/*
 * "git rebase" builtin command
 *
 * Copyright (c) 2018 Pratik Karki
 */

#include "builtin.h"
#include "run-command.h"
#include "exec-cmd.h"
#include "argv-array.h"
#include "dir.h"
#include "packfile.h"
#include "refs.h"
#include "quote.h"
#include "config.h"
#include "cache-tree.h"
#include "unpack-trees.h"
#include "lockfile.h"
#include "parse-options.h"
#include "commit.h"
#include "diff.h"
#include "wt-status.h"
#include "revision.h"
#include "rerere.h"

static char const * const builtin_rebase_usage[] = {
        N_("git rebase [-i] [options] [--exec <cmd>] [--onto <newbase>] "
                "[<upstream>] [<branch>]"),
        N_("git rebase [-i] [options] [--exec <cmd>] [--onto <newbase>] "
                "--root [<branch>]"),
        N_("git rebase --continue | --abort | --skip | --edit-todo"),
        NULL
};

static GIT_PATH_FUNC(apply_dir, "rebase-apply")
static GIT_PATH_FUNC(merge_dir, "rebase-merge")

enum rebase_type {
        REBASE_UNSPECIFIED = -1,
        REBASE_AM,
        REBASE_MERGE,
        REBASE_INTERACTIVE,
        REBASE_PRESERVE_MERGES
};

static int use_builtin_rebase(void)
{
        struct child_process cp = CHILD_PROCESS_INIT;
        struct strbuf out = STRBUF_INIT;
        int ret;

        argv_array_pushl(&cp.args,
                         "config", "--bool", "rebase.usebuiltin", NULL);
        cp.git_cmd = 1;
        if (capture_command(&cp, &out, 6)) {
                strbuf_release(&out);
                return 0;
        }

        strbuf_trim(&out);
        ret = !strcmp("true", out.buf);
        strbuf_release(&out);
        return ret;
}

static int apply_autostash(void)
{
        warning("TODO");
        return 0;
}

struct rebase_options {
        enum rebase_type type;
        const char *state_dir;
        struct commit *upstream;
        const char *upstream_name;
        const char *upstream_arg;
        char *head_name;
        struct object_id orig_head;
        struct commit *onto;
        const char *onto_name;
        const char *revisions;
        const char *switch_to;
        int root;
        struct commit *restrict_revision;
        int dont_finish_rebase;
        enum {
                REBASE_NO_QUIET = 1<<0,
                REBASE_VERBOSE = 1<<1,
                REBASE_DIFFSTAT = 1<<2,
                REBASE_FORCE = 1<<3,
                REBASE_INTERACTIVE_EXPLICIT = 1<<4,
        } flags;
        struct strbuf git_am_opt;
        const char *action;
        int signoff;
};

static int is_interactive(struct rebase_options *opts)
{
        return opts->type == REBASE_INTERACTIVE ||
                opts->type == REBASE_PRESERVE_MERGES;
}

/* Returns the filename prefixed by the state_dir */
static const char *state_dir_path(const char *filename, struct rebase_options *opts)
{
        static struct strbuf path = STRBUF_INIT;
        static size_t prefix_len;

        if (!prefix_len) {
                strbuf_addf(&path, "%s/", opts->state_dir);
                prefix_len = path.len;
        }

        strbuf_setlen(&path, prefix_len);
        strbuf_addstr(&path, filename);
        return path.buf;
}

/* Read one file, then strip line endings */
static int read_one(const char *path, struct strbuf *buf)
{
        if (strbuf_read_file(buf, path, 0) < 0)
                return error_errno(_("could not read '%s'"), path);
        strbuf_trim_trailing_newline(buf);
        return 0;
}

/* Initialize the rebase options from the state directory. */
static int read_basic_state(struct rebase_options *opts)
{
        struct strbuf head_name = STRBUF_INIT;
        struct strbuf buf = STRBUF_INIT;
        struct object_id oid;

        if (read_one(state_dir_path("head-name", opts), &head_name) ||
            read_one(state_dir_path("onto", opts), &buf))
                return -1;
        opts->head_name = starts_with(head_name.buf, "refs/") ?
                xstrdup(head_name.buf) : NULL;
        strbuf_release(&head_name);
        if (get_oid(buf.buf, &oid))
                return error(_("could not get 'onto': '%s'"), buf.buf);
        opts->onto = lookup_commit_or_die(&oid, buf.buf);

