%%--------------------------------------------------------------------
%% Copyright (c) 2018-2022 EMQ Technologies Co., Ltd. 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.
%%--------------------------------------------------------------------

-module(emqx_mountpoint).

-include("emqx.hrl").
-include("types.hrl").

-export([ mount/2
        , unmount/2
        ]).

-export([replvar/2]).

-export_type([mountpoint/0]).

-type(mountpoint() :: binary()).

-spec(mount(maybe(mountpoint()), Any) -> Any
  when Any :: emqx_types:topic()
            | emqx_types:message()
            | emqx_types:topic_filters()).
mount(undefined, Any) ->
    Any;
mount(MountPoint, Topic) when is_binary(Topic) ->
    prefix(MountPoint, Topic);
mount(MountPoint, Msg = #message{topic = Topic}) ->
    Msg#message{topic = prefix(MountPoint, Topic)};
mount(MountPoint, TopicFilters) when is_list(TopicFilters) ->
    [{prefix(MountPoint, Topic), SubOpts} || {Topic, SubOpts} <- TopicFilters].

%% @private
-compile({inline, [prefix/2]}).
prefix(MountPoint, Topic) ->
    <<MountPoint/binary, Topic/binary>>.

-spec(unmount(maybe(mountpoint()), Any) -> Any
  when Any :: emqx_types:topic()
            | emqx_types:message()).
unmount(undefined, Any) ->
    Any;
unmount(MountPoint, Topic) when is_binary(Topic) ->
    case string:prefix(Topic, MountPoint) of
        nomatch -> Topic;
        Topic1  -> Topic1
    end;
unmount(MountPoint, Msg = #message{topic = Topic}) ->
    case string:prefix(Topic, MountPoint) of
        nomatch -> Msg;
        Topic1  -> Msg#message{topic = Topic1}
    end.

-spec(replvar(maybe(mountpoint()), map()) -> maybe(mountpoint())).
replvar(undefined, _Vars) ->
    undefined;
replvar(MountPoint, #{clientid := ClientId, username := Username}) ->
    lists:foldl(fun feed_var/2, MountPoint,
                [{<<"%c">>, ClientId}, {<<"%u">>, Username}]).

feed_var({<<"%c">>, ClientId}, MountPoint) ->
    emqx_topic:feed_var(<<"%c">>, ClientId, MountPoint);
feed_var({<<"%u">>, undefined}, MountPoint) ->
    MountPoint;
feed_var({<<"%u">>, Username}, MountPoint) ->
    emqx_topic:feed_var(<<"%u">>, Username, MountPoint).