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diff --git a/layout/base/AccessibleCaretManager.h b/layout/base/AccessibleCaretManager.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef AccessibleCaretManager_h
+#define AccessibleCaretManager_h
+
+#include "AccessibleCaret.h"
+
+#include "mozilla/Attributes.h"
+#include "mozilla/dom/CaretStateChangedEvent.h"
+#include "mozilla/dom/MouseEventBinding.h"
+#include "mozilla/EnumSet.h"
+#include "mozilla/EventForwards.h"
+#include "mozilla/RefPtr.h"
+#include "mozilla/UniquePtr.h"
+#include "nsCOMPtr.h"
+#include "nsCoord.h"
+#include "nsIFrame.h"
+#include "nsISelectionListener.h"
+
+class nsFrameSelection;
+class nsIContent;
+
+struct nsPoint;
+
+namespace mozilla {
+class PresShell;
+namespace dom {
+class Element;
+class Selection;
+}  // namespace dom
+
+// -----------------------------------------------------------------------------
+// AccessibleCaretManager does not deal with events or callbacks directly. It
+// relies on AccessibleCaretEventHub to call its public methods to do the work.
+// All codes needed to interact with PresShell, Selection, and AccessibleCaret
+// should be written in AccessibleCaretManager.
+//
+// None the public methods in AccessibleCaretManager will flush layout or style
+// prior to performing its task. The caller must ensure the layout is up to
+// date.
+//
+// Please see the wiki page for more information.
+// https://wiki.mozilla.org/AccessibleCaret
+//
+class AccessibleCaretManager {
+ public:
+  explicit AccessibleCaretManager(PresShell* aPresShell);
+  virtual ~AccessibleCaretManager() = default;
+
+  // Called by AccessibleCaretEventHub to inform us that PresShell is destroyed.
+  void Terminate();
+
+  // The aPoint in the following public methods should be relative to root
+  // frame.
+
+  // Press caret on the given point. Return NS_OK if the point is actually on
+  // one of the carets.
+  MOZ_CAN_RUN_SCRIPT
+  virtual nsresult PressCaret(const nsPoint& aPoint, EventClassID aEventClass);
+
+  // Drag caret to the given point. It's required to call PressCaret()
+  // beforehand.
+  MOZ_CAN_RUN_SCRIPT
+  virtual nsresult DragCaret(const nsPoint& aPoint);
+
+  // Release caret from he previous press action. It's required to call
+  // PressCaret() beforehand.
+  MOZ_CAN_RUN_SCRIPT
+  virtual nsresult ReleaseCaret();
+
+  // A quick single tap on caret on given point without dragging.
+  MOZ_CAN_RUN_SCRIPT
+  virtual nsresult TapCaret(const nsPoint& aPoint);
+
+  // Select a word or bring up paste shortcut (if Gaia is listening) under the
+  // given point.
+  MOZ_CAN_RUN_SCRIPT
+  virtual nsresult SelectWordOrShortcut(const nsPoint& aPoint);
+
+  // Handle scroll-start event.
+  MOZ_CAN_RUN_SCRIPT
+  virtual void OnScrollStart();
+
+  // Handle scroll-end event.
+  MOZ_CAN_RUN_SCRIPT
+  virtual void OnScrollEnd();
+
+  // Handle ScrollPositionChanged from nsIScrollObserver. This might be called
+  // at anytime, not necessary between OnScrollStart and OnScrollEnd.
+  MOZ_CAN_RUN_SCRIPT
+  virtual void OnScrollPositionChanged();
+
+  // Handle reflow event from nsIReflowObserver.
+  MOZ_CAN_RUN_SCRIPT
+  virtual void OnReflow();
+
+  // Handle blur event from nsFocusManager.
+  MOZ_CAN_RUN_SCRIPT
+  virtual void OnBlur();
+
+  // Handle NotifySelectionChanged event from nsISelectionListener.
+  // @param aReason potentially multiple of the reasons defined in
+  //                nsISelectionListener.idl.
+  MOZ_CAN_RUN_SCRIPT
+  virtual nsresult OnSelectionChanged(dom::Document* aDoc, dom::Selection* aSel,
+                                      int16_t aReason);
+  // Handle key event.
