct submodule_update_clone *suc,
                                           struct strbuf *out)
{
        const struct submodule *sub = NULL;
        struct strbuf displaypath_sb = STRBUF_INIT;
        struct strbuf sb = STRBUF_INIT;
        const char *displaypath = NULL;
        char *url = NULL;
        int needs_cloning = 0;

        if (ce_stage(ce)) {
                if (suc->recursive_prefix)
                        strbuf_addf(&sb, "%s/%s", suc->recursive_prefix, ce->name);
                else
                        strbuf_addf(&sb, "%s", ce->name);
                strbuf_addf(out, _("Skipping unmerged submodule %s"), sb.buf);
                strbuf_addch(out, '\n');
                goto cleanup;
        }

        sub = submodule_from_path(null_sha1, ce->name);

        if (suc->recursive_prefix)
                displaypath = relative_path(suc->recursive_prefix,
                                            ce->name, &displaypath_sb);
        else
                displaypath = ce->name;

        if (!sub) {
                next_submodule_warn_missing(suc, out, displaypath);
                goto cleanup;
        }

        if (suc->update.type == SM_UPDATE_NONE
            || (suc->update.type == SM_UPDATE_UNSPECIFIED
                && sub->update_strategy.type == SM_UPDATE_NONE)) {
                strbuf_addf(out, _("Skipping submodule '%s'"), displaypath);
                strbuf_addch(out, '\n');
                goto cleanup;
        }

        /*
         * Looking up the url in .git/config.
         * We must not fall back to .gitmodules as we only want
         * to process configured submodules.
         */
        strbuf_reset(&sb);
        strbuf_addf(&sb, "submodule.%s.url", sub->name);
        git_config_get_string(sb.buf, &url);
        if (!url) {
                next_submodule_warn_missing(suc, out, displaypath);
                goto cleanup;
        }

        strbuf_reset(&sb);
        strbuf_addf(&sb, "%s/.git", ce->name);
        needs_cloning = !file_exists(sb.buf);

        strbuf_reset(&sb);
        strbuf_addf(&sb, "%06o %s %d %d\t%s\n", ce->ce_mode,
                        oid_to_hex(&ce->oid), ce_stage(ce),
                        needs_cloning, ce->name);
        string_list_append(&suc->projectlines, sb.buf);

        if (!needs_cloning)
                goto cleanup;

        child->git_cmd = 1;
        child->no_stdin = 1;
        child->stdout_to_stderr = 1;
        child->err = -1;
        argv_array_push(&child->args, "submodule--helper");
        argv_array_push(&child->args, "clone");
        if (suc->quiet)
                argv_array_push(&child->args, "--quiet");
        if (suc->prefix)
                argv_array_pushl(&child->args, "--prefix", suc->prefix, NULL);
        if (suc->recommend_shallow && sub->recommend_shallow == 1)
                argv_array_push(&child->args, "--depth=1");
        argv_array_pushl(&child->args, "--path", sub->path, NULL);
        argv_array_pushl(&child->args, "--name", sub->name, NULL);
        argv_array_pushl(&child->args, "--url", url, NULL);
        if (suc->references.nr) {
                struct string_list_item *item;
                for_each_string_list_item(item, &suc->references)
                        argv_array_pushl(&child->args, "--reference", item->string, NULL);
        }
        if (suc->depth)
                argv_array_push(&child->args, suc->depth);

cleanup:
        free(url);
        strbuf_reset(&displaypath_sb);
        strbuf_reset(&sb);

        return needs_cloning;
}

static int update_clone_get_next_task(struct child_process *child,
                                      struct strbuf *err,
                                      void *suc_cb,
                                      void **idx_task_cb)
{
        struct submodule_update_clone *suc = suc_cb;
        const struct cache_entry *ce;
        int index;

        for (; suc->current < suc->list.nr; suc->current++) {
                ce = suc->list.entries[suc->current];
                if (prepare_to_clone_next_submodule(ce, child, suc, err)) {
                        int *p = xmalloc(sizeof(*p));
                        *p = suc->current;
                        *idx_task_cb = p;
                        suc->current++;
                        return 1;
                }
        }

