#include "cache.h"
#include "tag.h"
#include "blob.h"
#include "tree.h"
#include "commit.h"
#include "diff.h"
#include "refs.h"
#include "revision.h"

static char *path_name(struct name_path *path, const char *name)
{
        struct name_path *p;
        char *n, *m;
        int nlen = strlen(name);
        int len = nlen + 1;

        for (p = path; p; p = p->up) {
                if (p->elem_len)
                        len += p->elem_len + 1;
        }
        n = xmalloc(len);
        m = n + len - (nlen + 1);
        strcpy(m, name);
        for (p = path; p; p = p->up) {
                if (p->elem_len) {
                        m -= p->elem_len + 1;
                        memcpy(m, p->elem, p->elem_len);
                        m[p->elem_len] = '/';
                }
        }
        return n;
}

void add_object(struct object *obj,
                struct object_array *p,
                struct name_path *path,
                const char *name)
{
        add_object_array(obj, path_name(path, name), p);
}

static void mark_blob_uninteresting(struct blob *blob)
{
        if (blob->object.flags & UNINTERESTING)
                return;
        blob->object.flags |= UNINTERESTING;
}

void mark_tree_uninteresting(struct tree *tree)
{
        struct tree_desc desc;
        struct name_entry entry;
        struct object *obj = &tree->object;

        if (obj->flags & UNINTERESTING)
                return;
        obj->flags |= UNINTERESTING;
        if (!has_sha1_file(obj->sha1))
                return;
        if (parse_tree(tree) < 0)
                die("bad tree %s", sha1_to_hex(obj->sha1));

        desc.buf = tree->buffer;
        desc.size = tree->size;
        while (tree_entry(&desc, &entry)) {
                if (S_ISDIR(entry.mode))
                        mark_tree_uninteresting(lookup_tree(entry.sha1));
                else
                        mark_blob_uninteresting(lookup_blob(entry.sha1));
        }

        /*
         * We don't care about the tree any more
         * after it has been marked uninteresting.
         */
        free(tree->buffer);
        tree->buffer = NULL;
}

void mark_parents_uninteresting(struct commit *commit)
{
        struct commit_list *parents = commit->parents;

        while (parents) {
                struct commit *commit = parents->item;
                if (!(commit->object.flags & UNINTERESTING)) {
                        commit->object.flags |= UNINTERESTING;

                        /*
                         * Normally we haven't parsed the parent
                         * yet, so we won't have a parent of a parent
                         * here. However, it may turn out that we've
                         * reached this commit some other way (where it
                         * wasn't uninteresting), in which case we need
                         * to mark its parents recursively too..
                         */
                        if (commit->parents)
                                mark_parents_uninteresting(commit);
                }

                /*
                 * A missing commit is ok iff its parent is marked
                 * uninteresting.
                 *
                 * We just mark such a thing parsed, so that when
                 * it is popped next time around, we won't be trying
                 * to parse it and get an error.
                 */
                if (!has_sha1_file(commit->object.sha1))
                        commit->object.parsed = 1;
                parents = parents->next;
        }
}

void add_pending_object(struct rev_info *revs, struct object *obj, const char *name)
{
        add_object_array(obj, name, &revs->pending);
}

static struct object *get_reference(struct rev_info *revs, const char *name, const unsigned char *sha1, unsigned int flags)
{
        struct object *object;

        object = parse_object(sha1);
        if (!object)
                die("bad object %s", name);
        object->flags |= flags;
        return object;
}

static struct commit *handle_commit(struct rev_info *revs, struct object *object, const char *name)
{
        unsigned long flags = object->flags;

        /*
         * Tag object? Look what it points to..
         */
        while (object->type == OBJ_TAG) {
                struct tag *tag = (struct tag *) object;
                if (revs->tag_objects && !(flags & UNINTERESTING))
                        add_pending_object(revs, object, tag->tag);
                object = parse_object(tag->tagged->sha1);
                if (!object)
                        die("bad object %s", sha1_to_hex(tag->tagged->sha1));
        }

