#include "cache.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"

static struct string_list config_name_for_path;
static struct string_list config_fetch_recurse_submodules_for_name;
static struct string_list config_ignore_for_name;
static int config_fetch_recurse_submodules = RECURSE_SUBMODULES_ON_DEMAND;
static struct string_list changed_submodule_paths;
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;

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

        strbuf_addf(&objects_directory, "%s/.git", path);
        git_dir = read_gitfile(objects_directory.buf);
        if (git_dir) {
                strbuf_reset(&objects_directory);
                strbuf_addstr(&objects_directory, git_dir);
        }
        strbuf_addstr(&objects_directory, "/objects/");
        if (!is_directory(objects_directory.buf)) {
                ret = -1;
                goto done;
        }
        /* avoid adding it twice */
        for (alt_odb = alt_odb_list; alt_odb; alt_odb = alt_odb->next)
                if (alt_odb->name - alt_odb->base == objects_directory.len &&
                                !strncmp(alt_odb->base, objects_directory.buf,
                                        objects_directory.len))
                        goto done;

        alt_odb = xmalloc(objects_directory.len + 42 + sizeof(*alt_odb));
        alt_odb->next = alt_odb_list;
        strcpy(alt_odb->base, objects_directory.buf);
        alt_odb->name = alt_odb->base + objects_directory.len;
        alt_odb->name[2] = '/';
        alt_odb->name[40] = '\0';
        alt_odb->name[41] = '\0';
        alt_odb_list = alt_odb;
        prepare_alt_odb();
done:
        strbuf_release(&objects_directory);
        return ret;
}

void set_diffopt_flags_from_submodule_config(struct diff_options *diffopt,
                                             const char *path)
{
        struct string_list_item *path_option, *ignore_option;
        path_option = unsorted_string_list_lookup(&config_name_for_path, path);
        if (path_option) {
                ignore_option = unsorted_string_list_lookup(&config_ignore_for_name, path_option->util);
                if (ignore_option)
                        handle_ignore_submodules_arg(diffopt, ignore_option->util);
                else if (gitmodules_is_unmerged)
                        DIFF_OPT_SET(diffopt, IGNORE_SUBMODULES);
        }
}

int submodule_config(const char *var, const char *value, void *cb)
{
        if (!prefixcmp(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;
                        }
                }

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

int parse_submodule_config_option(const char *var, const char *value)
{
        int len;
        struct string_list_item *config;
        struct strbuf submodname = STRBUF_INIT;

        var += 10;              /* Skip "submodule." */

        len = strlen(var);
        if ((len > 5) && !strcmp(var + len - 5, ".path")) {
                strbuf_add(&submodname, var, len - 5);
                config = unsorted_string_list_lookup(&config_name_for_path, value);
                if (config)
                        free(config->util);
                else
                        config = string_list_append(&config_name_for_path, xstrdup(value));
                config->util = strbuf_detach(&submodname, NULL);
                strbuf_release(&submodname);
        } else if ((len > 23) && !strcmp(var + len - 23, ".fetchrecursesubmodules")) {
                strbuf_add(&submodname, var, len - 23);
                config = unsorted_string_list_lookup(&config_fetch_recurse_submodules_for_name, submodname.buf);
                if (!config)
                        config = string_list_append(&config_fetch_recurse_submodules_for_name,
                                                    strbuf_detach(&submodname, NULL));
                config->util = (void *)(intptr_t)parse_fetch_recurse_submodules_arg(var, value);
                strbuf_release(&submodname);
        } else if ((len > 7) && !strcmp(var + len - 7, ".ignore")) {
                if (strcmp(value, "untracked") && strcmp(value, "dirty") &&
                    strcmp(value, "all") && strcmp(value, "none")) {
                        warning("Invalid parameter \"%s\" for config option \"submodule.%s.ignore\"", value, var);
                        return 0;
                }

                strbuf_add(&submodname, var, len - 7);
                config = unsorted_string_list_lookup(&config_ignore_for_name, submodname.buf);
                if (config)
                        free(config->util);
                else
                        config = string_list_append(&config_ignore_for_name,
                                                    strbuf_detach(&submodname, NULL));
                strbuf_release(&submodname);
                config->util = xstrdup(value);
                return 0;
        }
        return 0;
}