        /*
         * The loop above tried cloning each submodule once, now try the
         * stragglers again, which we can imagine as an extension of the
         * entry list.
         */
        index = suc->current - suc->list.nr;
        if (index < suc->failed_clones_nr) {
                int *p;
                ce = suc->failed_clones[index];
                if (!prepare_to_clone_next_submodule(ce, child, suc, err)) {
                        suc->current ++;
                        strbuf_addf(err, "BUG: submodule considered for cloning,"
                                    "doesn't need cloning any more?\n");
                        return 0;
                }
                p = xmalloc(sizeof(*p));
                *p = suc->current;
                *idx_task_cb = p;
                suc->current ++;
                return 1;
        }

        return 0;
}

static int update_clone_start_failure(struct strbuf *err,
                                      void *suc_cb,
                                      void *idx_task_cb)
{
        struct submodule_update_clone *suc = suc_cb;
        suc->quickstop = 1;
        return 1;
}

static int update_clone_task_finished(int result,
                                      struct strbuf *err,
                                      void *suc_cb,
                                      void *idx_task_cb)
{
        const struct cache_entry *ce;
        struct submodule_update_clone *suc = suc_cb;

        int *idxP = *(int**)idx_task_cb;
        int idx = *idxP;
        free(idxP);

        if (!result)
                return 0;

        if (idx < suc->list.nr) {
                ce  = suc->list.entries[idx];
                strbuf_addf(err, _("Failed to clone '%s'. Retry scheduled"),
                            ce->name);
                strbuf_addch(err, '\n');
                ALLOC_GROW(suc->failed_clones,
                           suc->failed_clones_nr + 1,
                           suc->failed_clones_alloc);
                suc->failed_clones[suc->failed_clones_nr++] = ce;
                return 0;
        } else {
                idx -= suc->list.nr;
                ce  = suc->failed_clones[idx];
                strbuf_addf(err, _("Failed to clone '%s' a second time, aborting"),
                            ce->name);
                strbuf_addch(err, '\n');
                suc->quickstop = 1;
                return 1;
        }

        return 0;
}

static int update_clone(int argc, const char **argv, const char *prefix)
{
        const char *update = NULL;
        int max_jobs = -1;
        struct string_list_item *item;
        struct pathspec pathspec;
        struct submodule_update_clone suc = SUBMODULE_UPDATE_CLONE_INIT;

        struct option module_update_clone_options[] = {
                OPT_STRING(0, "prefix", &prefix,
                           N_("path"),
                           N_("path into the working tree")),
                OPT_STRING(0, "recursive-prefix", &suc.recursive_prefix,
                           N_("path"),
                           N_("path into the working tree, across nested "
                              "submodule boundaries")),
                OPT_STRING(0, "update", &update,
                           N_("string"),
                           N_("rebase, merge, checkout or none")),
                OPT_STRING_LIST(0, "reference", &suc.references, N_("repo"),
                           N_("reference repository")),
                OPT_STRING(0, "depth", &suc.depth, "<depth>",
                           N_("Create a shallow clone truncated to the "
                              "specified number of revisions")),
                OPT_INTEGER('j', "jobs", &max_jobs,
                            N_("parallel jobs")),
                OPT_BOOL(0, "recommend-shallow", &suc.recommend_shallow,
                            N_("whether the initial clone should follow the shallow recommendation")),
                OPT__QUIET(&suc.quiet, N_("don't print cloning progress")),
                OPT_END()
        };

        const char *const git_submodule_helper_usage[] = {
                N_("git submodule--helper update_clone [--prefix=<path>] [<path>...]"),
                NULL
        };
        suc.prefix = prefix;

        argc = parse_options(argc, argv, prefix, module_update_clone_options,
                             git_submodule_helper_usage, 0);

        if (update)
                if (parse_submodule_update_strategy(update, &suc.update) < 0)
                        die(_("bad value for update parameter"));

        if (module_list_compute(argc, argv, prefix, &pathspec, &suc.list) < 0)
                return 1;

        if (pathspec.nr)
                suc.warn_if_uninitialized = 1;

