blenkernel/intern/collection.c

/*
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 */

/** \file
 * \ingroup bke
 */

#include <string.h>

#include "BLI_blenlib.h"
#include "BLI_iterator.h"
#include "BLI_listbase.h"
#include "BLI_math_base.h"
#include "BLI_threads.h"
#include "BLT_translation.h"

#include "BKE_anim_data.h"
#include "BKE_collection.h"
#include "BKE_icons.h"
#include "BKE_idprop.h"
#include "BKE_idtype.h"
#include "BKE_layer.h"
#include "BKE_lib_id.h"
#include "BKE_lib_query.h"
#include "BKE_lib_remap.h"
#include "BKE_main.h"
#include "BKE_object.h"
#include "BKE_rigidbody.h"
#include "BKE_scene.h"

#include "DNA_defaults.h"

#include "DNA_ID.h"
#include "DNA_collection_types.h"
#include "DNA_layer_types.h"
#include "DNA_object_types.h"
#include "DNA_rigidbody_types.h"
#include "DNA_scene_types.h"

#include "DEG_depsgraph.h"
#include "DEG_depsgraph_query.h"

#include "MEM_guardedalloc.h"

/* -------------------------------------------------------------------- */
/** \name Prototypes
 * \{ */

static bool collection_child_add(Collection *parent,
                                 Collection *collection,
                                 const int flag,
                                 const bool add_us);
static bool collection_child_remove(Collection *parent, Collection *collection);
static bool collection_object_add(
    Main *bmain, Collection *collection, Object *ob, int flag, const bool add_us);
static bool collection_object_remove(Main *bmain,
                                     Collection *collection,
                                     Object *ob,
                                     const bool free_us);

static CollectionChild *collection_find_child(Collection *parent, Collection *collection);
static CollectionParent *collection_find_parent(Collection *child, Collection *collection);

static bool collection_find_child_recursive(Collection *parent, Collection *collection);

/** \} */

/* -------------------------------------------------------------------- */
/** \name Collection Data-Block
 * \{ */

static void collection_init_data(ID *id)
{
  Collection *collection = (Collection *)id;
  BLI_assert(MEMCMP_STRUCT_AFTER_IS_ZERO(collection, id));

  MEMCPY_STRUCT_AFTER(collection, DNA_struct_default_get(Collection), id);
}

/**
 * Only copy internal data of Collection ID from source
 * to already allocated/initialized destination.
 * You probably never want to use that directly,
 * use #BKE_id_copy or #BKE_id_copy_ex for typical needs.
 *
 * WARNING! This function will not handle ID user count!
 *
 * \param flag: Copying options (see BKE_lib_id.h's LIB_ID_COPY_... flags for more).
 */
static void collection_copy_data(Main *bmain, ID *id_dst, const ID *id_src, const int flag)
{
  Collection *collection_dst = (Collection *)id_dst;
  const Collection *collection_src = (const Collection *)id_src;

  BLI_assert(((collection_src->flag & COLLECTION_IS_MASTER) != 0) ==
             ((collection_src->id.flag & LIB_EMBEDDED_DATA) != 0));

  /* Do not copy collection's preview (same behavior as for objects). */
  if ((flag & LIB_ID_COPY_NO_PREVIEW) == 0 && false) { /* XXX TODO temp hack */
    BKE_previewimg_id_copy(&collection_dst->id, &collection_src->id);
  }
  else {
    collection_dst->preview = NULL;
  }

  collection_dst->flag &= ~COLLECTION_HAS_OBJECT_CACHE;
  BLI_listbase_clear(&collection_dst->object_cache);

  BLI_listbase_clear(&collection_dst->gobject);
  BLI_listbase_clear(&collection_dst->children);
  BLI_listbase_clear(&collection_dst->parents);

  LISTBASE_FOREACH (CollectionChild *, child, &collection_src->children) {
    collection_child_add(collection_dst, child->collection, flag, false);
  }
  LISTBASE_FOREACH (CollectionObject *, cob, &collection_src->gobject) {
    collection_object_add(bmain, collection_dst, cob->ob, flag, false);
  }
}

static void collection_free_data(ID *id)
{
  Collection *collection = (Collection *)id;

  /* No animdata here. */
  BKE_previewimg_free(&collection->preview);

  BLI_freelistN(&collection->gobject);
  BLI_freelistN(&collection->children);
  BLI_freelistN(&collection->parents);

  BKE_collection_object_cache_free(collection);
}

static void collection_foreach_id(ID *id, LibraryForeachIDData *data)
{
  Collection *collection = (Collection *)id;

  LISTBASE_FOREACH (CollectionObject *, cob, &collection->gobject) {
    BKE_LIB_FOREACHID_PROCESS(data, cob->ob, IDWALK_CB_USER);
  }
  LISTBASE_FOREACH (CollectionChild *, child, &collection->children) {
    BKE_LIB_FOREACHID_PROCESS(data, child->collection, IDWALK_CB_NEVER_SELF | IDWALK_CB_USER);
  }
  LISTBASE_FOREACH (CollectionParent *, parent, &collection->parents) {
    /* XXX This is very weak. The whole idea of keeping pointers to private IDs is very bad
     * anyway... */
    const int cb_flag = ((parent->collection != NULL &&
                          (parent->collection->id.flag & LIB_EMBEDDED_DATA) != 0) ?
                             IDWALK_CB_EMBEDDED :
                             IDWALK_CB_NOP);
    BKE_LIB_FOREACHID_PROCESS(
        data, parent->collection, IDWALK_CB_NEVER_SELF | IDWALK_CB_LOOPBACK | cb_flag);
  }
}

IDTypeInfo IDType_ID_GR = {
    .id_code = ID_GR,
    .id_filter = FILTER_ID_GR,
    .main_listbase_index = INDEX_ID_GR,
    .struct_size = sizeof(Collection),
    .name = "Collection",
    .name_plural = "collections",
    .translation_context = BLT_I18NCONTEXT_ID_COLLECTION,
    .flags = IDTYPE_FLAGS_NO_ANIMDATA,

    .init_data = collection_init_data,
    .copy_data = collection_copy_data,
    .free_data = collection_free_data,
    .make_local = NULL,
    .foreach_id = collection_foreach_id,
    .foreach_cache = NULL,

    .blend_write = NULL,
    .blend_read_data = NULL,
    .blend_read_lib = NULL,
    .blend_read_expand = NULL,
};

/** \} */

/* -------------------------------------------------------------------- */
/** \name Add Collection
 * \{ */

/* Add new collection, without view layer syncing. */
static Collection *collection_add(Main *bmain,
                                  Collection *collection_parent,
                                  const char *name_custom)
{
  /* Determine new collection name. */
  char name[MAX_NAME];

  if (name_custom) {
    STRNCPY(name, name_custom);
  }
  else {
    BKE_collection_new_name_get(collection_parent, name);
  }

  /* Create new collection. */
  Collection *collection = BKE_id_new(bmain, ID_GR, name);

  /* We increase collection user count when linking to Collections. */
  id_us_min(&collection->id);

  /* Optionally add to parent collection. */
  if (collection_parent) {
    collection_child_add(collection_parent, collection, 0, true);
  }

  return collection;
}

/**
 * Add a collection to a collection ListBase and synchronize all render layers
 * The ListBase is NULL when the collection is to be added to the master collection
 */
Collection *BKE_collection_add(Main *bmain, Collection *collection_parent, const char *name_custom)
{
  Collection *collection = collection_add(bmain, collection_parent, name_custom);
  BKE_main_collection_sync(bmain);
  return collection;
}

