ax_tree.cc

// Copyright 2013 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "ui/accessibility/ax_tree.h"

#include <stddef.h>

#include <set>

#include "base/logging.h"
#include "base/strings/stringprintf.h"
#include "ui/accessibility/ax_node.h"
#include "ui/accessibility/ax_table_info.h"
#include "ui/gfx/transform.h"

namespace ui {

namespace {

std::string TreeToStringHelper(AXNode* node, int indent) {
  std::string result = std::string(2 * indent, ' ');
  result += node->data().ToString() + "\n";
  for (int i = 0; i < node->child_count(); ++i)
    result += TreeToStringHelper(node->ChildAtIndex(i), indent + 1);
  return result;
}

template <typename K, typename V>
bool KeyValuePairsKeysMatch(std::vector<std::pair<K, V>> pairs1,
                            std::vector<std::pair<K, V>> pairs2) {
  if (pairs1.size() != pairs2.size())
    return false;
  for (size_t i = 0; i < pairs1.size(); ++i) {
    if (pairs1[i].first != pairs2[i].first)
      return false;
  }
  return true;
}

template <typename K, typename V>
std::map<K, V> MapFromKeyValuePairs(std::vector<std::pair<K, V>> pairs) {
  std::map<K, V> result;
  for (size_t i = 0; i < pairs.size(); ++i)
    result[pairs[i].first] = pairs[i].second;
  return result;
}

// Given two vectors of <K, V> key, value pairs representing an "old" vs "new"
// state, or "before" vs "after", calls a callback function for each key that
// changed value. Note that if an attribute is removed, that will result in
// a call to the callback with the value changing from the previous value to
// |empty_value|, and similarly when an attribute is added.
template <typename K, typename V, typename F>
void CallIfAttributeValuesChanged(const std::vector<std::pair<K, V>>& pairs1,
                                  const std::vector<std::pair<K, V>>& pairs2,
                                  const V& empty_value,
                                  F callback) {
  // Fast path - if they both have the same keys in the same order.
  if (KeyValuePairsKeysMatch(pairs1, pairs2)) {
    for (size_t i = 0; i < pairs1.size(); ++i) {
      if (pairs1[i].second != pairs2[i].second)
        callback(pairs1[i].first, pairs1[i].second, pairs2[i].second);
    }
    return;
  }

  // Slower path - they don't have the same keys in the same order, so
  // check all keys against each other, using maps to prevent this from
  // becoming O(n^2) as the size grows.
  auto map1 = MapFromKeyValuePairs(pairs1);
  auto map2 = MapFromKeyValuePairs(pairs2);
  for (size_t i = 0; i < pairs1.size(); ++i) {
    const auto& new_iter = map2.find(pairs1[i].first);
    if (pairs1[i].second != empty_value && new_iter == map2.end())
      callback(pairs1[i].first, pairs1[i].second, empty_value);
  }

  for (size_t i = 0; i < pairs2.size(); ++i) {
    const auto& iter = map1.find(pairs2[i].first);
    if (iter == map1.end())
      callback(pairs2[i].first, empty_value, pairs2[i].second);
    else if (iter->second != pairs2[i].second)
      callback(pairs2[i].first, iter->second, pairs2[i].second);
  }
}

}  // namespace

// Intermediate state to keep track of during a tree update.
struct AXTreeUpdateState {
  AXTreeUpdateState() : new_root(nullptr) {}
  // Returns whether this update changes |node|.
  bool HasChangedNode(const AXNode* node) {
    return changed_node_ids.find(node->id()) != changed_node_ids.end();
  }

  // Returns whether this update removes |node|.
  bool HasRemovedNode(const AXNode* node) {
    return removed_node_ids.find(node->id()) != removed_node_ids.end();
  }

  // During an update, this keeps track of all nodes that have been
  // implicitly referenced as part of this update, but haven't been
  // updated yet. It's an error if there are any pending nodes at the
  // end of Unserialize.
  std::set<AXNode*> pending_nodes;