        /*
         * We always write to orig-head, but interactive rebase used to write to
         * head. Fall back to reading from head to cover for the case that the
         * user upgraded git with an ongoing interactive rebase.
         */
        strbuf_reset(&buf);
        if (file_exists(state_dir_path("orig-head", opts))) {
                if (read_one(state_dir_path("orig-head", opts), &buf))
                        return -1;
        } else if (read_one(state_dir_path("head", opts), &buf))
                return -1;
        if (get_oid(buf.buf, &opts->orig_head))
                return error(_("invalid orig-head: '%s'"), buf.buf);

        strbuf_reset(&buf);
        if (read_one(state_dir_path("quiet", opts), &buf))
                return -1;
        if (buf.len)
                opts->flags &= ~REBASE_NO_QUIET;
        else
                opts->flags |= REBASE_NO_QUIET;

        if (file_exists(state_dir_path("verbose", opts)))
                opts->flags |= REBASE_VERBOSE;

        if (file_exists(state_dir_path("signoff", opts))) {
                opts->signoff = 1;
                opts->flags |= REBASE_FORCE;
        }

        strbuf_release(&buf);

        return 0;
}

static int finish_rebase(struct rebase_options *opts)
{
        struct strbuf dir = STRBUF_INIT;
        const char *argv_gc_auto[] = { "gc", "--auto", NULL };

        delete_ref(NULL, "REBASE_HEAD", NULL, REF_NO_DEREF);
        apply_autostash();
        close_all_packs(the_repository->objects);
        /*
         * We ignore errors in 'gc --auto', since the
         * user should see them.
         */
        run_command_v_opt(argv_gc_auto, RUN_GIT_CMD);
        strbuf_addstr(&dir, opts->state_dir);
        remove_dir_recursively(&dir, 0);
        strbuf_release(&dir);

        return 0;
}

static struct commit *peel_committish(const char *name)
{
        struct object *obj;
        struct object_id oid;

        if (get_oid(name, &oid))
                return NULL;
        obj = parse_object(the_repository, &oid);
        return (struct commit *)peel_to_type(name, 0, obj, OBJ_COMMIT);
}

static void add_var(struct strbuf *buf, const char *name, const char *value)
{
        if (!value)
                strbuf_addf(buf, "unset %s; ", name);
        else {
                strbuf_addf(buf, "%s=", name);
                sq_quote_buf(buf, value);
                strbuf_addstr(buf, "; ");
        }
}

static int run_specific_rebase(struct rebase_options *opts)
{
        const char *argv[] = { NULL, NULL };
        struct strbuf script_snippet = STRBUF_INIT;
        int status;
        const char *backend, *backend_func;

        add_var(&script_snippet, "GIT_DIR", absolute_path(get_git_dir()));
        add_var(&script_snippet, "state_dir", opts->state_dir);

        add_var(&script_snippet, "upstream_name", opts->upstream_name);
        add_var(&script_snippet, "upstream", opts->upstream ?
                oid_to_hex(&opts->upstream->object.oid) : NULL);
        add_var(&script_snippet, "head_name",
                opts->head_name ? opts->head_name : "detached HEAD");
        add_var(&script_snippet, "orig_head", oid_to_hex(&opts->orig_head));
        add_var(&script_snippet, "onto", opts->onto ?
                oid_to_hex(&opts->onto->object.oid) : NULL);
        add_var(&script_snippet, "onto_name", opts->onto_name);
        add_var(&script_snippet, "revisions", opts->revisions);
        add_var(&script_snippet, "restrict_revision", opts->restrict_revision ?
                oid_to_hex(&opts->restrict_revision->object.oid) : NULL);
        add_var(&script_snippet, "GIT_QUIET",
                opts->flags & REBASE_NO_QUIET ? "" : "t");
        add_var(&script_snippet, "git_am_opt", opts->git_am_opt.buf);
        add_var(&script_snippet, "verbose",
                opts->flags & REBASE_VERBOSE ? "t" : "");
        add_var(&script_snippet, "diffstat",
                opts->flags & REBASE_DIFFSTAT ? "t" : "");
        add_var(&script_snippet, "force_rebase",
                opts->flags & REBASE_FORCE ? "t" : "");
        if (opts->switch_to)
                add_var(&script_snippet, "switch_to", opts->switch_to);
        add_var(&script_snippet, "action", opts->action ? opts->action : "");
        add_var(&script_snippet, "signoff", opts->signoff ? "--signoff" : "");

