%%--------------------------------------------------------------------
%% Copyright (c) 2020-2023 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_rule_engine).

-behaviour(gen_server).
-behaviour(emqx_config_handler).

-include("rule_engine.hrl").
-include_lib("emqx/include/logger.hrl").
-include_lib("stdlib/include/qlc.hrl").

-export([start_link/0]).

-export([
    post_config_update/5,
    config_key_path/0
]).

%% Rule Management

-export([load_rules/0]).

-export([
    create_rule/1,
    insert_rule/1,
    update_rule/1,
    delete_rule/1,
    get_rule/1
]).

-export([
    get_rules/0,
    get_rules_for_topic/1,
    get_rules_with_same_event/1,
    get_rule_ids_by_action/1,
    ensure_action_removed/2,
    get_rules_ordered_by_ts/0
]).

%% exported for cluster_call
-export([
    do_delete_rule/1,
    do_insert_rule/1
]).

-export([
    load_hooks_for_rule/1,
    unload_hooks_for_rule/1,
    maybe_add_metrics_for_rule/1,
    clear_metrics_for_rule/1,
    reset_metrics_for_rule/1
]).

%% exported for `emqx_telemetry'
-export([get_basic_usage_info/0]).

-export([now_ms/0]).

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

-define(RULE_ENGINE, ?MODULE).

-define(T_CALL, infinity).

%% NOTE: This order cannot be changed! This is to make the metric working during relup.
%% Append elements to this list to add new metrics.
-define(METRICS, [
    'matched',
    'passed',
    'failed',
    'failed.exception',
    'failed.no_result',
    'actions.total',
    'actions.success',
    'actions.failed',
    'actions.failed.out_of_service',
    'actions.failed.unknown'
]).

-define(RATE_METRICS, ['matched']).

-type action_name() :: binary() | #{function := binary()}.

config_key_path() ->
    [rule_engine, rules].

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

%%------------------------------------------------------------------------------
%% The config handler for emqx_rule_engine
%%------------------------------------------------------------------------------
post_config_update(_, _Req, NewRules, OldRules, _AppEnvs) ->
    #{added := Added, removed := Removed, changed := Updated} =
        emqx_map_lib:diff_maps(NewRules, OldRules),
    maps_foreach(
        fun({Id, {_Old, New}}) ->
            {ok, _} = update_rule(New#{id => bin(Id)})
        end,
        Updated
    ),
    maps_foreach(
        fun({Id, _Rule}) ->
            ok = delete_rule(bin(Id))
        end,
        Removed
    ),
    maps_foreach(
        fun({Id, Rule}) ->
            {ok, _} = create_rule(Rule#{id => bin(Id)})
        end,
        Added
    ),
    {ok, get_rules()}.

%%------------------------------------------------------------------------------
%% APIs for rules
%%------------------------------------------------------------------------------

-spec load_rules() -> ok.
load_rules() ->
    maps_foreach(
        fun
            ({Id, #{metadata := #{created_at := CreatedAt}} = Rule}) ->
                create_rule(Rule#{id => bin(Id)}, CreatedAt);
            ({Id, Rule}) ->
                create_rule(Rule#{id => bin(Id)})
        end,
        emqx:get_config([rule_engine, rules], #{})
    ).

-spec create_rule(map()) -> {ok, rule()} | {error, term()}.
create_rule(Params) ->
    create_rule(Params, now_ms()).

create_rule(Params = #{id := RuleId}, CreatedAt) when is_binary(RuleId) ->
    case get_rule(RuleId) of
        not_found -> parse_and_insert(Params, CreatedAt);
        {ok, _} -> {error, already_exists}
    end.

-spec update_rule(map()) -> {ok, rule()} | {error, term()}.
update_rule(Params = #{id := RuleId}) when is_binary(RuleId) ->
    case get_rule(RuleId) of
        not_found ->
            {error, not_found};
        {ok, #{created_at := CreatedAt}} ->
            parse_and_insert(Params, CreatedAt)
    end.

-spec delete_rule(RuleId :: rule_id()) -> ok.
delete_rule(RuleId) when is_binary(RuleId) ->
    gen_server:call(?RULE_ENGINE, {delete_rule, RuleId}, ?T_CALL).

-spec insert_rule(Rule :: rule()) -> ok.
insert_rule(Rule) ->
    gen_server:call(?RULE_ENGINE, {insert_rule, Rule}, ?T_CALL).

