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 // Created on: 2013-01-28
 // Created by: Kirill GAVRILOV
 // Copyright (c) 2013-2014 OPEN CASCADE SAS
 //
 // This file is part of Open CASCADE Technology software library.
 //
 // This library is free software; you can redistribute it and/or modify it under
 // the terms of the GNU Lesser General Public License version 2.1 as published
 // by the Free Software Foundation, with special exception defined in the file
 // OCCT_LGPL_EXCEPTION.txt. Consult the file LICENSE_LGPL_21.txt included in OCCT
 // distribution for complete text of the license and disclaimer of any warranty.
 //
 // Alternatively, this file may be used under the terms of Open CASCADE
 // commercial license or contractual agreement.
 
 #ifndef NCollection_UtfIterator_HeaderFile
 #define NCollection_UtfIterator_HeaderFile
 
 #include <Standard_Handle.hxx>
 
 //! Template class for Unicode strings support.
 //!
 //! It defines an iterator and provide correct way to read multi-byte text (UTF-8 and UTF-16)
 //! and convert it from one to another.
 //! The current value of iterator is returned as UTF-32 Unicode symbol.
 //!
 //! Here and below term "Unicode symbol" is used as
 //! synonym of "Unicode code point".
 template <typename Type>
 class NCollection_UtfIterator
 {
 
 public:
   //! Constructor.
   //! @param theString buffer to iterate
   NCollection_UtfIterator(const Type* theString)
       : myPosition(theString),
         myPosNext(theString),
         myCharIndex(0),
         myCharUtf32(0)
   {
     if (theString != nullptr)
     {
       ++(*this);
       myCharIndex = 0;
     }
   }
 
   //! Initialize iterator within specified NULL-terminated string.
   void Init(const Type* theString)
   {
     myPosition  = theString;
     myPosNext   = theString;
     myCharUtf32 = 0;
     if (theString != nullptr)
     {
       ++(*this);
     }
     myCharIndex = 0;
   }
 
   //! Pre-increment operator. Reads the next unicode symbol.
   //! Notice - no protection against overrun!
   NCollection_UtfIterator& operator++()
   {
     myPosition = myPosNext;
     ++myCharIndex;
     readNext(static_cast<const typename CharTypeChooser<Type>::type*>(nullptr));
     return *this;
   }
 
   //! Post-increment operator.
   //! Notice - no protection against overrun!
   NCollection_UtfIterator operator++(int)
   {
     NCollection_UtfIterator aCopy = *this;
     ++*this;
     return aCopy;
   }
 
   //! Equality operator.
   constexpr bool operator==(const NCollection_UtfIterator& theRight) const noexcept
   {
     return myPosition == theRight.myPosition;
   }
 
   //! Return true if Unicode symbol is within valid range.
   constexpr bool IsValid() const noexcept { return myCharUtf32 <= UTF32_MAX_LEGAL; }
 
   //! Dereference operator.
   //! @return the UTF-32 codepoint of the symbol currently pointed by iterator.
   constexpr char32_t operator*() const noexcept { return myCharUtf32; }
 
   //! Buffer-fetching getter.
   constexpr const Type* BufferHere() const noexcept { return myPosition; }
 
   //! Buffer-fetching getter. Dangerous! Iterator should be reinitialized on buffer change.
   Type* ChangeBufferHere() noexcept { return (Type*)myPosition; }
 
   //! Buffer-fetching getter.
   constexpr const Type* BufferNext() const noexcept { return myPosNext; }
 
   //! @return the index displacement from iterator initialization
   //!         (first symbol has index 0)
   constexpr int Index() const noexcept { return myCharIndex; }
 
   //! @return the advance in bytes to store current symbol in UTF-8.
   //! 0 means an invalid symbol;
   //! 1-4 bytes are valid range.
   int AdvanceBytesUtf8() const;
 
   //! @return the advance in bytes to store current symbol in UTF-16.
   //! 0 means an invalid symbol;
   //! 2 bytes is a general case;
   //! 4 bytes for surrogate pair.
   int AdvanceBytesUtf16() const;
 
   //! @return the advance in bytes to store current symbol in UTF-16.
   //! 0 means an invalid symbol;
   //! 1 16-bit code unit is a general case;
   //! 2 16-bit code units for surrogate pair.
   int AdvanceCodeUnitsUtf16() const;
 
   //! @return the advance in bytes to store current symbol in UTF-32.
   //! Always 4 bytes (method for consistency).
   constexpr int AdvanceBytesUtf32() const noexcept { return int(sizeof(char32_t)); }
 
   //! Fill the UTF-8 buffer within current Unicode symbol.
   //! Use method AdvanceUtf8() to allocate buffer with enough size.
   //! @param theBuffer buffer to fill
   //! @return new buffer position (for next char)
   char*          GetUtf8(char* theBuffer) const;
   unsigned char* GetUtf8(unsigned char* theBuffer) const;
 
   //! Fill the UTF-16 buffer within current Unicode symbol.
   //! Use method AdvanceUtf16() to allocate buffer with enough size.
   //! @param theBuffer buffer to fill
   //! @return new buffer position (for next char)
   char16_t* GetUtf16(char16_t* theBuffer) const;
 
   //! Fill the UTF-32 buffer within current Unicode symbol.
   //! Use method AdvanceUtf32() to allocate buffer with enough size.
   //! @param theBuffer buffer to fill
   //! @return new buffer position (for next char)
   char32_t* GetUtf32(char32_t* theBuffer) const;
 
