1 files changed, 66 insertions, 13 deletions

diff --git a/include/cru/common/StringUtil.hpp b/include/cru/common/StringUtil.hpp
index a44ae6b4..714f1d49 100644
--- a/include/cru/common/StringUtil.hpp
+++ b/include/cru/common/StringUtil.hpp
@@ -3,37 +3,90 @@
 
 namespace cru {
 using CodePoint = std::int32_t;
-constexpr CodePoint k_code_point_end = -1;
+constexpr CodePoint k_invalid_code_point = -1;
 
 class TextEncodeException : public std::runtime_error {
  public:
   using runtime_error::runtime_error;
 };
 
-class Utf8Iterator : public Object {
+inline bool IsSurrogatePair(char16_t c) { return c >= 0xD800 && c <= 0xDFFF; }
+
+inline bool IsSurrogatePairLeading(char16_t c) {
+  return c >= 0xD800 && c <= 0xDBFF;
+}
+
+inline bool IsSurrogatePairTrailing(char16_t c) {
+  return c >= 0xDC00 && c <= 0xDFFF;
+}
+
+class Utf16Iterator : public Object {
  public:
-  explicit Utf8Iterator(const std::string_view& string) : string_(string) {}
-  Utf8Iterator(const std::string_view& string, Index position)
-      : string_(string), position_(position) {}
+  explicit Utf16Iterator(std::u16string_view string)
+      : string_(std::move(string)) {}
+  Utf16Iterator(std::u16string_view string, Index position)
+      : string_(std::move(string)), position_(position) {}
 
-  CRU_DEFAULT_COPY(Utf8Iterator)
-  CRU_DEFAULT_MOVE(Utf8Iterator)
+  CRU_DEFAULT_COPY(Utf16Iterator)
+  CRU_DEFAULT_MOVE(Utf16Iterator)
 
-  ~Utf8Iterator() = default;
+  ~Utf16Iterator() = default;
 
  public:
-  void SetToHead() { position_ = 0; }
+  void SetPositionToHead() { position_ = 0; }
   void SetPosition(Index position) { position_ = position; }
 
-  // Advance current position and get next code point. Return k_code_point_end
-  // if there is no next code unit(point). Throw TextEncodeException if decoding
-  // fails.
+  // Backward current position and get previous code point. Return
+  // k_invalid_code_point if reach head. Throw TextEncodeException if encounter
+  // encoding problem.
+  CodePoint Previous();
+
+  // Advance current position and get next code point. Return
+  // k_invalid_code_point if reach tail. Throw TextEncodeException if encounter
+  // encoding problem.
   CodePoint Next();
 
   Index CurrentPosition() const { return this->position_; }
 
  private:
-  std::string_view string_;
+  std::u16string_view string_;
   Index position_ = 0;
 };
+
+Index PreviousIndex(std::u16string_view string, Index current);
+Index NextIndex(std::u16string_view string, Index current);
+
+std::string ToUtf8(const std::u16string& s);
+inline std::string ToUtf8(std::u16string_view s) {
+  return ToUtf8(std::u16string{s});
+}
+
+// class Utf8Iterator : public Object {
+//  public:
+//   explicit Utf8Iterator(const std::string_view& string) : string_(string) {}
+//   Utf8Iterator(const std::string_view& string, Index position)
+//       : string_(string), position_(position) {}
+
+//   CRU_DEFAULT_COPY(Utf8Iterator)
+//   CRU_DEFAULT_MOVE(Utf8Iterator)
+
+//   ~Utf8Iterator() = default;
+
+//  public:
+//   void SetToHead() { position_ = 0; }
+//   void SetPosition(Index position) { position_ = position; }
+
+//   // Advance current position and get next code point. Return
+//   k_invalid_code_point
+//   // if there is no next code unit(point). Throw TextEncodeException if
+//   decoding
+//   // fails.
+//   CodePoint Next();
+
+//   Index CurrentPosition() const { return this->position_; }
+
+//  private:
+//   std::string_view string_;
+//   Index position_ = 0;
+// };
 }  // namespace cru