package body Agila_Ports is
   use type Word;
   Max_Generation : constant Word := Word'Last / Max_Ports;
   function Valid (State : Manager; Handle : Word) return Boolean is
      Slot : constant Natural := Natural (Handle mod Max_Ports);
   begin
      return Handle >= Max_Ports
        and then State.Table (Slot).Active
        and then State.Table (Slot).Generation = Handle / Max_Ports;
   end Valid;

   procedure Create (State : in out Manager; Owner : Word;
                     Handle : out Word; Result : out Status) is
   begin
      Handle := 0;
      if Owner = 0 then Result := Invalid_Argument; return; end if;
      for Slot in State.Table'Range loop
         if not State.Table (Slot).Active and not State.Table (Slot).Retired then
            State.Table (Slot).Active := True;
            State.Table (Slot).Owner := Owner;
            State.Table (Slot).Allowed_Sender := 0;
            State.Table (Slot).Head := 0;
            State.Table (Slot).Count := 0;
            State.Table (Slot).Queue := [others => (0, 0)];
            Handle := State.Table (Slot).Generation * Max_Ports + Word (Slot);
            Result := Ok;
            return;
         end if;
      end loop;
      Result := Exhausted;
   end Create;

   procedure Allow_Sender (State : in out Manager; Handle, Owner, Sender : Word;
                           Result : out Status) is
      Slot : constant Natural := Natural (Handle mod Max_Ports);
   begin
      if not Valid (State, Handle) then Result := Invalid_Handle;
      elsif State.Table (Slot).Owner /= Owner then Result := Permission_Denied;
      elsif Sender = 0 then Result := Invalid_Argument;
      else State.Table (Slot).Allowed_Sender := Sender; Result := Ok;
      end if;
   end Allow_Sender;

   procedure Revoke_Sender (State : in out Manager; Handle, Owner, Sender : Word;
                            Result : out Status) is
      Slot : constant Natural := Natural (Handle mod Max_Ports);
   begin
      if not Valid (State, Handle) then Result := Invalid_Handle;
      elsif State.Table (Slot).Owner /= Owner then Result := Permission_Denied;
      elsif Sender = 0 or else State.Table (Slot).Allowed_Sender /= Sender then
         Result := Invalid_Argument;
      else State.Table (Slot).Allowed_Sender := 0; Result := Ok;
      end if;
   end Revoke_Sender;

   procedure Send (State : in out Manager; Handle, Caller, Value : Word;
                   Result : out Status) is
      Slot : constant Natural := Natural (Handle mod Max_Ports);
   begin
      if not Valid (State, Handle) then Result := Invalid_Handle; return; end if;
      declare
         P : Port renames State.Table (Slot);
      begin
         if Caller = 0 or else (Caller /= P.Owner and Caller /= P.Allowed_Sender) then
            Result := Permission_Denied;
         elsif P.Count = Queue_Capacity then Result := Full;
         else
            P.Queue ((P.Head + P.Count) mod Queue_Capacity) := (Caller, Value);
            P.Count := P.Count + 1;
            Result := Ok;
         end if;
      end;
   end Send;

   procedure Receive (State : in out Manager; Handle, Caller : Word;
                      Item : out Message; Result : out Status) is
      Slot : constant Natural := Natural (Handle mod Max_Ports);
   begin
      Item := (0, 0);
      if not Valid (State, Handle) then Result := Invalid_Handle; return; end if;
      declare
         P : Port renames State.Table (Slot);
      begin
         if Caller /= P.Owner then Result := Permission_Denied;
         elsif P.Count = 0 then Result := Empty;
         else
            Item := P.Queue (P.Head);
            P.Queue (P.Head) := (0, 0);
            P.Head := (P.Head + 1) mod Queue_Capacity;
            P.Count := P.Count - 1;
            Result := Ok;
         end if;
      end;
   end Receive;

   procedure Close (State : in out Manager; Handle, Caller : Word;
                    Result : out Status) is
      Slot : constant Natural := Natural (Handle mod Max_Ports);
   begin
      if not Valid (State, Handle) then Result := Invalid_Handle;
      elsif State.Table (Slot).Owner /= Caller then Result := Permission_Denied;
      else
         State.Table (Slot).Active := False;
         State.Table (Slot).Owner := 0;
         State.Table (Slot).Allowed_Sender := 0;
         State.Table (Slot).Count := 0;
         State.Table (Slot).Queue := [others => (0, 0)];
         if State.Table (Slot).Generation = Max_Generation then
            State.Table (Slot).Retired := True;
         else
            State.Table (Slot).Generation := State.Table (Slot).Generation + 1;
         end if;
         Result := Ok;
      end if;
   end Close;
end Agila_Ports;