%%%-------------------------------------------------------------------
%%% Created : 11 Jan 2017 by Evgeny Khramtsov <ekhramtsov@process-one.net>
%%%
%%%
%%% ejabberd, Copyright (C) 2002-2019   ProcessOne
%%%
%%% 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, write to the Free Software Foundation, Inc.,
%%% 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
%%%
%%%-------------------------------------------------------------------
-module(ejabberd_router_mnesia).
-behaviour(ejabberd_router).
-behaviour(gen_server).

%% API
-export([init/0, register_route/5, unregister_route/3, find_routes/1,
	 get_all_routes/0, use_cache/0]).
%% gen_server callbacks
-export([init/1, handle_cast/2, handle_call/3, handle_info/2,
	 terminate/2, code_change/3, start_link/0]).

-include("ejabberd_router.hrl").
-include("logger.hrl").
-include_lib("stdlib/include/ms_transform.hrl").

-record(state, {}).

%%%===================================================================
%%% API
%%%===================================================================
-spec init() -> ok | {error, any()}.
init() ->
    Spec = {?MODULE, {?MODULE, start_link, []},
	    transient, 5000, worker, [?MODULE]},
    case supervisor:start_child(ejabberd_backend_sup, Spec) of
	{ok, _Pid} -> ok;
	Err -> Err
    end.

-spec start_link() -> {ok, pid()} | {error, any()}.
start_link() ->
    gen_server:start_link({local, ?MODULE}, ?MODULE, [], []).

use_cache() ->
    false.

register_route(Domain, ServerHost, LocalHint, undefined, Pid) ->
    F = fun () ->
		mnesia:write(#route{domain = Domain,
				    pid = Pid,
				    server_host = ServerHost,
				    local_hint = LocalHint})
	end,
    transaction(F);
register_route(Domain, ServerHost, _LocalHint, N, Pid) ->
    F = fun () ->
		case mnesia:wread({route, Domain}) of
		    [] ->
			mnesia:write(#route{domain = Domain,
					    server_host = ServerHost,
					    pid = Pid,
					    local_hint = 1}),
			lists:foreach(
			  fun (I) ->
				  mnesia:write(
				    #route{domain = Domain,
					   pid = undefined,
					   server_host = ServerHost,
					   local_hint = I})
			  end,
			  lists:seq(2, N));
		    Rs ->
			lists:any(
			  fun (#route{pid = undefined,
				      local_hint = I} = R) ->
				  mnesia:write(
				    #route{domain = Domain,
					   pid = Pid,
					   server_host = ServerHost,
					   local_hint = I}),
				  mnesia:delete_object(R),
				  true;
			      (_) -> false
			  end,
			  Rs)
		end
	end,
    transaction(F).

unregister_route(Domain, undefined, Pid) ->
    F = fun () ->
		case mnesia:match_object(
		       #route{domain = Domain, pid = Pid, _ = '_'}) of
		    [R] -> mnesia:delete_object(R);
		    _ -> ok
		end
	end,
    transaction(F);
unregister_route(Domain, _, Pid) ->
    F = fun () ->
		case mnesia:match_object(
		       #route{domain = Domain, pid = Pid, _ = '_'}) of
		    [R] ->
			I = R#route.local_hint,
			ServerHost = R#route.server_host,
			mnesia:write(#route{domain = Domain,
					    server_host = ServerHost,
					    pid = undefined,
					    local_hint = I}),
			mnesia:delete_object(R);
		    _ -> ok
		end
	end,
    transaction(F).

find_routes(Domain) ->
    {ok, mnesia:dirty_read(route, Domain)}.

get_all_routes() ->
    {ok, mnesia:dirty_select(
	   route,
	   ets:fun2ms(
	     fun(#route{domain = Domain, server_host = ServerHost})
		   when Domain /= ServerHost -> Domain
	     end))}.

%%%===================================================================
%%% gen_server callbacks
%%%===================================================================
init([]) ->
    update_tables(),
    ejabberd_mnesia:create(?MODULE, route,
			   [{ram_copies, [node()]},
			    {type, bag},
			    {attributes, record_info(fields, route)}]),
    mnesia:subscribe({table, route, simple}),
    lists:foreach(
      fun (Pid) -> erlang:monitor(process, Pid) end,
      mnesia:dirty_select(route,
			  [{#route{pid = '$1', _ = '_'}, [], ['$1']}])),
    {ok, #state{}}.

handle_call(_Request, _From, State) ->
    Reply = ok,
    {reply, Reply, State}.

handle_cast(_Msg, State) ->
    {noreply, State}.

handle_info({mnesia_table_event,
	     {write, #route{pid = Pid}, _ActivityId}}, State) ->
    erlang:monitor(process, Pid),
    {noreply, State};
handle_info({mnesia_table_event, _}, State) ->
    {noreply, State};
handle_info({'DOWN', _Ref, _Type, Pid, _Info}, State) ->
    F = fun () ->
		Es = mnesia:select(route,
				   [{#route{pid = Pid, _ = '_'}, [], ['$_']}]),
		lists:foreach(
		  fun(E) ->
			  if is_integer(E#route.local_hint) ->
				  LDomain = E#route.domain,
				  I = E#route.local_hint,
				  ServerHost = E#route.server_host,
				  mnesia:write(#route{domain = LDomain,
						      server_host = ServerHost,
						      pid = undefined,
						      local_hint = I}),
				  mnesia:delete_object(E);
			     true ->
				  mnesia:delete_object(E)
			  end
		  end, Es)
	end,
    transaction(F),
    {noreply, State};
handle_info(Info, State) ->
    ?ERROR_MSG("unexpected info: ~p", [Info]),
    {noreply, State}.

terminate(_Reason, _State) ->
    ok.

code_change(_OldVsn, State, _Extra) ->
    {ok, State}.

%%%===================================================================
%%% Internal functions
%%%===================================================================
transaction(F) ->
    case mnesia:transaction(F) of
	{atomic, _} ->
	    ok;
	{aborted, Reason} ->
	    ?ERROR_MSG("Mnesia transaction failed: ~p", [Reason]),
	    {error, db_failure}
    end.

-spec update_tables() -> ok.
update_tables() ->
    try
	mnesia:transform_table(route, ignore, record_info(fields, route))
    catch exit:{aborted, {no_exists, _}} ->
	    ok
    end,
    case lists:member(local_route, mnesia:system_info(tables)) of
	true -> mnesia:delete_table(local_route);
	false -> ok
    end.