/**
 * Add \a collection_dst to all scene collections that reference object \a ob_src is in.
 * Used to replace an instance object with a collection (library override operator).
 *
 * Logic is very similar to #BKE_collection_object_add_from().
 */
void BKE_collection_add_from_object(Main *bmain,
                                    Scene *scene,
                                    const Object *ob_src,
                                    Collection *collection_dst)
{
  bool is_instantiated = false;

  FOREACH_SCENE_COLLECTION_BEGIN (scene, collection) {
    if (!ID_IS_LINKED(collection) && BKE_collection_has_object(collection, ob_src)) {
      collection_child_add(collection, collection_dst, 0, true);
      is_instantiated = true;
    }
  }
  FOREACH_SCENE_COLLECTION_END;

  if (!is_instantiated) {
    collection_child_add(scene->master_collection, collection_dst, 0, true);
  }

  BKE_main_collection_sync(bmain);
}

/**
 * Add \a collection_dst to all scene collections that reference collection \a collection_src is
 * in.
 *
 * Logic is very similar to #BKE_collection_object_add_from().
 */
void BKE_collection_add_from_collection(Main *bmain,
                                        Scene *scene,
                                        Collection *collection_src,
                                        Collection *collection_dst)
{
  bool is_instantiated = false;

  FOREACH_SCENE_COLLECTION_BEGIN (scene, collection) {
    if (!ID_IS_LINKED(collection) && BKE_collection_has_collection(collection, collection_src)) {
      collection_child_add(collection, collection_dst, 0, true);
      is_instantiated = true;
    }
  }
  FOREACH_SCENE_COLLECTION_END;

  if (!is_instantiated) {
    collection_child_add(scene->master_collection, collection_dst, 0, true);
  }

  BKE_main_collection_sync(bmain);
}

/** \} */

/* -------------------------------------------------------------------- */
/** \name Free and Delete Collection
 * \{ */

/** Free (or release) any data used by this collection (does not free the collection itself). */
void BKE_collection_free(Collection *collection)
{
  collection_free_data(&collection->id);
}

/**
 * Remove a collection, optionally removing its child objects or moving
 * them to parent collections.
 */
bool BKE_collection_delete(Main *bmain, Collection *collection, bool hierarchy)
{
  /* Master collection is not real datablock, can't be removed. */
  if (collection->flag & COLLECTION_IS_MASTER) {
    BLI_assert(!"Scene master collection can't be deleted");
    return false;
  }

  if (hierarchy) {
    /* Remove child objects. */
    CollectionObject *cob = collection->gobject.first;
    while (cob != NULL) {
      collection_object_remove(bmain, collection, cob->ob, true);
      cob = collection->gobject.first;
    }

    /* Delete all child collections recursively. */
    CollectionChild *child = collection->children.first;
    while (child != NULL) {
      BKE_collection_delete(bmain, child->collection, hierarchy);
      child = collection->children.first;
    }
  }
  else {
    /* Link child collections into parent collection. */
    LISTBASE_FOREACH (CollectionChild *, child, &collection->children) {
      LISTBASE_FOREACH (CollectionParent *, cparent, &collection->parents) {
        Collection *parent = cparent->collection;
        collection_child_add(parent, child->collection, 0, true);
      }
    }

    CollectionObject *cob = collection->gobject.first;
    while (cob != NULL) {
      /* Link child object into parent collections. */
      LISTBASE_FOREACH (CollectionParent *, cparent, &collection->parents) {
        Collection *parent = cparent->collection;
        collection_object_add(bmain, parent, cob->ob, 0, true);
      }

      /* Remove child object. */
      collection_object_remove(bmain, collection, cob->ob, true);
      cob = collection->gobject.first;
    }
  }

  BKE_id_delete(bmain, collection);

  BKE_main_collection_sync(bmain);

  return true;
}

/** \} */

/* -------------------------------------------------------------------- */
/** \name Collection Copy
 * \{ */

static Collection *collection_duplicate_recursive(Main *bmain,
                                                  Collection *parent,
                                                  Collection *collection_old,
                                                  const eDupli_ID_Flags duplicate_flags,
                                                  const eLibIDDuplicateFlags duplicate_options)
{
  Collection *collection_new;
  bool do_full_process = false;
  const bool is_collection_master = (collection_old->flag & COLLECTION_IS_MASTER) != 0;

  const bool do_objects = (duplicate_flags & USER_DUP_OBJECT) != 0;

  if (is_collection_master) {
    /* We never duplicate master collections here, but we can still deep-copy their objects and
     * collections. */
    BLI_assert(parent == NULL);
    collection_new = collection_old;
    do_full_process = true;
  }
  else if (collection_old->id.newid == NULL) {
    collection_new = (Collection *)BKE_id_copy_for_duplicate(
        bmain, (ID *)collection_old, duplicate_flags);

    if (collection_new == collection_old) {
      return collection_new;
    }

    do_full_process = true;
  }
  else {
    collection_new = (Collection *)collection_old->id.newid;
  }

  /* Optionally add to parent (we always want to do that,
   * even if collection_old had already been duplicated). */
  if (parent != NULL) {
    if (collection_child_add(parent, collection_new, 0, true)) {
      /* Put collection right after existing one. */
      CollectionChild *child = collection_find_child(parent, collection_old);
      CollectionChild *child_new = collection_find_child(parent, collection_new);

      if (child && child_new) {
        BLI_remlink(&parent->children, child_new);
        BLI_insertlinkafter(&parent->children, child, child_new);
      }
    }
  }

  /* If we are not doing any kind of deep-copy, we can return immediately.
   * False do_full_process means collection_old had already been duplicated,
   * no need to redo some deep-copy on it. */
  if (!do_full_process) {
    return collection_new;
  }

  if (do_objects) {
    /* We need to first duplicate the objects in a separate loop, to support the master collection
     * case, where both old and new collections are the same.
     * Otherwise, depending on naming scheme and sorting, we may end up duplicating the new objects
     * we just added, in some infinite loop. */
    LISTBASE_FOREACH (CollectionObject *, cob, &collection_old->gobject) {
      Object *ob_old = cob->ob;

      if (ob_old->id.newid == NULL) {
        BKE_object_duplicate(
            bmain, ob_old, duplicate_flags, duplicate_options | LIB_ID_DUPLICATE_IS_SUBPROCESS);
      }
    }

    /* We can loop on collection_old's objects, but have to consider it mutable because with master
     * collections collection_old and collection_new are the same data here. */
    LISTBASE_FOREACH_MUTABLE (CollectionObject *, cob, &collection_old->gobject) {
      Object *ob_old = cob->ob;
      Object *ob_new = (Object *)ob_old->id.newid;

      /* New object can be NULL in master collection case, since new and old objects are in same
       * collection. */
      if (ELEM(ob_new, ob_old, NULL)) {
        continue;
      }

      collection_object_add(bmain, collection_new, ob_new, 0, true);
      collection_object_remove(bmain, collection_new, ob_old, false);
    }
  }

  /* We can loop on collection_old's children,
   * that list is currently identical the collection_new' children, and won't be changed here. */
  LISTBASE_FOREACH_MUTABLE (CollectionChild *, child, &collection_old->children) {
    Collection *child_collection_old = child->collection;