+  MOZ_CAN_RUN_SCRIPT
+  virtual void OnKeyboardEvent();
+
+  // The canvas frame holding the accessible caret anonymous content elements
+  // was reconstructed, resulting in the content elements getting cloned.
+  virtual void OnFrameReconstruction();
+
+  // Update the manager with the last input source that was observed. This
+  // is used in part to determine if the carets should be shown or hidden.
+  void SetLastInputSource(uint16_t aInputSource);
+
+  // Returns True indicating that we should disable APZ to avoid jumpy carets.
+  bool ShouldDisableApz() const;
+
+ protected:
+  // This enum representing the number of AccessibleCarets on the screen.
+  enum class CaretMode : uint8_t {
+    // No caret on the screen.
+    None,
+
+    // One caret, i.e. the selection is collapsed.
+    Cursor,
+
+    // Two carets, i.e. the selection is not collapsed.
+    Selection
+  };
+
+  friend std::ostream& operator<<(std::ostream& aStream,
+                                  const CaretMode& aCaretMode);
+
+  enum class UpdateCaretsHint : uint8_t {
+    // Update everything including appearance and position.
+    Default,
+
+    // Update everything while respecting the old appearance. For example, if
+    // the caret in cursor mode is hidden due to blur, do not change its
+    // appearance to Normal.
+    RespectOldAppearance,
+
+    // No CaretStateChangedEvent will be dispatched in the end of
+    // UpdateCarets().
+    DispatchNoEvent,
+  };
+
+  using UpdateCaretsHintSet = mozilla::EnumSet<UpdateCaretsHint>;
+
+  friend std::ostream& operator<<(std::ostream& aStream,
+                                  const UpdateCaretsHint& aResult);
+
+  // Update carets based on current selection status. This function will flush
+  // layout, so caller must ensure the PresShell is still valid after calling
+  // this method.
+  MOZ_CAN_RUN_SCRIPT
+  void UpdateCarets(
+      const UpdateCaretsHintSet& aHints = UpdateCaretsHint::Default);
+
+  // Force hiding all carets regardless of the current selection status, and
+  // dispatch CaretStateChangedEvent if one of the carets is logically-visible.
+  MOZ_CAN_RUN_SCRIPT
+  void HideCaretsAndDispatchCaretStateChangedEvent();
+
+  MOZ_CAN_RUN_SCRIPT
+  void UpdateCaretsForCursorMode(const UpdateCaretsHintSet& aHints);
+
+  MOZ_CAN_RUN_SCRIPT
+  void UpdateCaretsForSelectionMode(const UpdateCaretsHintSet& aHints);
+
+  // A helper function to update mShouldDisableApz.
+  void UpdateShouldDisableApz();
+
+  // Provide haptic / touch feedback, primarily for select on longpress.
+  void ProvideHapticFeedback();
+
+  // Get the nearest enclosing focusable frame of aFrame.
+  // @return focusable frame if there is any; nullptr otherwise.
+  nsIFrame* GetFocusableFrame(nsIFrame* aFrame) const;
+
+  // Change focus to aFrame if it isn't nullptr. Otherwise, clear the old focus
+  // then re-focus the window.
+  MOZ_CAN_RUN_SCRIPT_BOUNDARY void ChangeFocusToOrClearOldFocus(
+      nsIFrame* aFrame) const;
+
+  MOZ_CAN_RUN_SCRIPT
+  nsresult SelectWord(nsIFrame* aFrame, const nsPoint& aPoint) const;
+  MOZ_CAN_RUN_SCRIPT void SetSelectionDragState(bool aState) const;
+
+  // Return true if the candidate string is a phone number.
+  bool IsPhoneNumber(nsAString& aCandidate) const;
+
+  // Extend the current selection forwards and backwards if it's already a
+  // phone number.
+  MOZ_CAN_RUN_SCRIPT
+  void SelectMoreIfPhoneNumber() const;
+
+  // Extend the current phone number selection in the requested direction.
+  MOZ_CAN_RUN_SCRIPT
+  void ExtendPhoneNumberSelection(const nsAString& aDirection) const;
+
+  void SetSelectionDirection(nsDirection aDir) const;
+
+  // If aDirection is eDirNext, get the frame for the range start in the first
+  // range from the current selection, and return the offset into that frame as
+  // well as the range start content and the content offset. Otherwise, get the
+  // frame and the offset for the range end in the last range instead.