%%------------------------------------------------------------------------------
%% Rule Management
%%------------------------------------------------------------------------------

-spec get_rules() -> [rule()].
get_rules() ->
    get_all_records(?RULE_TAB).

get_rules_ordered_by_ts() ->
    lists:sort(
        fun(#{created_at := CreatedA}, #{created_at := CreatedB}) ->
            CreatedA =< CreatedB
        end,
        get_rules()
    ).

-spec get_rules_for_topic(Topic :: binary()) -> [rule()].
get_rules_for_topic(Topic) ->
    [
        Rule
     || Rule = #{from := From} <- get_rules(),
        emqx_plugin_libs_rule:can_topic_match_oneof(Topic, From)
    ].

-spec get_rules_with_same_event(Topic :: binary()) -> [rule()].
get_rules_with_same_event(Topic) ->
    EventName = emqx_rule_events:event_name(Topic),
    [
        Rule
     || Rule = #{from := From} <- get_rules(),
        lists:any(fun(T) -> is_of_event_name(EventName, T) end, From)
    ].

-spec get_rule_ids_by_action(action_name()) -> [rule_id()].
get_rule_ids_by_action(ActionName) when is_binary(ActionName) ->
    [
        Id
     || #{actions := Acts, id := Id} <- get_rules(),
        lists:any(fun(A) -> A =:= ActionName end, Acts)
    ];
get_rule_ids_by_action(#{function := FuncName}) when is_binary(FuncName) ->
    {Mod, Fun} =
        case string:split(FuncName, ":", leading) of
            [M, F] -> {binary_to_module(M), F};
            [F] -> {emqx_rule_actions, F}
        end,
    [
        Id
     || #{actions := Acts, id := Id} <- get_rules(),
        contains_actions(Acts, Mod, Fun)
    ].

-spec ensure_action_removed(rule_id(), action_name()) -> ok.
ensure_action_removed(RuleId, ActionName) ->
    FilterFunc =
        fun
            (Func, Func) -> false;
            (#{<<"function">> := Func}, #{function := Func}) -> false;
            (_, _) -> true
        end,
    case emqx:get_raw_config([rule_engine, rules, RuleId], not_found) of
        not_found ->
            ok;
        #{<<"actions">> := Acts} ->
            NewActs = [AName || AName <- Acts, FilterFunc(AName, ActionName)],
            {ok, _} = emqx_conf:update(
                emqx_rule_engine:config_key_path() ++ [RuleId, actions],
                NewActs,
                #{override_to => cluster}
            ),
            ok
    end.

is_of_event_name(EventName, Topic) ->
    EventName =:= emqx_rule_events:event_name(Topic).

-spec get_rule(Id :: rule_id()) -> {ok, rule()} | not_found.
get_rule(Id) ->
    case ets:lookup(?RULE_TAB, Id) of
        [{Id, Rule}] -> {ok, Rule#{id => Id}};
        [] -> not_found
    end.

load_hooks_for_rule(#{from := Topics}) ->
    lists:foreach(fun emqx_rule_events:load/1, Topics).

maybe_add_metrics_for_rule(Id) ->
    case emqx_metrics_worker:has_metrics(rule_metrics, Id) of
        true ->
            ok = reset_metrics_for_rule(Id);
        false ->
            ok = emqx_metrics_worker:create_metrics(rule_metrics, Id, ?METRICS, ?RATE_METRICS)
    end.

clear_metrics_for_rule(Id) ->
    ok = emqx_metrics_worker:clear_metrics(rule_metrics, Id).

-spec reset_metrics_for_rule(rule_id()) -> ok.
reset_metrics_for_rule(Id) ->
    emqx_metrics_worker:reset_metrics(rule_metrics, Id).

unload_hooks_for_rule(#{id := Id, from := Topics}) ->
    lists:foreach(
        fun(Topic) ->
            case get_rules_with_same_event(Topic) of
                %% we are now deleting the last rule
                [#{id := Id0}] when Id0 == Id ->
                    emqx_rule_events:unload(Topic);
                _ ->
                    ok
            end
        end,
        Topics
    ).