    Collection *child_collection_new = collection_duplicate_recursive(
        bmain, collection_new, child_collection_old, duplicate_flags, duplicate_options);
    if (child_collection_new != child_collection_old) {
      collection_child_remove(collection_new, child_collection_old);
    }
  }

  return collection_new;
}

/**
 * Make a deep copy (aka duplicate) of the given collection and all of its children, recursively.
 *
 * \warning This functions will clear all \a bmain #ID.idnew pointers, unless \a
 * #LIB_ID_DUPLICATE_IS_SUBPROCESS duplicate option is passed on, in which case caller is
 * responsible to reconstruct collection dependencies information's
 * (i.e. call #BKE_main_collection_sync).
 */
Collection *BKE_collection_duplicate(Main *bmain,
                                     Collection *parent,
                                     Collection *collection,
                                     eDupli_ID_Flags duplicate_flags,
                                     eLibIDDuplicateFlags duplicate_options)
{
  const bool is_subprocess = (duplicate_options & LIB_ID_DUPLICATE_IS_SUBPROCESS) != 0;

  if (!is_subprocess) {
    BKE_main_id_tag_all(bmain, LIB_TAG_NEW, false);
    BKE_main_id_clear_newpoins(bmain);
    /* In case root duplicated ID is linked, assume we want to get a local copy of it and duplicate
     * all expected linked data. */
    if (ID_IS_LINKED(collection)) {
      duplicate_flags |= USER_DUP_LINKED_ID;
    }
  }

  Collection *collection_new = collection_duplicate_recursive(
      bmain, parent, collection, duplicate_flags, duplicate_options);

  if (!is_subprocess) {
    /* `collection_duplicate_recursive` will also tag our 'root' collection, which is not required
     * unless its duplication is a sub-process of another one. */
    collection_new->id.tag &= ~LIB_TAG_NEW;

    /* This code will follow into all ID links using an ID tagged with LIB_TAG_NEW.*/
    BKE_libblock_relink_to_newid(&collection_new->id);

#ifndef NDEBUG
    /* Call to `BKE_libblock_relink_to_newid` above is supposed to have cleared all those flags. */
    ID *id_iter;
    FOREACH_MAIN_ID_BEGIN (bmain, id_iter) {
      if (id_iter->tag & LIB_TAG_NEW) {
        BLI_assert((id_iter->tag & LIB_TAG_NEW) == 0);
      }
    }
    FOREACH_MAIN_ID_END;
#endif

    /* Cleanup. */
    BKE_main_id_tag_all(bmain, LIB_TAG_NEW, false);
    BKE_main_id_clear_newpoins(bmain);

    BKE_main_collection_sync(bmain);
  }

  return collection_new;
}

/** \} */

/* -------------------------------------------------------------------- */
/** \name Collection Naming
 * \{ */

/**
 * The automatic/fallback name of a new collection.
 */
void BKE_collection_new_name_get(Collection *collection_parent, char *rname)
{
  char *name;

  if (!collection_parent) {
    name = BLI_strdup("Collection");
  }
  else if (collection_parent->flag & COLLECTION_IS_MASTER) {
    name = BLI_sprintfN("Collection %d", BLI_listbase_count(&collection_parent->children) + 1);
  }
  else {
    const int number = BLI_listbase_count(&collection_parent->children) + 1;
    const int digits = integer_digits_i(number);
    const int max_len = sizeof(collection_parent->id.name) - 1 /* NULL terminator */ -
                        (1 + digits) /* " %d" */ - 2 /* ID */;
    name = BLI_sprintfN("%.*s %d", max_len, collection_parent->id.name + 2, number);
  }

  BLI_strncpy(rname, name, MAX_NAME);
  MEM_freeN(name);
}

/**
 * The name to show in the interface.
 */
const char *BKE_collection_ui_name_get(struct Collection *collection)
{
  if (collection->flag & COLLECTION_IS_MASTER) {
    return IFACE_("Scene Collection");
  }

  return collection->id.name + 2;
}

/** \} */

/* -------------------------------------------------------------------- */
/** \name Object List Cache
 * \{ */

static void collection_object_cache_fill(ListBase *lb, Collection *collection, int parent_restrict)
{
  int child_restrict = collection->flag | parent_restrict;

  LISTBASE_FOREACH (CollectionObject *, cob, &collection->gobject) {
    Base *base = BLI_findptr(lb, cob->ob, offsetof(Base, object));

    if (base == NULL) {
      base = MEM_callocN(sizeof(Base), "Object Base");
      base->object = cob->ob;
      BLI_addtail(lb, base);
    }

    /* Only collection flags are checked here currently, object restrict flag is checked
     * in FOREACH_COLLECTION_VISIBLE_OBJECT_RECURSIVE_BEGIN since it can be animated
     * without updating the cache. */
    if (((child_restrict & COLLECTION_RESTRICT_VIEWPORT) == 0)) {
      base->flag |= BASE_ENABLED_VIEWPORT;
    }
    if (((child_restrict & COLLECTION_RESTRICT_RENDER) == 0)) {
      base->flag |= BASE_ENABLED_RENDER;
    }
  }

  LISTBASE_FOREACH (CollectionChild *, child, &collection->children) {
    collection_object_cache_fill(lb, child->collection, child_restrict);
  }
}

ListBase BKE_collection_object_cache_get(Collection *collection)
{
  if (!(collection->flag & COLLECTION_HAS_OBJECT_CACHE)) {
    static ThreadMutex cache_lock = BLI_MUTEX_INITIALIZER;

    BLI_mutex_lock(&cache_lock);
    if (!(collection->flag & COLLECTION_HAS_OBJECT_CACHE)) {
      collection_object_cache_fill(&collection->object_cache, collection, 0);
      collection->flag |= COLLECTION_HAS_OBJECT_CACHE;
    }
    BLI_mutex_unlock(&cache_lock);
  }

  return collection->object_cache;
}

static void collection_object_cache_free(Collection *collection)
{
  /* Clear own cache an for all parents, since those are affected by changes as well. */
  collection->flag &= ~COLLECTION_HAS_OBJECT_CACHE;
  BLI_freelistN(&collection->object_cache);

  LISTBASE_FOREACH (CollectionParent *, parent, &collection->parents) {
    collection_object_cache_free(parent->collection);
  }
}

void BKE_collection_object_cache_free(Collection *collection)
{
  collection_object_cache_free(collection);
}

Base *BKE_collection_or_layer_objects(const ViewLayer *view_layer, Collection *collection)
{
  if (collection) {
    return BKE_collection_object_cache_get(collection).first;
  }

  return FIRSTBASE(view_layer);
}

/** \} */

/* -------------------------------------------------------------------- */
/** \name Scene Master Collection
 * \{ */

Collection *BKE_collection_master_add()
{
  /* Not an actual datablock, but owned by scene. */
  Collection *master_collection = MEM_callocN(sizeof(Collection), "Master Collection");
  STRNCPY(master_collection->id.name, "GRMaster Collection");
  master_collection->id.flag |= LIB_EMBEDDED_DATA;
  master_collection->flag |= COLLECTION_IS_MASTER;
  master_collection->color_tag = COLLECTION_COLOR_NONE;
  return master_collection;
}

