#include "cache.h"
#include "submodule-config.h"
#include "submodule.h"
#include "dir.h"
#include "diff.h"
#include "commit.h"
#include "revision.h"
#include "run-command.h"
#include "diffcore.h"
#include "refs.h"
#include "string-list.h"
#include "sha1-array.h"
#include "argv-array.h"
#include "blob.h"
#include "thread-utils.h"
#include "quote.h"
#include "worktree.h"

static int config_fetch_recurse_submodules = RECURSE_SUBMODULES_ON_DEMAND;
static int parallel_jobs = 1;
static struct string_list changed_submodule_paths = STRING_LIST_INIT_NODUP;
static int initialized_fetch_ref_tips;
static struct sha1_array ref_tips_before_fetch;
static struct sha1_array ref_tips_after_fetch;

/*
 * The following flag is set if the .gitmodules file is unmerged. We then
 * disable recursion for all submodules where .git/config doesn't have a
 * matching config entry because we can't guess what might be configured in
 * .gitmodules unless the user resolves the conflict. When a command line
 * option is given (which always overrides configuration) this flag will be
 * ignored.
 */
static int gitmodules_is_unmerged;

/*
 * This flag is set if the .gitmodules file had unstaged modifications on
 * startup. This must be checked before allowing modifications to the
 * .gitmodules file with the intention to stage them later, because when
 * continuing we would stage the modifications the user didn't stage herself
 * too. That might change in a future version when we learn to stage the
 * changes we do ourselves without staging any previous modifications.
 */
static int gitmodules_is_modified;

int is_staging_gitmodules_ok(void)
{
        return !gitmodules_is_modified;
}

/*
 * Try to update the "path" entry in the "submodule.<name>" section of the
 * .gitmodules file. Return 0 only if a .gitmodules file was found, a section
 * with the correct path=<oldpath> setting was found and we could update it.
 */
int update_path_in_gitmodules(const char *oldpath, const char *newpath)
{
        struct strbuf entry = STRBUF_INIT;
        const struct submodule *submodule;

        if (!file_exists(".gitmodules")) /* Do nothing without .gitmodules */
                return -1;

        if (gitmodules_is_unmerged)
                die(_("Cannot change unmerged .gitmodules, resolve merge conflicts first"));

        submodule = submodule_from_path(null_sha1, oldpath);
        if (!submodule || !submodule->name) {
                warning(_("Could not find section in .gitmodules where path=%s"), oldpath);
                return -1;
        }
        strbuf_addstr(&entry, "submodule.");
        strbuf_addstr(&entry, submodule->name);
        strbuf_addstr(&entry, ".path");
        if (git_config_set_in_file_gently(".gitmodules", entry.buf, newpath) < 0) {
                /* Maybe the user already did that, don't error out here */
                warning(_("Could not update .gitmodules entry %s"), entry.buf);
                strbuf_release(&entry);
                return -1;
        }
        strbuf_release(&entry);
        return 0;
}

/*
 * Try to remove the "submodule.<name>" section from .gitmodules where the given
 * path is configured. Return 0 only if a .gitmodules file was found, a section
 * with the correct path=<path> setting was found and we could remove it.
 */
int remove_path_from_gitmodules(const char *path)
{
        struct strbuf sect = STRBUF_INIT;
        const struct submodule *submodule;

        if (!file_exists(".gitmodules")) /* Do nothing without .gitmodules */
                return -1;

        if (gitmodules_is_unmerged)
                die(_("Cannot change unmerged .gitmodules, resolve merge conflicts first"));

        submodule = submodule_from_path(null_sha1, path);
        if (!submodule || !submodule->name) {
                warning(_("Could not find section in .gitmodules where path=%s"), path);
                return -1;
        }
        strbuf_addstr(&sect, "submodule.");
        strbuf_addstr(&sect, submodule->name);
        if (git_config_rename_section_in_file(".gitmodules", sect.buf, NULL) < 0) {
                /* Maybe the user already did that, don't error out here */
                warning(_("Could not remove .gitmodules entry for %s"), path);
                strbuf_release(&sect);
                return -1;
        }
        strbuf_release(&sect);
        return 0;
}

void stage_updated_gitmodules(void)
{
        if (add_file_to_cache(".gitmodules", 0))
                die(_("staging updated .gitmodules failed"));
}

static int add_submodule_odb(const char *path)
{
        struct strbuf objects_directory = STRBUF_INIT;
        int ret = 0;

        ret = strbuf_git_path_submodule(&objects_directory, path, "objects/");
        if (ret)
                goto done;
        if (!is_directory(objects_directory.buf)) {
                ret = -1;
                goto done;
        }
        add_to_alternates_memory(objects_directory.buf);
done:
        strbuf_release(&objects_directory);
        return ret;
}

void set_diffopt_flags_from_submodule_config(struct diff_options *diffopt,
                                             const char *path)
{
        const struct submodule *submodule = submodule_from_path(null_sha1, path);
        if (submodule) {
                if (submodule->ignore)
                        handle_ignore_submodules_arg(diffopt, submodule->ignore);
                else if (gitmodules_is_unmerged)
                        DIFF_OPT_SET(diffopt, IGNORE_SUBMODULES);
        }
}

int submodule_config(const char *var, const char *value, void *cb)
{
        if (!strcmp(var, "submodule.fetchjobs")) {
                parallel_jobs = git_config_int(var, value);
                if (parallel_jobs < 0)
                        die(_("negative values not allowed for submodule.fetchJobs"));
                return 0;
        } else if (starts_with(var, "submodule."))
                return parse_submodule_config_option(var, value);
        else if (!strcmp(var, "fetch.recursesubmodules")) {
                config_fetch_recurse_submodules = parse_fetch_recurse_submodules_arg(var, value);
                return 0;
        }
        return 0;
}