        /*
         * Commit object? Just return it, we'll do all the complex
         * reachability crud.
         */
        if (object->type == OBJ_COMMIT) {
                struct commit *commit = (struct commit *)object;
                if (parse_commit(commit) < 0)
                        die("unable to parse commit %s", name);
                if (flags & UNINTERESTING) {
                        commit->object.flags |= UNINTERESTING;
                        mark_parents_uninteresting(commit);
                        revs->limited = 1;
                }
                return commit;
        }

        /*
         * Tree object? Either mark it uniniteresting, or add it
         * to the list of objects to look at later..
         */
        if (object->type == OBJ_TREE) {
                struct tree *tree = (struct tree *)object;
                if (!revs->tree_objects)
                        return NULL;
                if (flags & UNINTERESTING) {
                        mark_tree_uninteresting(tree);
                        return NULL;
                }
                add_pending_object(revs, object, "");
                return NULL;
        }

        /*
         * Blob object? You know the drill by now..
         */
        if (object->type == OBJ_BLOB) {
                struct blob *blob = (struct blob *)object;
                if (!revs->blob_objects)
                        return NULL;
                if (flags & UNINTERESTING) {
                        mark_blob_uninteresting(blob);
                        return NULL;
                }
                add_pending_object(revs, object, "");
                return NULL;
        }
        die("%s is unknown object", name);
}

static int everybody_uninteresting(struct commit_list *orig)
{
        struct commit_list *list = orig;
        while (list) {
                struct commit *commit = list->item;
                list = list->next;
                if (commit->object.flags & UNINTERESTING)
                        continue;
                return 0;
        }
        return 1;
}

static int tree_difference = REV_TREE_SAME;

static void file_add_remove(struct diff_options *options,
                    int addremove, unsigned mode,
                    const unsigned char *sha1,
                    const char *base, const char *path)
{
        int diff = REV_TREE_DIFFERENT;

        /*
         * Is it an add of a new file? It means that the old tree
         * didn't have it at all, so we will turn "REV_TREE_SAME" ->
         * "REV_TREE_NEW", but leave any "REV_TREE_DIFFERENT" alone
         * (and if it already was "REV_TREE_NEW", we'll keep it
         * "REV_TREE_NEW" of course).
         */
        if (addremove == '+') {
                diff = tree_difference;
                if (diff != REV_TREE_SAME)
                        return;
                diff = REV_TREE_NEW;
        }
        tree_difference = diff;
}

static void file_change(struct diff_options *options,
                 unsigned old_mode, unsigned new_mode,
                 const unsigned char *old_sha1,
                 const unsigned char *new_sha1,
                 const char *base, const char *path)
{
        tree_difference = REV_TREE_DIFFERENT;
}

int rev_compare_tree(struct rev_info *revs, struct tree *t1, struct tree *t2)
{
        if (!t1)
                return REV_TREE_NEW;
        if (!t2)
                return REV_TREE_DIFFERENT;
        tree_difference = REV_TREE_SAME;
        if (diff_tree_sha1(t1->object.sha1, t2->object.sha1, "",
                           &revs->pruning) < 0)
                return REV_TREE_DIFFERENT;
        return tree_difference;
}

int rev_same_tree_as_empty(struct rev_info *revs, struct tree *t1)
{
        int retval;
        void *tree;
        struct tree_desc empty, real;

        if (!t1)
                return 0;

        tree = read_object_with_reference(t1->object.sha1, tree_type, &real.size, NULL);
        if (!tree)
                return 0;
        real.buf = tree;

        empty.buf = "";
        empty.size = 0;

        tree_difference = 0;
        retval = diff_tree(&empty, &real, "", &revs->pruning);
        free(tree);

        return retval >= 0 && !tree_difference;
}

static void try_to_simplify_commit(struct rev_info *revs, struct commit *commit)
{
        struct commit_list **pp, *parent;
        int tree_changed = 0, tree_same = 0;

        if (!commit->tree)
                return;

        if (!commit->parents) {
                if (!rev_same_tree_as_empty(revs, commit->tree))
                        commit->object.flags |= TREECHANGE;
                return;
        }

        pp = &commit->parents;
        while ((parent = *pp) != NULL) {
                struct commit *p = parent->item;