+  nsIFrame* GetFrameForFirstRangeStartOrLastRangeEnd(
+      nsDirection aDirection, int32_t* aOutOffset,
+      nsIContent** aOutContent = nullptr,
+      int32_t* aOutContentOffset = nullptr) const;
+
+  MOZ_CAN_RUN_SCRIPT nsresult DragCaretInternal(const nsPoint& aPoint);
+  nsPoint AdjustDragBoundary(const nsPoint& aPoint) const;
+
+  // Start the selection scroll timer if the caret is being dragged out of
+  // the scroll port.
+  MOZ_CAN_RUN_SCRIPT
+  void StartSelectionAutoScrollTimer(const nsPoint& aPoint) const;
+  void StopSelectionAutoScrollTimer() const;
+
+  void ClearMaintainedSelection() const;
+
+  enum class Terminated : bool { No, Yes };
+
+  static dom::Element* GetEditingHostForFrame(const nsIFrame* aFrame);
+  dom::Selection* GetSelection() const;
+  already_AddRefed<nsFrameSelection> GetFrameSelection() const;
+
+  MOZ_CAN_RUN_SCRIPT
+  nsAutoString StringifiedSelection() const;
+
+  // Get the union of all the child frame scrollable overflow rects for aFrame,
+  // which is used as a helper function to restrict the area where the caret can
+  // be dragged. Returns the rect relative to aFrame.
+  nsRect GetAllChildFrameRectsUnion(nsIFrame* aFrame) const;
+
+  // Restrict the active caret's dragging position based on
+  // sCaretsAllowDraggingAcrossOtherCaret. If the active caret is the first
+  // caret, the `limit` will be the previous character of the second caret.
+  // Otherwise, the `limit` will be the next character of the first caret.
+  //
+  // @param aOffsets is the new position of the active caret, and it will be set
+  // to the `limit` when 1) sCaretsAllowDraggingAcrossOtherCaret is false and
+  // it's being dragged past the limit. 2) sCaretsAllowDraggingAcrossOtherCaret
+  // is true and the active caret's position is the same as the inactive's
+  // position.
+  // @return true if the aOffsets is suitable for changing the selection.
+  bool RestrictCaretDraggingOffsets(nsIFrame::ContentOffsets& aOffsets);
+
+  // ---------------------------------------------------------------------------
+  // The following functions are made virtual for stubbing or mocking in gtest.
+  //
+  // @return Yes if Terminate() had been called.
+  virtual Terminated IsTerminated() const {
+    return mPresShell ? Terminated::No : Terminated::Yes;
+  }
+
+  // Get caret mode based on current selection.
+  virtual CaretMode GetCaretMode() const;
+
+  // @return true if aStartFrame comes before aEndFrame.
+  virtual bool CompareTreePosition(nsIFrame* aStartFrame,
+                                   nsIFrame* aEndFrame) const;
+
+  // Check if the two carets is overlapping to become tilt.
+  // @return true if the two carets become tilt; false, otherwise.
+  virtual bool UpdateCaretsForOverlappingTilt();
+
+  // Make the two carets always tilt.
+  virtual void UpdateCaretsForAlwaysTilt(const nsIFrame* aStartFrame,
+                                         const nsIFrame* aEndFrame);
+
+  // Check whether AccessibleCaret is displayable in cursor mode or not.
+  // @param aOutFrame returns frame of the cursor if it's displayable.
+  // @param aOutOffset returns frame offset as well.
+  virtual bool IsCaretDisplayableInCursorMode(
+      nsIFrame** aOutFrame = nullptr, int32_t* aOutOffset = nullptr) const;
+
+  virtual bool HasNonEmptyTextContent(nsINode* aNode) const;
+
+  // This function will flush layout, so caller must ensure the PresShell is
+  // still valid after calling this method.