        /* Overlay the parsed .gitmodules file with .git/config */
        gitmodules_config();
        git_config(submodule_config, NULL);

        if (max_jobs < 0)
                max_jobs = parallel_submodules();

        run_processes_parallel(max_jobs,
                               update_clone_get_next_task,
                               update_clone_start_failure,
                               update_clone_task_finished,
                               &suc);

        /*
         * We saved the output and put it out all at once now.
         * That means:
         * - the listener does not have to interleave their (checkout)
         *   work with our fetching.  The writes involved in a
         *   checkout involve more straightforward sequential I/O.
         * - the listener can avoid doing any work if fetching failed.
         */
        if (suc.quickstop)
                return 1;

        for_each_string_list_item(item, &suc.projectlines)
                utf8_fprintf(stdout, "%s", item->string);

        return 0;
}

static int resolve_relative_path(int argc, const char **argv, const char *prefix)
{
        struct strbuf sb = STRBUF_INIT;
        if (argc != 3)
                die("submodule--helper relative-path takes exactly 2 arguments, got %d", argc);

        printf("%s", relative_path(argv[1], argv[2], &sb));
        strbuf_release(&sb);
        return 0;
}

static const char *remote_submodule_branch(const char *path)
{
        const struct submodule *sub;
        gitmodules_config();
        git_config(submodule_config, NULL);

        sub = submodule_from_path(null_sha1, path);
        if (!sub)
                return NULL;

        if (!sub->branch)
                return "master";

        if (!strcmp(sub->branch, ".")) {
                unsigned char sha1[20];
                const char *refname = resolve_ref_unsafe("HEAD", 0, sha1, NULL);

                if (!refname)
                        die(_("No such ref: %s"), "HEAD");

                /* detached HEAD */
                if (!strcmp(refname, "HEAD"))
                        die(_("Submodule (%s) branch configured to inherit "
                              "branch from superproject, but the superproject "
                              "is not on any branch"), sub->name);

                if (!skip_prefix(refname, "refs/heads/", &refname))
                        die(_("Expecting a full ref name, got %s"), refname);
                return refname;
        }

        return sub->branch;
}

static int resolve_remote_submodule_branch(int argc, const char **argv,
                const char *prefix)
{
        const char *ret;
        struct strbuf sb = STRBUF_INIT;
        if (argc != 2)
                die("submodule--helper remote-branch takes exactly one arguments, got %d", argc);

        ret = remote_submodule_branch(argv[1]);
        if (!ret)
                die("submodule %s doesn't exist", argv[1]);

        printf("%s", ret);
        strbuf_release(&sb);
        return 0;
}

struct cmd_struct {
        const char *cmd;
        int (*fn)(int, const char **, const char *);
};

static struct cmd_struct commands[] = {
        {"list", module_list},
        {"name", module_name},
        {"clone", module_clone},
        {"update-clone", update_clone},
        {"relative-path", resolve_relative_path},
        {"resolve-relative-url", resolve_relative_url},
        {"resolve-relative-url-test", resolve_relative_url_test},
        {"init", module_init},
        {"remote-branch", resolve_remote_submodule_branch}
};

int cmd_submodule__helper(int argc, const char **argv, const char *prefix)
{
        int i;
        if (argc < 2)
                die(_("submodule--helper subcommand must be "
                      "called with a subcommand"));

        for (i = 0; i < ARRAY_SIZE(commands); i++)
                if (!strcmp(argv[1], commands[i].cmd))
                        return commands[i].fn(argc - 1, argv + 1, prefix);

        die(_("'%s' is not a valid submodule--helper "
              "subcommand"), argv[1]);
}