                parse_commit(p);
                switch (rev_compare_tree(revs, p->tree, commit->tree)) {
                case REV_TREE_SAME:
                        tree_same = 1;
                        if (!revs->simplify_history || (p->object.flags & UNINTERESTING)) {
                                /* Even if a merge with an uninteresting
                                 * side branch brought the entire change
                                 * we are interested in, we do not want
                                 * to lose the other branches of this
                                 * merge, so we just keep going.
                                 */
                                pp = &parent->next;
                                continue;
                        }
                        parent->next = NULL;
                        commit->parents = parent;
                        return;

                case REV_TREE_NEW:
                        if (revs->remove_empty_trees &&
                            rev_same_tree_as_empty(revs, p->tree)) {
                                /* We are adding all the specified
                                 * paths from this parent, so the
                                 * history beyond this parent is not
                                 * interesting.  Remove its parents
                                 * (they are grandparents for us).
                                 * IOW, we pretend this parent is a
                                 * "root" commit.
                                 */
                                parse_commit(p);
                                p->parents = NULL;
                        }
                /* fallthrough */
                case REV_TREE_DIFFERENT:
                        tree_changed = 1;
                        pp = &parent->next;
                        continue;
                }
                die("bad tree compare for commit %s", sha1_to_hex(commit->object.sha1));
        }
        if (tree_changed && !tree_same)
                commit->object.flags |= TREECHANGE;
}

static void add_parents_to_list(struct rev_info *revs, struct commit *commit, struct commit_list **list)
{
        struct commit_list *parent = commit->parents;

        if (commit->object.flags & ADDED)
                return;
        commit->object.flags |= ADDED;

        /*
         * If the commit is uninteresting, don't try to
         * prune parents - we want the maximal uninteresting
         * set.
         *
         * Normally we haven't parsed the parent
         * yet, so we won't have a parent of a parent
         * here. However, it may turn out that we've
         * reached this commit some other way (where it
         * wasn't uninteresting), in which case we need
         * to mark its parents recursively too..
         */
        if (commit->object.flags & UNINTERESTING) {
                while (parent) {
                        struct commit *p = parent->item;
                        parent = parent->next;
                        parse_commit(p);
                        p->object.flags |= UNINTERESTING;
                        if (p->parents)
                                mark_parents_uninteresting(p);
                        if (p->object.flags & SEEN)
                                continue;
                        p->object.flags |= SEEN;
                        insert_by_date(p, list);
                }
                return;
        }

        /*
         * Ok, the commit wasn't uninteresting. Try to
         * simplify the commit history and find the parent
         * that has no differences in the path set if one exists.
         */
        if (revs->prune_fn)
                revs->prune_fn(revs, commit);

        if (revs->no_walk)
                return;

        parent = commit->parents;
        while (parent) {
                struct commit *p = parent->item;

                parent = parent->next;

                parse_commit(p);
                if (p->object.flags & SEEN)
                        continue;
                p->object.flags |= SEEN;
                insert_by_date(p, list);
        }
}

static void limit_list(struct rev_info *revs)
{
        struct commit_list *list = revs->commits;
        struct commit_list *newlist = NULL;
        struct commit_list **p = &newlist;

        while (list) {
                struct commit_list *entry = list;
                struct commit *commit = list->item;
                struct object *obj = &commit->object;

                list = list->next;
                free(entry);