void gitmodules_config(void)
{
        const char *work_tree = get_git_work_tree();
        if (work_tree) {
                struct strbuf gitmodules_path = STRBUF_INIT;
                int pos;
                strbuf_addstr(&gitmodules_path, work_tree);
                strbuf_addstr(&gitmodules_path, "/.gitmodules");
                if (read_cache() < 0)
                        die("index file corrupt");
                pos = cache_name_pos(".gitmodules", 11);
                if (pos < 0) { /* .gitmodules not found or isn't merged */
                        pos = -1 - pos;
                        if (active_nr > pos) {  /* there is a .gitmodules */
                                const struct cache_entry *ce = active_cache[pos];
                                if (ce_namelen(ce) == 11 &&
                                    !memcmp(ce->name, ".gitmodules", 11))
                                        gitmodules_is_unmerged = 1;
                        }
                } else if (pos < active_nr) {
                        struct stat st;
                        if (lstat(".gitmodules", &st) == 0 &&
                            ce_match_stat(active_cache[pos], &st, 0) & DATA_CHANGED)
                                gitmodules_is_modified = 1;
                }

                if (!gitmodules_is_unmerged)
                        git_config_from_file(submodule_config, gitmodules_path.buf, NULL);
                strbuf_release(&gitmodules_path);
        }
}

void gitmodules_config_sha1(const unsigned char *commit_sha1)
{
        struct strbuf rev = STRBUF_INIT;
        unsigned char sha1[20];

        if (gitmodule_sha1_from_commit(commit_sha1, sha1, &rev)) {
                git_config_from_blob_sha1(submodule_config, rev.buf,
                                          sha1, NULL);
        }
        strbuf_release(&rev);
}

/*
 * Determine if a submodule has been initialized at a given 'path'
 */
int is_submodule_initialized(const char *path)
{
        int ret = 0;
        const struct submodule *module = NULL;

        module = submodule_from_path(null_sha1, path);

        if (module) {
                char *key = xstrfmt("submodule.%s.url", module->name);
                char *value = NULL;

                ret = !git_config_get_string(key, &value);

                free(value);
                free(key);
        }

        return ret;
}

int is_submodule_populated_gently(const char *path, int *return_error_code)
{
        int ret = 0;
        char *gitdir = xstrfmt("%s/.git", path);

        if (resolve_gitdir_gently(gitdir, return_error_code))
                ret = 1;

        free(gitdir);
        return ret;
}

int parse_submodule_update_strategy(const char *value,
                struct submodule_update_strategy *dst)
{
        free((void*)dst->command);
        dst->command = NULL;
        if (!strcmp(value, "none"))
                dst->type = SM_UPDATE_NONE;
        else if (!strcmp(value, "checkout"))
                dst->type = SM_UPDATE_CHECKOUT;
        else if (!strcmp(value, "rebase"))
                dst->type = SM_UPDATE_REBASE;
        else if (!strcmp(value, "merge"))
                dst->type = SM_UPDATE_MERGE;
        else if (skip_prefix(value, "!", &value)) {
                dst->type = SM_UPDATE_COMMAND;
                dst->command = xstrdup(value);
        } else
                return -1;
        return 0;
}

const char *submodule_strategy_to_string(const struct submodule_update_strategy *s)
{
        struct strbuf sb = STRBUF_INIT;
        switch (s->type) {
        case SM_UPDATE_CHECKOUT:
                return "checkout";
        case SM_UPDATE_MERGE:
                return "merge";
        case SM_UPDATE_REBASE:
                return "rebase";
        case SM_UPDATE_NONE:
                return "none";
        case SM_UPDATE_UNSPECIFIED:
                return NULL;
        case SM_UPDATE_COMMAND:
                strbuf_addf(&sb, "!%s", s->command);
                return strbuf_detach(&sb, NULL);
        }
        return NULL;
}

void handle_ignore_submodules_arg(struct diff_options *diffopt,
                                  const char *arg)
{
        DIFF_OPT_CLR(diffopt, IGNORE_SUBMODULES);
        DIFF_OPT_CLR(diffopt, IGNORE_UNTRACKED_IN_SUBMODULES);
        DIFF_OPT_CLR(diffopt, IGNORE_DIRTY_SUBMODULES);

        if (!strcmp(arg, "all"))
                DIFF_OPT_SET(diffopt, IGNORE_SUBMODULES);
        else if (!strcmp(arg, "untracked"))
                DIFF_OPT_SET(diffopt, IGNORE_UNTRACKED_IN_SUBMODULES);
        else if (!strcmp(arg, "dirty"))
                DIFF_OPT_SET(diffopt, IGNORE_DIRTY_SUBMODULES);
        else if (strcmp(arg, "none"))
                die("bad --ignore-submodules argument: %s", arg);
}

static int prepare_submodule_summary(struct rev_info *rev, const char *path,
                struct commit *left, struct commit *right,
                struct commit_list *merge_bases)
{
        struct commit_list *list;

        init_revisions(rev, NULL);
        setup_revisions(0, NULL, rev, NULL);
        rev->left_right = 1;
        rev->first_parent_only = 1;
        left->object.flags |= SYMMETRIC_LEFT;
        add_pending_object(rev, &left->object, path);
        add_pending_object(rev, &right->object, path);
        for (list = merge_bases; list; list = list->next) {
                list->item->object.flags |= UNINTERESTING;
                add_pending_object(rev, &list->item->object,
                        oid_to_hex(&list->item->object.oid));
        }
        return prepare_revision_walk(rev);
}

static void print_submodule_summary(struct rev_info *rev, FILE *f,
                const char *line_prefix,
                const char *del, const char *add, const char *reset)
{
        static const char format[] = "  %m %s";
        struct strbuf sb = STRBUF_INIT;
        struct commit *commit;

        while ((commit = get_revision(rev))) {
                struct pretty_print_context ctx = {0};
                ctx.date_mode = rev->date_mode;
                ctx.output_encoding = get_log_output_encoding();
                strbuf_setlen(&sb, 0);
                strbuf_addstr(&sb, line_prefix);
                if (commit->object.flags & SYMMETRIC_LEFT) {
                        if (del)
                                strbuf_addstr(&sb, del);
                }
                else if (add)
                        strbuf_addstr(&sb, add);
                format_commit_message(commit, format, &sb, &ctx);
                if (reset)
                        strbuf_addstr(&sb, reset);
                strbuf_addch(&sb, '\n');
                fprintf(f, "%s", sb.buf);
        }
        strbuf_release(&sb);
}

