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

--                                                                          --

--                         GNAT LIBRARY COMPONENTS                          --

--                                                                          --

--                ADA.CONTAINERS.RED_BLACK_TREES.GENERIC_KEYS               --

--                                                                          --

--                                 B o d y                                  --

--                                                                          --

--          Copyright (C) 2004-2011, 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.Red_Black_Trees.Generic_Keys is

   package Ops renames Tree_Operations;

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

   -- Ceiling --

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

   --  AKA Lower_Bound

   function Ceiling (Tree : Tree_Type; Key : Key_Type) return Node_Access is

      Y : Node_Access;

      X : Node_Access;

   begin

      X := Tree.Root;

      while X /= null loop

         if Is_Greater_Key_Node (Key, X) then

            X := Ops.Right (X);

         else

            Y := X;

            X := Ops.Left (X);

         end if;

      end loop;

      return Y;

   end Ceiling;

   ----------

   -- Find --

   ----------

   function Find (Tree : Tree_Type; Key  : Key_Type) return Node_Access is

      Y : Node_Access;

      X : Node_Access;

   begin

      X := Tree.Root;

      while X /= null loop

         if Is_Greater_Key_Node (Key, X) then

            X := Ops.Right (X);

         else

            Y := X;

            X := Ops.Left (X);

         end if;

      end loop;

      if Y = null then

         return null;

      end if;

      if Is_Less_Key_Node (Key, Y) then

         return null;

      end if;

      return Y;

   end Find;

   -----------

   -- Floor --

   -----------

   function Floor (Tree : Tree_Type; Key  : Key_Type) return Node_Access is

      Y : Node_Access;

      X : Node_Access;

   begin

      X := Tree.Root;

      while X /= null loop

         if Is_Less_Key_Node (Key, X) then

            X := Ops.Left (X);

         else

            Y := X;

            X := Ops.Right (X);

         end if;

      end loop;

      return Y;

   end Floor;

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

   -- Generic_Conditional_Insert --

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

   procedure Generic_Conditional_Insert

     (Tree     : in out Tree_Type;

      Key      : Key_Type;

      Node     : out Node_Access;

      Inserted : out Boolean)

   is

      Y : Node_Access := null;

      X : Node_Access := Tree.Root;

   begin

      --  This is a "conditional" insertion, meaning that the insertion request

      --  can "fail" in the sense that no new node is created. If the Key is

      --  equivalent to an existing node, then we return the existing node and

      --  Inserted is set to False. Otherwise, we allocate a new node (via

      --  Insert_Post) and Inserted is set to True.

      --  Note that we are testing for equivalence here, not equality. Key must

      --  be strictly less than its next neighbor, and strictly greater than

      --  its previous neighbor, in order for the conditional insertion to

      --  succeed.

      --  We search the tree to find the nearest neighbor of Key, which is

      --  either the smallest node greater than Key (Inserted is True), or the

      --  largest node less or equivalent to Key (Inserted is False).

      Inserted := True;

      while X /= null loop

         Y := X;

         Inserted := Is_Less_Key_Node (Key, X);

         X := (if Inserted then Ops.Left (X) else Ops.Right (X));

      end loop;

      if Inserted then

         --  Either Tree is empty, or Key is less than Y. If Y is the first

         --  node in the tree, then there are no other nodes that we need to

         --  search for, and we insert a new node into the tree.

         if Y = Tree.First then

            Insert_Post (Tree, Y, True, Node);

            return;

         end if;

         --  Y is the next nearest-neighbor of Key. We know that Key is not

         --  equivalent to Y (because Key is strictly less than Y), so we move

         --  to the previous node, the nearest-neighbor just smaller or

         --  equivalent to Key.

         Node := Ops.Previous (Y);

      else

         --  Y is the previous nearest-neighbor of Key. We know that Key is not

         --  less than Y, which means either that Key is equivalent to Y, or

         --  greater than Y.