                if (revs->max_age != -1 && (commit->date < revs->max_age))
                        obj->flags |= UNINTERESTING;
                if (revs->unpacked && has_sha1_pack(obj->sha1))
                        obj->flags |= UNINTERESTING;
                add_parents_to_list(revs, commit, &list);
                if (obj->flags & UNINTERESTING) {
                        mark_parents_uninteresting(commit);
                        if (everybody_uninteresting(list))
                                break;
                        continue;
                }
                if (revs->min_age != -1 && (commit->date > revs->min_age))
                        continue;
                p = &commit_list_insert(commit, p)->next;
        }
        if (revs->boundary) {
                /* mark the ones that are on the result list first */
                for (list = newlist; list; list = list->next) {
                        struct commit *commit = list->item;
                        commit->object.flags |= TMP_MARK;
                }
                for (list = newlist; list; list = list->next) {
                        struct commit *commit = list->item;
                        struct object *obj = &commit->object;
                        struct commit_list *parent;
                        if (obj->flags & UNINTERESTING)
                                continue;
                        for (parent = commit->parents;
                             parent;
                             parent = parent->next) {
                                struct commit *pcommit = parent->item;
                                if (!(pcommit->object.flags & UNINTERESTING))
                                        continue;
                                pcommit->object.flags |= BOUNDARY;
                                if (pcommit->object.flags & TMP_MARK)
                                        continue;
                                pcommit->object.flags |= TMP_MARK;
                                p = &commit_list_insert(pcommit, p)->next;
                        }
                }
                for (list = newlist; list; list = list->next) {
                        struct commit *commit = list->item;
                        commit->object.flags &= ~TMP_MARK;
                }
        }
        revs->commits = newlist;
}

static int all_flags;
static struct rev_info *all_revs;

static int handle_one_ref(const char *path, const unsigned char *sha1)
{
        struct object *object = get_reference(all_revs, path, sha1, all_flags);
        add_pending_object(all_revs, object, "");
        return 0;
}

static void handle_all(struct rev_info *revs, unsigned flags)
{
        all_revs = revs;
        all_flags = flags;
        for_each_ref(handle_one_ref);
}

static int add_parents_only(struct rev_info *revs, const char *arg, int flags)
{
        unsigned char sha1[20];
        struct object *it;
        struct commit *commit;
        struct commit_list *parents;

        if (*arg == '^') {
                flags ^= UNINTERESTING;
                arg++;
        }
        if (get_sha1(arg, sha1))
                return 0;
        while (1) {
                it = get_reference(revs, arg, sha1, 0);
                if (it->type != OBJ_TAG)
                        break;
                hashcpy(sha1, ((struct tag*)it)->tagged->sha1);
        }
        if (it->type != OBJ_COMMIT)
                return 0;
        commit = (struct commit *)it;
        for (parents = commit->parents; parents; parents = parents->next) {
                it = &parents->item->object;
                it->flags |= flags;
                add_pending_object(revs, it, arg);
        }
        return 1;
}

void init_revisions(struct rev_info *revs, const char *prefix)
{
        memset(revs, 0, sizeof(*revs));

        revs->abbrev = DEFAULT_ABBREV;
        revs->ignore_merges = 1;
        revs->simplify_history = 1;
        revs->pruning.recursive = 1;
        revs->pruning.add_remove = file_add_remove;
        revs->pruning.change = file_change;
        revs->lifo = 1;
        revs->dense = 1;
        revs->prefix = prefix;
        revs->max_age = -1;
        revs->min_age = -1;
        revs->max_count = -1;

        revs->prune_fn = NULL;
        revs->prune_data = NULL;

        revs->topo_setter = topo_sort_default_setter;
        revs->topo_getter = topo_sort_default_getter;

        revs->commit_format = CMIT_FMT_DEFAULT;

        diff_setup(&revs->diffopt);
}

static void add_pending_commit_list(struct rev_info *revs,
                                    struct commit_list *commit_list,
                                    unsigned int flags)
{
        while (commit_list) {
                struct object *object = &commit_list->item->object;
                object->flags |= flags;
                add_pending_object(revs, object, sha1_to_hex(object->sha1));
                commit_list = commit_list->next;
        }
}

static void prepare_show_merge(struct rev_info *revs)
{
        struct commit_list *bases;
        struct commit *head, *other;
        unsigned char sha1[20];
        const char **prune = NULL;
        int i, prune_num = 1; /* counting terminating NULL */

        if (get_sha1("HEAD", sha1) || !(head = lookup_commit(sha1)))
                die("--merge without HEAD?");
        if (get_sha1("MERGE_HEAD", sha1) || !(other = lookup_commit(sha1)))
                die("--merge without MERGE_HEAD?");
        add_pending_object(revs, &head->object, "HEAD");
        add_pending_object(revs, &other->object, "MERGE_HEAD");
        bases = get_merge_bases(head, other, 1);
        while (bases) {
                struct commit *it = bases->item;
                struct commit_list *n = bases->next;
                free(bases);
                bases = n;
                it->object.flags |= UNINTERESTING;
                add_pending_object(revs, &it->object, "(merge-base)");
        }