        switch (opts->type) {
        case REBASE_AM:
                backend = "git-rebase--am";
                backend_func = "git_rebase__am";
                break;
        case REBASE_INTERACTIVE:
                backend = "git-rebase--interactive";
                backend_func = "git_rebase__interactive";
                break;
        case REBASE_MERGE:
                backend = "git-rebase--merge";
                backend_func = "git_rebase__merge";
                break;
        case REBASE_PRESERVE_MERGES:
                backend = "git-rebase--preserve-merges";
                backend_func = "git_rebase__preserve_merges";
                break;
        default:
                BUG("Unhandled rebase type %d", opts->type);
                break;
        }

        strbuf_addf(&script_snippet,
                    ". git-sh-setup && . git-rebase--common &&"
                    " . %s && %s", backend, backend_func);
        argv[0] = script_snippet.buf;

        status = run_command_v_opt(argv, RUN_USING_SHELL);
        if (opts->dont_finish_rebase)
                ; /* do nothing */
        else if (status == 0) {
                if (!file_exists(state_dir_path("stopped-sha", opts)))
                        finish_rebase(opts);
        } else if (status == 2) {
                struct strbuf dir = STRBUF_INIT;

                apply_autostash();
                strbuf_addstr(&dir, opts->state_dir);
                remove_dir_recursively(&dir, 0);
                strbuf_release(&dir);
                die("Nothing to do");
        }

        strbuf_release(&script_snippet);

        return status ? -1 : 0;
}

#define GIT_REFLOG_ACTION_ENVIRONMENT "GIT_REFLOG_ACTION"

static int reset_head(struct object_id *oid, const char *action,
                      const char *switch_to_branch, int detach_head)
{
        struct object_id head_oid;
        struct tree_desc desc;
        struct lock_file lock = LOCK_INIT;
        struct unpack_trees_options unpack_tree_opts;
        struct tree *tree;
        const char *reflog_action;
        struct strbuf msg = STRBUF_INIT;
        size_t prefix_len;
        struct object_id *orig = NULL, oid_orig,
                *old_orig = NULL, oid_old_orig;
        int ret = 0;

        if (switch_to_branch && !starts_with(switch_to_branch, "refs/"))
                BUG("Not a fully qualified branch: '%s'", switch_to_branch);

        if (hold_locked_index(&lock, LOCK_REPORT_ON_ERROR) < 0)
                return -1;

        if (!oid) {
                if (get_oid("HEAD", &head_oid)) {
                        rollback_lock_file(&lock);
                        return error(_("could not determine HEAD revision"));
                }
                oid = &head_oid;
        }

        memset(&unpack_tree_opts, 0, sizeof(unpack_tree_opts));
        setup_unpack_trees_porcelain(&unpack_tree_opts, action);
        unpack_tree_opts.head_idx = 1;
        unpack_tree_opts.src_index = the_repository->index;
        unpack_tree_opts.dst_index = the_repository->index;
        unpack_tree_opts.fn = oneway_merge;
        unpack_tree_opts.update = 1;
        unpack_tree_opts.merge = 1;
        if (!detach_head)
                unpack_tree_opts.reset = 1;

        if (read_index_unmerged(the_repository->index) < 0) {
                rollback_lock_file(&lock);
                return error(_("could not read index"));
        }

        if (!fill_tree_descriptor(&desc, oid)) {
                error(_("failed to find tree of %s"), oid_to_hex(oid));
                rollback_lock_file(&lock);
                free((void *)desc.buffer);
                return -1;
        }

        if (unpack_trees(1, &desc, &unpack_tree_opts)) {
                rollback_lock_file(&lock);
                free((void *)desc.buffer);
                return -1;
        }

        tree = parse_tree_indirect(oid);
        prime_cache_tree(the_repository->index, tree);

        if (write_locked_index(the_repository->index, &lock, COMMIT_LOCK) < 0)
                ret = error(_("could not write index"));
        free((void *)desc.buffer);

        if (ret)
                return ret;