Scene *BKE_collection_master_scene_search(const Main *bmain, const Collection *master_collection)
{
  BLI_assert((master_collection->flag & COLLECTION_IS_MASTER) != 0);

  for (Scene *scene = bmain->scenes.first; scene != NULL; scene = scene->id.next) {
    if (scene->master_collection == master_collection) {
      return scene;
    }
  }

  return NULL;
}

/** \} */

/* -------------------------------------------------------------------- */
/** \name Cyclic Checks
 * \{ */

static bool collection_object_cyclic_check_internal(Object *object, Collection *collection)
{
  if (object->instance_collection) {
    Collection *dup_collection = object->instance_collection;
    if ((dup_collection->id.tag & LIB_TAG_DOIT) == 0) {
      /* Cycle already exists in collections, let's prevent further crappyness */
      return true;
    }
    /* flag the object to identify cyclic dependencies in further dupli collections */
    dup_collection->id.tag &= ~LIB_TAG_DOIT;

    if (dup_collection == collection) {
      return true;
    }

    FOREACH_COLLECTION_OBJECT_RECURSIVE_BEGIN (dup_collection, collection_object) {
      if (collection_object_cyclic_check_internal(collection_object, dup_collection)) {
        return true;
      }
    }
    FOREACH_COLLECTION_OBJECT_RECURSIVE_END;

    /* un-flag the object, it's allowed to have the same collection multiple times in parallel */
    dup_collection->id.tag |= LIB_TAG_DOIT;
  }

  return false;
}

bool BKE_collection_object_cyclic_check(Main *bmain, Object *object, Collection *collection)
{
  /* first flag all collections */
  BKE_main_id_tag_listbase(&bmain->collections, LIB_TAG_DOIT, true);

  return collection_object_cyclic_check_internal(object, collection);
}

/** \} */

/* -------------------------------------------------------------------- */
/** \name Collection Object Membership
 * \{ */

bool BKE_collection_has_object(Collection *collection, const Object *ob)
{
  if (ELEM(NULL, collection, ob)) {
    return false;
  }

  return (BLI_findptr(&collection->gobject, ob, offsetof(CollectionObject, ob)));
}

bool BKE_collection_has_object_recursive(Collection *collection, Object *ob)
{
  if (ELEM(NULL, collection, ob)) {
    return false;
  }

  const ListBase objects = BKE_collection_object_cache_get(collection);
  return (BLI_findptr(&objects, ob, offsetof(Base, object)));
}

static Collection *collection_next_find(Main *bmain, Scene *scene, Collection *collection)
{
  if (scene && collection == scene->master_collection) {
    return bmain->collections.first;
  }

  return collection->id.next;
}

Collection *BKE_collection_object_find(Main *bmain,
                                       Scene *scene,
                                       Collection *collection,
                                       Object *ob)
{
  if (collection) {
    collection = collection_next_find(bmain, scene, collection);
  }
  else if (scene) {
    collection = scene->master_collection;
  }
  else {
    collection = bmain->collections.first;
  }

  while (collection) {
    if (BKE_collection_has_object(collection, ob)) {
      return collection;
    }
    collection = collection_next_find(bmain, scene, collection);
  }
  return NULL;
}

bool BKE_collection_is_empty(Collection *collection)
{
  return BLI_listbase_is_empty(&collection->gobject) &&
         BLI_listbase_is_empty(&collection->children);
}

/** \} */

/* -------------------------------------------------------------------- */
/** \name Collection Objects
 * \{ */

static void collection_tag_update_parent_recursive(Main *bmain,
                                                   Collection *collection,
                                                   const int flag)
{
  if (collection->flag & COLLECTION_IS_MASTER) {
    return;
  }

  DEG_id_tag_update_ex(bmain, &collection->id, flag);

  LISTBASE_FOREACH (CollectionParent *, collection_parent, &collection->parents) {
    if (collection_parent->collection->flag & COLLECTION_IS_MASTER) {
      /* We don't care about scene/master collection here. */
      continue;
    }
    collection_tag_update_parent_recursive(bmain, collection_parent->collection, flag);
  }
}

static Collection *collection_parent_editable_find_recursive(Collection *collection)
{
  if (!ID_IS_LINKED(collection) && !ID_IS_OVERRIDE_LIBRARY(collection)) {
    return collection;
  }

  if (collection->flag & COLLECTION_IS_MASTER) {
    return NULL;
  }

  LISTBASE_FOREACH (CollectionParent *, collection_parent, &collection->parents) {
    if (!ID_IS_LINKED(collection_parent->collection) &&
        !ID_IS_OVERRIDE_LIBRARY(collection_parent->collection)) {
      return collection_parent->collection;
    }
    Collection *editable_collection = collection_parent_editable_find_recursive(
        collection_parent->collection);
    if (editable_collection != NULL) {
      return editable_collection;
    }
  }

  return NULL;
}

static bool collection_object_add(
    Main *bmain, Collection *collection, Object *ob, int flag, const bool add_us)
{
  if (ob->instance_collection) {
    /* Cyclic dependency check. */
    if (collection_find_child_recursive(ob->instance_collection, collection) ||
        ob->instance_collection == collection) {
      return false;
    }
  }

  CollectionObject *cob = BLI_findptr(&collection->gobject, ob, offsetof(CollectionObject, ob));
  if (cob) {
    return false;
  }

  cob = MEM_callocN(sizeof(CollectionObject), __func__);
  cob->ob = ob;
  BLI_addtail(&collection->gobject, cob);
  BKE_collection_object_cache_free(collection);

  if (add_us && (flag & LIB_ID_CREATE_NO_USER_REFCOUNT) == 0) {
    id_us_plus(&ob->id);
  }

  if ((flag & LIB_ID_CREATE_NO_MAIN) == 0) {
    collection_tag_update_parent_recursive(bmain, collection, ID_RECALC_COPY_ON_WRITE);
  }

  if ((flag & LIB_ID_CREATE_NO_MAIN) == 0) {
    BKE_rigidbody_main_collection_object_add(bmain, collection, ob);
  }

  return true;
}

static bool collection_object_remove(Main *bmain,
                                     Collection *collection,
                                     Object *ob,
                                     const bool free_us)
{
  CollectionObject *cob = BLI_findptr(&collection->gobject, ob, offsetof(CollectionObject, ob));
  if (cob == NULL) {
    return false;
  }

  BLI_freelinkN(&collection->gobject, cob);
  BKE_collection_object_cache_free(collection);

  if (free_us) {
    BKE_id_free_us(bmain, ob);
  }
  else {
    id_us_min(&ob->id);
  }

  collection_tag_update_parent_recursive(bmain, collection, ID_RECALC_COPY_ON_WRITE);

  return true;
}

/**
 * Add object to collection
 */
bool BKE_collection_object_add(Main *bmain, Collection *collection, Object *ob)
{
  if (ELEM(NULL, collection, ob)) {
    return false;
  }

  collection = collection_parent_editable_find_recursive(collection);

  /* Only case where this pointer can be NULL is when scene itself is linked, this case should
   * never be reached. */
  BLI_assert(collection != NULL);
  if (collection == NULL) {
    return false;
  }

  if (!collection_object_add(bmain, collection, ob, 0, true)) {
    return false;
  }

  if (BKE_collection_is_in_scene(collection)) {
    BKE_main_collection_sync(bmain);
  }

  return true;
}

/**
 * Add \a ob_dst to all scene collections that reference object \a ob_src is in.
 * Used for copying objects.
 *
 * Logic is very similar to #BKE_collection_add_from_object()
 */
void BKE_collection_object_add_from(Main *bmain, Scene *scene, Object *ob_src, Object *ob_dst)
{
  bool is_instantiated = false;

