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 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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#ifndef THIRD_PARTY_BLINK_RENDERER_CORE_EDITING_ITERATORS_SIMPLIFIED_BACKWARDS_TEXT_ITERATOR_H_
#define THIRD_PARTY_BLINK_RENDERER_CORE_EDITING_ITERATORS_SIMPLIFIED_BACKWARDS_TEXT_ITERATOR_H_

#include "third_party/blink/renderer/core/editing/forward.h"
#include "third_party/blink/renderer/core/editing/iterators/backwards_text_buffer.h"
#include "third_party/blink/renderer/core/editing/iterators/fully_clipped_state_stack.h"
#include "third_party/blink/renderer/core/editing/iterators/text_iterator_behavior.h"
#include "third_party/blink/renderer/core/editing/iterators/text_iterator_text_state.h"
#include "third_party/blink/renderer/platform/heap/heap.h"

namespace blink {

class LayoutText;

// Iterates through the DOM range, returning all the text, and 0-length
// boundaries at points where replaced elements break up the text flow. The text
// comes back in chunks so as to optimize for performance of the iteration.
template <typename Strategy>
class SimplifiedBackwardsTextIteratorAlgorithm {
  STACK_ALLOCATED();

 public:
  // Note: Usage of |behavior| should be limited, e.g.
  //  - EmitsObjectReplacementCharacter
  //  - StopsOnFormControls
  // Please ask editing-dev if you want to use other behaviors.
  SimplifiedBackwardsTextIteratorAlgorithm(
      const EphemeralRangeTemplate<Strategy>&,
      const TextIteratorBehavior& = TextIteratorBehavior());

  bool AtEnd() const { return !text_state_.PositionNode() || should_stop_; }
  void Advance();

  int length() const { return text_state_.length(); }

  // Note: |characterAt()| returns characters in the reversed order, since
  // the iterator is backwards. For example, if the current text is "abc",
  // then |characterAt(0)| returns 'c'.
  UChar CharacterAt(unsigned index) const;

  const Node* GetNode() const { return node_; }

  // Calculate the minimum |actualLength >= minLength| such that code units
  // with offset range [position, position + actualLength) are whole code
  // points. Prepend these code points to |output| and return |actualLength|.
  int CopyTextTo(BackwardsTextBuffer* output,
                 int position,
                 int min_length) const;
  int CopyTextTo(BackwardsTextBuffer* output, int position = 0) const;

  // TODO(editing-dev): We should consider code sharing between |TextIterator|
  // and |SimplifiedBackwardsTextIterator| for
  //  - StartContainer()
  //  - EndOffset()
  //  - StartContainer()
  //  - EndPosition()
  // TODO(editing-dev): We should rename |StartContainer()| to
  // |CurrentContainer()| as |TextIterator|.
  const Node* StartContainer() const;
  int EndOffset() const;
  PositionTemplate<Strategy> StartPosition() const;
  PositionTemplate<Strategy> EndPosition() const;

 private:
  void Init(const Node* start_node,
            const Node* end_node,
            int start_offset,
            int end_offset);
  void ExitNode();
  bool HandleTextNode();
  LayoutText* HandleFirstLetter(int& start_offset, int& offset_in_node);
  bool HandleReplacedElement();
  bool HandleNonTextNode();
  bool AdvanceRespectingRange(const Node*);

  bool IsBetweenSurrogatePair(int position) const;

  // TODO(editing-dev): We should consider code sharing between |TextIterator|
  // and |SimplifiedBackwardsTextIterator| for
  //  - EnsurePositionContainer()
  //  - StartOffset()
  void EnsurePositionContainer() const;
  int StartOffset() const;

  TextIteratorBehavior behavior_;

  // Contains state of emitted text.
  TextIteratorTextState text_state_;

  // Current position, not necessarily of the text being returned, but position
  // as we walk through the DOM tree.
  Member<const Node> node_;
  int offset_;
  bool handled_node_;
  bool handled_children_;
  FullyClippedStateStackAlgorithm<Strategy> fully_clipped_stack_;

  // End of the range.
  Member<const Node> start_node_;
  int start_offset_;
  // Start of the range.
  Member<const Node> end_node_;
  int end_offset_;

  // Whether |node_| has advanced beyond the iteration range (i.e. start_node_).
  bool have_passed_start_node_;

  // Should handle first-letter layoutObject in the next call to handleTextNode.
  bool should_handle_first_letter_;

  // Used when behavior_.StopOnFormControls() is true to determine if the
  // iterator should keep advancing.
  bool should_stop_;
};

extern template class CORE_EXTERN_TEMPLATE_EXPORT
    SimplifiedBackwardsTextIteratorAlgorithm<EditingStrategy>;
extern template class CORE_EXTERN_TEMPLATE_EXPORT
    SimplifiedBackwardsTextIteratorAlgorithm<EditingInFlatTreeStrategy>;

using SimplifiedBackwardsTextIterator =
    SimplifiedBackwardsTextIteratorAlgorithm<EditingStrategy>;

}  // namespace blink

#endif  // THIRD_PARTY_BLINK_RENDERER_CORE_EDITING_ITERATORS_SIMPLIFIED_BACKWARDS_TEXT_ITERATOR_H_