%%--------------------------------------------------------------------
%% Copyright (c) 2017-2022 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_pool_sup).

-behaviour(supervisor).

-include("types.hrl").

-export([spec/1, spec/2]).

-export([ start_link/0
        , start_link/3
        , start_link/4
        ]).

-export([init/1]).

-define(POOL, emqx_pool).

-spec(spec(list()) -> supervisor:child_spec()).
spec(Args) ->
    spec(pool_sup, Args).

-spec(spec(any(), list()) -> supervisor:child_spec()).
spec(ChildId, Args) ->
    #{id       => ChildId,
      start    => {?MODULE, start_link, Args},
      restart  => transient,
      shutdown => infinity,
      type     => supervisor,
      modules  => [?MODULE]}.

%% @doc Start the default pool supervisor.
start_link() ->
    start_link(?POOL, random, {?POOL, start_link, []}).

-spec(start_link(atom() | tuple(), atom(), mfargs())
      -> {ok, pid()} | {error, term()}).
start_link(Pool, Type, MFA) ->
    start_link(Pool, Type, emqx_vm:schedulers(), MFA).

-spec(start_link(atom() | tuple(), atom(), pos_integer(), mfargs())
      -> {ok, pid()} | {error, term()}).
start_link(Pool, Type, Size, MFA) ->
    supervisor:start_link(?MODULE, [Pool, Type, Size, MFA]).

init([Pool, Type, Size, {M, F, Args}]) ->
    ok = ensure_pool(Pool, Type, [{size, Size}]),
    {ok, {{one_for_one, 10, 3600}, [
        begin
            ensure_pool_worker(Pool, {Pool, I}, I),
            #{id => {M, I},
              start => {M, F, [Pool, I | Args]},
              restart => transient,
              shutdown => 5000,
              type => worker,
              modules => [M]}
        end || I <- lists:seq(1, Size)]}}.

ensure_pool(Pool, Type, Opts) ->
    try gproc_pool:new(Pool, Type, Opts)
    catch
        error:exists -> ok
    end.

ensure_pool_worker(Pool, Name, Slot) ->
    try gproc_pool:add_worker(Pool, Name, Slot)
    catch
        error:exists -> ok
    end.