------------------------------------------------------------------------------
--                                                                          --
--                         GNAT RUN-TIME COMPONENTS                         --
--                                                                          --
--                     S Y S T E M . D I R E C T _ I O                      --
--                                                                          --
--                                 S p e c                                  --
--                                                                          --
--          Copyright (C) 1992-2026, Free Software Foundation, Inc.         --
--                                                                          --
-- 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 3,  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.                                     --
--                                                                          --
-- As a special exception under Section 7 of GPL version 3, you are granted --
-- additional permissions described in the GCC Runtime Library Exception,   --
-- version 3.1, as published by the Free Software Foundation.               --
--                                                                          --
-- You should have received a copy of the GNU General Public License and    --
-- a copy of the GCC Runtime Library Exception along with this program;     --
-- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --
-- <http://www.gnu.org/licenses/>.                                          --
--                                                                          --
-- GNAT was originally developed  by the GNAT team at  New York University. --
-- Extensive contributions were provided by Ada Core Technologies Inc.      --
--                                                                          --
------------------------------------------------------------------------------

--  This package contains the declaration of the control block used for
--  Direct_IO. This must be declared at the outer library level. It also
--  contains code that is shared between instances of Direct_IO.

with Interfaces.C_Streams;
with Ada.Streams;
with System.File_Control_Block;
with System.Storage_Elements;

package System.Direct_IO is

   package FCB renames System.File_Control_Block;

   type Operation is (Op_Read, Op_Write, Op_Other);
   --  Type used to record last operation (to optimize sequential operations)

   subtype Count is Interfaces.C_Streams.int64;
   --  The Count type in each instantiation is derived from this type

   subtype Positive_Count is Count range 1 .. Count'Last;

   type Direct_AFCB is new FCB.AFCB with record
      Index : Count := 1;
      --  Current Index value

      Bytes : Interfaces.C_Streams.size_t;
      --  Length of item in bytes (set from inside generic template)

      Last_Op : Operation := Op_Other;
      --  Last operation performed on file, used to avoid unnecessary
      --  repositioning between successive read or write operations.
   end record;

   function AFCB_Allocate (Control_Block : Direct_AFCB) return FCB.AFCB_Ptr;

   procedure AFCB_Close (File : not null access Direct_AFCB);
   procedure AFCB_Free  (File : not null access Direct_AFCB);

   procedure Read
     (File : in out Direct_AFCB;
      Item : out Ada.Streams.Stream_Element_Array;
      Last : out Ada.Streams.Stream_Element_Offset);
   --  Required overriding of Read, not actually used for Direct_IO

   procedure Write
     (File : in out Direct_AFCB;
      Item : Ada.Streams.Stream_Element_Array);
   --  Required overriding of Write, not actually used for Direct_IO

   type File_Type is access all Direct_AFCB;
   --  File_Type in individual instantiations is derived from this type

   procedure Create
     (File : in out File_Type;
      Mode : FCB.File_Mode := FCB.Inout_File;
      Name : String := "";
      Form : String := "");

   function End_Of_File (File : File_Type) return Boolean;

   function Index (File : File_Type) return Positive_Count;

   procedure Open
     (File : in out File_Type;
      Mode : FCB.File_Mode;
      Name : String;
      Form : String := "");

   procedure Read
     (File : File_Type;
      Item : System.Address;
      Size : Interfaces.C_Streams.size_t;
      From : Positive_Count);

   procedure Read
     (File : File_Type;
      Item : System.Address;
      Size : Interfaces.C_Streams.size_t);

   procedure Reset (File : in out File_Type; Mode : FCB.File_Mode);
   procedure Reset (File : in out File_Type);

   procedure Set_Index (File : File_Type; To : Positive_Count);

   function Size (File : File_Type) return Count;

   procedure Write
     (File   : File_Type;
      Item   : System.Address;
      Size   : Interfaces.C_Streams.size_t;
      Zeroes : System.Storage_Elements.Storage_Array);
   --  Note: Zeroes is the buffer of zeroes used to fill out partial records

   --  The following procedures have a File_Type formal of mode IN OUT because
   --  they may close the original file. The Close operation may raise an
   --  exception, but in that case we want any assignment to the formal to
   --  be effective anyway, so it must be passed by reference (or the caller
   --  will be left with a dangling pointer).

   pragma Export_Procedure
     (Internal        => Reset,
      External        => "",
      Parameter_Types => (File_Type),
      Mechanism       => Reference);
   pragma Export_Procedure
     (Internal        => Reset,
      External        => "",
      Parameter_Types => (File_Type, FCB.File_Mode),
      Mechanism       => (File => Reference));

end System.Direct_IO;
