%%--------------------------------------------------------------------
%% Copyright (c) 2021-2022 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.
%%--------------------------------------------------------------------

%% @doc Manage the server status and reload strategy
-module(emqx_exhook_mgr).

-behaviour(gen_server).

-include("emqx_exhook.hrl").
-include_lib("emqx/include/logger.hrl").
-include_lib("snabbkaffe/include/snabbkaffe.hrl").

%% APIs
-export([start_link/0]).

%% Mgmt API
-export([
    list/0,
    lookup/1,
    enable/1,
    disable/1,
    server_info/1,
    all_servers_info/0,
    server_hooks_metrics/1
]).

%% Helper funcs
-export([
    running/0,
    server/1,
    hooks/1,
    init_ref_counter_table/0
]).

-export([
    update_config/2,
    pre_config_update/3,
    post_config_update/5
]).

%% gen_server callbacks
-export([
    init/1,
    handle_call/3,
    handle_cast/2,
    handle_info/2,
    terminate/2,
    code_change/3
]).

-export([roots/0]).

%% Running servers
-type state() :: #{servers := servers()}.

-type server_options() :: map().
-type server_name() :: binary().

-type status() ::
    connected
    | connecting
    | disconnected
    | disabled.

-type server() :: #{
    status := status(),
    timer := reference(),
    order := integer(),
    %% include the content of server_options
    atom() => any()
}.
-type servers() :: #{server_name() => server()}.

-type position() ::
    front
    | rear
    | {before, binary()}
    | {'after', binary()}.

-define(DEFAULT_TIMEOUT, 60000).
-define(REFRESH_INTERVAL, timer:seconds(5)).

-export_type([servers/0, server/0]).

%%--------------------------------------------------------------------
%% APIs
%%--------------------------------------------------------------------

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

list() ->
    call(list).

-spec lookup(server_name()) -> not_found | server().
lookup(Name) ->
    call({lookup, Name}).

enable(Name) ->
    update_config([exhook, servers], {enable, Name, true}).

disable(Name) ->
    update_config([exhook, servers], {enable, Name, false}).

server_info(Name) ->
    call({?FUNCTION_NAME, Name}).

all_servers_info() ->
    call(?FUNCTION_NAME).

server_hooks_metrics(Name) ->
    call({?FUNCTION_NAME, Name}).

call(Req) ->
    gen_server:call(?MODULE, Req, ?DEFAULT_TIMEOUT).

init_ref_counter_table() ->
    _ = ets:new(?HOOKS_REF_COUNTER, [named_table, public]).

%%=====================================================================
%% Hocon schema
roots() ->
    emqx_exhook_schema:server_config().

update_config(KeyPath, UpdateReq) ->
    case emqx_conf:update(KeyPath, UpdateReq, #{override_to => cluster}) of
        {ok, UpdateResult} ->
            #{post_config_update := #{?MODULE := Result}} = UpdateResult,
            {ok, Result};
        Error ->
            Error
    end.

pre_config_update(_, {add, #{<<"name">> := Name} = Conf}, OldConf) ->
    case lists:any(fun(#{<<"name">> := ExistedName}) -> ExistedName =:= Name end, OldConf) of
        true ->
            throw(already_exists);
        false ->
            NConf = maybe_write_certs(Conf),
            {ok, OldConf ++ [NConf]}
    end;
pre_config_update(_, {update, Name, Conf}, OldConf) ->
    case replace_conf(Name, fun(_) -> Conf end, OldConf) of
        not_found -> throw(not_found);
        NewConf -> {ok, lists:map(fun maybe_write_certs/1, NewConf)}
    end;
pre_config_update(_, {delete, ToDelete}, OldConf) ->
    case do_delete(ToDelete, OldConf) of
        not_found -> throw(not_found);
        NewConf -> {ok, NewConf}
    end;
pre_config_update(_, {move, Name, Position}, OldConf) ->
    case do_move(Name, Position, OldConf) of
        not_found -> throw(not_found);
        NewConf -> {ok, NewConf}
    end;
pre_config_update(_, {enable, Name, Enable}, OldConf) ->
    case
        replace_conf(
            Name,
            fun(Conf) -> Conf#{<<"enable">> => Enable} end,
            OldConf
        )
    of
        not_found -> throw(not_found);
        NewConf -> {ok, lists:map(fun maybe_write_certs/1, NewConf)}
    end.