  // This is similar to above, but we store node ids here because this list gets
  // generated before any nodes get created or re-used. Its purpose is to allow
  // us to know what nodes will be updated so we can make more intelligent
  // decisions about when to notify delegates of removals or reparenting.
  std::set<int> changed_node_ids;

  // Keeps track of new nodes created during this update.
  std::set<AXNode*> new_nodes;

  // The new root in this update, if any.
  AXNode* new_root;

  // Keeps track of any nodes removed. Used to identify re-parented nodes.
  std::set<int> removed_node_ids;
};

AXTreeDelegate::AXTreeDelegate() = default;
AXTreeDelegate::~AXTreeDelegate() = default;

AXTree::AXTree() {
  AXNodeData root;
  root.id = -1;

  AXTreeUpdate initial_state;
  initial_state.root_id = -1;
  initial_state.nodes.push_back(root);
  CHECK(Unserialize(initial_state)) << error();
}

AXTree::AXTree(const AXTreeUpdate& initial_state) {
  CHECK(Unserialize(initial_state)) << error();
}

AXTree::~AXTree() {
  if (root_)
    DestroyNodeAndSubtree(root_, nullptr);
  for (auto& entry : table_info_map_)
    delete entry.second;
  table_info_map_.clear();
}

void AXTree::SetDelegate(AXTreeDelegate* delegate) {
  delegate_ = delegate;
}

AXNode* AXTree::GetFromId(int32_t id) const {
  auto iter = id_map_.find(id);
  return iter != id_map_.end() ? iter->second : nullptr;
}

void AXTree::UpdateData(const AXTreeData& new_data) {
  if (data_ == new_data)
    return;

  AXTreeData old_data = data_;
  data_ = new_data;
  if (delegate_)
    delegate_->OnTreeDataChanged(this, old_data, new_data);
}

gfx::RectF AXTree::RelativeToTreeBounds(const AXNode* node,
                                        gfx::RectF bounds,
                                        bool* offscreen,
                                        bool clip_bounds) const {
  // If |bounds| is uninitialized, which is not the same as empty,
  // start with the node bounds.
  if (bounds.width() == 0 && bounds.height() == 0) {
    bounds = node->data().location;

    // If the node bounds is empty (either width or height is zero),
    // try to compute good bounds from the children.
    if (bounds.IsEmpty()) {
      for (size_t i = 0; i < node->children().size(); i++) {
        ui::AXNode* child = node->children()[i];
        bounds.Union(GetTreeBounds(child));
      }
      if (bounds.width() > 0 && bounds.height() > 0) {
        return bounds;
      }
    }
  } else {
    bounds.Offset(node->data().location.x(), node->data().location.y());
  }

  while (node != nullptr) {
    if (node->data().transform)
      node->data().transform->TransformRect(&bounds);
    const AXNode* container;

    // Normally we apply any transforms and offsets for each node and
    // then walk up to its offset container - however, if the node has
    // no width or height, walk up to its nearest ancestor until we find
    // one that has bounds.
    if (bounds.width() == 0 && bounds.height() == 0)
      container = node->parent();
    else
      container = GetFromId(node->data().offset_container_id);
    if (!container && container != root())
      container = root();
    if (!container || container == node)
      break;

    gfx::RectF container_bounds = container->data().location;
    bounds.Offset(container_bounds.x(), container_bounds.y());

    // If we don't have any size yet, take the size from this ancestor.
    // The rationale is that it's not useful to the user for an object to
    // have no width or height and it's probably a bug; it's better to
    // reflect the bounds of the nearest ancestor rather than a 0x0 box.
    // Tag this node as 'offscreen' because it has no true size, just a
    // size inherited from the ancestor.
    if (bounds.width() == 0 && bounds.height() == 0) {
      bounds.set_size(container_bounds.size());
      if (offscreen != nullptr)
        *offscreen |= true;
    }

    int scroll_x = 0;
    int scroll_y = 0;
    if (container->data().GetIntAttribute(ax::mojom::IntAttribute::kScrollX,
                                          &scroll_x) &&
        container->data().GetIntAttribute(ax::mojom::IntAttribute::kScrollY,
                                          &scroll_y)) {
      bounds.Offset(-scroll_x, -scroll_y);
    }

