%%
%% %CopyrightBegin%
%% 
%% Copyright Ericsson AB 1997-2017. All Rights Reserved.
%% 
%% Licensed under the Apache License, Version 2.0 (the "License");
%% you may not use this file except in compliance with the License.
%% You may obtain a copy of the License at
%%
%%     http://www.apache.org/licenses/LICENSE-2.0
%%
%% Unless required by applicable law or agreed to in writing, software
%% distributed under the License is distributed on an "AS IS" BASIS,
%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
%% See the License for the specific language governing permissions and
%% limitations under the License.
%% 
%% %CopyrightEnd%
%%
%%
-module(asn1ct_name).

-export([start/0,
	 curr/1,
	 clear/0,
	 prev/1,
	 next/1,
	 all/1,
	 new/1]).

start() ->
    Parent = self(),
    case get(?MODULE) of
	undefined ->
            put(?MODULE, spawn_link(fun() ->
                            Ref = monitor(process, Parent),
                            name_server_loop({Ref,Parent},[])
                    end)),
            ok;
	_Pid ->
	    %% Already started. Clear the variables.
	    clear()
    end.

name_server_loop({Ref, Parent} = Monitor,Vars) ->
    receive
	{_From,clear} ->
	    name_server_loop(Monitor, []);
	{From,{current,Variable}} ->
	    From ! {?MODULE,get_curr(Vars,Variable)},
	    name_server_loop(Monitor,Vars);
	{_From,{new,Variable}} ->
	    name_server_loop(Monitor,new_var(Vars,Variable));
	{From,{prev,Variable}} ->
	    From ! {?MODULE,get_prev(Vars,Variable)},
	    name_server_loop(Monitor,Vars);
	{From,{next,Variable}} ->
	    From ! {?MODULE,get_next(Vars,Variable)},
	    name_server_loop(Monitor,Vars);
	{'DOWN', Ref, process, Parent, Reason} ->
	    exit(Reason)
    end.

req(Req) ->
    Pid = get(?MODULE),
    Ref = monitor(process, Pid),
    Pid ! {self(), Req},
    receive
        {?MODULE, Reply} ->
	    Reply;
	{'DOWN', Ref, process, Pid, Reason} ->
            error({name_server_died,Reason})
    end.

cast(Req) ->
    get(?MODULE) ! {self(), Req},
    ok.

clear() ->     cast(clear).
curr(V) ->     req({current,V}).
new(V) ->      cast({new,V}).

prev(V) ->
    case req({prev,V}) of
	none ->
	    exit('cant get prev of none');
	Rep -> Rep
    end.

next(V) ->
    req({next,V}).
    
all(V) ->
    Curr = curr(V),
    if Curr == V -> [];
	true ->
	    lists:reverse(generate(V,last(Curr),[],0))
    end.

generate(V,Number,Res,Pos) ->
    Ell = Pos+1,
    if
	Ell > Number ->
	    Res;
	true ->
	    generate(V,Number,[list_to_atom(lists:concat([V,Ell]))|Res],Ell)
    end.
		
last(V) ->
    last2(lists:reverse(atom_to_list(V))).

last2(RevL) ->
    list_to_integer(lists:reverse(get_digs(RevL))).
    
    
get_digs([H|T]) ->
    if
	H < $9+1,
	H > $0-1 ->
	    [H|get_digs(T)];
	true ->
	    []
    end.

get_curr([], Variable) ->
    Variable;
get_curr([{Variable,Digit}|_Tail], Variable) ->
    list_to_atom(lists:concat([Variable,Digit]));
get_curr([_|Tail], Variable) ->
    get_curr(Tail, Variable).

new_var(Vars, Variable) ->
    case lists:keyfind(Variable, 1, Vars) of
	false ->
	    [{Variable,1}|Vars];
	{Variable,Digit} ->
	    NewVars = lists:keydelete(Variable, 1, Vars),
	    [{Variable,Digit+1}|NewVars]
    end.

get_prev(Vars, Variable) ->
    case lists:keyfind(Variable, 1, Vars) of
	false ->
	    none;
	{Variable,Digit} when Digit =< 1 ->
	    Variable;
	{Variable,Digit} when Digit > 1 ->
	    list_to_atom(lists:concat([Variable,Digit-1]))
    end.

get_next(Vars, Variable) ->
    case lists:keyfind(Variable, 1, Vars) of
	false ->
	    list_to_atom(lists:concat([Variable,"1"]));
	{Variable,Digit} when Digit >= 0 ->
	    list_to_atom(lists:concat([Variable,Digit+1]))
    end.