        reflog_action = getenv(GIT_REFLOG_ACTION_ENVIRONMENT);
        strbuf_addf(&msg, "%s: ", reflog_action ? reflog_action : "rebase");
        prefix_len = msg.len;

        if (!get_oid("ORIG_HEAD", &oid_old_orig))
                old_orig = &oid_old_orig;
        if (!get_oid("HEAD", &oid_orig)) {
                orig = &oid_orig;
                strbuf_addstr(&msg, "updating ORIG_HEAD");
                update_ref(msg.buf, "ORIG_HEAD", orig, old_orig, 0,
                           UPDATE_REFS_MSG_ON_ERR);
        } else if (old_orig)
                delete_ref(NULL, "ORIG_HEAD", old_orig, 0);
        strbuf_setlen(&msg, prefix_len);
        strbuf_addstr(&msg, "updating HEAD");
        if (!switch_to_branch)
                ret = update_ref(msg.buf, "HEAD", oid, orig, REF_NO_DEREF,
                                 UPDATE_REFS_MSG_ON_ERR);
        else {
                ret = create_symref("HEAD", switch_to_branch, msg.buf);
                if (!ret)
                        ret = update_ref(msg.buf, "HEAD", oid, NULL, 0,
                                         UPDATE_REFS_MSG_ON_ERR);
        }

        strbuf_release(&msg);
        return ret;
}

static int rebase_config(const char *var, const char *value, void *data)
{
        struct rebase_options *opts = data;

        if (!strcmp(var, "rebase.stat")) {
                if (git_config_bool(var, value))
                        opts->flags |= REBASE_DIFFSTAT;
                else
                        opts->flags &= !REBASE_DIFFSTAT;
                return 0;
        }

        return git_default_config(var, value, data);
}

/*
 * Determines whether the commits in from..to are linear, i.e. contain
 * no merge commits. This function *expects* `from` to be an ancestor of
 * `to`.
 */
static int is_linear_history(struct commit *from, struct commit *to)
{
        while (to && to != from) {
                parse_commit(to);
                if (!to->parents)
                        return 1;
                if (to->parents->next)
                        return 0;
                to = to->parents->item;
        }
        return 1;
}

static int can_fast_forward(struct commit *onto, struct object_id *head_oid,
                            struct object_id *merge_base)
{
        struct commit *head = lookup_commit(the_repository, head_oid);
        struct commit_list *merge_bases;
        int res;

        if (!head)
                return 0;

        merge_bases = get_merge_bases(onto, head);
        if (merge_bases && !merge_bases->next) {
                oidcpy(merge_base, &merge_bases->item->object.oid);
                res = !oidcmp(merge_base, &onto->object.oid);
        } else {
                oidcpy(merge_base, &null_oid);
                res = 0;
        }
        free_commit_list(merge_bases);
        return res && is_linear_history(onto, head);
}

/* -i followed by -m is still -i */
static int parse_opt_merge(const struct option *opt, const char *arg, int unset)
{
        struct rebase_options *opts = opt->value;

        if (!is_interactive(opts))
                opts->type = REBASE_MERGE;

        return 0;
}

/* -i followed by -p is still explicitly interactive, but -p alone is not */
static int parse_opt_interactive(const struct option *opt, const char *arg,
                                 int unset)
{
        struct rebase_options *opts = opt->value;

        opts->type = REBASE_INTERACTIVE;
        opts->flags |= REBASE_INTERACTIVE_EXPLICIT;