    // Get the intersection between the bounds and the container.
    gfx::RectF intersection = bounds;
    intersection.Intersect(container_bounds);

    // Calculate the clipped bounds to determine offscreen state.
    gfx::RectF clipped = bounds;
    // If this is the root web area, make sure we clip the node to fit.
    if (container->data().GetBoolAttribute(
            ax::mojom::BoolAttribute::kClipsChildren)) {
      if (!intersection.IsEmpty()) {
        // We can simply clip it to the container.
        clipped = intersection;
      } else {
        // Totally offscreen. Find the nearest edge or corner.
        // Make the minimum dimension 1 instead of 0.
        if (clipped.x() >= container_bounds.width()) {
          clipped.set_x(container_bounds.right() - 1);
          clipped.set_width(1);
        } else if (clipped.x() + clipped.width() <= 0) {
          clipped.set_x(container_bounds.x());
          clipped.set_width(1);
        }
        if (clipped.y() >= container_bounds.height()) {
          clipped.set_y(container_bounds.bottom() - 1);
          clipped.set_height(1);
        } else if (clipped.y() + clipped.height() <= 0) {
          clipped.set_y(container_bounds.y());
          clipped.set_height(1);
        }
      }
    }

    if (clip_bounds)
      bounds = clipped;

    if (container->data().GetBoolAttribute(
            ax::mojom::BoolAttribute::kClipsChildren) &&
        intersection.IsEmpty() && !clipped.IsEmpty()) {
      // If it is offscreen with respect to its parent, and the node itself is
      // not empty, label it offscreen.
      // Here we are extending the definition of offscreen to include elements
      // that are clipped by their parents in addition to those clipped by
      // the rootWebArea.
      // No need to update |offscreen| if |intersection| is not empty, because
      // it should be false by default.
      if (offscreen != nullptr)
        *offscreen |= true;
    }

    node = container;
  }

  return bounds;
}

gfx::RectF AXTree::GetTreeBounds(const AXNode* node,
                                 bool* offscreen,
                                 bool clip_bounds) const {
  return RelativeToTreeBounds(node, gfx::RectF(), offscreen, clip_bounds);
}

std::set<int32_t> AXTree::GetReverseRelations(ax::mojom::IntAttribute attr,
                                              int32_t dst_id) const {
  DCHECK(IsNodeIdIntAttribute(attr));

  // Conceptually, this is the "const" version of:
  //   return int_reverse_relations_[attr][dst_id];
  const auto& attr_relations = int_reverse_relations_.find(attr);
  if (attr_relations != int_reverse_relations_.end()) {
    const auto& result = attr_relations->second.find(dst_id);
    if (result != attr_relations->second.end())
      return result->second;
  }
  return std::set<int32_t>();
}

std::set<int32_t> AXTree::GetReverseRelations(ax::mojom::IntListAttribute attr,
                                              int32_t dst_id) const {
  DCHECK(IsNodeIdIntListAttribute(attr));

  // Conceptually, this is the "const" version of:
  //   return intlist_reverse_relations_[attr][dst_id];
  const auto& attr_relations = intlist_reverse_relations_.find(attr);
  if (attr_relations != intlist_reverse_relations_.end()) {
    const auto& result = attr_relations->second.find(dst_id);
    if (result != attr_relations->second.end())
      return result->second;
  }
  return std::set<int32_t>();
}

std::set<int32_t> AXTree::GetNodeIdsForChildTreeId(
    AXTreeID child_tree_id) const {
  // Conceptually, this is the "const" version of:
  //   return child_tree_id_reverse_map_[child_tree_id];
  const auto& result = child_tree_id_reverse_map_.find(child_tree_id);
  if (result != child_tree_id_reverse_map_.end())
    return result->second;
  return std::set<int32_t>();
}

bool AXTree::Unserialize(const AXTreeUpdate& update) {
  AXTreeUpdateState update_state;
  int32_t old_root_id = root_ ? root_->id() : 0;