post_config_update(_KeyPath, UpdateReq, NewConf, OldConf, _AppEnvs) ->
    Result = call({update_config, UpdateReq, NewConf}),
    try_clear_ssl_files(UpdateReq, NewConf, OldConf),
    {ok, Result}.

%%=====================================================================

%%--------------------------------------------------------------------
%% gen_server callbacks
%%--------------------------------------------------------------------

init([]) ->
    process_flag(trap_exit, true),
    emqx_conf:add_handler([exhook, servers], ?MODULE),
    ServerL = emqx:get_config([exhook, servers]),
    Servers = load_all_servers(ServerL),
    Servers2 = reorder(ServerL, Servers),
    refresh_tick(),
    {ok, #{servers => Servers2}}.

-spec load_all_servers(list(server_options())) -> servers().
load_all_servers(ServerL) ->
    load_all_servers(ServerL, #{}).

load_all_servers([#{name := Name} = Options | More], Servers) ->
    {_, Server} = do_load_server(options_to_server(Options)),
    load_all_servers(More, Servers#{Name => Server});
load_all_servers([], Servers) ->
    Servers.

handle_call(
    list,
    _From,
    State = #{servers := Servers}
) ->
    Infos = get_servers_info(Servers),
    OrderServers = sort_name_by_order(Infos, Servers),
    {reply, OrderServers, State};
handle_call(
    {update_config, {move, _Name, _Position}, NewConfL},
    _From,
    #{servers := Servers} = State
) ->
    Servers2 = reorder(NewConfL, Servers),
    {reply, ok, State#{servers := Servers2}};
handle_call({update_config, {delete, ToDelete}, _}, _From, State) ->
    emqx_exhook_metrics:on_server_deleted(ToDelete),

    #{servers := Servers} = State2 = do_unload_server(ToDelete, State),

    Servers2 = maps:remove(ToDelete, Servers),

    {reply, ok, update_servers(Servers2, State2)};
handle_call(
    {update_config, {add, RawConf}, NewConfL},
    _From,
    #{servers := Servers} = State
) ->
    {_, #{name := Name} = Conf} = emqx_config:check_config(?MODULE, RawConf),
    {Result, Server} = do_load_server(options_to_server(Conf)),
    Servers2 = Servers#{Name => Server},
    Servers3 = reorder(NewConfL, Servers2),
    {reply, Result, State#{servers := Servers3}};
handle_call({lookup, Name}, _From, State) ->
    {reply, where_is_server(Name, State), State};
handle_call({update_config, {update, Name, _Conf}, NewConfL}, _From, State) ->
    {Result, State2} = restart_server(Name, NewConfL, State),
    {reply, Result, State2};
handle_call({update_config, {enable, Name, _Enable}, NewConfL}, _From, State) ->
    {Result, State2} = restart_server(Name, NewConfL, State),
    {reply, Result, State2};
handle_call({server_info, Name}, _From, State) ->
    case where_is_server(Name, State) of
        not_found ->
            Result = not_found;
        #{status := Status} ->
            HooksMetrics = emqx_exhook_metrics:server_metrics(Name),
            Result = #{
                status => Status,
                metrics => HooksMetrics
            }
    end,
    {reply, Result, State};
handle_call(
    all_servers_info,
    _From,
    #{servers := Servers} = State
) ->
    Status = maps:map(fun(_Name, #{status := Status}) -> Status end, Servers),
    Metrics = emqx_exhook_metrics:servers_metrics(),

    Result = #{
        status => Status,
        metrics => Metrics
    },

    {reply, Result, State};
handle_call({server_hooks_metrics, Name}, _From, State) ->
    Result = emqx_exhook_metrics:hooks_metrics(Name),
    {reply, Result, State};
handle_call(_Request, _From, State) ->
    Reply = ok,
    {reply, Reply, State}.