        return 0;
}

int cmd_rebase(int argc, const char **argv, const char *prefix)
{
        struct rebase_options options = {
                .type = REBASE_UNSPECIFIED,
                .flags = REBASE_NO_QUIET,
                .git_am_opt = STRBUF_INIT,
        };
        const char *branch_name;
        int ret, flags, total_argc, in_progress = 0;
        int ok_to_skip_pre_rebase = 0;
        struct strbuf msg = STRBUF_INIT;
        struct strbuf revisions = STRBUF_INIT;
        struct strbuf buf = STRBUF_INIT;
        struct object_id merge_base;
        enum {
                NO_ACTION,
                ACTION_CONTINUE,
                ACTION_SKIP,
                ACTION_ABORT,
                ACTION_QUIT,
                ACTION_EDIT_TODO,
                ACTION_SHOW_CURRENT_PATCH,
        } action = NO_ACTION;
        struct option builtin_rebase_options[] = {
                OPT_STRING(0, "onto", &options.onto_name,
                           N_("revision"),
                           N_("rebase onto given branch instead of upstream")),
                OPT_BOOL(0, "no-verify", &ok_to_skip_pre_rebase,
                         N_("allow pre-rebase hook to run")),
                OPT_NEGBIT('q', "quiet", &options.flags,
                           N_("be quiet. implies --no-stat"),
                           REBASE_NO_QUIET| REBASE_VERBOSE | REBASE_DIFFSTAT),
                OPT_BIT('v', "verbose", &options.flags,
                        N_("display a diffstat of what changed upstream"),
                        REBASE_NO_QUIET | REBASE_VERBOSE | REBASE_DIFFSTAT),
                {OPTION_NEGBIT, 'n', "no-stat", &options.flags, NULL,
                        N_("do not show diffstat of what changed upstream"),
                        PARSE_OPT_NOARG, NULL, REBASE_DIFFSTAT },
                OPT_BOOL(0, "signoff", &options.signoff,
                         N_("add a Signed-off-by: line to each commit")),
                OPT_BIT('f', "force-rebase", &options.flags,
                        N_("cherry-pick all commits, even if unchanged"),
                        REBASE_FORCE),
                OPT_BIT(0, "no-ff", &options.flags,
                        N_("cherry-pick all commits, even if unchanged"),
                        REBASE_FORCE),
                OPT_CMDMODE(0, "continue", &action, N_("continue"),
                            ACTION_CONTINUE),
                OPT_CMDMODE(0, "skip", &action,
                            N_("skip current patch and continue"), ACTION_SKIP),
                OPT_CMDMODE(0, "abort", &action,
                            N_("abort and check out the original branch"),
                            ACTION_ABORT),
                OPT_CMDMODE(0, "quit", &action,
                            N_("abort but keep HEAD where it is"), ACTION_QUIT),
                OPT_CMDMODE(0, "edit-todo", &action, N_("edit the todo list "
                            "during an interactive rebase"), ACTION_EDIT_TODO),
                OPT_CMDMODE(0, "show-current-patch", &action,
                            N_("show the patch file being applied or merged"),
                            ACTION_SHOW_CURRENT_PATCH),
                { OPTION_CALLBACK, 'm', "merge", &options, NULL,
                        N_("use merging strategies to rebase"),
                        PARSE_OPT_NOARG | PARSE_OPT_NONEG,
                        parse_opt_merge },
                { OPTION_CALLBACK, 'i', "interactive", &options, NULL,
                        N_("let the user edit the list of commits to rebase"),
                        PARSE_OPT_NOARG | PARSE_OPT_NONEG,
                        parse_opt_interactive },
                OPT_SET_INT('p', "preserve-merges", &options.type,
                            N_("try to recreate merges instead of ignoring "
                               "them"), REBASE_PRESERVE_MERGES),
                OPT_END(),
        };

        /*
         * NEEDSWORK: Once the builtin rebase has been tested enough
         * and git-legacy-rebase.sh is retired to contrib/, this preamble
         * can be removed.
         */

        if (!use_builtin_rebase()) {
                const char *path = mkpath("%s/git-legacy-rebase",
                                          git_exec_path());

                if (sane_execvp(path, (char **)argv) < 0)
                        die_errno(_("could not exec %s"), path);
                else
                        BUG("sane_execvp() returned???");
        }

        if (argc == 2 && !strcmp(argv[1], "-h"))
                usage_with_options(builtin_rebase_usage,
                                   builtin_rebase_options);

        prefix = setup_git_directory();
        trace_repo_setup(prefix);
        setup_work_tree();

        git_config(rebase_config, &options);

        strbuf_reset(&buf);
        strbuf_addf(&buf, "%s/applying", apply_dir());
        if(file_exists(buf.buf))
                die(_("It looks like 'git am' is in progress. Cannot rebase."));