/* Helper function to display the submodule header line prior to the full
 * summary output. If it can locate the submodule objects directory it will
 * attempt to lookup both the left and right commits and put them into the
 * left and right pointers.
 */
static void show_submodule_header(FILE *f, const char *path,
                const char *line_prefix,
                struct object_id *one, struct object_id *two,
                unsigned dirty_submodule, const char *meta,
                const char *reset,
                struct commit **left, struct commit **right,
                struct commit_list **merge_bases)
{
        const char *message = NULL;
        struct strbuf sb = STRBUF_INIT;
        int fast_forward = 0, fast_backward = 0;

        if (dirty_submodule & DIRTY_SUBMODULE_UNTRACKED)
                fprintf(f, "%sSubmodule %s contains untracked content\n",
                        line_prefix, path);
        if (dirty_submodule & DIRTY_SUBMODULE_MODIFIED)
                fprintf(f, "%sSubmodule %s contains modified content\n",
                        line_prefix, path);

        if (is_null_oid(one))
                message = "(new submodule)";
        else if (is_null_oid(two))
                message = "(submodule deleted)";

        if (add_submodule_odb(path)) {
                if (!message)
                        message = "(not initialized)";
                goto output_header;
        }

        /*
         * Attempt to lookup the commit references, and determine if this is
         * a fast forward or fast backwards update.
         */
        *left = lookup_commit_reference(one->hash);
        *right = lookup_commit_reference(two->hash);

        /*
         * Warn about missing commits in the submodule project, but only if
         * they aren't null.
         */
        if ((!is_null_oid(one) && !*left) ||
             (!is_null_oid(two) && !*right))
                message = "(commits not present)";

        *merge_bases = get_merge_bases(*left, *right);
        if (*merge_bases) {
                if ((*merge_bases)->item == *left)
                        fast_forward = 1;
                else if ((*merge_bases)->item == *right)
                        fast_backward = 1;
        }

        if (!oidcmp(one, two)) {
                strbuf_release(&sb);
                return;
        }

output_header:
        strbuf_addf(&sb, "%s%sSubmodule %s ", line_prefix, meta, path);
        strbuf_add_unique_abbrev(&sb, one->hash, DEFAULT_ABBREV);
        strbuf_addstr(&sb, (fast_backward || fast_forward) ? ".." : "...");
        strbuf_add_unique_abbrev(&sb, two->hash, DEFAULT_ABBREV);
        if (message)
                strbuf_addf(&sb, " %s%s\n", message, reset);
        else
                strbuf_addf(&sb, "%s:%s\n", fast_backward ? " (rewind)" : "", reset);
        fwrite(sb.buf, sb.len, 1, f);

        strbuf_release(&sb);
}

void show_submodule_summary(FILE *f, const char *path,
                const char *line_prefix,
                struct object_id *one, struct object_id *two,
                unsigned dirty_submodule, const char *meta,
                const char *del, const char *add, const char *reset)
{
        struct rev_info rev;
        struct commit *left = NULL, *right = NULL;
        struct commit_list *merge_bases = NULL;

        show_submodule_header(f, path, line_prefix, one, two, dirty_submodule,
                              meta, reset, &left, &right, &merge_bases);

        /*
         * If we don't have both a left and a right pointer, there is no
         * reason to try and display a summary. The header line should contain
         * all the information the user needs.
         */
        if (!left || !right)
                goto out;

        /* Treat revision walker failure the same as missing commits */
        if (prepare_submodule_summary(&rev, path, left, right, merge_bases)) {
                fprintf(f, "%s(revision walker failed)\n", line_prefix);
                goto out;
        }

        print_submodule_summary(&rev, f, line_prefix, del, add, reset);

out:
        if (merge_bases)
                free_commit_list(merge_bases);
        clear_commit_marks(left, ~0);
        clear_commit_marks(right, ~0);
}

void show_submodule_inline_diff(FILE *f, const char *path,
                const char *line_prefix,
                struct object_id *one, struct object_id *two,
                unsigned dirty_submodule, const char *meta,
                const char *del, const char *add, const char *reset,
                const struct diff_options *o)
{
        const struct object_id *old = &empty_tree_oid, *new = &empty_tree_oid;
        struct commit *left = NULL, *right = NULL;
        struct commit_list *merge_bases = NULL;
        struct strbuf submodule_dir = STRBUF_INIT;
        struct child_process cp = CHILD_PROCESS_INIT;

        show_submodule_header(f, path, line_prefix, one, two, dirty_submodule,
                              meta, reset, &left, &right, &merge_bases);

        /* We need a valid left and right commit to display a difference */
        if (!(left || is_null_oid(one)) ||
            !(right || is_null_oid(two)))
                goto done;

        if (left)
                old = one;
        if (right)
                new = two;

        fflush(f);
        cp.git_cmd = 1;
        cp.dir = path;
        cp.out = dup(fileno(f));
        cp.no_stdin = 1;

        /* TODO: other options may need to be passed here. */
        argv_array_push(&cp.args, "diff");
        argv_array_pushf(&cp.args, "--line-prefix=%s", line_prefix);
        if (DIFF_OPT_TST(o, REVERSE_DIFF)) {
                argv_array_pushf(&cp.args, "--src-prefix=%s%s/",
                                 o->b_prefix, path);
                argv_array_pushf(&cp.args, "--dst-prefix=%s%s/",
                                 o->a_prefix, path);
        } else {
                argv_array_pushf(&cp.args, "--src-prefix=%s%s/",
                                 o->a_prefix, path);
                argv_array_pushf(&cp.args, "--dst-prefix=%s%s/",
                                 o->b_prefix, path);
        }
        argv_array_push(&cp.args, oid_to_hex(old));
        /*
         * If the submodule has modified content, we will diff against the
         * work tree, under the assumption that the user has asked for the
         * diff format and wishes to actually see all differences even if they
         * haven't yet been committed to the submodule yet.
         */
        if (!(dirty_submodule & DIRTY_SUBMODULE_MODIFIED))
                argv_array_push(&cp.args, oid_to_hex(new));

        if (run_command(&cp))
                fprintf(f, "(diff failed)\n");

done:
        strbuf_release(&submodule_dir);
        if (merge_bases)
                free_commit_list(merge_bases);
        if (left)
                clear_commit_marks(left, ~0);
        if (right)
                clear_commit_marks(right, ~0);
}

void set_config_fetch_recurse_submodules(int value)
{
        config_fetch_recurse_submodules = value;
}