   //! @return the advance in TypeWrite chars needed to store current symbol
   template <typename TypeWrite>
   inline int AdvanceBytesUtf() const
   {
     return advanceBytes(static_cast<const typename CharTypeChooser<TypeWrite>::type*>(nullptr));
   }
 
   //! Fill the UTF-** buffer within current Unicode symbol.
   //! Use method AdvanceUtf**() to allocate buffer with enough size.
   //! @param theBuffer buffer to fill
   //! @return new buffer position (for next char)
   template <typename TypeWrite>
   inline TypeWrite* GetUtf(TypeWrite* theBuffer) const
   {
     return (
       TypeWrite*)(getUtf(reinterpret_cast<typename CharTypeChooser<TypeWrite>::type*>(theBuffer)));
   }
 
 private:
   //! Helper template class dispatching its argument class
   //! to the equivalent (by size) character (Unicode code unit) type.
   //! The code unit type is defined as nested typedef "type".
   //!
   //! In practice this is relevant for wchar_t type:
   //! typename CharTypeChooser<wchar_t>::type resolves to
   //! char16_t on Windows and to char32_t on Linux.
   template <typename TypeChar>
   class CharTypeChooser
       : public std::conditional<
           sizeof(TypeChar) == 1,
           char,
           typename std::conditional<
             sizeof(TypeChar) == 2,
             char16_t,
             typename std::conditional<sizeof(TypeChar) == 4, char32_t, void>::type>::type>
   {
   };
 
   //! Helper function for reading a single Unicode symbol from the UTF-8 string.
   //! Updates internal state appropriately.
   void readUTF8();
 
   //! Helper function for reading a single Unicode symbol from the UTF-16 string.
   //! Updates internal state appropriately.
   void readUTF16();
 
   //! Helper overload methods to dispatch reading function depending on code unit size
   void readNext(const char*) { readUTF8(); }
 
   void readNext(const char16_t*) { readUTF16(); }
 
   void readNext(const char32_t*) noexcept { myCharUtf32 = *myPosNext++; }
 
   //! Helper overload methods to dispatch advance function depending on code unit size
   int advanceBytes(const char*) const { return AdvanceBytesUtf8(); }
 
   int advanceBytes(const char16_t*) const { return AdvanceBytesUtf16(); }
 
   constexpr int advanceBytes(const char32_t*) const noexcept { return AdvanceBytesUtf32(); }
 
   //! Helper overload methods to dispatch getter function depending on code unit size
   char* getUtf(char* theBuffer) const { return GetUtf8(theBuffer); }
 
   char16_t* getUtf(char16_t* theBuffer) const { return GetUtf16(theBuffer); }
 
   char32_t* getUtf(char32_t* theBuffer) const { return GetUtf32(theBuffer); }
 
 private: //! @name unicode magic numbers
   //! The first character in a UTF-8 sequence indicates how many bytes to read (among other things).
   static constexpr unsigned char UTF8_BYTES_MINUS_ONE[256] = {
     0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
     0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
     0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
     0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
     0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
     0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
     1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
     2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 5, 5, 5, 5};
 
   //! Magic values subtracted from a buffer value during UTF-8 conversion.
   //! This table contains as many values as there might be trailing bytes in a UTF-8 sequence.
   static constexpr char32_t offsetsFromUTF8[6] =
     {0x00000000UL, 0x00003080UL, 0x000E2080UL, 0x03C82080UL, 0xFA082080UL, 0x82082080UL};
 
   //! The first character in a UTF-8 sequence indicates how many bytes to read.
   static constexpr unsigned char UTF8_FIRST_BYTE_MARK[7] =
     {0x00, 0x00, 0xC0, 0xE0, 0xF0, 0xF8, 0xFC};
 
   // Magic numbers for UTF encoding/decoding
   static constexpr char32_t UTF8_BYTE_MASK             = 0xBF;
   static constexpr char32_t UTF8_BYTE_MARK             = 0x80;
   static constexpr char32_t UTF16_SURROGATE_HIGH_START = 0xD800;
   static constexpr char32_t UTF16_SURROGATE_HIGH_END   = 0xDBFF;
   static constexpr char32_t UTF16_SURROGATE_LOW_START  = 0xDC00;
   static constexpr char32_t UTF16_SURROGATE_LOW_END    = 0xDFFF;
   static constexpr char32_t UTF16_SURROGATE_HIGH_SHIFT = 10;
   static constexpr char32_t UTF16_SURROGATE_LOW_BASE   = 0x0010000UL;
   static constexpr char32_t UTF16_SURROGATE_LOW_MASK   = 0x3FFUL;
   static constexpr char32_t UTF32_MAX_BMP              = 0x0000FFFFUL;
   static constexpr char32_t UTF32_MAX_LEGAL            = 0x0010FFFFUL;
 
 private:                   //! @name private fields
   const Type* myPosition;  //!< buffer position of the first element in the current symbol
   const Type* myPosNext;   //!< buffer position of the first element in the next symbol
   int         myCharIndex; //!< index displacement from iterator initialization
   char32_t    myCharUtf32; //!< Unicode symbol stored at the current buffer position
 };
 
 // template implementation
 #include <NCollection_UtfIterator.lxx>
 
 #endif // _NCollection_UtfIterator_H__

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