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

handle_info({timeout, _Ref, {reload, Name}}, State) ->
    {_, NState} = do_reload_server(Name, State),
    {noreply, NState};
handle_info(refresh_tick, State) ->
    refresh_tick(),
    emqx_exhook_metrics:update(?REFRESH_INTERVAL),
    {noreply, State};
handle_info(_Info, State) ->
    {noreply, State}.

terminate(Reason, State = #{servers := Servers}) ->
    _ = unload_exhooks(),
    _ = maps:fold(
        fun(Name, _, AccIn) ->
            do_unload_server(Name, AccIn)
        end,
        State,
        Servers
    ),
    ?tp(info, exhook_mgr_terminated, #{reason => Reason, servers => Servers}),
    ok.

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

%%--------------------------------------------------------------------
%% Internal funcs
%%--------------------------------------------------------------------

unload_exhooks() ->
    [
        emqx_hooks:del(Name, {M, F})
     || {Name, {M, F, _A}} <- ?ENABLED_HOOKS
    ].

do_load_server(#{name := Name} = Server) ->
    case emqx_exhook_server:load(Name, Server) of
        {ok, ServerState} ->
            save(Name, ServerState),
            {ok, Server#{status => connected}};
        disable ->
            {ok, set_disable(Server)};
        {ErrorType, Reason} = Error ->
            ?SLOG(
                error,
                #{
                    msg => "failed_to_load_exhook_callback_server",
                    reason => Reason,
                    name => Name
                }
            ),
            case ErrorType of
                load_error ->
                    {ok, ensure_reload_timer(Server)};
                _ ->
                    {Error, Server#{status => disconnected}}
            end
    end.

do_load_server(#{name := Name} = Server, #{servers := Servers} = State) ->
    {Result, Server2} = do_load_server(Server),
    {Result, update_servers(Servers#{Name => Server2}, State)}.

-spec do_reload_server(server_name(), state()) ->
    {{error, term()}, state()}
    | {ok, state()}.
do_reload_server(Name, State) ->
    case where_is_server(Name, State) of
        not_found ->
            {{error, not_found}, State};
        #{timer := undefined} ->
            {ok, State};
        Server ->
            clean_reload_timer(Server),
            do_load_server(Server, State)
    end.

-spec do_unload_server(server_name(), state()) -> state().
do_unload_server(Name, #{servers := Servers} = State) ->
    case where_is_server(Name, State) of
        not_found ->
            State;
        #{status := disabled} ->
            State;
        Server ->
            clean_reload_timer(Server),
            case server(Name) of
                undefined ->
                    State;
                Service ->
                    ok = unsave(Name),
                    ok = emqx_exhook_server:unload(Service),
                    Servers2 = Servers#{Name := set_disable(Server)},
                    State#{servers := Servers2}
            end
    end.

ensure_reload_timer(#{name := Name, auto_reconnect := Intv} = Server) when is_integer(Intv) ->
    clean_reload_timer(Server),
    Ref = erlang:start_timer(Intv, self(), {reload, Name}),
    Server#{status := connecting, timer := Ref};
ensure_reload_timer(Server) ->
    Server#{status := disconnected}.

-spec clean_reload_timer(server()) -> ok.
clean_reload_timer(#{timer := undefined}) ->
    ok;
clean_reload_timer(#{timer := Timer}) ->
    _ = erlang:cancel_timer(Timer),
    ok.