  // First, make a note of any nodes we will touch as part of this update.
  for (size_t i = 0; i < update.nodes.size(); ++i)
    update_state.changed_node_ids.insert(update.nodes[i].id);

  if (update.has_tree_data)
    UpdateData(update.tree_data);

  // We distinguish between updating the root, e.g. changing its children or
  // some of its attributes, or replacing the root completely.
  bool root_updated = false;
  if (update.node_id_to_clear != 0) {
    AXNode* node = GetFromId(update.node_id_to_clear);

    // Only destroy the root if the root was replaced and not if it's simply
    // updated. To figure out if  the root was simply updated, we compare the ID
    // of the new root with the existing root ID.
    if (node && node == root_) {
      if (update.root_id != old_root_id) {
        // Clear root_ before calling DestroySubtree so that root_ doesn't ever
        // point to an invalid node.
        AXNode* old_root = root_;
        root_ = nullptr;
        DestroySubtree(old_root, &update_state);
      } else {
        root_updated = true;
      }
    }

    // If the root has simply been updated, we treat it like an update to any
    // other node.
    if (node && root_ && (node != root_ || root_updated)) {
      for (int i = 0; i < node->child_count(); ++i)
        DestroySubtree(node->ChildAtIndex(i), &update_state);
      std::vector<AXNode*> children;
      node->SwapChildren(children);
      update_state.pending_nodes.insert(node);
    }
  }

  bool root_exists = GetFromId(update.root_id) != nullptr;
  for (size_t i = 0; i < update.nodes.size(); ++i) {
    bool is_new_root = !root_exists && update.nodes[i].id == update.root_id;
    if (!UpdateNode(update.nodes[i], is_new_root, &update_state))
      return false;
  }

  if (!root_) {
    error_ = "Tree has no root.";
    return false;
  }

  if (!update_state.pending_nodes.empty()) {
    error_ = "Nodes left pending by the update:";
    for (const AXNode* pending : update_state.pending_nodes)
      error_ += base::StringPrintf(" %d", pending->id());
    return false;
  }

  // Look for changes to nodes that are a descendant of a table,
  // and invalidate their table info if so.  We have to walk up the
  // ancestry of every node that was updated potentially, so keep track of
  // ids that were checked to eliminate duplicate work.
  std::set<int32_t> table_ids_checked;
  for (size_t i = 0; i < update.nodes.size(); ++i) {
    AXNode* node = GetFromId(update.nodes[i].id);
    while (node) {
      if (table_ids_checked.find(node->id()) != table_ids_checked.end())
        break;
      // Remove any table infos.
      const auto& table_info_entry = table_info_map_.find(node->id());
      if (table_info_entry != table_info_map_.end())
        table_info_entry->second->Invalidate();
      table_ids_checked.insert(node->id());
      node = node->parent();
    }
  }

  if (delegate_) {
    std::set<AXNode*>& new_nodes = update_state.new_nodes;
    std::vector<AXTreeDelegate::Change> changes;
    changes.reserve(update.nodes.size());
    for (size_t i = 0; i < update.nodes.size(); ++i) {
      AXNode* node = GetFromId(update.nodes[i].id);
      if (!node)
        continue;

      bool is_new_node = new_nodes.find(node) != new_nodes.end();
      bool is_reparented_node =
          is_new_node && update_state.HasRemovedNode(node);