        if (is_directory(apply_dir())) {
                options.type = REBASE_AM;
                options.state_dir = apply_dir();
        } else if (is_directory(merge_dir())) {
                strbuf_reset(&buf);
                strbuf_addf(&buf, "%s/rewritten", merge_dir());
                if (is_directory(buf.buf)) {
                        options.type = REBASE_PRESERVE_MERGES;
                        options.flags |= REBASE_INTERACTIVE_EXPLICIT;
                } else {
                        strbuf_reset(&buf);
                        strbuf_addf(&buf, "%s/interactive", merge_dir());
                        if(file_exists(buf.buf)) {
                                options.type = REBASE_INTERACTIVE;
                                options.flags |= REBASE_INTERACTIVE_EXPLICIT;
                        } else
                                options.type = REBASE_MERGE;
                }
                options.state_dir = merge_dir();
        }

        if (options.type != REBASE_UNSPECIFIED)
                in_progress = 1;

        total_argc = argc;
        argc = parse_options(argc, argv, prefix,
                             builtin_rebase_options,
                             builtin_rebase_usage, 0);

        if (action != NO_ACTION && total_argc != 2) {
                usage_with_options(builtin_rebase_usage,
                                   builtin_rebase_options);
        }

        if (argc > 2)
                usage_with_options(builtin_rebase_usage,
                                   builtin_rebase_options);

        if (action != NO_ACTION && !in_progress)
                die(_("No rebase in progress?"));

        if (action == ACTION_EDIT_TODO && !is_interactive(&options))
                die(_("The --edit-todo action can only be used during "
                      "interactive rebase."));

        switch (action) {
        case ACTION_CONTINUE: {
                struct object_id head;
                struct lock_file lock_file = LOCK_INIT;
                int fd;

                options.action = "continue";

                /* Sanity check */
                if (get_oid("HEAD", &head))
                        die(_("Cannot read HEAD"));

                fd = hold_locked_index(&lock_file, 0);
                if (read_index(the_repository->index) < 0)
                        die(_("could not read index"));
                refresh_index(the_repository->index, REFRESH_QUIET, NULL, NULL,
                              NULL);
                if (0 <= fd)
                        update_index_if_able(the_repository->index,
                                             &lock_file);
                rollback_lock_file(&lock_file);

                if (has_unstaged_changes(1)) {
                        puts(_("You must edit all merge conflicts and then\n"
                               "mark them as resolved using git add"));
                        exit(1);
                }
                if (read_basic_state(&options))
                        exit(1);
                goto run_rebase;
        }
        case ACTION_SKIP: {
                struct string_list merge_rr = STRING_LIST_INIT_DUP;

                options.action = "skip";

                rerere_clear(&merge_rr);
                string_list_clear(&merge_rr, 1);

                if (reset_head(NULL, "reset", NULL, 0) < 0)
                        die(_("could not discard worktree changes"));
                if (read_basic_state(&options))
                        exit(1);
                goto run_rebase;
        }
        case ACTION_ABORT: {
                struct string_list merge_rr = STRING_LIST_INIT_DUP;
                options.action = "abort";

                rerere_clear(&merge_rr);
                string_list_clear(&merge_rr, 1);

                if (read_basic_state(&options))
                        exit(1);
                if (reset_head(&options.orig_head, "reset",
                               options.head_name, 0) < 0)
                        die(_("could not move back to %s"),
                            oid_to_hex(&options.orig_head));
                ret = finish_rebase(&options);
                goto cleanup;
        }
        case ACTION_QUIT: {
                strbuf_reset(&buf);
                strbuf_addstr(&buf, options.state_dir);
                ret = !!remove_dir_recursively(&buf, 0);
                if (ret)
                        die(_("could not remove '%s'"), options.state_dir);
                goto cleanup;
        }
        case ACTION_EDIT_TODO:
                options.action = "edit-todo";
                options.dont_finish_rebase = 1;
                goto run_rebase;
        case ACTION_SHOW_CURRENT_PATCH:
                options.action = "show-current-patch";
                options.dont_finish_rebase = 1;
                goto run_rebase;
        case NO_ACTION:
                break;
        default:
                BUG("action: %d", action);
        }

