--  Type interning - set of unique objects.
--  Copyright (C) 2019 Tristan Gingold
--
--  This program is free software: you can redistribute it and/or modify
--  it under the terms of the GNU General Public License as published by
--  the Free Software Foundation, either version 2 of the License, or
--  (at your option) any later version.
--
--  This program is distributed in the hope that it will be useful,
--  but WITHOUT 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
--  along with this program.  If not, see <gnu.org/licenses>.

with Hash; use Hash;
with Dyn_Maps;

--  This generic package provides a factory to build unique objects.
--  Get will return an existing object or create a new one.
generic
   --  Parameters of the object to be created.
   type Params_Type (<>) is private;

   --  Object to be built and stored.
   type Object_Type is private;

   --  Reduce PARAMS to a small value.
   --  The required property is: Hash(P1) /= Hash(P2) => P1 /= P2.
   with function Hash (Params : Params_Type) return Hash_Value_Type;

   --  Create an object from PARAMS.
   with function Build (Params : Params_Type) return Object_Type;

   --  Return True iff OBJ is the object corresponding to PARAMS.
   with function Equal (Obj : Object_Type; Params : Params_Type)
                       return Boolean;
package Dyn_Interning is
   type No_Value_Type is null record;
   function Build_No_Value (Obj : Object_Type) return No_Value_Type;

   package Map is new Dyn_Maps
     (Params_Type => Params_Type,
      Object_Type => Object_Type,
      Value_Type  => No_Value_Type,
      Hash        => Hash,
      Build       => Build,
      Build_Value => Build_No_Value,
      Equal       => Equal);

   subtype Instance is Map.Instance;

   --  Initialize.  Required before any other operation.
   procedure Init (Inst : out Instance) renames Map.Init;

   procedure Free (Inst : in out Instance) renames Map.Free;

   --  Export Index_Type...
   subtype Index_Type is Map.Index_Type;
   function "+" (L, R : Index_Type) return Index_Type renames Map."+";
   function ">" (L, R : Index_Type) return Boolean renames Map.">";
   function "<=" (L, R : Index_Type) return Boolean renames Map."<=";

   No_Index : constant Index_Type := Map.No_Index;
   First_Index : constant Index_Type := Map.First_Index;

   --  If there is already an existing object for PARAMS, return it.
   --  Otherwise create it.
   procedure Get
     (Inst : in out Instance; Params : Params_Type; Res : out Object_Type);

   --  Likewise, but return its index.
   procedure Get_Index
     (Inst : in out Instance; Params : Params_Type; Idx : out Index_Type)
     renames Map.Get_Index;

   --  Get the number of elements in the table.
   function Last_Index (Inst : Instance) return Index_Type
     renames Map.Last_Index;

   --  Get an element by index.  The index has no real meaning, but the
   --  current implementation allocates index incrementally.
   function Get_By_Index (Inst : Instance; Index : Index_Type)
                          return Object_Type
     renames Map.Get_By_Index;
end Dyn_Interning;