static int has_remote(const char *refname, const struct object_id *oid,
                      int flags, void *cb_data)
{
        return 1;
}

static int append_sha1_to_argv(const unsigned char sha1[20], void *data)
{
        struct argv_array *argv = data;
        argv_array_push(argv, sha1_to_hex(sha1));
        return 0;
}

static int check_has_commit(const unsigned char sha1[20], void *data)
{
        int *has_commit = data;

        if (!lookup_commit_reference(sha1))
                *has_commit = 0;

        return 0;
}

static int submodule_has_commits(const char *path, struct sha1_array *commits)
{
        int has_commit = 1;

        if (add_submodule_odb(path))
                return 0;

        sha1_array_for_each_unique(commits, check_has_commit, &has_commit);
        return has_commit;
}

static int submodule_needs_pushing(const char *path, struct sha1_array *commits)
{
        if (!submodule_has_commits(path, commits))
                /*
                 * NOTE: We do consider it safe to return "no" here. The
                 * correct answer would be "We do not know" instead of
                 * "No push needed", but it is quite hard to change
                 * the submodule pointer without having the submodule
                 * around. If a user did however change the submodules
                 * without having the submodule around, this indicates
                 * an expert who knows what they are doing or a
                 * maintainer integrating work from other people. In
                 * both cases it should be safe to skip this check.
                 */
                return 0;

        if (for_each_remote_ref_submodule(path, has_remote, NULL) > 0) {
                struct child_process cp = CHILD_PROCESS_INIT;
                struct strbuf buf = STRBUF_INIT;
                int needs_pushing = 0;

                argv_array_push(&cp.args, "rev-list");
                sha1_array_for_each_unique(commits, append_sha1_to_argv, &cp.args);
                argv_array_pushl(&cp.args, "--not", "--remotes", "-n", "1" , NULL);

                prepare_submodule_repo_env(&cp.env_array);
                cp.git_cmd = 1;
                cp.no_stdin = 1;
                cp.out = -1;
                cp.dir = path;
                if (start_command(&cp))
                        die("Could not run 'git rev-list <commits> --not --remotes -n 1' command in submodule %s",
                                        path);
                if (strbuf_read(&buf, cp.out, 41))
                        needs_pushing = 1;
                finish_command(&cp);
                close(cp.out);
                strbuf_release(&buf);
                return needs_pushing;
        }

        return 0;
}

static struct sha1_array *submodule_commits(struct string_list *submodules,
                                            const char *path)
{
        struct string_list_item *item;

        item = string_list_insert(submodules, path);
        if (item->util)
                return (struct sha1_array *) item->util;

        /* NEEDSWORK: should we have sha1_array_init()? */
        item->util = xcalloc(1, sizeof(struct sha1_array));
        return (struct sha1_array *) item->util;
}

static void collect_submodules_from_diff(struct diff_queue_struct *q,
                                         struct diff_options *options,
                                         void *data)
{
        int i;
        struct string_list *submodules = data;

        for (i = 0; i < q->nr; i++) {
                struct diff_filepair *p = q->queue[i];
                struct sha1_array *commits;
                if (!S_ISGITLINK(p->two->mode))
                        continue;
                commits = submodule_commits(submodules, p->two->path);
                sha1_array_append(commits, p->two->oid.hash);
        }
}

static void find_unpushed_submodule_commits(struct commit *commit,
                struct string_list *needs_pushing)
{
        struct rev_info rev;

        init_revisions(&rev, NULL);
        rev.diffopt.output_format |= DIFF_FORMAT_CALLBACK;
        rev.diffopt.format_callback = collect_submodules_from_diff;
        rev.diffopt.format_callback_data = needs_pushing;
        diff_tree_combined_merge(commit, 1, &rev);
}

static void free_submodules_sha1s(struct string_list *submodules)
{
        struct string_list_item *item;
        for_each_string_list_item(item, submodules)
                sha1_array_clear((struct sha1_array *) item->util);
        string_list_clear(submodules, 1);
}

int find_unpushed_submodules(struct sha1_array *commits,
                const char *remotes_name, struct string_list *needs_pushing)
{
        struct rev_info rev;
        struct commit *commit;
        struct string_list submodules = STRING_LIST_INIT_DUP;
        struct string_list_item *submodule;
        struct argv_array argv = ARGV_ARRAY_INIT;

        init_revisions(&rev, NULL);

        /* argv.argv[0] will be ignored by setup_revisions */
        argv_array_push(&argv, "find_unpushed_submodules");
        sha1_array_for_each_unique(commits, append_sha1_to_argv, &argv);
        argv_array_push(&argv, "--not");
        argv_array_pushf(&argv, "--remotes=%s", remotes_name);

        setup_revisions(argv.argc, argv.argv, &rev, NULL);
        if (prepare_revision_walk(&rev))
                die("revision walk setup failed");

        while ((commit = get_revision(&rev)) != NULL)
                find_unpushed_submodule_commits(commit, &submodules);

        reset_revision_walk();
        argv_array_clear(&argv);

        for_each_string_list_item(submodule, &submodules) {
                struct sha1_array *commits = (struct sha1_array *) submodule->util;

                if (submodule_needs_pushing(submodule->string, commits))
                        string_list_insert(needs_pushing, submodule->string);
        }
        free_submodules_sha1s(&submodules);

        return needs_pushing->nr;
}

static int push_submodule(const char *path, int dry_run)
{
        if (add_submodule_odb(path))
                return 1;

        if (for_each_remote_ref_submodule(path, has_remote, NULL) > 0) {
                struct child_process cp = CHILD_PROCESS_INIT;
                argv_array_push(&cp.args, "push");
                if (dry_run)
                        argv_array_push(&cp.args, "--dry-run");

                prepare_submodule_repo_env(&cp.env_array);
                cp.git_cmd = 1;
                cp.no_stdin = 1;
                cp.dir = path;
                if (run_command(&cp))
                        return 0;
                close(cp.out);
        }

        return 1;
}

int push_unpushed_submodules(struct sha1_array *commits,
                             const char *remotes_name,
                             int dry_run)
{
        int i, ret = 1;
        struct string_list needs_pushing = STRING_LIST_INIT_DUP;

        if (!find_unpushed_submodules(commits, remotes_name, &needs_pushing))
                return 1;