  FOREACH_SCENE_COLLECTION_BEGIN (scene, collection) {
    if (!ID_IS_LINKED(collection) && !ID_IS_OVERRIDE_LIBRARY(collection) &&
        BKE_collection_has_object(collection, ob_src)) {
      collection_object_add(bmain, collection, ob_dst, 0, true);
      is_instantiated = true;
    }
  }
  FOREACH_SCENE_COLLECTION_END;

  if (!is_instantiated) {
    /* In case we could not find any non-linked collections in which instantiate our ob_dst,
     * fallback to scene's master collection... */
    collection_object_add(bmain, scene->master_collection, ob_dst, 0, true);
  }

  BKE_main_collection_sync(bmain);
}

/**
 * Remove object from collection.
 */
bool BKE_collection_object_remove(Main *bmain,
                                  Collection *collection,
                                  Object *ob,
                                  const bool free_us)
{
  if (ELEM(NULL, collection, ob)) {
    return false;
  }

  if (!collection_object_remove(bmain, collection, ob, free_us)) {
    return false;
  }

  if (BKE_collection_is_in_scene(collection)) {
    BKE_main_collection_sync(bmain);
  }

  return true;
}

/**
 * Remove object from all collections of scene
 * \param collection_skip: Don't remove base from this collection.
 */
static bool scene_collections_object_remove(
    Main *bmain, Scene *scene, Object *ob, const bool free_us, Collection *collection_skip)
{
  bool removed = false;

  if (collection_skip == NULL) {
    BKE_scene_remove_rigidbody_object(bmain, scene, ob, free_us);
  }

  FOREACH_SCENE_COLLECTION_BEGIN (scene, collection) {
    if (collection != collection_skip) {
      removed |= collection_object_remove(bmain, collection, ob, free_us);
    }
  }
  FOREACH_SCENE_COLLECTION_END;

  BKE_main_collection_sync(bmain);

  return removed;
}

/**
 * Remove object from all collections of scene
 */
bool BKE_scene_collections_object_remove(Main *bmain, Scene *scene, Object *ob, const bool free_us)
{
  return scene_collections_object_remove(bmain, scene, ob, free_us, NULL);
}

/*
 * Remove all NULL objects from collections.
 * This is used for library remapping, where these pointers have been set to NULL.
 * Otherwise this should never happen.
 */
static void collection_object_remove_nulls(Collection *collection)
{
  bool changed = false;

  for (CollectionObject *cob = collection->gobject.first, *cob_next = NULL; cob; cob = cob_next) {
    cob_next = cob->next;

    if (cob->ob == NULL) {
      BLI_freelinkN(&collection->gobject, cob);
      changed = true;
    }
  }

  if (changed) {
    BKE_collection_object_cache_free(collection);
  }
}

void BKE_collections_object_remove_nulls(Main *bmain)
{
  for (Scene *scene = bmain->scenes.first; scene; scene = scene->id.next) {
    collection_object_remove_nulls(scene->master_collection);
  }

  for (Collection *collection = bmain->collections.first; collection;
       collection = collection->id.next) {
    collection_object_remove_nulls(collection);
  }
}

static void collection_null_children_remove(Collection *collection)
{
  for (CollectionChild *child = collection->children.first, *child_next = NULL; child;
       child = child_next) {
    child_next = child->next;

    if (child->collection == NULL) {
      BLI_freelinkN(&collection->children, child);
    }
  }
}

static void collection_missing_parents_remove(Collection *collection)
{
  for (CollectionParent *parent = collection->parents.first, *parent_next; parent != NULL;
       parent = parent_next) {
    parent_next = parent->next;
    if ((parent->collection == NULL) || !collection_find_child(parent->collection, collection)) {
      BLI_freelinkN(&collection->parents, parent);
    }
  }
}

/**
 * Remove all NULL children from parent collections of changed \a collection.
 * This is used for library remapping, where these pointers have been set to NULL.
 * Otherwise this should never happen.
 *
 * \note caller must ensure #BKE_main_collection_sync_remap() is called afterwards!
 *
 * \param collection: may be \a NULL,
 * in which case whole \a bmain database of collections is checked.
 */
void BKE_collections_child_remove_nulls(Main *bmain, Collection *collection)
{
  if (collection == NULL) {
    /* We need to do the checks in two steps when more than one collection may be involved,
     * otherwise we can miss some cases...
     * Also, master collections are not in bmain, so we also need to loop over scenes.
     */
    for (collection = bmain->collections.first; collection != NULL;
         collection = collection->id.next) {
      collection_null_children_remove(collection);
    }
    for (Scene *scene = bmain->scenes.first; scene != NULL; scene = scene->id.next) {
      collection_null_children_remove(scene->master_collection);
    }

    for (collection = bmain->collections.first; collection != NULL;
         collection = collection->id.next) {
      collection_missing_parents_remove(collection);
    }
    for (Scene *scene = bmain->scenes.first; scene != NULL; scene = scene->id.next) {
      collection_missing_parents_remove(scene->master_collection);
    }
  }
  else {
    for (CollectionParent *parent = collection->parents.first, *parent_next; parent;
         parent = parent_next) {
      parent_next = parent->next;

      collection_null_children_remove(parent->collection);

      if (!collection_find_child(parent->collection, collection)) {
        BLI_freelinkN(&collection->parents, parent);
      }
    }
  }
}

/**
 * Move object from a collection into another
 *
 * If source collection is NULL move it from all the existing collections.
 */
void BKE_collection_object_move(
    Main *bmain, Scene *scene, Collection *collection_dst, Collection *collection_src, Object *ob)
{
  /* In both cases we first add the object, then remove it from the other collections.
   * Otherwise we lose the original base and whether it was active and selected. */
  if (collection_src != NULL) {
    if (BKE_collection_object_add(bmain, collection_dst, ob)) {
      BKE_collection_object_remove(bmain, collection_src, ob, false);
    }
  }
  else {
    /* Adding will fail if object is already in collection.
     * However we still need to remove it from the other collections. */
    BKE_collection_object_add(bmain, collection_dst, ob);
    scene_collections_object_remove(bmain, scene, ob, false, collection_dst);
  }
}

/** \} */

/* -------------------------------------------------------------------- */
/** \name Collection Scene Membership
 * \{ */

bool BKE_collection_is_in_scene(Collection *collection)
{
  if (collection->flag & COLLECTION_IS_MASTER) {
    return true;
  }

  LISTBASE_FOREACH (CollectionParent *, cparent, &collection->parents) {
    if (BKE_collection_is_in_scene(cparent->collection)) {
      return true;
    }
  }

  return false;
}

void BKE_collections_after_lib_link(Main *bmain)
{
  /* Need to update layer collections because objects might have changed
   * in linked files, and because undo push does not include updated base
   * flags since those are refreshed after the operator completes. */
  BKE_main_collection_sync(bmain);
}