        if (!active_nr)
                read_cache();
        for (i = 0; i < active_nr; i++) {
                struct cache_entry *ce = active_cache[i];
                if (!ce_stage(ce))
                        continue;
                if (ce_path_match(ce, revs->prune_data)) {
                        prune_num++;
                        prune = xrealloc(prune, sizeof(*prune) * prune_num);
                        prune[prune_num-2] = ce->name;
                        prune[prune_num-1] = NULL;
                }
                while ((i+1 < active_nr) &&
                       ce_same_name(ce, active_cache[i+1]))
                        i++;
        }
        revs->prune_data = prune;
}

/*
 * Parse revision information, filling in the "rev_info" structure,
 * and removing the used arguments from the argument list.
 *
 * Returns the number of arguments left that weren't recognized
 * (which are also moved to the head of the argument list)
 */
int setup_revisions(int argc, const char **argv, struct rev_info *revs, const char *def)
{
        int i, flags, seen_dashdash, show_merge;
        const char **unrecognized = argv + 1;
        int left = 1;

        /* First, search for "--" */
        seen_dashdash = 0;
        for (i = 1; i < argc; i++) {
                const char *arg = argv[i];
                if (strcmp(arg, "--"))
                        continue;
                argv[i] = NULL;
                argc = i;
                revs->prune_data = get_pathspec(revs->prefix, argv + i + 1);
                seen_dashdash = 1;
                break;
        }

        flags = show_merge = 0;
        for (i = 1; i < argc; i++) {
                struct object *object;
                const char *arg = argv[i];
                unsigned char sha1[20];
                char *dotdot;
                int local_flags;

