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

--                                                                          --

--                         GNAT LIBRARY COMPONENTS                          --

--                                                                          --

--                  ADA.CONTAINERS.BOUNDED_PRIORITY_QUEUES                  --

--                                                                          --

--                                 B o d y                                  --

--                                                                          --

--            Copyright (C) 2011, 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/>.                                          --

--                                                                          --

-- This unit was originally developed by Matthew J Heaney.                  --

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

package body Ada.Containers.Bounded_Priority_Queues is

   package body Implementation is

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

      -- Dequeue --

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

      procedure Dequeue

        (List    : in out List_Type;

         Element : out Queue_Interfaces.Element_Type)

      is

      begin

         Element := List.Container.First_Element;

         List.Container.Delete_First;

      end Dequeue;

      procedure Dequeue

        (List     : in out List_Type;

         At_Least : Queue_Priority;

         Element  : in out Queue_Interfaces.Element_Type;

         Success  : out Boolean)

      is

      begin

         --  This operation dequeues a high priority item if it exists in the

         --  queue. By "high priority" we mean an item whose priority is equal

         --  or greater than the value At_Least. The generic formal operation

         --  Before has the meaning "has higher priority than". To dequeue an

         --  item (meaning that we return True as our Success value), we need

         --  as our predicate the equivalent of "has equal or higher priority

         --  than", but we cannot say that directly, so we require some logical

         --  gymnastics to make it so.

         --  If E is the element at the head of the queue, and symbol ">"

         --  refers to the "is higher priority than" function Before, then we

         --  derive our predicate as follows:

         --    original: P(E) >= At_Least

         --    same as:  not (P(E) < At_Least)

         --    same as:  not (At_Least > P(E))

         --    same as:  not Before (At_Least, P(E))

         --  But that predicate needs to be true in order to successfully

         --  dequeue an item. If it's false, it means no item is dequeued, and

         --  we return False as the Success value.

         if List.Length = 0

           or else Before (At_Least,

                           Get_Priority (List.Container.First_Element))

         then

            Success := False;

            return;

         end if;

         List.Dequeue (Element);

         Success := True;

      end Dequeue;

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

      -- Enqueue --

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

      procedure Enqueue

        (List     : in out List_Type;

         New_Item : Queue_Interfaces.Element_Type)

      is

         P : constant Queue_Priority := Get_Priority (New_Item);

         C : List_Types.Cursor;

         use List_Types;

         Count : Count_Type;

      begin

         C := List.Container.First;

         while Has_Element (C) loop

            --  ??? why is following commented out ???

            --  if Before (P, Get_Priority (List.Constant_Reference (C))) then

            if Before (P, Get_Priority (Element (C))) then

               List.Container.Insert (C, New_Item);

               exit;

            end if;

            Next (C);

         end loop;

         if not Has_Element (C) then

            List.Container.Append (New_Item);

         end if;

         Count := List.Container.Length;

         if Count > List.Max_Length then

            List.Max_Length := Count;

         end if;

      end Enqueue;

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

      -- First_Element --

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

      function First_Element

        (List : List_Type) return Queue_Interfaces.Element_Type

      is

      begin

         --  Use Constant_Reference for this.  ???

         return List.Container.First_Element;

      end First_Element;

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

      -- Length --

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

      function Length (List : List_Type) return Count_Type is

      begin

         return List.Container.Length;

      end Length;

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

      -- Max_Length --

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

      function Max_Length (List : List_Type) return Count_Type is

      begin

         return List.Max_Length;

      end Max_Length;

   end Implementation;

   protected body Queue is

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

      --  Current_Use --

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

      function Current_Use return Count_Type is

      begin

         return List.Length;

      end Current_Use;

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

      --  Dequeue --

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

      entry Dequeue (Element : out Queue_Interfaces.Element_Type)

        when List.Length > 0

      is

      begin

         List.Dequeue (Element);

      end Dequeue;

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

      -- Dequeue_Only_High_Priority --

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

      procedure Dequeue_Only_High_Priority

        (At_Least : Queue_Priority;

         Element  : in out Queue_Interfaces.Element_Type;

         Success  : out Boolean)

      is

      begin

         List.Dequeue (At_Least, Element, Success);

      end Dequeue_Only_High_Priority;

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

      --  Enqueue --

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

      entry Enqueue (New_Item : Queue_Interfaces.Element_Type)

        when List.Length < Capacity

      is

      begin

         List.Enqueue (New_Item);

      end Enqueue;

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

      --  Peak_Use --

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

      function Peak_Use return Count_Type is

      begin

         return List.Max_Length;

      end Peak_Use;

   end Queue;

end Ada.Containers.Bounded_Priority_Queues;