        /* Make sure no rebase is in progress */
        if (in_progress) {
                const char *last_slash = strrchr(options.state_dir, '/');
                const char *state_dir_base =
                        last_slash ? last_slash + 1 : options.state_dir;
                const char *cmd_live_rebase =
                        "git rebase (--continue | --abort | --skip)";
                strbuf_reset(&buf);
                strbuf_addf(&buf, "rm -fr \"%s\"", options.state_dir);
                die(_("It seems that there is already a %s directory, and\n"
                      "I wonder if you are in the middle of another rebase.  "
                      "If that is the\n"
                      "case, please try\n\t%s\n"
                      "If that is not the case, please\n\t%s\n"
                      "and run me again.  I am stopping in case you still "
                      "have something\n"
                      "valuable there.\n"),
                    state_dir_base, cmd_live_rebase, buf.buf);
        }

        if (!(options.flags & REBASE_NO_QUIET))
                strbuf_addstr(&options.git_am_opt, " -q");

        switch (options.type) {
        case REBASE_MERGE:
        case REBASE_INTERACTIVE:
        case REBASE_PRESERVE_MERGES:
                options.state_dir = merge_dir();
                break;
        case REBASE_AM:
                options.state_dir = apply_dir();
                break;
        default:
                /* the default rebase backend is `--am` */
                options.type = REBASE_AM;
                options.state_dir = apply_dir();
                break;
        }

        if (options.signoff) {
                if (options.type == REBASE_PRESERVE_MERGES)
                        die("cannot combine '--signoff' with "
                            "'--preserve-merges'");
                strbuf_addstr(&options.git_am_opt, " --signoff");
                options.flags |= REBASE_FORCE;
        }

        if (!options.root) {
                if (argc < 1)
                        die("TODO: handle @{upstream}");
                else {
                        options.upstream_name = argv[0];
                        argc--;
                        argv++;
                        if (!strcmp(options.upstream_name, "-"))
                                options.upstream_name = "@{-1}";
                }
                options.upstream = peel_committish(options.upstream_name);
                if (!options.upstream)
                        die(_("invalid upstream '%s'"), options.upstream_name);
                options.upstream_arg = options.upstream_name;
        } else
                die("TODO: upstream for --root");

        /* Make sure the branch to rebase onto is valid. */
        if (!options.onto_name)
                options.onto_name = options.upstream_name;
        if (strstr(options.onto_name, "...")) {
                if (get_oid_mb(options.onto_name, &merge_base) < 0)
                        die(_("'%s': need exactly one merge base"),
                            options.onto_name);
                options.onto = lookup_commit_or_die(&merge_base,
                                                    options.onto_name);
        } else {
                options.onto = peel_committish(options.onto_name);
                if (!options.onto)
                        die(_("Does not point to a valid commit '%s'"),
                                options.onto_name);
        }

        /*
         * If the branch to rebase is given, that is the branch we will rebase
         * branch_name -- branch/commit being rebased, or
         *                HEAD (already detached)
         * orig_head -- commit object name of tip of the branch before rebasing
         * head_name -- refs/heads/<that-branch> or NULL (detached HEAD)
         */
        if (argc == 1) {
                /* Is it "rebase other branchname" or "rebase other commit"? */
                branch_name = argv[0];
                options.switch_to = argv[0];

                /* Is it a local branch? */
                strbuf_reset(&buf);
                strbuf_addf(&buf, "refs/heads/%s", branch_name);
                if (!read_ref(buf.buf, &options.orig_head))
                        options.head_name = xstrdup(buf.buf);
                /* If not is it a valid ref (branch or commit)? */
                else if (!get_oid(branch_name, &options.orig_head))
                        options.head_name = NULL;
                else
                        die(_("fatal: no such branch/commit '%s'"),
                            branch_name);
        } else if (argc == 0) {
                /* Do not need to switch branches, we are already on it. */
                options.head_name =
                        xstrdup_or_null(resolve_ref_unsafe("HEAD", 0, NULL,
                                         &flags));
                if (!options.head_name)
                        die(_("No such ref: %s"), "HEAD");
                if (flags & REF_ISSYMREF) {
                        if (!skip_prefix(options.head_name,
                                         "refs/heads/", &branch_name))
                                branch_name = options.head_name;

                } else {
                        free(options.head_name);
                        options.head_name = NULL;
                        branch_name = "HEAD";
                }
                if (get_oid("HEAD", &options.orig_head))
                        die(_("Could not resolve HEAD to a revision"));
        } else
                BUG("unexpected number of arguments left to parse");

        if (read_index(the_repository->index) < 0)
                die(_("could not read index"));

        if (require_clean_work_tree("rebase",
                                    _("Please commit or stash them."), 1, 1)) {
                ret = 1;
                goto cleanup;
        }