      AXTreeDelegate::ChangeType change = AXTreeDelegate::NODE_CHANGED;
      if (is_new_node) {
        if (is_reparented_node) {
          // A reparented subtree is any new node whose parent either doesn't
          // exist, or whose parent is not new.
          // Note that we also need to check for the special case when we update
          // the root without replacing it.
          bool is_subtree = !node->parent() ||
                            new_nodes.find(node->parent()) == new_nodes.end() ||
                            (node->parent() == root_ && root_updated);
          change = is_subtree ? AXTreeDelegate::SUBTREE_REPARENTED
                              : AXTreeDelegate::NODE_REPARENTED;
        } else {
          // A new subtree is any new node whose parent is either not new, or
          // whose parent happens to be new only because it has been reparented.
          // Note that we also need to check for the special case when we update
          // the root without replacing it.
          bool is_subtree = !node->parent() ||
                            new_nodes.find(node->parent()) == new_nodes.end() ||
                            update_state.HasRemovedNode(node->parent()) ||
                            (node->parent() == root_ && root_updated);
          change = is_subtree ? AXTreeDelegate::SUBTREE_CREATED
                              : AXTreeDelegate::NODE_CREATED;
        }
      }
      changes.push_back(AXTreeDelegate::Change(node, change));
    }
    delegate_->OnAtomicUpdateFinished(
        this, root_->id() != old_root_id, changes);
  }

  return true;
}

AXTableInfo* AXTree::GetTableInfo(const AXNode* const_table_node) const {
  // Note: the const_casts are here because we want this function to be able
  // to be called from a const virtual function on AXNode. AXTableInfo is
  // computed on demand and cached, but that's an implementation detail
  // we want to hide from users of this API.
  AXNode* table_node = const_cast<AXNode*>(const_table_node);
  AXTree* tree = const_cast<AXTree*>(this);

  DCHECK(table_node);
  const auto& cached = table_info_map_.find(table_node->id());
  if (cached != table_info_map_.end()) {
    // Get existing table info, and update if invalid because the
    // tree has changed since the last time we accessed it.
    AXTableInfo* table_info = cached->second;
    if (!table_info->valid()) {
      bool success = table_info->Update();
      if (!success) {
        // If Update() returned false, this is no longer a valid table.
        // Remove it from the map.
        delete table_info;
        table_info_map_.erase(table_node->id());
      }
      // See note about const_cast, above.
      if (delegate_)
        delegate_->OnNodeChanged(tree, table_node);
    }
    return table_info;
  }

  AXTableInfo* table_info = AXTableInfo::Create(tree, table_node);
  if (!table_info)
    return nullptr;

  table_info_map_[table_node->id()] = table_info;
  if (delegate_)
    delegate_->OnNodeChanged(tree, table_node);

  return table_info;
}

std::string AXTree::ToString() const {
  return "AXTree" + data_.ToString() + "\n" + TreeToStringHelper(root_, 0);
}

AXNode* AXTree::CreateNode(AXNode* parent,
                           int32_t id,
                           int32_t index_in_parent,
                           AXTreeUpdateState* update_state) {
  AXNode* new_node = new AXNode(this, parent, id, index_in_parent);
  id_map_[new_node->id()] = new_node;
  if (delegate_) {
    if (update_state->HasChangedNode(new_node) &&
        !update_state->HasRemovedNode(new_node))
      delegate_->OnNodeCreated(this, new_node);
    else
      delegate_->OnNodeReparented(this, new_node);
  }
  return new_node;
}

bool AXTree::UpdateNode(const AXNodeData& src,
                        bool is_new_root,
                        AXTreeUpdateState* update_state) {
  // This method updates one node in the tree based on serialized data
  // received in an AXTreeUpdate. See AXTreeUpdate for pre and post
  // conditions.

  // Look up the node by id. If it's not found, then either the root
  // of the tree is being swapped, or we're out of sync with the source
  // and this is a serious error.
  AXNode* node = GetFromId(src.id);
  if (node) {
    update_state->pending_nodes.erase(node);

    // TODO(accessibility): CallNodeChangeCallbacks should not pass |node|,
    // since the tree and the node data are not yet in a consistent
    // state. Possibly only pass id.
    if (update_state->new_nodes.find(node) == update_state->new_nodes.end())
      CallNodeChangeCallbacks(node, src);
    UpdateReverseRelations(node, src);
    node->SetData(src);
  } else {
    if (!is_new_root) {
      error_ = base::StringPrintf(
          "%d is not in the tree and not the new root", src.id);
      return false;
    }

    update_state->new_root = CreateNode(nullptr, src.id, 0, update_state);
    node = update_state->new_root;
    update_state->new_nodes.insert(node);
    UpdateReverseRelations(node, src);
    node->SetData(src);
  }

  if (delegate_)
    delegate_->OnNodeChanged(this, node);