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,
                int *fast_forward, int *fast_backward)
{
        struct commit_list *merge_bases, *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);
        merge_bases = get_merge_bases(left, right, 1);
        if (merge_bases) {
                if (merge_bases->item == left)
                        *fast_forward = 1;
                else if (merge_bases->item == right)
                        *fast_backward = 1;
        }
        for (list = merge_bases; list; list = list->next) {
                list->item->object.flags |= UNINTERESTING;
                add_pending_object(rev, &list->item->object,
                        sha1_to_hex(list->item->object.sha1));
        }
        return prepare_revision_walk(rev);
}

static void print_submodule_summary(struct rev_info *rev, FILE *f,
                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;
                strbuf_setlen(&sb, 0);
                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);
}

int parse_fetch_recurse_submodules_arg(const char *opt, const char *arg)
{
        switch (git_config_maybe_bool(opt, arg)) {
        case 1:
                return RECURSE_SUBMODULES_ON;
        case 0:
                return RECURSE_SUBMODULES_OFF;
        default:
                if (!strcmp(arg, "on-demand"))
                        return RECURSE_SUBMODULES_ON_DEMAND;
                die("bad %s argument: %s", opt, arg);
        }
}

void show_submodule_summary(FILE *f, const char *path,
                unsigned char one[20], unsigned char two[20],
                unsigned dirty_submodule,
                const char *del, const char *add, const char *reset)
{
        struct rev_info rev;
        struct commit *left = left, *right = right;
        const char *message = NULL;
        struct strbuf sb = STRBUF_INIT;
        int fast_forward = 0, fast_backward = 0;

        if (is_null_sha1(two))
                message = "(submodule deleted)";
        else if (add_submodule_odb(path))
                message = "(not checked out)";
        else if (is_null_sha1(one))
                message = "(new submodule)";
        else if (!(left = lookup_commit_reference(one)) ||
                 !(right = lookup_commit_reference(two)))
                message = "(commits not present)";

        if (!message &&
            prepare_submodule_summary(&rev, path, left, right,
                                        &fast_forward, &fast_backward))
                message = "(revision walker failed)";

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

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

        strbuf_addf(&sb, "Submodule %s %s..", path,
                        find_unique_abbrev(one, DEFAULT_ABBREV));
        if (!fast_backward && !fast_forward)
                strbuf_addch(&sb, '.');
        strbuf_addf(&sb, "%s", find_unique_abbrev(two, DEFAULT_ABBREV));
        if (message)
                strbuf_addf(&sb, " %s\n", message);
        else
                strbuf_addf(&sb, "%s:\n", fast_backward ? " (rewind)" : "");
        fwrite(sb.buf, sb.len, 1, f);

        if (!message) {
                print_submodule_summary(&rev, f, del, add, reset);
                clear_commit_marks(left, ~0);
                clear_commit_marks(right, ~0);
        }

        strbuf_release(&sb);
}

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

static int has_remote(const char *refname, const unsigned char *sha1, int flags, void *cb_data)
{
        return 1;
}

static int submodule_needs_pushing(const char *path, const unsigned char sha1[20])
{
        if (add_submodule_odb(path) || !lookup_commit_reference(sha1))
                return 0;

        if (for_each_remote_ref_submodule(path, has_remote, NULL) > 0) {
                struct child_process cp;
                const char *argv[] = {"rev-list", NULL, "--not", "--remotes", "-n", "1" , NULL};
                struct strbuf buf = STRBUF_INIT;
                int needs_pushing = 0;

                argv[1] = sha1_to_hex(sha1);
                memset(&cp, 0, sizeof(cp));
                cp.argv = argv;
                cp.env = local_repo_env;
                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 %s --not --remotes -n 1' command in submodule %s",
                                sha1_to_hex(sha1), 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 void collect_submodules_from_diff(struct diff_queue_struct *q,
                                         struct diff_options *options,
                                         void *data)
{
        int i;
        int *needs_pushing = data;

        for (i = 0; i < q->nr; i++) {
                struct diff_filepair *p = q->queue[i];
                if (!S_ISGITLINK(p->two->mode))
                        continue;
                if (submodule_needs_pushing(p->two->path, p->two->sha1)) {
                        *needs_pushing = 1;
                        break;
                }
        }
}


static void commit_need_pushing(struct commit *commit, int *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);
}

int check_submodule_needs_pushing(unsigned char new_sha1[20], const char *remotes_name)
{
        struct rev_info rev;
        struct commit *commit;
        const char *argv[] = {NULL, NULL, "--not", "NULL", NULL};
        int argc = ARRAY_SIZE(argv) - 1;
        char *sha1_copy;
        int needs_pushing = 0;
        struct strbuf remotes_arg = STRBUF_INIT;

        strbuf_addf(&remotes_arg, "--remotes=%s", remotes_name);
        init_revisions(&rev, NULL);
        sha1_copy = xstrdup(sha1_to_hex(new_sha1));
        argv[1] = sha1_copy;
        argv[3] = remotes_arg.buf;
        setup_revisions(argc, argv, &rev, NULL);
        if (prepare_revision_walk(&rev))
                die("revision walk setup failed");

        while ((commit = get_revision(&rev)) && !needs_pushing)
                commit_need_pushing(commit, &needs_pushing);

        free(sha1_copy);
        strbuf_release(&remotes_arg);

        return needs_pushing;
}

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;
                const char *argv[] = {"rev-list", "-n", "1", NULL, "--not", "--all", NULL};
                struct strbuf buf = STRBUF_INIT;

                argv[3] = sha1_to_hex(sha1);
                memset(&cp, 0, sizeof(cp));
                cp.argv = argv;
                cp.env = local_repo_env;
                cp.git_cmd = 1;
                cp.no_stdin = 1;
                cp.out = -1;
                cp.dir = path;
                if (!run_command(&cp) && !strbuf_read(&buf, cp.out, 1024))
                        is_present = 1;

                close(cp.out);
                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->sha1))
                                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 unsigned char *sha1,
                             int flags, void *data)
{
        sha1_array_append(data, sha1);
        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 void add_sha1_to_argv(const unsigned char sha1[20], void *data)
{
        argv_array_push(data, sha1_to_hex(sha1));
}