                if (*arg == '-') {
                        int opts;
                        if (!strncmp(arg, "--max-count=", 12)) {
                                revs->max_count = atoi(arg + 12);
                                continue;
                        }
                        /* accept -<digit>, like traditional "head" */
                        if ((*arg == '-') && isdigit(arg[1])) {
                                revs->max_count = atoi(arg + 1);
                                continue;
                        }
                        if (!strcmp(arg, "-n")) {
                                if (argc <= i + 1)
                                        die("-n requires an argument");
                                revs->max_count = atoi(argv[++i]);
                                continue;
                        }
                        if (!strncmp(arg,"-n",2)) {
                                revs->max_count = atoi(arg + 2);
                                continue;
                        }
                        if (!strncmp(arg, "--max-age=", 10)) {
                                revs->max_age = atoi(arg + 10);
                                continue;
                        }
                        if (!strncmp(arg, "--since=", 8)) {
                                revs->max_age = approxidate(arg + 8);
                                continue;
                        }
                        if (!strncmp(arg, "--after=", 8)) {
                                revs->max_age = approxidate(arg + 8);
                                continue;
                        }
                        if (!strncmp(arg, "--min-age=", 10)) {
                                revs->min_age = atoi(arg + 10);
                                continue;
                        }
                        if (!strncmp(arg, "--before=", 9)) {
                                revs->min_age = approxidate(arg + 9);
                                continue;
                        }
                        if (!strncmp(arg, "--until=", 8)) {
                                revs->min_age = approxidate(arg + 8);
                                continue;
                        }
                        if (!strcmp(arg, "--all")) {
                                handle_all(revs, flags);
                                continue;
                        }
                        if (!strcmp(arg, "--not")) {
                                flags ^= UNINTERESTING;
                                continue;
                        }
                        if (!strcmp(arg, "--default")) {
                                if (++i >= argc)
                                        die("bad --default argument");
                                def = argv[i];
                                continue;
                        }
                        if (!strcmp(arg, "--merge")) {
                                show_merge = 1;
                                continue;
                        }
                        if (!strcmp(arg, "--topo-order")) {
                                revs->topo_order = 1;
                                continue;
                        }
                        if (!strcmp(arg, "--date-order")) {
                                revs->lifo = 0;
                                revs->topo_order = 1;
                                continue;
                        }
                        if (!strcmp(arg, "--parents")) {
                                revs->parents = 1;
                                continue;
                        }
                        if (!strcmp(arg, "--dense")) {
                                revs->dense = 1;
                                continue;
                        }
                        if (!strcmp(arg, "--sparse")) {
                                revs->dense = 0;
                                continue;
                        }
                        if (!strcmp(arg, "--remove-empty")) {
                                revs->remove_empty_trees = 1;
                                continue;
                        }
                        if (!strcmp(arg, "--no-merges")) {
                                revs->no_merges = 1;
                                continue;
                        }
                        if (!strcmp(arg, "--boundary")) {
                                revs->boundary = 1;
                                continue;
                        }
                        if (!strcmp(arg, "--objects")) {
                                revs->tag_objects = 1;
                                revs->tree_objects = 1;
                                revs->blob_objects = 1;
                                continue;
                        }
                        if (!strcmp(arg, "--objects-edge")) {
                                revs->tag_objects = 1;
                                revs->tree_objects = 1;
                                revs->blob_objects = 1;
                                revs->edge_hint = 1;
                                continue;
                        }
                        if (!strcmp(arg, "--unpacked")) {
                                revs->unpacked = 1;
                                continue;
                        }
                        if (!strcmp(arg, "-r")) {
                                revs->diff = 1;
                                revs->diffopt.recursive = 1;
                                continue;
                        }
                        if (!strcmp(arg, "-t")) {
                                revs->diff = 1;
                                revs->diffopt.recursive = 1;
                                revs->diffopt.tree_in_recursive = 1;
                                continue;
                        }
                        if (!strcmp(arg, "-m")) {
                                revs->ignore_merges = 0;
                                continue;
                        }
                        if (!strcmp(arg, "-c")) {
                                revs->diff = 1;
                                revs->dense_combined_merges = 0;
                                revs->combine_merges = 1;
                                continue;
                        }
                        if (!strcmp(arg, "--cc")) {
                                revs->diff = 1;
                                revs->dense_combined_merges = 1;
                                revs->combine_merges = 1;
                                continue;
                        }
                        if (!strcmp(arg, "-v")) {
                                revs->verbose_header = 1;
                                continue;
                        }
                        if (!strncmp(arg, "--pretty", 8)) {
                                revs->verbose_header = 1;
                                revs->commit_format = get_commit_format(arg+8);
                                continue;
                        }
                        if (!strcmp(arg, "--root")) {
                                revs->show_root_diff = 1;
                                continue;
                        }
                        if (!strcmp(arg, "--no-commit-id")) {
                                revs->no_commit_id = 1;
                                continue;
                        }
                        if (!strcmp(arg, "--always")) {
                                revs->always_show_header = 1;
                                continue;
                        }
                        if (!strcmp(arg, "--no-abbrev")) {
                                revs->abbrev = 0;
                                continue;
                        }
                        if (!strcmp(arg, "--abbrev")) {
                                revs->abbrev = DEFAULT_ABBREV;
                                continue;
                        }
                        if (!strncmp(arg, "--abbrev=", 9)) {
                                revs->abbrev = strtoul(arg + 9, NULL, 10);
                                if (revs->abbrev < MINIMUM_ABBREV)
                                        revs->abbrev = MINIMUM_ABBREV;
                                else if (revs->abbrev > 40)
                                        revs->abbrev = 40;
                                continue;
                        }
                        if (!strcmp(arg, "--abbrev-commit")) {
                                revs->abbrev_commit = 1;
                                continue;
                        }
                        if (!strcmp(arg, "--full-diff")) {
                                revs->diff = 1;
                                revs->full_diff = 1;
                                continue;
                        }
                        if (!strcmp(arg, "--full-history")) {
                                revs->simplify_history = 0;
                                continue;
                        }
                        if (!strcmp(arg, "--relative-date")) {
                                revs->relative_date = 1;
                                continue;
                        }
                        opts = diff_opt_parse(&revs->diffopt, argv+i, argc-i);
                        if (opts > 0) {
                                revs->diff = 1;
                                i += opts - 1;
                                continue;
                        }
                        *unrecognized++ = arg;
                        left++;
                        continue;
                }
                dotdot = strstr(arg, "..");
                if (dotdot) {
                        unsigned char from_sha1[20];
                        const char *next = dotdot + 2;
                        const char *this = arg;
                        int symmetric = *next == '.';
                        unsigned int flags_exclude = flags ^ UNINTERESTING;