  // First, delete nodes that used to be children of this node but aren't
  // anymore.
  if (!DeleteOldChildren(node, src.child_ids, update_state)) {
    // If DeleteOldChildren failed, we need to carefully clean up before
    // returning false as well. In particular, if this node was a new root,
    // we need to safely destroy the whole tree.
    if (update_state->new_root) {
      AXNode* old_root = root_;
      root_ = nullptr;

      DestroySubtree(old_root, update_state);

      // Delete |node|'s subtree too as long as it wasn't already removed
      // or added elsewhere in the tree.
      if (update_state->removed_node_ids.find(src.id) ==
              update_state->removed_node_ids.end() &&
          update_state->new_nodes.find(node) != update_state->new_nodes.end()) {
        DestroySubtree(node, update_state);
      }
    }
    return false;
  }

  // Now build a new children vector, reusing nodes when possible,
  // and swap it in.
  std::vector<AXNode*> new_children;
  bool success = CreateNewChildVector(
      node, src.child_ids, &new_children, update_state);
  node->SwapChildren(new_children);

  // Update the root of the tree if needed.
  if (is_new_root) {
    // Make sure root_ always points to something valid or null_, even inside
    // DestroySubtree.
    AXNode* old_root = root_;
    root_ = node;
    if (old_root && old_root != node)
      DestroySubtree(old_root, update_state);
  }

  return success;
}

void AXTree::CallNodeChangeCallbacks(AXNode* node, const AXNodeData& new_data) {
  if (!delegate_)
    return;

  const AXNodeData& old_data = node->data();
  delegate_->OnNodeDataWillChange(this, old_data, new_data);

  if (old_data.role != new_data.role)
    delegate_->OnRoleChanged(this, node, old_data.role, new_data.role);

  if (old_data.state != new_data.state) {
    for (int32_t i = static_cast<int32_t>(ax::mojom::State::kNone) + 1;
         i <= static_cast<int32_t>(ax::mojom::State::kMaxValue); ++i) {
      ax::mojom::State state = static_cast<ax::mojom::State>(i);
      if (old_data.HasState(state) != new_data.HasState(state))
        delegate_->OnStateChanged(this, node, state, new_data.HasState(state));
    }
  }

  auto string_callback = [this, node](ax::mojom::StringAttribute attr,
                                      const std::string& old_string,
                                      const std::string& new_string) {
    delegate_->OnStringAttributeChanged(this, node, attr, old_string,
                                        new_string);
  };
  CallIfAttributeValuesChanged(old_data.string_attributes,
                               new_data.string_attributes, std::string(),
                               string_callback);

  auto bool_callback = [this, node](ax::mojom::BoolAttribute attr,
                                    const bool& old_bool,
                                    const bool& new_bool) {
    delegate_->OnBoolAttributeChanged(this, node, attr, new_bool);
  };
  CallIfAttributeValuesChanged(old_data.bool_attributes,
                               new_data.bool_attributes, false, bool_callback);

  auto float_callback = [this, node](ax::mojom::FloatAttribute attr,
                                     const float& old_float,
                                     const float& new_float) {
    delegate_->OnFloatAttributeChanged(this, node, attr, old_float, new_float);
  };
  CallIfAttributeValuesChanged(old_data.float_attributes,
                               new_data.float_attributes, 0.0f, float_callback);

  auto int_callback = [this, node](ax::mojom::IntAttribute attr,
                                   const int& old_int, const int& new_int) {
    delegate_->OnIntAttributeChanged(this, node, attr, old_int, new_int);
  };
  CallIfAttributeValuesChanged(old_data.int_attributes, new_data.int_attributes,
                               0, int_callback);