        /*
         * Now we are rebasing commits upstream..orig_head (or with --root,
         * everything leading up to orig_head) on top of onto.
         */

        /*
         * Check if we are already based on onto with linear history,
         * but this should be done only when upstream and onto are the same
         * and if this is not an interactive rebase.
         */
        if (can_fast_forward(options.onto, &options.orig_head, &merge_base) &&
            !is_interactive(&options) && !options.restrict_revision &&
            !oidcmp(&options.upstream->object.oid, &options.onto->object.oid)) {
                int flag;

                if (!(options.flags & REBASE_FORCE)) {
                        /* Lazily switch to the target branch if needed... */
                        if (options.switch_to) {
                                struct object_id oid;

                                if (get_oid(options.switch_to, &oid) < 0) {
                                        ret = !!error(_("could not parse '%s'"),
                                                      options.switch_to);
                                        goto cleanup;
                                }

                                strbuf_reset(&buf);
                                strbuf_addf(&buf, "rebase: checkout %s",
                                            options.switch_to);
                                if (reset_head(&oid, "checkout",
                                               options.head_name, 0) < 0) {
                                        ret = !!error(_("could not switch to "
                                                        "%s"),
                                                      options.switch_to);
                                        goto cleanup;
                                }
                        }

                        if (!(options.flags & REBASE_NO_QUIET))
                                ; /* be quiet */
                        else if (!strcmp(branch_name, "HEAD") &&
                                 resolve_ref_unsafe("HEAD", 0, NULL, &flag))
                                puts(_("HEAD is up to date."));
                        else
                                printf(_("Current branch %s is up to date.\n"),
                                       branch_name);
                        ret = !!finish_rebase(&options);
                        goto cleanup;
                } else if (!(options.flags & REBASE_NO_QUIET))
                        ; /* be quiet */
                else if (!strcmp(branch_name, "HEAD") &&
                         resolve_ref_unsafe("HEAD", 0, NULL, &flag))
                        puts(_("HEAD is up to date, rebase forced."));
                else
                        printf(_("Current branch %s is up to date, rebase "
                                 "forced.\n"), branch_name);
        }

        /* If a hook exists, give it a chance to interrupt*/
        if (!ok_to_skip_pre_rebase &&
            run_hook_le(NULL, "pre-rebase", options.upstream_arg,
                        argc ? argv[0] : NULL, NULL))
                die(_("The pre-rebase hook refused to rebase."));

        if (options.flags & REBASE_DIFFSTAT) {
                struct diff_options opts;

                if (options.flags & REBASE_VERBOSE)
                        printf(_("Changes from %s to %s:\n"),
                                oid_to_hex(&merge_base),
                                oid_to_hex(&options.onto->object.oid));

                /* We want color (if set), but no pager */
                diff_setup(&opts);
                opts.stat_width = -1; /* use full terminal width */
                opts.stat_graph_width = -1; /* respect statGraphWidth config */
                opts.output_format |=
                        DIFF_FORMAT_SUMMARY | DIFF_FORMAT_DIFFSTAT;
                opts.detect_rename = DIFF_DETECT_RENAME;
                diff_setup_done(&opts);
                diff_tree_oid(&merge_base, &options.onto->object.oid,
                              "", &opts);
                diffcore_std(&opts);
                diff_flush(&opts);
        }

        if (is_interactive(&options))
                goto run_rebase;

        /* Detach HEAD and reset the tree */
        if (options.flags & REBASE_NO_QUIET)
                printf(_("First, rewinding head to replay your work on top of "
                         "it...\n"));

        strbuf_addf(&msg, "rebase: checkout %s", options.onto_name);
        if (reset_head(&options.onto->object.oid, "checkout", NULL, 1))
                die(_("Could not detach HEAD"));
        strbuf_release(&msg);

        strbuf_addf(&revisions, "%s..%s",
                    options.root ? oid_to_hex(&options.onto->object.oid) :
                    (options.restrict_revision ?
                     oid_to_hex(&options.restrict_revision->object.oid) :
                     oid_to_hex(&options.upstream->object.oid)),
                    oid_to_hex(&options.orig_head));

        options.revisions = revisions.buf;

run_rebase:
        ret = !!run_specific_rebase(&options);

cleanup:
        strbuf_release(&revisions);
        free(options.head_name);
        return ret;
}