/** \} */

/* -------------------------------------------------------------------- */
/** \name Collection Children
 * \{ */

static bool collection_instance_find_recursive(Collection *collection,
                                               Collection *instance_collection)
{
  LISTBASE_FOREACH (CollectionObject *, collection_object, &collection->gobject) {
    if (collection_object->ob != NULL &&
        /* Object from a given collection should never instantiate that collection either. */
        ELEM(collection_object->ob->instance_collection, instance_collection, collection)) {
      return true;
    }
  }

  LISTBASE_FOREACH (CollectionChild *, collection_child, &collection->children) {
    if (collection_instance_find_recursive(collection_child->collection, instance_collection)) {
      return true;
    }
  }

  return false;
}

/**
 * Find potential cycles in collections.
 *
 * \param new_ancestor: the potential new owner of given \a collection,
 * or the collection to check if the later is NULL.
 * \param collection: the collection we want to add to \a new_ancestor,
 * may be NULL if we just want to ensure \a new_ancestor does not already have cycles.
 * \return true if a cycle is found.
 */
bool BKE_collection_cycle_find(Collection *new_ancestor, Collection *collection)
{
  if (collection == new_ancestor) {
    return true;
  }

  if (collection == NULL) {
    collection = new_ancestor;
  }

  LISTBASE_FOREACH (CollectionParent *, parent, &new_ancestor->parents) {
    if (BKE_collection_cycle_find(parent->collection, collection)) {
      return true;
    }
  }

  /* Find possible objects in collection or its children, that would instantiate the given ancestor
   * collection (that would also make a fully invalid cycle of dependencies) .*/
  return collection_instance_find_recursive(collection, new_ancestor);
}

static bool collection_instance_fix_recursive(Collection *parent_collection,
                                              Collection *collection)
{
  bool cycles_found = false;

  LISTBASE_FOREACH (CollectionObject *, collection_object, &parent_collection->gobject) {
    if (collection_object->ob != NULL &&
        collection_object->ob->instance_collection == collection) {
      id_us_min(&collection->id);
      collection_object->ob->instance_collection = NULL;
      cycles_found = true;
    }
  }

  LISTBASE_FOREACH (CollectionChild *, collection_child, &parent_collection->children) {
    if (collection_instance_fix_recursive(collection_child->collection, collection)) {
      cycles_found = true;
    }
  }

  return cycles_found;
}

static bool collection_cycle_fix_recursive(Main *bmain,
                                           Collection *parent_collection,
                                           Collection *collection)
{
  bool cycles_found = false;

  LISTBASE_FOREACH_MUTABLE (CollectionParent *, parent, &parent_collection->parents) {
    if (BKE_collection_cycle_find(parent->collection, collection)) {
      BKE_collection_child_remove(bmain, parent->collection, parent_collection);
      cycles_found = true;
    }
    else if (collection_cycle_fix_recursive(bmain, parent->collection, collection)) {
      cycles_found = true;
    }
  }

  return cycles_found;
}

/**
 * Find and fix potential cycles in collections.
 *
 * \param collection: The collection to check for existing cycles.
 * \return true if cycles are found and fixed.
 */
bool BKE_collection_cycles_fix(Main *bmain, Collection *collection)
{
  return collection_cycle_fix_recursive(bmain, collection, collection) ||
         collection_instance_fix_recursive(collection, collection);
}

static CollectionChild *collection_find_child(Collection *parent, Collection *collection)
{
  return BLI_findptr(&parent->children, collection, offsetof(CollectionChild, collection));
}

static bool collection_find_child_recursive(Collection *parent, Collection *collection)
{
  LISTBASE_FOREACH (CollectionChild *, child, &parent->children) {
    if (child->collection == collection) {
      return true;
    }

    if (collection_find_child_recursive(child->collection, collection)) {
      return true;
    }
  }

  return false;
}

bool BKE_collection_has_collection(Collection *parent, Collection *collection)
{
  return collection_find_child_recursive(parent, collection);
}

static CollectionParent *collection_find_parent(Collection *child, Collection *collection)
{
  return BLI_findptr(&child->parents, collection, offsetof(CollectionParent, collection));
}

static bool collection_child_add(Collection *parent,
                                 Collection *collection,
                                 const int flag,
                                 const bool add_us)
{
  CollectionChild *child = collection_find_child(parent, collection);
  if (child) {
    return false;
  }
  if (BKE_collection_cycle_find(parent, collection)) {
    return false;
  }

  child = MEM_callocN(sizeof(CollectionChild), "CollectionChild");
  child->collection = collection;
  BLI_addtail(&parent->children, child);

  /* Don't add parent links for depsgraph datablocks, these are not kept in sync. */
  if ((flag & LIB_ID_CREATE_NO_MAIN) == 0) {
    CollectionParent *cparent = MEM_callocN(sizeof(CollectionParent), "CollectionParent");
    cparent->collection = parent;
    BLI_addtail(&collection->parents, cparent);
  }

  if (add_us) {
    id_us_plus(&collection->id);
  }

  BKE_collection_object_cache_free(parent);

  return true;
}

static bool collection_child_remove(Collection *parent, Collection *collection)
{
  CollectionChild *child = collection_find_child(parent, collection);
  if (child == NULL) {
    return false;
  }

  CollectionParent *cparent = collection_find_parent(collection, parent);
  BLI_freelinkN(&collection->parents, cparent);
  BLI_freelinkN(&parent->children, child);

  id_us_min(&collection->id);

  BKE_collection_object_cache_free(parent);

  return true;
}

bool BKE_collection_child_add(Main *bmain, Collection *parent, Collection *child)
{
  if (!collection_child_add(parent, child, 0, true)) {
    return false;
  }

  BKE_main_collection_sync(bmain);
  return true;
}

bool BKE_collection_child_add_no_sync(Collection *parent, Collection *child)
{
  return collection_child_add(parent, child, 0, true);
}

bool BKE_collection_child_remove(Main *bmain, Collection *parent, Collection *child)
{
  if (!collection_child_remove(parent, child)) {
    return false;
  }

  BKE_main_collection_sync(bmain);
  return true;
}

/**
 * Rebuild parent relationships from child ones, for all children of given \a collection.
 *
 * \note Given collection is assumed to already have valid parents.
 */
void BKE_collection_parent_relations_rebuild(Collection *collection)
{
  for (CollectionChild *child = collection->children.first, *child_next = NULL; child;
       child = child_next) {
    child_next = child->next;

    if (child->collection == NULL || BKE_collection_cycle_find(collection, child->collection)) {
      BLI_freelinkN(&collection->children, child);
    }
    else {
      CollectionParent *cparent = MEM_callocN(sizeof(CollectionParent), __func__);
      cparent->collection = collection;
      BLI_addtail(&child->collection->parents, cparent);
    }
  }
}

static void collection_parents_rebuild_recursive(Collection *collection)
{
  BKE_collection_parent_relations_rebuild(collection);
  collection->tag &= ~COLLECTION_TAG_RELATION_REBUILD;

  for (CollectionChild *child = collection->children.first; child != NULL; child = child->next) {
    collection_parents_rebuild_recursive(child->collection);
  }
}

/**
 * Rebuild parent relationships from child ones, for all collections in given \a bmain.
 */
void BKE_main_collections_parent_relations_rebuild(Main *bmain)
{
  /* Only collections not in bmain (master ones in scenes) have no parent... */
  for (Collection *collection = bmain->collections.first; collection != NULL;
       collection = collection->id.next) {
    BLI_freelistN(&collection->parents);

    collection->tag |= COLLECTION_TAG_RELATION_REBUILD;
  }

  /* Scene's master collections will be 'root' parent of most of our collections, so start with
   * them. */
  for (Scene *scene = bmain->scenes.first; scene != NULL; scene = scene->id.next) {
    /* This function can be called from readfile.c, when this pointer is not guaranteed to be NULL.
     */
    if (scene->master_collection != NULL) {
      collection_parents_rebuild_recursive(scene->master_collection);
    }
  }