  auto intlist_callback = [this, node](
                              ax::mojom::IntListAttribute attr,
                              const std::vector<int32_t>& old_intlist,
                              const std::vector<int32_t>& new_intlist) {
    delegate_->OnIntListAttributeChanged(this, node, attr, old_intlist,
                                         new_intlist);
  };
  CallIfAttributeValuesChanged(old_data.intlist_attributes,
                               new_data.intlist_attributes,
                               std::vector<int32_t>(), intlist_callback);

  auto stringlist_callback =
      [this, node](ax::mojom::StringListAttribute attr,
                   const std::vector<std::string>& old_stringlist,
                   const std::vector<std::string>& new_stringlist) {
        delegate_->OnStringListAttributeChanged(this, node, attr,
                                                old_stringlist, new_stringlist);
      };
  CallIfAttributeValuesChanged(old_data.stringlist_attributes,
                               new_data.stringlist_attributes,
                               std::vector<std::string>(), stringlist_callback);
}

void AXTree::UpdateReverseRelations(AXNode* node, const AXNodeData& new_data) {
  const AXNodeData& old_data = node->data();
  int id = new_data.id;
  auto int_callback = [this, id](ax::mojom::IntAttribute attr,
                                 const int& old_id, const int& new_id) {
    if (!IsNodeIdIntAttribute(attr))
      return;

    // Remove old_id -> id from the map, and clear map keys if their
    // values are now empty.
    auto& map = int_reverse_relations_[attr];
    if (map.find(old_id) != map.end()) {
      map[old_id].erase(id);
      if (map[old_id].empty())
        map.erase(old_id);
    }

    // Add new_id -> id to the map, unless new_id is zero indicating that
    // we're only removing a relation.
    if (new_id)
      map[new_id].insert(id);
  };
  CallIfAttributeValuesChanged(old_data.int_attributes, new_data.int_attributes,
                               0, int_callback);

  auto intlist_callback = [this, id](ax::mojom::IntListAttribute attr,
                                     const std::vector<int32_t>& old_idlist,
                                     const std::vector<int32_t>& new_idlist) {
    if (!IsNodeIdIntListAttribute(attr))
      return;

    auto& map = intlist_reverse_relations_[attr];
    for (int32_t old_id : old_idlist) {
      if (map.find(old_id) != map.end()) {
        map[old_id].erase(id);
        if (map[old_id].empty())
          map.erase(old_id);
      }
    }
    for (int32_t new_id : new_idlist)
      intlist_reverse_relations_[attr][new_id].insert(id);
  };
  CallIfAttributeValuesChanged(old_data.intlist_attributes,
                               new_data.intlist_attributes,
                               std::vector<int32_t>(), intlist_callback);

  auto string_callback = [this, id](ax::mojom::StringAttribute attr,
                                    const std::string& old_string,
                                    const std::string& new_string) {
    if (attr == ax::mojom::StringAttribute::kChildTreeId) {
      // Remove old_string -> id from the map, and clear map keys if
      // their values are now empty.
      AXTreeID old_ax_tree_id = AXTreeID::FromString(old_string);
      if (child_tree_id_reverse_map_.find(old_ax_tree_id) !=
          child_tree_id_reverse_map_.end()) {
        child_tree_id_reverse_map_[old_ax_tree_id].erase(id);
        if (child_tree_id_reverse_map_[old_ax_tree_id].empty())
          child_tree_id_reverse_map_.erase(old_ax_tree_id);
      }

      // Add new_string -> id to the map, unless new_id is zero indicating that
      // we're only removing a relation.
      if (!new_string.empty()) {
        AXTreeID new_ax_tree_id = AXTreeID::FromString(new_string);
        child_tree_id_reverse_map_[new_ax_tree_id].insert(id);
      }
    }
  };