         Node := Y;

      end if;

      --  Key is equivalent to or greater than Node. We must resolve which is

      --  the case, to determine whether the conditional insertion succeeds.

      if Is_Greater_Key_Node (Key, Node) then

         --  Key is strictly greater than Node, which means that Key is not

         --  equivalent to Node. In this case, the insertion succeeds, and we

         --  insert a new node into the tree.

         Insert_Post (Tree, Y, Inserted, Node);

         Inserted := True;

         return;

      end if;

      --  Key is equivalent to Node. This is a conditional insertion, so we do

      --  not insert a new node in this case. We return the existing node and

      --  report that no insertion has occurred.

      Inserted := False;

   end Generic_Conditional_Insert;

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

   -- Generic_Conditional_Insert_With_Hint --

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

   procedure Generic_Conditional_Insert_With_Hint

     (Tree      : in out Tree_Type;

      Position  : Node_Access;

      Key       : Key_Type;

      Node      : out Node_Access;

      Inserted  : out Boolean)

   is

   begin

      --  The purpose of a hint is to avoid a search from the root of

      --  tree. If we have it hint it means we only need to traverse the

      --  subtree rooted at the hint to find the nearest neighbor. Note

      --  that finding the neighbor means merely walking the tree; this

      --  is not a search and the only comparisons that occur are with

      --  the hint and its neighbor.

      --  If Position is null, this is interpreted to mean that Key is

      --  large relative to the nodes in the tree. If the tree is empty,

      --  or Key is greater than the last node in the tree, then we're

      --  done; otherwise the hint was "wrong" and we must search.

      if Position = null then  -- largest

         if Tree.Last = null

           or else Is_Greater_Key_Node (Key, Tree.Last)

         then

            Insert_Post (Tree, Tree.Last, False, Node);

            Inserted := True;

         else

            Conditional_Insert_Sans_Hint (Tree, Key, Node, Inserted);

         end if;

         return;

      end if;

      pragma Assert (Tree.Length > 0);

      --  A hint can either name the node that immediately follows Key,

      --  or immediately precedes Key. We first test whether Key is

      --  less than the hint, and if so we compare Key to the node that

      --  precedes the hint. If Key is both less than the hint and

      --  greater than the hint's preceding neighbor, then we're done;

      --  otherwise we must search.

      --  Note also that a hint can either be an anterior node or a leaf

      --  node. A new node is always inserted at the bottom of the tree

      --  (at least prior to rebalancing), becoming the new left or

      --  right child of leaf node (which prior to the insertion must

      --  necessarily be null, since this is a leaf). If the hint names

      --  an anterior node then its neighbor must be a leaf, and so

      --  (here) we insert after the neighbor. If the hint names a leaf

      --  then its neighbor must be anterior and so we insert before the

      --  hint.

      if Is_Less_Key_Node (Key, Position) then

         declare

            Before : constant Node_Access := Ops.Previous (Position);

         begin

            if Before = null then

               Insert_Post (Tree, Tree.First, True, Node);

               Inserted := True;

            elsif Is_Greater_Key_Node (Key, Before) then

               if Ops.Right (Before) = null then

                  Insert_Post (Tree, Before, False, Node);

               else

                  Insert_Post (Tree, Position, True, Node);

               end if;

               Inserted := True;

            else

               Conditional_Insert_Sans_Hint (Tree, Key, Node, Inserted);

            end if;

         end;

         return;

      end if;

      --  We know that Key isn't less than the hint so we try again,

      --  this time to see if it's greater than the hint. If so we

      --  compare Key to the node that follows the hint. If Key is both

      --  greater than the hint and less than the hint's next neighbor,

      --  then we're done; otherwise we must search.

      if Is_Greater_Key_Node (Key, Position) then

         declare

            After : constant Node_Access := Ops.Next (Position);

         begin

            if After = null then

               Insert_Post (Tree, Tree.Last, False, Node);

               Inserted := True;

            elsif Is_Less_Key_Node (Key, After) then

               if Ops.Right (Position) = null then

                  Insert_Post (Tree, Position, False, Node);

               else

                  Insert_Post (Tree, After, True, Node);

               end if;

               Inserted := True;

            else

               Conditional_Insert_Sans_Hint (Tree, Key, Node, Inserted);

            end if;

         end;

         return;

      end if;

      --  We know that Key is neither less than the hint nor greater

      --  than the hint, and that's the definition of equivalence.

