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------------------------------------------------------------------------------

--                                                                          --

--                         GNAT RUN-TIME COMPONENTS                         --

--                                                                          --

--                    G N A T . D E C O D E _ S T R I N G                   --

--                                                                          --

--                                 S p e c                                  --

--                                                                          --

--                       Copyright (C) 2007, AdaCore                        --

--                                                                          --

-- GNAT is free software;  you can  redistribute it  and/or modify it under --

-- terms of the  GNU General Public License as published  by the Free Soft- --

-- ware  Foundation;  either version 2,  or (at your option) any later ver- --

-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --

-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --

-- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --

-- for  more details.  You should have  received  a copy of the GNU General --

-- Public License  distributed with GNAT;  see file COPYING.  If not, write --

-- to  the  Free Software Foundation,  51  Franklin  Street,  Fifth  Floor, --

-- Boston, MA 02110-1301, USA.                                              --

--                                                                          --

-- As a special exception,  if other files  instantiate  generics from this --

-- unit, or you link  this unit with other files  to produce an executable, --

-- this  unit  does not  by itself cause  the resulting  executable  to  be --

-- covered  by the  GNU  General  Public  License.  This exception does not --

-- however invalidate  any other reasons why  the executable file  might be --

-- covered by the  GNU Public License.                                      --

--                                                                          --

-- GNAT was originally developed  by the GNAT team at  New York University. --

-- Extensive contributions were provided by Ada Core Technologies Inc.      --

--                                                                          --

------------------------------------------------------------------------------

--  This generic package provides utility routines for converting from an

--  encoded string to a corresponding Wide_String or Wide_Wide_String value

--  using a specified encoding convention, which is supplied as the generic

--  parameter. UTF-8 is handled especially efficiently, and if the encoding

--  method is known at compile time to be WCEM_UTF8, then the instantiation

--  is specialized to handle only the UTF-8 case and exclude code for the

--  other encoding methods. The package also provides positioning routines

--  for skipping encoded characters in either direction, and for validating

--  strings for correct encodings.

--  Note: this package is only about decoding sequences of 8-bit characters

--  into corresponding 16-bit Wide_String or 32-bit Wide_Wide_String values.

--  It knows nothing at all about the character encodings being used for the

--  resulting Wide_Character and Wide_Wide_Character values. Most often this

--  will be Unicode/ISO-10646 as specified by the Ada RM, but this package

--  does not make any assumptions about the character coding. See also the

--  packages Ada.Wide_[Wide_]Characters.Unicode for unicode specific functions.

--  Note on the use of brackets encoding (WCEM_Brackets). The brackets encoding

--  method is ambiguous in the context of this package, since there is no way

--  to tell if ["1234"] is eight unencoded characters or one encoded character.

--  In the context of Ada sources, any sequence starting [" must be the start

--  of an encoding (since that sequence is not valid in Ada source otherwise).

--  The routines in this package use the same approach. If the input string

--  contains the sequence [" then this is assumed to be the start of a brackets

--  encoding sequence, and if it does not match the syntax, an error is raised.

--  In the case of the Prev functions, a sequence ending with "] is assumed to

--  be a valid brackets sequence, and an error is raised if it is not.

with System.WCh_Con;

generic

   Encoding_Method : System.WCh_Con.WC_Encoding_Method;

package GNAT.Decode_String is

   pragma Pure;

   function Decode_Wide_String (S : String) return Wide_String;

   pragma Inline (Decode_Wide_String);

   --  Decode the given String, which is encoded using the indicated coding

   --  method, returning the corresponding decoded Wide_String value. If S

   --  contains a character code that cannot be represented with the given

   --  encoding, then Constraint_Error is raised.

   procedure Decode_Wide_String

     (S      : String;

      Result : out Wide_String;

      Length : out Natural);

   --  Similar to the above function except that the result is stored in the

   --  given Wide_String variable Result, starting at Result (Result'First). On

   --  return, Length is set to the number of characters stored in Result. The

   --  caller must ensure that Result is long enough (an easy choice is to set

   --  the length equal to the S'Length, since decoding can never increase the

   --  string length). If the length of Result is insufficient Constraint_Error

   --  will be raised.

   function Decode_Wide_Wide_String (S : String) return Wide_Wide_String;

   pragma Inline (Decode_Wide_Wide_String);

   --  Same as above function but for Wide_Wide_String output

   procedure Decode_Wide_Wide_String

     (S      : String;

      Result : out Wide_Wide_String;

      Length : out Natural);

   --  Same as above procedure, but for Wide_Wide_String output

   function Validate_Wide_String (S : String) return Boolean;

   --  This function inspects the string S to determine if it contains only

   --  valid encodings corresponding to Wide_Character values using the

   --  given encoding. If a call to Decode_Wide_String (S) would return

   --  without raising Constraint_Error, then Validate_Wide_String will

   --  return True. If the call would have raised Constraint_Error, then

   --  Validate_Wide_String will return False.

   function Validate_Wide_Wide_String (S : String) return Boolean;

   --  Similar to Validate_Wide_String, except that it succeeds if the string

   --  contains only encodings corresponding to Wide_Wide_Character values.

   procedure Decode_Wide_Character

     (Input  : String;

      Ptr    : in out Natural;

      Result : out Wide_Character);

   pragma Inline (Decode_Wide_Character);

   --  This is a lower level procedure that decodes a single character using

   --  the given encoding method. The encoded character is stored in Input,

   --  starting at Input (Ptr). The resulting output character is stored in

   --  Result, and on return Ptr is updated past the input character or

   --  encoding sequence. Constraint_Error will be raised if the input has

   --  has a character that cannot be represented using the given encoding,

   --  or if Ptr is outside the bounds of the Input string.

   procedure Decode_Wide_Wide_Character

     (Input  : String;

      Ptr    : in out Natural;

      Result : out Wide_Wide_Character);

   --  Same as above procedure but with Wide_Wide_Character input

   procedure Next_Wide_Character (Input : String; Ptr : in out Natural);

   --  This procedure examines the input string starting at Input (Ptr), and

   --  advances Ptr past one character in the encoded string, so that on return

   --  Ptr points to the next encoded character. Constraint_Error is raised if

   --  an invalid encoding is encountered, or the end of the string is reached

   --  or if Ptr is less than String'First on entry, or if the character

   --  skipped is not a valid Wide_Character code. This call may be more

   --  efficient than calling Decode_Wide_Character and discarding the result.

   procedure Prev_Wide_Character (Input : String; Ptr : in out Natural);

   --  This procedure is similar to Next_Encoded_Character except that it moves

   --  backwards in the string, so that on return, Ptr is set to point to the

   --  previous encoded character. Constraint_Error is raised if the start of

   --  the string is encountered. It is valid for Ptr to be one past the end

   --  of the string for this call (in which case on return it will point to

   --  the last encoded character).

   --

   --  Note: it is not generally possible to do this function efficiently with

   --  all encodings, the current implementation is only efficient for the case

   --  of UTF-8 (Encoding_Method = WCEM_UTF8) and Brackets (Encoding_Method =

   --  WCEM_Brackets). For all other encodings, we work by starting at the

   --  beginning of the string and moving forward till Ptr is reached, which

   --  is correct but slow.

   procedure Next_Wide_Wide_Character (Input : String; Ptr : in out Natural);

   --  Similar to Next_Wide_Character except that codes skipped must be valid

   --  Wide_Wide_Character codes.

   procedure Prev_Wide_Wide_Character (Input : String; Ptr : in out Natural);

   --  Similar to Prev_Wide_Character except that codes skipped must be valid

   --  Wide_Wide_Character codes.

end GNAT.Decode_String;