  /* We may have parent chains outside of scene's master_collection context? At least, readfile's
   * lib_link_collection_data() seems to assume that, so do the same here. */
  for (Collection *collection = bmain->collections.first; collection != NULL;
       collection = collection->id.next) {
    if (collection->tag & COLLECTION_TAG_RELATION_REBUILD) {
      /* Note: we do not have easy access to 'which collections is root' info in that case, which
       * means test for cycles in collection relationships may fail here. I don't think that is an
       * issue in practice here, but worth keeping in mind... */
      collection_parents_rebuild_recursive(collection);
    }
  }
}

/** \} */

/* -------------------------------------------------------------------- */
/** \name Collection Index
 * \{ */

static Collection *collection_from_index_recursive(Collection *collection,
                                                   const int index,
                                                   int *index_current)
{
  if (index == (*index_current)) {
    return collection;
  }

  (*index_current)++;

  LISTBASE_FOREACH (CollectionChild *, child, &collection->children) {
    Collection *nested = collection_from_index_recursive(child->collection, index, index_current);
    if (nested != NULL) {
      return nested;
    }
  }
  return NULL;
}

/**
 * Return Scene Collection for a given index.
 *
 * The index is calculated from top to bottom counting the children before the siblings.
 */
Collection *BKE_collection_from_index(Scene *scene, const int index)
{
  int index_current = 0;
  Collection *master_collection = scene->master_collection;
  return collection_from_index_recursive(master_collection, index, &index_current);
}

static bool collection_objects_select(ViewLayer *view_layer, Collection *collection, bool deselect)
{
  bool changed = false;

  if (collection->flag & COLLECTION_RESTRICT_SELECT) {
    return false;
  }

  LISTBASE_FOREACH (CollectionObject *, cob, &collection->gobject) {
    Base *base = BKE_view_layer_base_find(view_layer, cob->ob);

    if (base) {
      if (deselect) {
        if (base->flag & BASE_SELECTED) {
          base->flag &= ~BASE_SELECTED;
          changed = true;
        }
      }
      else {
        if ((base->flag & BASE_SELECTABLE) && !(base->flag & BASE_SELECTED)) {
          base->flag |= BASE_SELECTED;
          changed = true;
        }
      }
    }
  }

  LISTBASE_FOREACH (CollectionChild *, child, &collection->children) {
    if (collection_objects_select(view_layer, collection, deselect)) {
      changed = true;
    }
  }

  return changed;
}

/**
 * Select all the objects in this Collection (and its nested collections) for this ViewLayer.
 * Return true if any object was selected.
 */
bool BKE_collection_objects_select(ViewLayer *view_layer, Collection *collection, bool deselect)
{
  LayerCollection *layer_collection = BKE_layer_collection_first_from_scene_collection(view_layer,
                                                                                       collection);

  if (layer_collection != NULL) {
    return BKE_layer_collection_objects_select(view_layer, layer_collection, deselect);
  }

  return collection_objects_select(view_layer, collection, deselect);
}

/** \} */

/* -------------------------------------------------------------------- */
/** \name Collection move (outliner drag & drop)
 * \{ */

/* Local temporary storage for layer collection flags. */
typedef struct LayerCollectionFlag {
  struct LayerCollectionFlag *next, *prev;
  /** The view layer for the collections being moved, NULL for their children. */
  ViewLayer *view_layer;
  /** The original #LayerCollection's collection field. */
  Collection *collection;
  /** The original #LayerCollection's flag. */
  int flag;
  /** Corresponds to #LayerCollection->layer_collections. */
  ListBase children;
} LayerCollectionFlag;

static void layer_collection_flags_store_recursive(const LayerCollection *layer_collection,
                                                   LayerCollectionFlag *flag)
{
  flag->collection = layer_collection->collection;
  flag->flag = layer_collection->flag;

  LISTBASE_FOREACH (const LayerCollection *, child, &layer_collection->layer_collections) {
    LayerCollectionFlag *child_flag = MEM_callocN(sizeof(LayerCollectionFlag), __func__);
    BLI_addtail(&flag->children, child_flag);
    layer_collection_flags_store_recursive(child, child_flag);
  }
}

/**
 * For every view layer, find the \a collection and save flags
 * for it and its children in a temporary tree structure.
 */
static void layer_collection_flags_store(Main *bmain,
                                         const Collection *collection,
                                         ListBase *r_layer_level_list)
{
  BLI_listbase_clear(r_layer_level_list);
  LISTBASE_FOREACH (Scene *, scene, &bmain->scenes) {
    LISTBASE_FOREACH (ViewLayer *, view_layer, &scene->view_layers) {
      LayerCollection *layer_collection = BKE_layer_collection_first_from_scene_collection(
          view_layer, collection);
      /* Skip this view layer if the collection isn't found for some reason. */
      if (layer_collection == NULL) {
        continue;
      }

      /* Store the flags for the collection and all of its children. */
      LayerCollectionFlag *flag = MEM_callocN(sizeof(LayerCollectionFlag), __func__);
      flag->view_layer = view_layer;

      /* Recursively save flags from collection children. */
      layer_collection_flags_store_recursive(layer_collection, flag);

      BLI_addtail(r_layer_level_list, flag);
    }
  }
}

static void layer_collection_flags_restore_recursive(LayerCollection *layer_collection,
                                                     LayerCollectionFlag *flag)
{
  /* There should be a flag struct for every layer collection. */
  BLI_assert(BLI_listbase_count(&layer_collection->layer_collections) ==
             BLI_listbase_count(&flag->children));
  /* The flag and the the layer collection should actually correspond. */
  BLI_assert(flag->collection == layer_collection->collection);

  LayerCollectionFlag *child_flag = flag->children.first;
  LISTBASE_FOREACH (LayerCollection *, child, &layer_collection->layer_collections) {
    layer_collection_flags_restore_recursive(child, child_flag);

    child_flag = child_flag->next;
  }
  BLI_freelistN(&flag->children);

  /* We treat exclude as a special case.
   *
   * If in a different view layer the parent collection was disabled (e.g., background)
   * and now we moved a new collection to be part of the background this collection should
   * probably be disabled.
   *
   * Note: If we were to also keep the exclude flag we would need to re-sync the collections.
   */
  layer_collection->flag = flag->flag | (layer_collection->flag & LAYER_COLLECTION_EXCLUDE);
}

/**
 * Restore a collection's (and its children's) flags for each view layer
 * from the structure built in #layer_collection_flags_store.
 */
static void layer_collection_flags_restore(ListBase *flags, const Collection *collection)
{
  LISTBASE_FOREACH (LayerCollectionFlag *, flag, flags) {
    ViewLayer *view_layer = flag->view_layer;
    /* The top level of flag structs must have this set. */
    BLI_assert(view_layer != NULL);