      --  There's nothing else we need to do, since a search would just

      --  reach the same conclusion.

      Node := Position;

      Inserted := False;

   end Generic_Conditional_Insert_With_Hint;

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

   -- Generic_Insert_Post --

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

   procedure Generic_Insert_Post

     (Tree   : in out Tree_Type;

      Y      : Node_Access;

      Before : Boolean;

      Z      : out Node_Access)

   is

   begin

      if Tree.Length = Count_Type'Last then

         raise Constraint_Error with "too many elements";

      end if;

      if Tree.Busy > 0 then

         raise Program_Error with

           "attempt to tamper with cursors (container is busy)";

      end if;

      Z := New_Node;

      pragma Assert (Z /= null);

      pragma Assert (Ops.Color (Z) = Red);

      if Y = null then

         pragma Assert (Tree.Length = 0);

         pragma Assert (Tree.Root = null);

         pragma Assert (Tree.First = null);

         pragma Assert (Tree.Last = null);

         Tree.Root := Z;

         Tree.First := Z;

         Tree.Last := Z;

      elsif Before then

         pragma Assert (Ops.Left (Y) = null);

         Ops.Set_Left (Y, Z);

         if Y = Tree.First then

            Tree.First := Z;

         end if;

      else

         pragma Assert (Ops.Right (Y) = null);

         Ops.Set_Right (Y, Z);

         if Y = Tree.Last then

            Tree.Last := Z;

         end if;

      end if;

      Ops.Set_Parent (Z, Y);

      Ops.Rebalance_For_Insert (Tree, Z);

      Tree.Length := Tree.Length + 1;

   end Generic_Insert_Post;

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

   -- Generic_Iteration --

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

   procedure Generic_Iteration

     (Tree : Tree_Type;

      Key  : Key_Type)

   is

      procedure Iterate (Node : Node_Access);

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

      -- Iterate --

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

      procedure Iterate (Node : Node_Access) is

         N : Node_Access;

      begin

         N := Node;

         while N /= null loop

            if Is_Less_Key_Node (Key, N) then

               N := Ops.Left (N);

            elsif Is_Greater_Key_Node (Key, N) then

               N := Ops.Right (N);

            else

               Iterate (Ops.Left (N));

               Process (N);

               N := Ops.Right (N);

            end if;

         end loop;

      end Iterate;

   --  Start of processing for Generic_Iteration

   begin

      Iterate (Tree.Root);

   end Generic_Iteration;

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

   -- Generic_Reverse_Iteration --

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

   procedure Generic_Reverse_Iteration

     (Tree : Tree_Type;

      Key  : Key_Type)

   is

      procedure Iterate (Node : Node_Access);

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

      -- Iterate --

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

      procedure Iterate (Node : Node_Access) is

         N : Node_Access;

      begin

         N := Node;

         while N /= null loop

            if Is_Less_Key_Node (Key, N) then

               N := Ops.Left (N);

            elsif Is_Greater_Key_Node (Key, N) then

               N := Ops.Right (N);

            else

               Iterate (Ops.Right (N));

               Process (N);

               N := Ops.Left (N);

            end if;

         end loop;

      end Iterate;

   --  Start of processing for Generic_Reverse_Iteration

   begin

      Iterate (Tree.Root);

   end Generic_Reverse_Iteration;

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

   -- Generic_Unconditional_Insert --

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

   procedure Generic_Unconditional_Insert

     (Tree : in out Tree_Type;

      Key  : Key_Type;

      Node : out Node_Access)

   is

      Y : Node_Access;

      X : Node_Access;

      Before : Boolean;

   begin

      Y := null;

      Before := False;

      X := Tree.Root;

      while X /= null loop

         Y := X;

         Before := Is_Less_Key_Node (Key, X);

         X := (if Before then Ops.Left (X) else Ops.Right (X));

      end loop;

      Insert_Post (Tree, Y, Before, Node);

   end Generic_Unconditional_Insert;

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

   -- Generic_Unconditional_Insert_With_Hint --

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

   procedure Generic_Unconditional_Insert_With_Hint

     (Tree : in out Tree_Type;

      Hint : Node_Access;

      Key  : Key_Type;

      Node : out Node_Access)

   is

   begin

      --  There are fewer constraints for an unconditional insertion

      --  than for a conditional insertion, since we allow duplicate

      --  keys. So instead of having to check (say) whether Key is

      --  (strictly) greater than the hint's previous neighbor, here we

      --  allow Key to be equal to or greater than the previous node.