        for (i = 0; i < needs_pushing.nr; i++) {
                const char *path = needs_pushing.items[i].string;
                fprintf(stderr, "Pushing submodule '%s'\n", path);
                if (!push_submodule(path, dry_run)) {
                        fprintf(stderr, "Unable to push submodule '%s'\n", path);
                        ret = 0;
                }
        }

        string_list_clear(&needs_pushing, 0);

        return ret;
}

static int is_submodule_commit_present(const char *path, unsigned char sha1[20])
{
        int is_present = 0;
        if (!add_submodule_odb(path) && lookup_commit_reference(sha1)) {
                /* Even if the submodule is checked out and the commit is
                 * present, make sure it is reachable from a ref. */
                struct child_process cp = CHILD_PROCESS_INIT;
                const char *argv[] = {"rev-list", "-n", "1", NULL, "--not", "--all", NULL};
                struct strbuf buf = STRBUF_INIT;

                argv[3] = sha1_to_hex(sha1);
                cp.argv = argv;
                prepare_submodule_repo_env(&cp.env_array);
                cp.git_cmd = 1;
                cp.no_stdin = 1;
                cp.dir = path;
                if (!capture_command(&cp, &buf, 1024) && !buf.len)
                        is_present = 1;

                strbuf_release(&buf);
        }
        return is_present;
}

static void submodule_collect_changed_cb(struct diff_queue_struct *q,
                                         struct diff_options *options,
                                         void *data)
{
        int i;
        for (i = 0; i < q->nr; i++) {
                struct diff_filepair *p = q->queue[i];
                if (!S_ISGITLINK(p->two->mode))
                        continue;

                if (S_ISGITLINK(p->one->mode)) {
                        /* NEEDSWORK: We should honor the name configured in
                         * the .gitmodules file of the commit we are examining
                         * here to be able to correctly follow submodules
                         * being moved around. */
                        struct string_list_item *path;
                        path = unsorted_string_list_lookup(&changed_submodule_paths, p->two->path);
                        if (!path && !is_submodule_commit_present(p->two->path, p->two->oid.hash))
                                string_list_append(&changed_submodule_paths, xstrdup(p->two->path));
                } else {
                        /* Submodule is new or was moved here */
                        /* NEEDSWORK: When the .git directories of submodules
                         * live inside the superprojects .git directory some
                         * day we should fetch new submodules directly into
                         * that location too when config or options request
                         * that so they can be checked out from there. */
                        continue;
                }
        }
}

static int add_sha1_to_array(const char *ref, const struct object_id *oid,
                             int flags, void *data)
{
        sha1_array_append(data, oid->hash);
        return 0;
}

void check_for_new_submodule_commits(unsigned char new_sha1[20])
{
        if (!initialized_fetch_ref_tips) {
                for_each_ref(add_sha1_to_array, &ref_tips_before_fetch);
                initialized_fetch_ref_tips = 1;
        }

        sha1_array_append(&ref_tips_after_fetch, new_sha1);
}

static int add_sha1_to_argv(const unsigned char sha1[20], void *data)
{
        argv_array_push(data, sha1_to_hex(sha1));
        return 0;
}

static void calculate_changed_submodule_paths(void)
{
        struct rev_info rev;
        struct commit *commit;
        struct argv_array argv = ARGV_ARRAY_INIT;

        /* No need to check if there are no submodules configured */
        if (!submodule_from_path(NULL, NULL))
                return;

        init_revisions(&rev, NULL);
        argv_array_push(&argv, "--"); /* argv[0] program name */
        sha1_array_for_each_unique(&ref_tips_after_fetch,
                                   add_sha1_to_argv, &argv);
        argv_array_push(&argv, "--not");
        sha1_array_for_each_unique(&ref_tips_before_fetch,
                                   add_sha1_to_argv, &argv);
        setup_revisions(argv.argc, argv.argv, &rev, NULL);
        if (prepare_revision_walk(&rev))
                die("revision walk setup failed");

        /*
         * Collect all submodules (whether checked out or not) for which new
         * commits have been recorded upstream in "changed_submodule_paths".
         */
        while ((commit = get_revision(&rev))) {
                struct commit_list *parent = commit->parents;
                while (parent) {
                        struct diff_options diff_opts;
                        diff_setup(&diff_opts);
                        DIFF_OPT_SET(&diff_opts, RECURSIVE);
                        diff_opts.output_format |= DIFF_FORMAT_CALLBACK;
                        diff_opts.format_callback = submodule_collect_changed_cb;
                        diff_setup_done(&diff_opts);
                        diff_tree_sha1(parent->item->object.oid.hash, commit->object.oid.hash, "", &diff_opts);
                        diffcore_std(&diff_opts);
                        diff_flush(&diff_opts);
                        parent = parent->next;
                }
        }

        argv_array_clear(&argv);
        sha1_array_clear(&ref_tips_before_fetch);
        sha1_array_clear(&ref_tips_after_fetch);
        initialized_fetch_ref_tips = 0;
}

struct submodule_parallel_fetch {
        int count;
        struct argv_array args;
        const char *work_tree;
        const char *prefix;
        int command_line_option;
        int quiet;
        int result;
};
#define SPF_INIT {0, ARGV_ARRAY_INIT, NULL, NULL, 0, 0, 0}

static int get_next_submodule(struct child_process *cp,
                              struct strbuf *err, void *data, void **task_cb)
{
        int ret = 0;
        struct submodule_parallel_fetch *spf = data;

        for (; spf->count < active_nr; spf->count++) {
                struct strbuf submodule_path = STRBUF_INIT;
                struct strbuf submodule_git_dir = STRBUF_INIT;
                struct strbuf submodule_prefix = STRBUF_INIT;
                const struct cache_entry *ce = active_cache[spf->count];
                const char *git_dir, *default_argv;
                const struct submodule *submodule;

                if (!S_ISGITLINK(ce->ce_mode))
                        continue;

                submodule = submodule_from_path(null_sha1, ce->name);
                if (!submodule)
                        submodule = submodule_from_name(null_sha1, ce->name);