  CallIfAttributeValuesChanged(old_data.string_attributes,
                               new_data.string_attributes, std::string(),
                               string_callback);
}

void AXTree::DestroySubtree(AXNode* node,
                            AXTreeUpdateState* update_state) {
  DCHECK(update_state);
  if (delegate_) {
    if (!update_state->HasChangedNode(node))
      delegate_->OnSubtreeWillBeDeleted(this, node);
    else
      delegate_->OnSubtreeWillBeReparented(this, node);
  }
  DestroyNodeAndSubtree(node, update_state);
}

void AXTree::DestroyNodeAndSubtree(AXNode* node,
                                   AXTreeUpdateState* update_state) {
  // Clear out any reverse relations.
  AXNodeData empty_data;
  empty_data.id = node->id();
  UpdateReverseRelations(node, empty_data);

  // Remove any table infos.
  const auto& table_info_entry = table_info_map_.find(node->id());
  if (table_info_entry != table_info_map_.end()) {
    delete table_info_entry->second;
    table_info_map_.erase(node->id());
  }

  if (delegate_) {
    if (!update_state || !update_state->HasChangedNode(node))
      delegate_->OnNodeWillBeDeleted(this, node);
    else
      delegate_->OnNodeWillBeReparented(this, node);
  }
  id_map_.erase(node->id());
  for (int i = 0; i < node->child_count(); ++i)
    DestroyNodeAndSubtree(node->ChildAtIndex(i), update_state);
  if (update_state) {
    update_state->pending_nodes.erase(node);
    update_state->removed_node_ids.insert(node->id());
  }
  node->Destroy();
}

bool AXTree::DeleteOldChildren(AXNode* node,
                               const std::vector<int32_t>& new_child_ids,
                               AXTreeUpdateState* update_state) {
  // Create a set of child ids in |src| for fast lookup, and return false
  // if a duplicate is found;
  std::set<int32_t> new_child_id_set;
  for (size_t i = 0; i < new_child_ids.size(); ++i) {
    if (new_child_id_set.find(new_child_ids[i]) != new_child_id_set.end()) {
      error_ = base::StringPrintf("Node %d has duplicate child id %d",
                                  node->id(), new_child_ids[i]);
      return false;
    }
    new_child_id_set.insert(new_child_ids[i]);
  }

  // Delete the old children.
  const std::vector<AXNode*>& old_children = node->children();
  for (size_t i = 0; i < old_children.size(); ++i) {
    int old_id = old_children[i]->id();
    if (new_child_id_set.find(old_id) == new_child_id_set.end())
      DestroySubtree(old_children[i], update_state);
  }

  return true;
}

bool AXTree::CreateNewChildVector(AXNode* node,
                                  const std::vector<int32_t>& new_child_ids,
                                  std::vector<AXNode*>* new_children,
                                  AXTreeUpdateState* update_state) {
  bool success = true;
  for (size_t i = 0; i < new_child_ids.size(); ++i) {
    int32_t child_id = new_child_ids[i];
    int32_t index_in_parent = static_cast<int32_t>(i);
    AXNode* child = GetFromId(child_id);
    if (child) {
      if (child->parent() != node) {
        // This is a serious error - nodes should never be reparented.
        // If this case occurs, continue so this node isn't left in an
        // inconsistent state, but return failure at the end.
        error_ = base::StringPrintf(
            "Node %d reparented from %d to %d",
            child->id(),
            child->parent() ? child->parent()->id() : 0,
            node->id());
        success = false;
        continue;
      }
      child->SetIndexInParent(index_in_parent);
    } else {
      child = CreateNode(node, child_id, index_in_parent, update_state);
      update_state->pending_nodes.insert(child);
      update_state->new_nodes.insert(child);
    }
    new_children->push_back(child);
  }

  return success;
}

void AXTree::SetEnableExtraMacNodes(bool enabled) {
  DCHECK(enable_extra_mac_nodes_ != enabled);
  DCHECK_EQ(0U, table_info_map_.size());
  enable_extra_mac_nodes_ = enabled;
}

int32_t AXTree::GetNextNegativeInternalNodeId() {
  int32_t return_value = next_negative_internal_node_id_;
  next_negative_internal_node_id_--;
  if (next_negative_internal_node_id_ > 0)
    next_negative_internal_node_id_ = -1;
  return return_value;
}

}  // namespace ui