      --  There is the issue of what to do if Key is equivalent to the

      --  hint. Does the new node get inserted before or after the hint?

      --  We decide that it gets inserted after the hint, reasoning that

      --  this is consistent with behavior for non-hint insertion, which

      --  inserts a new node after existing nodes with equivalent keys.

      --  First we check whether the hint is null, which is interpreted

      --  to mean that Key is large relative to existing nodes.

      --  Following our rule above, if Key is equal to or greater than

      --  the last node, then we insert the new node immediately after

      --  last. (We don't have an operation for testing whether a key is

      --  "equal to or greater than" a node, so we must say instead "not

      --  less than", which is equivalent.)

      if Hint = null then  -- largest

         if Tree.Last = null then

            Insert_Post (Tree, null, False, Node);

         elsif Is_Less_Key_Node (Key, Tree.Last) then

            Unconditional_Insert_Sans_Hint (Tree, Key, Node);

         else

            Insert_Post (Tree, Tree.Last, False, Node);

         end if;

         return;

      end if;

      pragma Assert (Tree.Length > 0);

      --  We decide here whether to insert the new node prior to the

      --  hint. Key could be equivalent to the hint, so in theory we

      --  could write the following test as "not greater than" (same as

      --  "less than or equal to"). If Key were equivalent to the hint,

      --  that would mean that the new node gets inserted before an

      --  equivalent node. That wouldn't break any container invariants,

      --  but our rule above says that new nodes always get inserted

      --  after equivalent nodes. So here we test whether Key is both

      --  less than the hint and equal to or greater than the hint's

      --  previous neighbor, and if so insert it before the hint.

      if Is_Less_Key_Node (Key, Hint) then

         declare

            Before : constant Node_Access := Ops.Previous (Hint);

         begin

            if Before = null then

               Insert_Post (Tree, Hint, True, Node);

            elsif Is_Less_Key_Node (Key, Before) then

               Unconditional_Insert_Sans_Hint (Tree, Key, Node);

            elsif Ops.Right (Before) = null then

               Insert_Post (Tree, Before, False, Node);

            else

               Insert_Post (Tree, Hint, True, Node);

            end if;

         end;

         return;

      end if;

      --  We know that Key isn't less than the hint, so it must be equal

      --  or greater. So we just test whether Key is less than or equal

      --  to (same as "not greater than") the hint's next neighbor, and

      --  if so insert it after the hint.

      declare

         After : constant Node_Access := Ops.Next (Hint);

      begin

         if After = null then

            Insert_Post (Tree, Hint, False, Node);

         elsif Is_Greater_Key_Node (Key, After) then

            Unconditional_Insert_Sans_Hint (Tree, Key, Node);

         elsif Ops.Right (Hint) = null then

            Insert_Post (Tree, Hint, False, Node);

         else

            Insert_Post (Tree, After, True, Node);

         end if;

      end;

   end Generic_Unconditional_Insert_With_Hint;

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

   -- Upper_Bound --

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

   function Upper_Bound

     (Tree : Tree_Type;

      Key  : Key_Type) return Node_Access

   is

      Y : Node_Access;

      X : Node_Access;

   begin

      X := Tree.Root;

      while X /= null loop

         if Is_Less_Key_Node (Key, X) then

            Y := X;

            X := Ops.Left (X);

         else

            X := Ops.Right (X);

         end if;

      end loop;

      return Y;

   end Upper_Bound;

end Ada.Containers.Red_Black_Trees.Generic_Keys;