                        *dotdot = 0;
                        next += symmetric;

                        if (!*next)
                                next = "HEAD";
                        if (dotdot == arg)
                                this = "HEAD";
                        if (!get_sha1(this, from_sha1) &&
                            !get_sha1(next, sha1)) {
                                struct commit *a, *b;
                                struct commit_list *exclude;

                                a = lookup_commit_reference(from_sha1);
                                b = lookup_commit_reference(sha1);
                                if (!a || !b) {
                                        die(symmetric ?
                                            "Invalid symmetric difference expression %s...%s" :
                                            "Invalid revision range %s..%s",
                                            arg, next);
                                }

                                if (!seen_dashdash) {
                                        *dotdot = '.';
                                        verify_non_filename(revs->prefix, arg);
                                }

                                if (symmetric) {
                                        exclude = get_merge_bases(a, b, 1);
                                        add_pending_commit_list(revs, exclude,
                                                                flags_exclude);
                                        free_commit_list(exclude);
                                        a->object.flags |= flags;
                                } else
                                        a->object.flags |= flags_exclude;
                                b->object.flags |= flags;
                                add_pending_object(revs, &a->object, this);
                                add_pending_object(revs, &b->object, next);
                                continue;
                        }
                        *dotdot = '.';
                }
                dotdot = strstr(arg, "^@");
                if (dotdot && !dotdot[2]) {
                        *dotdot = 0;
                        if (add_parents_only(revs, arg, flags))
                                continue;
                        *dotdot = '^';
                }
                local_flags = 0;
                if (*arg == '^') {
                        local_flags = UNINTERESTING;
                        arg++;
                }
                if (get_sha1(arg, sha1)) {
                        int j;

                        if (seen_dashdash || local_flags)
                                die("bad revision '%s'", arg);

                        /* If we didn't have a "--":
                         * (1) all filenames must exist;
                         * (2) all rev-args must not be interpretable
                         *     as a valid filename.
                         * but the latter we have checked in the main loop.
                         */
                        for (j = i; j < argc; j++)
                                verify_filename(revs->prefix, argv[j]);

                        revs->prune_data = get_pathspec(revs->prefix, argv + i);
                        break;
                }
                if (!seen_dashdash)
                        verify_non_filename(revs->prefix, arg);
                object = get_reference(revs, arg, sha1, flags ^ local_flags);
                add_pending_object(revs, object, arg);
        }
        if (show_merge)
                prepare_show_merge(revs);
        if (def && !revs->pending.nr) {
                unsigned char sha1[20];
                struct object *object;
                if (get_sha1(def, sha1))
                        die("bad default revision '%s'", def);
                object = get_reference(revs, def, sha1, 0);
                add_pending_object(revs, object, def);
        }

        if (revs->topo_order || revs->unpacked)
                revs->limited = 1;

        if (revs->prune_data) {
                diff_tree_setup_paths(revs->prune_data, &revs->pruning);
                revs->prune_fn = try_to_simplify_commit;
                if (!revs->full_diff)
                        diff_tree_setup_paths(revs->prune_data, &revs->diffopt);
        }
        if (revs->combine_merges) {
                revs->ignore_merges = 0;
                if (revs->dense_combined_merges && !revs->diffopt.output_format)
                        revs->diffopt.output_format = DIFF_FORMAT_PATCH;
        }
        revs->diffopt.abbrev = revs->abbrev;
        if (diff_setup_done(&revs->diffopt) < 0)
                die("diff_setup_done failed");

        return left;
}

void prepare_revision_walk(struct rev_info *revs)
{
        int nr = revs->pending.nr;
        struct object_array_entry *list = revs->pending.objects;

