%% Copyright (c) 2018 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(wolff_client_sup).

-behaviour(supervisor).

-export([start_link/0, init/1]).

-export([ensure_present/3, ensure_absence/1, find_client/1]).

-define(SUPERVISOR, ?MODULE).

start_link() -> supervisor:start_link({local, ?SUPERVISOR}, ?MODULE, []).

init([]) ->
  SupFlags = #{strategy => one_for_one,
               intensity => 10,
               period => 5
              },
  Children = [], %% dynamically added/stopped
  {ok, {SupFlags, Children}}.

%% ensure a client started under supervisor
-spec ensure_present(wolff:client_id(), [wolff:host()], wolff_client:config()) ->
  {ok, pid()} | {error, client_not_running}.
ensure_present(ClientId, Hosts, Config) ->
  ChildSpec = child_spec(ClientId, Hosts, Config),
  case supervisor:start_child(?SUPERVISOR, ChildSpec) of
    {ok, Pid} -> {ok, Pid};
    {error, {already_started, Pid}} -> {ok, Pid};
    {error, already_present} -> {error, client_not_running}
  end.

%% ensure client stopped and deleted under supervisor
-spec ensure_absence(wolff:client_id()) -> ok.
ensure_absence(ClientId) ->
  case supervisor:terminate_child(?SUPERVISOR, ClientId) of
    ok -> ok = supervisor:delete_child(?SUPERVISOR, ClientId);
    {error, not_found} -> ok
  end.

%% find client pid from client id
-spec find_client(wolff:client_id()) -> {ok, pid()} | {error, any()}.
find_client(ClientId) ->
  Children = supervisor:which_children(?SUPERVISOR),
  case lists:keyfind(ClientId, 1, Children) of
    {ClientId, Client, _, _} when is_pid(Client) ->
      {ok, Client};
    {ClientId, Restarting, _, _} ->
      {error, Restarting};
    false ->
      {error, no_such_client}
  end.

child_spec(ClientId, Hosts, Config) ->
  #{id => ClientId,
    start => {wolff_client, start_link, [ClientId, Hosts, Config]},
    restart => transient,
    type => worker,
    modules => [wolff_client]
   }.