                default_argv = "yes";
                if (spf->command_line_option == RECURSE_SUBMODULES_DEFAULT) {
                        if (submodule &&
                            submodule->fetch_recurse !=
                                                RECURSE_SUBMODULES_NONE) {
                                if (submodule->fetch_recurse ==
                                                RECURSE_SUBMODULES_OFF)
                                        continue;
                                if (submodule->fetch_recurse ==
                                                RECURSE_SUBMODULES_ON_DEMAND) {
                                        if (!unsorted_string_list_lookup(&changed_submodule_paths, ce->name))
                                                continue;
                                        default_argv = "on-demand";
                                }
                        } else {
                                if ((config_fetch_recurse_submodules == RECURSE_SUBMODULES_OFF) ||
                                    gitmodules_is_unmerged)
                                        continue;
                                if (config_fetch_recurse_submodules == RECURSE_SUBMODULES_ON_DEMAND) {
                                        if (!unsorted_string_list_lookup(&changed_submodule_paths, ce->name))
                                                continue;
                                        default_argv = "on-demand";
                                }
                        }
                } else if (spf->command_line_option == RECURSE_SUBMODULES_ON_DEMAND) {
                        if (!unsorted_string_list_lookup(&changed_submodule_paths, ce->name))
                                continue;
                        default_argv = "on-demand";
                }

                strbuf_addf(&submodule_path, "%s/%s", spf->work_tree, ce->name);
                strbuf_addf(&submodule_git_dir, "%s/.git", submodule_path.buf);
                strbuf_addf(&submodule_prefix, "%s%s/", spf->prefix, ce->name);
                git_dir = read_gitfile(submodule_git_dir.buf);
                if (!git_dir)
                        git_dir = submodule_git_dir.buf;
                if (is_directory(git_dir)) {
                        child_process_init(cp);
                        cp->dir = strbuf_detach(&submodule_path, NULL);
                        prepare_submodule_repo_env(&cp->env_array);
                        cp->git_cmd = 1;
                        if (!spf->quiet)
                                strbuf_addf(err, "Fetching submodule %s%s\n",
                                            spf->prefix, ce->name);
                        argv_array_init(&cp->args);
                        argv_array_pushv(&cp->args, spf->args.argv);
                        argv_array_push(&cp->args, default_argv);
                        argv_array_push(&cp->args, "--submodule-prefix");
                        argv_array_push(&cp->args, submodule_prefix.buf);
                        ret = 1;
                }
                strbuf_release(&submodule_path);
                strbuf_release(&submodule_git_dir);
                strbuf_release(&submodule_prefix);
                if (ret) {
                        spf->count++;
                        return 1;
                }
        }
        return 0;
}

static int fetch_start_failure(struct strbuf *err,
                               void *cb, void *task_cb)
{
        struct submodule_parallel_fetch *spf = cb;

        spf->result = 1;

        return 0;
}

static int fetch_finish(int retvalue, struct strbuf *err,
                        void *cb, void *task_cb)
{
        struct submodule_parallel_fetch *spf = cb;

        if (retvalue)
                spf->result = 1;

        return 0;
}

int fetch_populated_submodules(const struct argv_array *options,
                               const char *prefix, int command_line_option,
                               int quiet, int max_parallel_jobs)
{
        int i;
        struct submodule_parallel_fetch spf = SPF_INIT;

        spf.work_tree = get_git_work_tree();
        spf.command_line_option = command_line_option;
        spf.quiet = quiet;
        spf.prefix = prefix;

        if (!spf.work_tree)
                goto out;

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

        argv_array_push(&spf.args, "fetch");
        for (i = 0; i < options->argc; i++)
                argv_array_push(&spf.args, options->argv[i]);
        argv_array_push(&spf.args, "--recurse-submodules-default");
        /* default value, "--submodule-prefix" and its value are added later */

        if (max_parallel_jobs < 0)
                max_parallel_jobs = parallel_jobs;

        calculate_changed_submodule_paths();
        run_processes_parallel(max_parallel_jobs,
                               get_next_submodule,
                               fetch_start_failure,
                               fetch_finish,
                               &spf);

        argv_array_clear(&spf.args);
out:
        string_list_clear(&changed_submodule_paths, 1);
        return spf.result;
}

unsigned is_submodule_modified(const char *path, int ignore_untracked)
{
        ssize_t len;
        struct child_process cp = CHILD_PROCESS_INIT;
        const char *argv[] = {
                "status",
                "--porcelain",
                NULL,
                NULL,
        };
        struct strbuf buf = STRBUF_INIT;
        unsigned dirty_submodule = 0;
        const char *line, *next_line;
        const char *git_dir;

        strbuf_addf(&buf, "%s/.git", path);
        git_dir = read_gitfile(buf.buf);
        if (!git_dir)
                git_dir = buf.buf;
        if (!is_directory(git_dir)) {
                strbuf_release(&buf);
                /* The submodule is not checked out, so it is not modified */
                return 0;

        }
        strbuf_reset(&buf);

        if (ignore_untracked)
                argv[2] = "-uno";

        cp.argv = argv;
        prepare_submodule_repo_env(&cp.env_array);
        cp.git_cmd = 1;
        cp.no_stdin = 1;
        cp.out = -1;
        cp.dir = path;
        if (start_command(&cp))
                die("Could not run 'git status --porcelain' in submodule %s", path);

        len = strbuf_read(&buf, cp.out, 1024);
        line = buf.buf;
        while (len > 2) {
                if ((line[0] == '?') && (line[1] == '?')) {
                        dirty_submodule |= DIRTY_SUBMODULE_UNTRACKED;
                        if (dirty_submodule & DIRTY_SUBMODULE_MODIFIED)
                                break;
                } else {
                        dirty_submodule |= DIRTY_SUBMODULE_MODIFIED;
                        if (ignore_untracked ||
                            (dirty_submodule & DIRTY_SUBMODULE_UNTRACKED))
                                break;
                }
                next_line = strchr(line, '\n');
                if (!next_line)
                        break;
                next_line++;
                len -= (next_line - line);
                line = next_line;
        }
        close(cp.out);

        if (finish_command(&cp))
                die("'git status --porcelain' failed in submodule %s", path);

        strbuf_release(&buf);
        return dirty_submodule;
}

int submodule_uses_gitfile(const char *path)
{
        struct child_process cp = CHILD_PROCESS_INIT;
        const char *argv[] = {
                "submodule",
                "foreach",
                "--quiet",
                "--recursive",
                "test -f .git",
                NULL,
        };
        struct strbuf buf = STRBUF_INIT;
        const char *git_dir;

        strbuf_addf(&buf, "%s/.git", path);
        git_dir = read_gitfile(buf.buf);
        if (!git_dir) {
                strbuf_release(&buf);
                return 0;
        }
        strbuf_release(&buf);