-spec do_move(binary(), position(), list(server_options())) ->
    not_found | list(server_options()).
do_move(Name, Position, ConfL) ->
    move(ConfL, Name, Position, []).

move([#{<<"name">> := Name} = Server | T], Name, Position, HeadL) ->
    move_to(Position, Server, lists:reverse(HeadL) ++ T);
move([Server | T], Name, Position, HeadL) ->
    move(T, Name, Position, [Server | HeadL]);
move([], _Name, _Position, _HeadL) ->
    not_found.

move_to(?CMD_MOVE_FRONT, Server, ServerL) ->
    [Server | ServerL];
move_to(?CMD_MOVE_REAR, Server, ServerL) ->
    ServerL ++ [Server];
move_to(Position, Server, ServerL) ->
    move_to(ServerL, Position, Server, []).

move_to([#{<<"name">> := Name} | _] = T, ?CMD_MOVE_BEFORE(Name), Server, HeadL) ->
    lists:reverse(HeadL) ++ [Server | T];
move_to([#{<<"name">> := Name} = H | T], ?CMD_MOVE_AFTER(Name), Server, HeadL) ->
    lists:reverse(HeadL) ++ [H, Server | T];
move_to([H | T], Position, Server, HeadL) ->
    move_to(T, Position, Server, [H | HeadL]);
move_to([], _Position, _Server, _HeadL) ->
    not_found.

-spec do_delete(binary(), list(server_options())) ->
    not_found | list(server_options()).
do_delete(ToDelete, OldConf) ->
    case lists:any(fun(#{<<"name">> := ExistedName}) -> ExistedName =:= ToDelete end, OldConf) of
        true ->
            lists:filter(
                fun(#{<<"name">> := Name}) -> Name =/= ToDelete end,
                OldConf
            );
        false ->
            not_found
    end.

-spec reorder(list(server_options()), servers()) -> servers().
reorder(ServerL, Servers) ->
    Orders = reorder(ServerL, 1, Servers),
    update_order(Orders),
    Orders.

reorder([#{name := Name} | T], Order, Servers) ->
    reorder(T, Order + 1, update_order(Name, Servers, Order));
reorder([], _Order, Servers) ->
    Servers.

update_order(Name, Servers, Order) ->
    Server = maps:get(Name, Servers),
    Servers#{Name := Server#{order := Order}}.

get_servers_info(Svrs) ->
    Fold = fun(Name, Conf, Acc) ->
        [
            maps:merge(Conf, #{hooks => hooks(Name)})
            | Acc
        ]
    end,
    maps:fold(Fold, [], Svrs).

where_is_server(Name, #{servers := Servers}) ->
    maps:get(Name, Servers, not_found).

-type replace_fun() :: fun((server_options()) -> server_options()).

-spec replace_conf(binary(), replace_fun(), list(server_options())) ->
    not_found
    | list(server_options()).
replace_conf(Name, ReplaceFun, ConfL) ->
    replace_conf(ConfL, Name, ReplaceFun, []).

replace_conf([#{<<"name">> := Name} = H | T], Name, ReplaceFun, HeadL) ->
    New = ReplaceFun(H),
    lists:reverse(HeadL) ++ [New | T];
replace_conf([H | T], Name, ReplaceFun, HeadL) ->
    replace_conf(T, Name, ReplaceFun, [H | HeadL]);
replace_conf([], _, _, _) ->
    not_found.

-spec restart_server(binary(), list(server_options()), state()) ->
    {ok, state()}
    | {{error, term()}, state()}.
restart_server(Name, ConfL, State) ->
    case lists:search(fun(#{name := CName}) -> CName =:= Name end, ConfL) of
        false ->
            {{error, not_found}, State};
        {value, Conf} ->
            case where_is_server(Name, State) of
                not_found ->
                    {{error, not_found}, State};
                Server ->
                    Server2 = maps:merge(Server, Conf),
                    State2 = do_unload_server(Name, State),
                    do_load_server(Server2, State2)
            end
    end.

