Implementing directional selection strategy in Blink.

Source/core/editing/GranularityStrategy.h

Index: Source/core/editing/GranularityStrategy.h
diff --git a/Source/core/editing/GranularityStrategy.h b/Source/core/editing/GranularityStrategy.h
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+// 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/SelectionStrategy.h"
+#include "core/editing/VisibleSelection.h"
+
+namespace blink {
+
+class GranularityStrategy {
+public:
+    virtual ~GranularityStrategy();
+    virtual SelectionStrategy GetType() const = 0;
+    virtual void Clear() = 0;
+
+    // Calculates and returns the new selection based on the updated user
+    // selection extent |extentPosition| and the granularity strategy.
+    virtual VisibleSelection updateExtent(const VisiblePosition& extentPosition, const VisibleSelection&) = 0;
+
+protected:
+    GranularityStrategy();
+};
+
+// Always uses character granularity.
+class CharacterGranularityStrategy final : public GranularityStrategy {
+public:
+    CharacterGranularityStrategy();
+    ~CharacterGranularityStrategy() final;
+
+    // GranularityStrategy:
+    SelectionStrategy GetType() const final;
+    void Clear() final;
+    VisibleSelection updateExtent(const VisiblePosition& extentPosition, const VisibleSelection&) 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".
+class DirectionGranularityStrategy final : public GranularityStrategy {
+public:
+    DirectionGranularityStrategy();
+    ~DirectionGranularityStrategy() final;
+
+    // GranularityStrategy:
+    SelectionStrategy GetType() const final;
+    void Clear() final;
+    VisibleSelection updateExtent(const VisiblePosition&, const VisibleSelection&) final;
+
+private:
+    enum class BoundAdjust {CurrentPosIfOnBound, NextBoundIfOnBound};
+    enum class SearchDirection {SearchBackwards, SearchForward};
+
+    // Returns the next word boundary starting from |pos|. |direction| specifies
+    // the direction in which to search for the next bound. nextIfOnBound
+    // controls whether |pos| or the next boundary is returned when |pos| is
+    // located exactly on word boundary.
+    VisiblePosition nextWordBound(const VisiblePosition& /*pos*/, SearchDirection /*direction*/, BoundAdjust /*nextIfOnBound*/);
+
+    // Current selection granularity being used
+    TextGranularity m_granularity;
+    // Set to true if the selection was shrunk (without changing relative
+    // base/extent order) as a result of the most recent updateExtent call.
+    bool m_lastMoveShrunkSelection;
+};
+
+} // namespace blink
+
+#endif // GranularityStrategy_h