third_party/blink/renderer/modules/accessibility/ax_relation_cache.h

// Copyright 2017 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.

#ifndef THIRD_PARTY_BLINK_RENDERER_MODULES_ACCESSIBILITY_AX_RELATION_CACHE_H_
#define THIRD_PARTY_BLINK_RENDERER_MODULES_ACCESSIBILITY_AX_RELATION_CACHE_H_

#include "base/macros.h"
#include "third_party/blink/renderer/modules/accessibility/ax_object_cache_impl.h"
#include "third_party/blink/renderer/modules/modules_export.h"
#include "third_party/blink/renderer/platform/wtf/allocator/allocator.h"
#include "third_party/blink/renderer/platform/wtf/hash_map.h"
#include "third_party/blink/renderer/platform/wtf/hash_set.h"

namespace blink {

// This class should only be used from inside the accessibility directory.
class AXRelationCache {
  USING_FAST_MALLOC(AXRelationCache);

 public:
  explicit AXRelationCache(AXObjectCacheImpl*);
  virtual ~AXRelationCache();

  // Scan the initial document.
  void Init();

  // Returns true if the given object's position in the tree was due to
  // aria-owns.
  bool IsAriaOwned(const AXObject*) const;

  // Returns the parent of the given object due to aria-owns.
  AXObject* GetAriaOwnedParent(const AXObject*) const;

  // Given an object that has an aria-owns attributes, and a vector of ids from
  // the value of that attribute, updates the internal state to reflect the new
  // set of children owned by this object, returning the result in
  // |ownedChildren|. The result is validated - illegal, duplicate, or cyclical
  // references have been removed.
  void UpdateAriaOwns(const AXObject* owner,
                      const Vector<String>& id_vector,
                      HeapVector<Member<AXObject>>& owned_children);

  // Return true if any label ever pointed to the element via the for attribute.
  bool MayHaveHTMLLabelViaForAttribute(const HTMLElement&);

  // Given an element in the DOM tree that was either just added or whose id
  // just changed, check to see if another object wants to be its parent due to
  // aria-owns. If so, update the tree by calling childrenChanged() on the
  // potential owner, possibly reparenting this element.
  void UpdateRelatedTree(Node*);

  // Remove given AXID from cache.
  void RemoveAXID(AXID);

  // Update map of ids to related objects.
  // If one or more ids aren't found, they're added to a lookup table so that if
  // an element with that id appears later, it can be added when you call
  // UpdateRelatedTree.
  void UpdateReverseRelations(const AXObject* relation_source,
                              const Vector<String>& target_ids);

  void LabelChanged(Node*);

 private:
  // If any object is related to this object via <label for>, aria-owns,
  // aria-describedby or aria-labeledby, update the text for the related object.
  void UpdateRelatedText(Node*);

  bool IsValidOwnsRelation(AXObject* owner, AXObject* child) const;
  void UnmapOwnedChildren(const AXObject* owner, Vector<AXID>);
  void MapOwnedChildren(const AXObject* owner, Vector<AXID>);
  void GetReverseRelated(Node*, HeapVector<Member<AXObject>>& sources);

  WeakPersistent<AXObjectCacheImpl> object_cache_;

  // Map from the AXID of the owner to the AXIDs of the children.
  // This is a validated map, it doesn't contain illegal, duplicate,
  // or cyclical matches, or references to IDs that don't exist.
  HashMap<AXID, Vector<AXID>> aria_owner_to_children_mapping_;

  // Map from the AXID of a child to the AXID of the parent that owns it.
  HashMap<AXID, AXID> aria_owned_child_to_owner_mapping_;

  // Map from the AXID of a child to the AXID of its real parent in the tree if
  // we ignored aria-owns. This is needed in case the owner no longer wants to
  // own it.
  HashMap<AXID, AXID> aria_owned_child_to_real_parent_mapping_;

  // Reverse relation map from an ID (the ID attribute of a DOM element) to the
  // set of elements that at some time pointed to that ID via aria-owns,
  // aria-labelledby, aria-desribedby. This is *unvalidated*, it includes
  // possible extras and duplicates.
  // This is used so that:
  // - When an element with an ID is added to the tree or changes its ID, we can
  //   quickly determine if it affects an aria-owns relationship.
  // - When text changes, we can recompute any label or description based on it
  //   and fire the appropriate change events.
  HashMap<String, HashSet<AXID>> id_attr_to_related_mapping_;

  // HTML id attributes that at one time havehad a <label for> pointing to it.
  // IDs are not necessarily removed from this set. It is not necessary to
  // remove IDs as false positives are ok. Being able to determine that a
  // labelable element has never had an associated label allows the accessible
  // name calculation to be optimized.
  HashSet<AtomicString> all_previously_seen_label_target_ids_;

  // Helpers that call back into object cache
  AXObject* ObjectFromAXID(AXID) const;
  AXObject* GetOrCreate(Node*);
  AXObject* Get(Node*);
  void ChildrenChanged(AXObject*);
  void TextChanged(AXObject*);

  DISALLOW_COPY_AND_ASSIGN(AXRelationCache);
};

}  // namespace blink

#endif