        /* Now test that all nested submodules use a gitfile too */
        cp.argv = argv;
        prepare_submodule_repo_env(&cp.env_array);
        cp.git_cmd = 1;
        cp.no_stdin = 1;
        cp.no_stderr = 1;
        cp.no_stdout = 1;
        cp.dir = path;
        if (run_command(&cp))
                return 0;

        return 1;
}

/*
 * Check if it is a bad idea to remove a submodule, i.e. if we'd lose data
 * when doing so.
 *
 * Return 1 if we'd lose data, return 0 if the removal is fine,
 * and negative values for errors.
 */
int bad_to_remove_submodule(const char *path, unsigned flags)
{
        ssize_t len;
        struct child_process cp = CHILD_PROCESS_INIT;
        struct strbuf buf = STRBUF_INIT;
        int ret = 0;

        if (!file_exists(path) || is_empty_dir(path))
                return 0;

        if (!submodule_uses_gitfile(path))
                return 1;

        argv_array_pushl(&cp.args, "status", "--porcelain",
                                   "--ignore-submodules=none", NULL);

        if (flags & SUBMODULE_REMOVAL_IGNORE_UNTRACKED)
                argv_array_push(&cp.args, "-uno");
        else
                argv_array_push(&cp.args, "-uall");

        if (!(flags & SUBMODULE_REMOVAL_IGNORE_IGNORED_UNTRACKED))
                argv_array_push(&cp.args, "--ignored");

        prepare_submodule_repo_env(&cp.env_array);
        cp.git_cmd = 1;
        cp.no_stdin = 1;
        cp.out = -1;
        cp.dir = path;
        if (start_command(&cp)) {
                if (flags & SUBMODULE_REMOVAL_DIE_ON_ERROR)
                        die(_("could not start 'git status in submodule '%s'"),
                                path);
                ret = -1;
                goto out;
        }

        len = strbuf_read(&buf, cp.out, 1024);
        if (len > 2)
                ret = 1;
        close(cp.out);

        if (finish_command(&cp)) {
                if (flags & SUBMODULE_REMOVAL_DIE_ON_ERROR)
                        die(_("could not run 'git status in submodule '%s'"),
                                path);
                ret = -1;
        }
out:
        strbuf_release(&buf);
        return ret;
}

static int find_first_merges(struct object_array *result, const char *path,
                struct commit *a, struct commit *b)
{
        int i, j;
        struct object_array merges = OBJECT_ARRAY_INIT;
        struct commit *commit;
        int contains_another;

        char merged_revision[42];
        const char *rev_args[] = { "rev-list", "--merges", "--ancestry-path",
                                   "--all", merged_revision, NULL };
        struct rev_info revs;
        struct setup_revision_opt rev_opts;

        memset(result, 0, sizeof(struct object_array));
        memset(&rev_opts, 0, sizeof(rev_opts));

        /* get all revisions that merge commit a */
        snprintf(merged_revision, sizeof(merged_revision), "^%s",
                        oid_to_hex(&a->object.oid));
        init_revisions(&revs, NULL);
        rev_opts.submodule = path;
        setup_revisions(ARRAY_SIZE(rev_args)-1, rev_args, &revs, &rev_opts);

        /* save all revisions from the above list that contain b */
        if (prepare_revision_walk(&revs))
                die("revision walk setup failed");
        while ((commit = get_revision(&revs)) != NULL) {
                struct object *o = &(commit->object);
                if (in_merge_bases(b, commit))
                        add_object_array(o, NULL, &merges);
        }
        reset_revision_walk();

        /* Now we've got all merges that contain a and b. Prune all
         * merges that contain another found merge and save them in
         * result.
         */
        for (i = 0; i < merges.nr; i++) {
                struct commit *m1 = (struct commit *) merges.objects[i].item;

                contains_another = 0;
                for (j = 0; j < merges.nr; j++) {
                        struct commit *m2 = (struct commit *) merges.objects[j].item;
                        if (i != j && in_merge_bases(m2, m1)) {
                                contains_another = 1;
                                break;
                        }
                }

                if (!contains_another)
                        add_object_array(merges.objects[i].item, NULL, result);
        }

        free(merges.objects);
        return result->nr;
}

static void print_commit(struct commit *commit)
{
        struct strbuf sb = STRBUF_INIT;
        struct pretty_print_context ctx = {0};
        ctx.date_mode.type = DATE_NORMAL;
        format_commit_message(commit, " %h: %m %s", &sb, &ctx);
        fprintf(stderr, "%s\n", sb.buf);
        strbuf_release(&sb);
}

#define MERGE_WARNING(path, msg) \
        warning("Failed to merge submodule %s (%s)", path, msg);

int merge_submodule(unsigned char result[20], const char *path,
                    const unsigned char base[20], const unsigned char a[20],
                    const unsigned char b[20], int search)
{
        struct commit *commit_base, *commit_a, *commit_b;
        int parent_count;
        struct object_array merges;

        int i;

        /* store a in result in case we fail */
        hashcpy(result, a);

        /* we can not handle deletion conflicts */
        if (is_null_sha1(base))
                return 0;
        if (is_null_sha1(a))
                return 0;
        if (is_null_sha1(b))
                return 0;

        if (add_submodule_odb(path)) {
                MERGE_WARNING(path, "not checked out");
                return 0;
        }

        if (!(commit_base = lookup_commit_reference(base)) ||
            !(commit_a = lookup_commit_reference(a)) ||
            !(commit_b = lookup_commit_reference(b))) {
                MERGE_WARNING(path, "commits not present");
                return 0;
        }

        /* check whether both changes are forward */
        if (!in_merge_bases(commit_base, commit_a) ||
            !in_merge_bases(commit_base, commit_b)) {
                MERGE_WARNING(path, "commits don't follow merge-base");
                return 0;
        }

        /* Case #1: a is contained in b or vice versa */
        if (in_merge_bases(commit_a, commit_b)) {
                hashcpy(result, b);
                return 1;
        }
        if (in_merge_bases(commit_b, commit_a)) {
                hashcpy(result, a);
                return 1;
        }