+  MOZ_CAN_RUN_SCRIPT
+  virtual void DispatchCaretStateChangedEvent(dom::CaretChangedReason aReason);
+
+  // ---------------------------------------------------------------------------
+  // Member variables
+  //
+  nscoord mOffsetYToCaretLogicalPosition = NS_UNCONSTRAINEDSIZE;
+
+  // AccessibleCaretEventHub owns us by a UniquePtr. When it's destroyed, we'll
+  // also be destroyed. No need to worry if we outlive mPresShell.
+  //
+  // mPresShell will be set to nullptr in Terminate(). Therefore mPresShell is
+  // nullptr either we are in gtest or PresShell::IsDestroying() is true.
+  PresShell* MOZ_NON_OWNING_REF mPresShell = nullptr;
+
+  // First caret is attached to nsCaret in cursor mode, and is attached to
+  // selection highlight as the left caret in selection mode.
+  UniquePtr<AccessibleCaret> mFirstCaret;
+
+  // Second caret is used solely in selection mode, and is attached to selection
+  // highlight as the right caret.
+  UniquePtr<AccessibleCaret> mSecondCaret;
+
+  // The caret being pressed or dragged.
+  AccessibleCaret* mActiveCaret = nullptr;
+
+  // The caret mode since last update carets.
+  CaretMode mLastUpdateCaretMode = CaretMode::None;
+
+  // The last input source that the event hub saw. We use this to decide whether
+  // or not show the carets when the selection is updated, as we want to hide
+  // the carets for mouse-triggered selection changes but show them for other
+  // input types such as touch.
+  uint16_t mLastInputSource = dom::MouseEvent_Binding::MOZ_SOURCE_UNKNOWN;
+
+  // Set to true in OnScrollStart() and set to false in OnScrollEnd().
+  bool mIsScrollStarted = false;
+
+  class LayoutFlusher final {
+   public:
+    ~LayoutFlusher();
+
+    // This method could kill the shell, so callers to methods that call
+    // MaybeFlush should ensure the event hub that owns us is still alive.
+    //
+    // See the mRefCnt assertions in AccessibleCaretEventHub.
+    //
+    // @return aAccessibleCaretManager.IsTerminated().
+    [[nodiscard]] MOZ_CAN_RUN_SCRIPT Terminated
+    MaybeFlush(const AccessibleCaretManager& aAccessibleCaretManager);
+
+    // Set to false to disallow flushing layout in some callbacks such as
+    // OnReflow(), OnScrollStart(), OnScrollStart(), or
+    // OnScrollPositionChanged().
+    bool mAllowFlushing = true;
+
+  private:
+    // Whether we're flushing layout, used for sanity-checking.
+    bool mFlushing = false;
+  };
+
+  LayoutFlusher mLayoutFlusher;
+
+  // Set to True if one of the caret's position is changed in last update.
+  bool mIsCaretPositionChanged = false;
+
+  class DesiredAsyncPanZoomState final {
+   public:
+    void Update(const AccessibleCaretManager& aAccessibleCaretManager);
+
+    enum class Value : bool { Disabled, Enabled };
+
+    Value Get() const { return mValue; }
+
+   private:
+    Value mValue = Value::Enabled;
+  };
+
+  DesiredAsyncPanZoomState mDesiredAsyncPanZoomState;
+
+  static const int32_t kAutoScrollTimerDelay = 30;
+
+  // Clicking on the boundary of input or textarea will move the caret to the
+  // front or end of the content. To avoid this, we need to deflate the content
+  // boundary by 61 app units, which is 1 pixel + 1 app unit as defined in
+  // AppUnit.h.
+  static const int32_t kBoundaryAppUnits = 61;
+
+  enum ScriptUpdateMode : int32_t {
+    // By default, always hide carets for selection changes due to JS calls.
+    kScriptAlwaysHide,
+    // Update any visible carets for selection changes due to JS calls,
+    // but don't show carets if carets are hidden.
+    kScriptUpdateVisible,
+    // Always show carets for selection changes due to JS calls.
+    kScriptAlwaysShow
+  };
+};
+
+std::ostream& operator<<(std::ostream& aStream,
+                         const AccessibleCaretManager::CaretMode& aCaretMode);
+
+std::ostream& operator<<(
+    std::ostream& aStream,
+    const AccessibleCaretManager::UpdateCaretsHint& aResult);
+
+}  // namespace mozilla
+
+#endif  // AccessibleCaretManager_h