    LayerCollection *layer_collection = BKE_layer_collection_first_from_scene_collection(
        view_layer, collection);
    /* The flags should only be added if the collection is in the view layer. */
    BLI_assert(layer_collection != NULL);

    layer_collection_flags_restore_recursive(layer_collection, flag);
  }

  BLI_freelistN(flags);
}

bool BKE_collection_move(Main *bmain,
                         Collection *to_parent,
                         Collection *from_parent,
                         Collection *relative,
                         bool relative_after,
                         Collection *collection)
{
  if (collection->flag & COLLECTION_IS_MASTER) {
    return false;
  }
  if (BKE_collection_cycle_find(to_parent, collection)) {
    return false;
  }

  /* Move to new parent collection */
  if (from_parent) {
    collection_child_remove(from_parent, collection);
  }

  collection_child_add(to_parent, collection, 0, true);

  /* Move to specified location under parent. */
  if (relative) {
    CollectionChild *child = collection_find_child(to_parent, collection);
    CollectionChild *relative_child = collection_find_child(to_parent, relative);

    if (relative_child) {
      BLI_remlink(&to_parent->children, child);

      if (relative_after) {
        BLI_insertlinkafter(&to_parent->children, relative_child, child);
      }
      else {
        BLI_insertlinkbefore(&to_parent->children, relative_child, child);
      }

      BKE_collection_object_cache_free(to_parent);
    }
  }

  /* Make sure we store the flag of the layer collections before we remove and re-create them.
   * Otherwise they will get lost and everything will be copied from the new parent collection.
   * Don't use flag syncing when moving a collection to a different scene, as it no longer exists
   * in the same view layers anyway. */
  const bool do_flag_sync = BKE_scene_find_from_collection(bmain, to_parent) ==
                            BKE_scene_find_from_collection(bmain, collection);
  ListBase layer_flags;
  if (do_flag_sync) {
    layer_collection_flags_store(bmain, collection, &layer_flags);
  }

  /* Create and remove layer collections. */
  BKE_main_collection_sync(bmain);

  /* Restore the original layer collection flags. */
  if (do_flag_sync) {
    layer_collection_flags_restore(&layer_flags, collection);
  }

  /* We need to sync it again to pass the correct flags to the collections objects. */
  BKE_main_collection_sync(bmain);

  return true;
}

/** \} */

/* -------------------------------------------------------------------- */
/** \name Iterators
 * \{ */

/* scene collection iteractor */

typedef struct CollectionsIteratorData {
  Scene *scene;
  void **array;
  int tot, cur;
} CollectionsIteratorData;

static void scene_collection_callback(Collection *collection,
                                      BKE_scene_collections_Cb callback,
                                      void *data)
{
  callback(collection, data);

  LISTBASE_FOREACH (CollectionChild *, child, &collection->children) {
    scene_collection_callback(child->collection, callback, data);
  }
}

static void scene_collections_count(Collection *UNUSED(collection), void *data)
{
  int *tot = data;
  (*tot)++;
}

static void scene_collections_build_array(Collection *collection, void *data)
{
  Collection ***array = data;
  **array = collection;
  (*array)++;
}

static void scene_collections_array(Scene *scene, Collection ***collections_array, int *tot)
{
  Collection *collection;
  Collection **array;

  *collections_array = NULL;
  *tot = 0;

  if (scene == NULL) {
    return;
  }

  collection = scene->master_collection;
  BLI_assert(collection != NULL);
  scene_collection_callback(collection, scene_collections_count, tot);

  if (*tot == 0) {
    return;
  }

  *collections_array = array = MEM_mallocN(sizeof(Collection *) * (*tot), "CollectionArray");
  scene_collection_callback(collection, scene_collections_build_array, &array);
}

/**
 * Only use this in non-performance critical situations
 * (it iterates over all scene collections twice)
 */
void BKE_scene_collections_iterator_begin(BLI_Iterator *iter, void *data_in)
{
  Scene *scene = data_in;
  CollectionsIteratorData *data = MEM_callocN(sizeof(CollectionsIteratorData), __func__);

  data->scene = scene;
  iter->data = data;
  iter->valid = true;

  scene_collections_array(scene, (Collection ***)&data->array, &data->tot);
  BLI_assert(data->tot != 0);

  data->cur = 0;
  iter->current = data->array[data->cur];
}

void BKE_scene_collections_iterator_next(struct BLI_Iterator *iter)
{
  CollectionsIteratorData *data = iter->data;

  if (++data->cur < data->tot) {
    iter->current = data->array[data->cur];
  }
  else {
    iter->valid = false;
  }
}

void BKE_scene_collections_iterator_end(struct BLI_Iterator *iter)
{
  CollectionsIteratorData *data = iter->data;

  if (data) {
    if (data->array) {
      MEM_freeN(data->array);
    }
    MEM_freeN(data);
  }
  iter->valid = false;
}

/* scene objects iterator */

typedef struct SceneObjectsIteratorData {
  GSet *visited;
  CollectionObject *cob_next;
  BLI_Iterator scene_collection_iter;
} SceneObjectsIteratorData;

void BKE_scene_objects_iterator_begin(BLI_Iterator *iter, void *data_in)
{
  Scene *scene = data_in;
  SceneObjectsIteratorData *data = MEM_callocN(sizeof(SceneObjectsIteratorData), __func__);
  iter->data = data;

  /* lookup list ot make sure each object is object called once */
  data->visited = BLI_gset_ptr_new(__func__);

  /* we wrap the scenecollection iterator here to go over the scene collections */
  BKE_scene_collections_iterator_begin(&data->scene_collection_iter, scene);

  Collection *collection = data->scene_collection_iter.current;
  data->cob_next = collection->gobject.first;

  BKE_scene_objects_iterator_next(iter);
}

/**
 * Ensures we only get each object once, even when included in several collections.
 */
static CollectionObject *object_base_unique(GSet *gs, CollectionObject *cob)
{
  for (; cob != NULL; cob = cob->next) {
    Object *ob = cob->ob;
    void **ob_key_p;
    if (!BLI_gset_ensure_p_ex(gs, ob, &ob_key_p)) {
      *ob_key_p = ob;
      return cob;
    }
  }
  return NULL;
}

void BKE_scene_objects_iterator_next(BLI_Iterator *iter)
{
  SceneObjectsIteratorData *data = iter->data;
  CollectionObject *cob = data->cob_next ? object_base_unique(data->visited, data->cob_next) :
                                           NULL;

  if (cob) {
    data->cob_next = cob->next;
    iter->current = cob->ob;
  }
  else {
    /* if this is the last object of this ListBase look at the next Collection */
    Collection *collection;
    BKE_scene_collections_iterator_next(&data->scene_collection_iter);
    do {
      collection = data->scene_collection_iter.current;
      /* get the first unique object of this collection */
      CollectionObject *new_cob = object_base_unique(data->visited, collection->gobject.first);
      if (new_cob) {
        data->cob_next = new_cob->next;
        iter->current = new_cob->ob;
        return;
      }
      BKE_scene_collections_iterator_next(&data->scene_collection_iter);
    } while (data->scene_collection_iter.valid);

    if (!data->scene_collection_iter.valid) {
      iter->valid = false;
    }
  }
}

void BKE_scene_objects_iterator_end(BLI_Iterator *iter)
{
  SceneObjectsIteratorData *data = iter->data;
  if (data) {
    BKE_scene_collections_iterator_end(&data->scene_collection_iter);
    BLI_gset_free(data->visited, NULL);
    MEM_freeN(data);
  }
}

/** \} */