third_party/WebKit/Source/core/editing/GranularityStrategy.h

// Copyright 2015 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 GranularityStrategy_h
#define GranularityStrategy_h

#include "core/editing/Forward.h"
#include "core/editing/SelectionStrategy.h"
#include "platform/geometry/IntSize.h"
#include "platform/wtf/Allocator.h"

namespace blink {

class IntPoint;
class LocalFrame;

enum class TextGranularity;

class GranularityStrategy {
  USING_FAST_MALLOC(GranularityStrategy);

 public:
  virtual ~GranularityStrategy();
  virtual SelectionStrategy GetType() const = 0;
  virtual void Clear() = 0;

  // Calculates and returns the new selection based on the updated extent
  // location in absolute coordinates.
  virtual SelectionInDOMTree UpdateExtent(const IntPoint&, LocalFrame*) = 0;

 protected:
  GranularityStrategy();
};

// Always uses character granularity.
class CharacterGranularityStrategy final : public GranularityStrategy {
 public:
  CharacterGranularityStrategy();
  ~CharacterGranularityStrategy() final;

  // GranularityStrategy:
  SelectionStrategy GetType() const final;
  void Clear() final;
  SelectionInDOMTree UpdateExtent(const IntPoint&, LocalFrame*) final;
};

// "Expand by word, shrink by character" selection strategy.
// Uses character granularity when selection is shrinking. If the selection is
// expanding, granularity doesn't change until a word boundary is passed, after
// which the granularity switches to "word".
// In word granularity, the word is not selected until the extent point passes
// the middle of the word.
//
// The "offset" feature:
// The offset is the horizontal distance between the extent point (passed in
// updateExtent) and the end of the selection. In character granularity the
// offset is typically zero or near zero, however in word granularity it can be
// significant. When the offset is positive and the extent point moved to the
// left, the offset is preserved, i.e. the selection tracks the extent point
// with the constant offset. When the offset is positive and the extent point
// is moved to the right, the offset gets reduced. Selection will not grow
// until the offset is reduced all the way to zero.
//
// This behavior is best illustrated by an example:
//
// ^ marks base, | marks extent point, > marks selection end:
// Lorem ip^sum|> dolor sit amet, consectetur
//
// Move extent over the middle of "dolor". Granularity should change to word
// granularity and the selection end should jump to the end of the word.
// Lorem ip^sum dolo|r> sit amet, consectetur
//
// Move extent back one character. Granularity changes to "character". The
// selection end should move back one character as well. Note an offset between
// the extent and the selection end.
// Lorem ip^sum dol|o>r sit amet, consectetur
//
// Move extent forward one character. The offset is reduced to 0. Selection end
// doesn't change.
// Lorem ip^sum dolo|>r sit amet, consectetur
//
// Move forward one character. End moves with extent in character granularity.
// Lorem ip^sum dolor|> sit amet, consectetur
class DirectionGranularityStrategy final : public GranularityStrategy {
 public:
  DirectionGranularityStrategy();
  ~DirectionGranularityStrategy() final;

  // GranularityStrategy:
  SelectionStrategy GetType() const final;
  void Clear() final;
  SelectionInDOMTree UpdateExtent(const IntPoint&, LocalFrame*) final;

 private:
  enum class StrategyState {
    // Starting state.
    // Selection was cleared and there were no extent updates since then.
    // One an update is performed, the strategy goes into the Expanding
    // state unless the update shrinks the selection without changing
    // relative base/extent order, in which case the strategy goes into the
    // Shrinking state.
    kCleared,
    // Last time the selection was changed by updateExtent - it was expanded
    // or the relative base/extent order was changed.
    kExpanding,
    // Last time the selection was changed by updateExtent - it was shrunk
    // (without changing relative base/extent order).
    kShrinking
  };

  StrategyState state_;

  // Current selection granularity being used.
  TextGranularity granularity_;

  // Horizontal offset in pixels in absolute coordinates applied to the extent
  // point.
  int offset_;

  // This defines location of the offset-adjusted extent point (from the
  // latest updateExtent call) relative to the location of extent's
  // VisiblePosition. It is used to detect sub-position extent movement.
  IntSize diff_extent_point_from_extent_position_;
};

}  // namespace blink

#endif  // GranularityStrategy_h