        /*
         * Case #2: There are one or more merges that contain a and b in
         * the submodule. If there is only one, then present it as a
         * suggestion to the user, but leave it marked unmerged so the
         * user needs to confirm the resolution.
         */

        /* Skip the search if makes no sense to the calling context.  */
        if (!search)
                return 0;

        /* find commit which merges them */
        parent_count = find_first_merges(&merges, path, commit_a, commit_b);
        switch (parent_count) {
        case 0:
                MERGE_WARNING(path, "merge following commits not found");
                break;

        case 1:
                MERGE_WARNING(path, "not fast-forward");
                fprintf(stderr, "Found a possible merge resolution "
                                "for the submodule:\n");
                print_commit((struct commit *) merges.objects[0].item);
                fprintf(stderr,
                        "If this is correct simply add it to the index "
                        "for example\n"
                        "by using:\n\n"
                        "  git update-index --cacheinfo 160000 %s \"%s\"\n\n"
                        "which will accept this suggestion.\n",
                        oid_to_hex(&merges.objects[0].item->oid), path);
                break;

        default:
                MERGE_WARNING(path, "multiple merges found");
                for (i = 0; i < merges.nr; i++)
                        print_commit((struct commit *) merges.objects[i].item);
        }

        free(merges.objects);
        return 0;
}

int parallel_submodules(void)
{
        return parallel_jobs;
}

void prepare_submodule_repo_env(struct argv_array *out)
{
        const char * const *var;

        for (var = local_repo_env; *var; var++) {
                if (strcmp(*var, CONFIG_DATA_ENVIRONMENT))
                        argv_array_push(out, *var);
        }
        argv_array_pushf(out, "%s=%s", GIT_DIR_ENVIRONMENT,
                         DEFAULT_GIT_DIR_ENVIRONMENT);
}

/*
 * Embeds a single submodules git directory into the superprojects git dir,
 * non recursively.
 */
static void relocate_single_git_dir_into_superproject(const char *prefix,
                                                      const char *path)
{
        char *old_git_dir = NULL, *real_old_git_dir = NULL, *real_new_git_dir = NULL;
        const char *new_git_dir;
        const struct submodule *sub;

        if (submodule_uses_worktrees(path))
                die(_("relocate_gitdir for submodule '%s' with "
                      "more than one worktree not supported"), path);

        old_git_dir = xstrfmt("%s/.git", path);
        if (read_gitfile(old_git_dir))
                /* If it is an actual gitfile, it doesn't need migration. */
                return;

        real_old_git_dir = real_pathdup(old_git_dir);

        sub = submodule_from_path(null_sha1, path);
        if (!sub)
                die(_("could not lookup name for submodule '%s'"), path);

        new_git_dir = git_path("modules/%s", sub->name);
        if (safe_create_leading_directories_const(new_git_dir) < 0)
                die(_("could not create directory '%s'"), new_git_dir);
        real_new_git_dir = real_pathdup(new_git_dir);

        if (!prefix)
                prefix = get_super_prefix();

        fprintf(stderr, _("Migrating git directory of '%s%s' from\n'%s' to\n'%s'\n"),
                prefix ? prefix : "", path,
                real_old_git_dir, real_new_git_dir);

        relocate_gitdir(path, real_old_git_dir, real_new_git_dir);

        free(old_git_dir);
        free(real_old_git_dir);
        free(real_new_git_dir);
}

/*
 * Migrate the git directory of the submodule given by path from
 * having its git directory within the working tree to the git dir nested
 * in its superprojects git dir under modules/.
 */
void absorb_git_dir_into_superproject(const char *prefix,
                                      const char *path,
                                      unsigned flags)
{
        int err_code;
        const char *sub_git_dir;
        struct strbuf gitdir = STRBUF_INIT;
        strbuf_addf(&gitdir, "%s/.git", path);
        sub_git_dir = resolve_gitdir_gently(gitdir.buf, &err_code);

        /* Not populated? */
        if (!sub_git_dir) {
                const struct submodule *sub;

                if (err_code == READ_GITFILE_ERR_STAT_FAILED) {
                        /* unpopulated as expected */
                        strbuf_release(&gitdir);
                        return;
                }

                if (err_code != READ_GITFILE_ERR_NOT_A_REPO)
                        /* We don't know what broke here. */
                        read_gitfile_error_die(err_code, path, NULL);

                /*
                * Maybe populated, but no git directory was found?
                * This can happen if the superproject is a submodule
                * itself and was just absorbed. The absorption of the
                * superproject did not rewrite the git file links yet,
                * fix it now.
                */
                sub = submodule_from_path(null_sha1, path);
                if (!sub)
                        die(_("could not lookup name for submodule '%s'"), path);
                connect_work_tree_and_git_dir(path,
                        git_path("modules/%s", sub->name));
        } else {
                /* Is it already absorbed into the superprojects git dir? */
                char *real_sub_git_dir = real_pathdup(sub_git_dir);
                char *real_common_git_dir = real_pathdup(get_git_common_dir());

                if (!starts_with(real_sub_git_dir, real_common_git_dir))
                        relocate_single_git_dir_into_superproject(prefix, path);

                free(real_sub_git_dir);
                free(real_common_git_dir);
        }
        strbuf_release(&gitdir);

        if (flags & ABSORB_GITDIR_RECURSE_SUBMODULES) {
                struct child_process cp = CHILD_PROCESS_INIT;
                struct strbuf sb = STRBUF_INIT;

                if (flags & ~ABSORB_GITDIR_RECURSE_SUBMODULES)
                        die("BUG: we don't know how to pass the flags down?");

                if (get_super_prefix())
                        strbuf_addstr(&sb, get_super_prefix());
                strbuf_addstr(&sb, path);
                strbuf_addch(&sb, '/');

                cp.dir = path;
                cp.git_cmd = 1;
                cp.no_stdin = 1;
                argv_array_pushl(&cp.args, "--super-prefix", sb.buf,
                                           "submodule--helper",
                                           "absorb-git-dirs", NULL);
                prepare_submodule_repo_env(&cp.env_array);
                if (run_command(&cp))
                        die(_("could not recurse into submodule '%s'"), path);

                strbuf_release(&sb);
        }
}