sort_name_by_order(Names, Orders) ->
    lists:sort(
        fun
            (A, B) when is_binary(A) ->
                emqx_map_lib:deep_get([A, order], Orders) <
                    emqx_map_lib:deep_get([B, order], Orders);
            (#{name := A}, #{name := B}) ->
                emqx_map_lib:deep_get([A, order], Orders) <
                    emqx_map_lib:deep_get([B, order], Orders)
        end,
        Names
    ).

refresh_tick() ->
    erlang:send_after(?REFRESH_INTERVAL, self(), ?FUNCTION_NAME).

options_to_server(Options) ->
    maps:merge(Options, #{status => disconnected, timer => undefined, order => 0}).

update_servers(Servers, State) ->
    update_order(Servers),
    State#{servers := Servers}.

set_disable(Server) ->
    Server#{status := disabled, timer := undefined}.

%%--------------------------------------------------------------------
%% Server state persistent
save(Name, ServerState) ->
    Saved = persistent_term:get(?APP, []),
    persistent_term:put(?APP, lists:reverse([Name | Saved])),
    persistent_term:put({?APP, Name}, ServerState).

unsave(Name) ->
    case persistent_term:get(?APP, []) of
        [] ->
            ok;
        Saved ->
            case lists:member(Name, Saved) of
                false ->
                    ok;
                true ->
                    persistent_term:put(?APP, lists:delete(Name, Saved))
            end
    end,
    persistent_term:erase({?APP, Name}),
    ok.

running() ->
    persistent_term:get(?APP, []).

server(Name) ->
    case persistent_term:get({?APP, Name}, undefined) of
        undefined -> undefined;
        Service -> Service
    end.

update_order(Servers) ->
    Running = running(),
    Orders = maps:filter(
        fun
            (Name, #{status := connected}) ->
                lists:member(Name, Running);
            (_, _) ->
                false
        end,
        Servers
    ),
    Running2 = sort_name_by_order(Running, Orders),
    persistent_term:put(?APP, Running2).

hooks(Name) ->
    case server(Name) of
        undefined ->
            [];
        Service ->
            emqx_exhook_server:hooks(Service)
    end.

maybe_write_certs(#{<<"name">> := Name} = Conf) ->
    case
        emqx_tls_lib:ensure_ssl_files(
            ssl_file_path(Name), maps:get(<<"ssl">>, Conf, undefined)
        )
    of
        {ok, SSL} ->
            new_ssl_source(Conf, SSL);
        {error, Reason} ->
            ?SLOG(error, Reason#{msg => "bad_ssl_config"}),
            throw({bad_ssl_config, Reason})
    end.

ssl_file_path(Name) ->
    filename:join(["exhook", Name]).

new_ssl_source(Source, undefined) ->
    Source;
new_ssl_source(Source, SSL) ->
    Source#{<<"ssl">> => SSL}.

try_clear_ssl_files({delete, Name}, _NewConf, OldConfs) ->
    OldSSL = find_server_ssl_cfg(Name, OldConfs),
    emqx_tls_lib:delete_ssl_files(ssl_file_path(Name), undefined, OldSSL);
try_clear_ssl_files({Op, Name, _}, NewConfs, OldConfs) when
    Op =:= update; Op =:= enable
->
    NewSSL = find_server_ssl_cfg(Name, NewConfs),
    OldSSL = find_server_ssl_cfg(Name, OldConfs),
    emqx_tls_lib:delete_ssl_files(ssl_file_path(Name), NewSSL, OldSSL);
try_clear_ssl_files(_Req, _NewConf, _OldConf) ->
    ok.

search_server_cfg(Name, Confs) ->
    lists:search(
        fun
            (#{name := SvrName}) when SvrName =:= Name ->
                true;
            (_) ->
                false
        end,
        Confs
    ).

find_server_ssl_cfg(Name, Confs) ->
    case search_server_cfg(Name, Confs) of
        {value, Value} ->
            maps:get(ssl, Value, undefined);
        false ->
            undefined
    end.