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 (!config_name_for_path.nr)
                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;
                        if (diff_setup_done(&diff_opts) < 0)
                                die("diff_setup_done failed");
                        diff_tree_sha1(parent->item->object.sha1, commit->object.sha1, "", &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;
}

int fetch_populated_submodules(int num_options, const char **options,
                               const char *prefix, int command_line_option,
                               int quiet)
{
        int i, result = 0, argc = 0, default_argc;
        struct child_process cp;
        const char **argv;
        struct string_list_item *name_for_path;
        const char *work_tree = get_git_work_tree();
        if (!work_tree)
                goto out;

        if (!the_index.initialized)
                if (read_cache() < 0)
                        die("index file corrupt");

        /* 6: "fetch" (options) --recurse-submodules-default default "--submodule-prefix" prefix NULL */
        argv = xcalloc(num_options + 6, sizeof(const char *));
        argv[argc++] = "fetch";
        for (i = 0; i < num_options; i++)
                argv[argc++] = options[i];
        argv[argc++] = "--recurse-submodules-default";
        default_argc = argc++;
        argv[argc++] = "--submodule-prefix";

        memset(&cp, 0, sizeof(cp));
        cp.argv = argv;
        cp.env = local_repo_env;
        cp.git_cmd = 1;
        cp.no_stdin = 1;

        calculate_changed_submodule_paths();

        for (i = 0; i < active_nr; i++) {
                struct strbuf submodule_path = STRBUF_INIT;
                struct strbuf submodule_git_dir = STRBUF_INIT;
                struct strbuf submodule_prefix = STRBUF_INIT;
                struct cache_entry *ce = active_cache[i];
                const char *git_dir, *name, *default_argv;

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

                name = ce->name;
                name_for_path = unsorted_string_list_lookup(&config_name_for_path, ce->name);
                if (name_for_path)
                        name = name_for_path->util;

                default_argv = "yes";
                if (command_line_option == RECURSE_SUBMODULES_DEFAULT) {
                        struct string_list_item *fetch_recurse_submodules_option;
                        fetch_recurse_submodules_option = unsorted_string_list_lookup(&config_fetch_recurse_submodules_for_name, name);
                        if (fetch_recurse_submodules_option) {
                                if ((intptr_t)fetch_recurse_submodules_option->util == RECURSE_SUBMODULES_OFF)
                                        continue;
                                if ((intptr_t)fetch_recurse_submodules_option->util == 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 (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", work_tree, ce->name);
                strbuf_addf(&submodule_git_dir, "%s/.git", submodule_path.buf);
                strbuf_addf(&submodule_prefix, "%s%s/", 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)) {
                        if (!quiet)
                                printf("Fetching submodule %s%s\n", prefix, ce->name);
                        cp.dir = submodule_path.buf;
                        argv[default_argc] = default_argv;
                        argv[argc] = submodule_prefix.buf;
                        if (run_command(&cp))
                                result = 1;
                }
                strbuf_release(&submodule_path);
                strbuf_release(&submodule_git_dir);
                strbuf_release(&submodule_prefix);
        }
        free(argv);
out:
        string_list_clear(&changed_submodule_paths, 1);
        return result;
}

unsigned is_submodule_modified(const char *path, int ignore_untracked)
{
        ssize_t len;
        struct child_process cp;
        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";

        memset(&cp, 0, sizeof(cp));
        cp.argv = argv;
        cp.env = local_repo_env;
        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;
}

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;
        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(&merges, 0, sizeof(merges));
        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",
                        sha1_to_hex(a->object.sha1));
        init_revisions(&revs, NULL);
        rev_opts.submodule = path;
        setup_revisions(sizeof(rev_args)/sizeof(char *)-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, 1))
                        add_object_array(o, NULL, &merges);
        }

        /* 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, 1)) {
                                contains_another = 1;
                                break;
                        }
                }

                if (!contains_another)
                        add_object_array(merges.objects[i].item,
                                         merges.objects[i].name, 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 = 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, 1) ||
            !in_merge_bases(commit_base, &commit_b, 1)) {
                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, 1)) {
                hashcpy(result, b);
                return 1;
        }
        if (in_merge_bases(commit_b, &commit_a, 1)) {
                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",
                        sha1_to_hex(merges.objects[0].item->sha1), 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;
}