        revs->pending.nr = 0;
        revs->pending.alloc = 0;
        revs->pending.objects = NULL;
        while (--nr >= 0) {
                struct commit *commit = handle_commit(revs, list->item, list->name);
                if (commit) {
                        if (!(commit->object.flags & SEEN)) {
                                commit->object.flags |= SEEN;
                                insert_by_date(commit, &revs->commits);
                        }
                }
                list++;
        }

        if (revs->no_walk)
                return;
        if (revs->limited)
                limit_list(revs);
        if (revs->topo_order)
                sort_in_topological_order_fn(&revs->commits, revs->lifo,
                                             revs->topo_setter,
                                             revs->topo_getter);
}

static int rewrite_one(struct rev_info *revs, struct commit **pp)
{
        for (;;) {
                struct commit *p = *pp;
                if (!revs->limited)
                        add_parents_to_list(revs, p, &revs->commits);
                if (p->parents && p->parents->next)
                        return 0;
                if (p->object.flags & (TREECHANGE | UNINTERESTING))
                        return 0;
                if (!p->parents)
                        return -1;
                *pp = p->parents->item;
        }
}

static void rewrite_parents(struct rev_info *revs, struct commit *commit)
{
        struct commit_list **pp = &commit->parents;
        while (*pp) {
                struct commit_list *parent = *pp;
                if (rewrite_one(revs, &parent->item) < 0) {
                        *pp = parent->next;
                        continue;
                }
                pp = &parent->next;
        }
}

static void mark_boundary_to_show(struct commit *commit)
{
        struct commit_list *p = commit->parents;
        while (p) {
                commit = p->item;
                p = p->next;
                if (commit->object.flags & BOUNDARY)
                        commit->object.flags |= BOUNDARY_SHOW;
        }
}

struct commit *get_revision(struct rev_info *revs)
{
        struct commit_list *list = revs->commits;

        if (!list)
                return NULL;

        /* Check the max_count ... */
        switch (revs->max_count) {
        case -1:
                break;
        case 0:
                return NULL;
        default:
                revs->max_count--;
        }

        do {
                struct commit_list *entry = revs->commits;
                struct commit *commit = entry->item;

                revs->commits = entry->next;
                free(entry);

                /*
                 * If we haven't done the list limiting, we need to look at
                 * the parents here. We also need to do the date-based limiting
                 * that we'd otherwise have done in limit_list().
                 */
                if (!revs->limited) {
                        if ((revs->unpacked &&
                             has_sha1_pack(commit->object.sha1)) ||
                            (revs->max_age != -1 &&
                             (commit->date < revs->max_age)))
                                continue;
                        add_parents_to_list(revs, commit, &revs->commits);
                }
                if (commit->object.flags & SHOWN)
                        continue;

                /* We want to show boundary commits only when their
                 * children are shown.  When path-limiter is in effect,
                 * rewrite_parents() drops some commits from getting shown,
                 * and there is no point showing boundary parents that
                 * are not shown.  After rewrite_parents() rewrites the
                 * parents of a commit that is shown, we mark the boundary
                 * parents with BOUNDARY_SHOW.
                 */
                if (commit->object.flags & BOUNDARY_SHOW) {
                        commit->object.flags |= SHOWN;
                        return commit;
                }
                if (commit->object.flags & UNINTERESTING)
                        continue;
                if (revs->min_age != -1 && (commit->date > revs->min_age))
                        continue;
                if (revs->no_merges &&
                    commit->parents && commit->parents->next)
                        continue;
                if (revs->prune_fn && revs->dense) {
                        /* Commit without changes? */
                        if (!(commit->object.flags & TREECHANGE)) {
                                /* drop merges unless we want parenthood */
                                if (!revs->parents)
                                        continue;
                                /* non-merge - always ignore it */
                                if (!commit->parents || !commit->parents->next)
                                        continue;
                        }
                        if (revs->parents)
                                rewrite_parents(revs, commit);
                }
                if (revs->boundary)
                        mark_boundary_to_show(commit);
                commit->object.flags |= SHOWN;
                return commit;
        } while (revs->commits);
        return NULL;
}