%%------------------------------------------------------------------------------
%% Telemetry helper functions
%%------------------------------------------------------------------------------

-spec get_basic_usage_info() ->
    #{
        num_rules => non_neg_integer(),
        referenced_bridges =>
            #{BridgeType => non_neg_integer()}
    }
when
    BridgeType :: atom().
get_basic_usage_info() ->
    try
        Rules = get_rules(),
        EnabledRules =
            lists:filter(
                fun(#{enable := Enabled}) -> Enabled end,
                Rules
            ),
        NumRules = length(EnabledRules),
        ReferencedBridges =
            lists:foldl(
                fun(#{actions := Actions, from := From}, Acc) ->
                    BridgeIDs0 = [BridgeID || <<"$bridges/", BridgeID/binary>> <- From],
                    BridgeIDs1 = lists:filter(fun is_binary/1, Actions),
                    tally_referenced_bridges(BridgeIDs0 ++ BridgeIDs1, Acc)
                end,
                #{},
                EnabledRules
            ),
        #{
            num_rules => NumRules,
            referenced_bridges => ReferencedBridges
        }
    catch
        _:_ ->
            #{
                num_rules => 0,
                referenced_bridges => #{}
            }
    end.

tally_referenced_bridges(BridgeIDs, Acc0) ->
    lists:foldl(
        fun(BridgeID, Acc) ->
            {BridgeType, _BridgeName} = emqx_bridge_resource:parse_bridge_id(BridgeID),
            maps:update_with(
                BridgeType,
                fun(X) -> X + 1 end,
                1,
                Acc
            )
        end,
        Acc0,
        BridgeIDs
    ).

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

init([]) ->
    _TableId = ets:new(?KV_TAB, [
        named_table,
        set,
        public,
        {write_concurrency, true},
        {read_concurrency, true}
    ]),
    ok = emqx_config_handler:add_handler(
        [rule_engine, jq_implementation_module],
        emqx_rule_engine_schema
    ),
    {ok, #{}}.

handle_call({insert_rule, Rule}, _From, State) ->
    do_insert_rule(Rule),
    {reply, ok, State};
handle_call({delete_rule, Rule}, _From, State) ->
    do_delete_rule(Rule),
    {reply, ok, State};
handle_call(Req, _From, State) ->
    ?SLOG(error, #{msg => "unexpected_call", request => Req}),
    {reply, ignored, State}.

handle_cast(Msg, State) ->
    ?SLOG(error, #{msg => "unexpected_cast", request => Msg}),
    {noreply, State}.

handle_info(Info, State) ->
    ?SLOG(error, #{msg => "unexpected_info", request => Info}),
    {noreply, State}.

terminate(_Reason, _State) ->
    ok.

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

%%------------------------------------------------------------------------------
%% Internal Functions
%%------------------------------------------------------------------------------

parse_and_insert(Params = #{id := RuleId, sql := Sql, actions := Actions}, CreatedAt) ->
    case emqx_rule_sqlparser:parse(Sql) of
        {ok, Select} ->
            Rule = #{
                id => RuleId,
                name => maps:get(name, Params, <<"">>),
                created_at => CreatedAt,
                updated_at => now_ms(),
                enable => maps:get(enable, Params, true),
                sql => Sql,
                actions => parse_actions(Actions),
                description => maps:get(description, Params, ""),
                %% -- calculated fields:
                from => emqx_rule_sqlparser:select_from(Select),
                is_foreach => emqx_rule_sqlparser:select_is_foreach(Select),
                fields => emqx_rule_sqlparser:select_fields(Select),
                doeach => emqx_rule_sqlparser:select_doeach(Select),
                incase => emqx_rule_sqlparser:select_incase(Select),
                conditions => emqx_rule_sqlparser:select_where(Select)
                %% -- calculated fields end
            },
            ok = insert_rule(Rule),
            {ok, Rule};
        {error, Reason} ->
            {error, Reason}
    end.

do_insert_rule(#{id := Id} = Rule) ->
    ok = load_hooks_for_rule(Rule),
    ok = maybe_add_metrics_for_rule(Id),
    true = ets:insert(?RULE_TAB, {Id, maps:remove(id, Rule)}),
    ok.

do_delete_rule(RuleId) ->
    case get_rule(RuleId) of
        {ok, Rule} ->
            ok = unload_hooks_for_rule(Rule),
            ok = clear_metrics_for_rule(RuleId),
            true = ets:delete(?RULE_TAB, RuleId),
            ok;
        not_found ->
            ok
    end.

parse_actions(Actions) ->
    [do_parse_action(Act) || Act <- Actions].

do_parse_action(Action) when is_map(Action) ->
    emqx_rule_actions:parse_action(Action);
do_parse_action(BridgeChannelId) when is_binary(BridgeChannelId) ->
    BridgeChannelId.

get_all_records(Tab) ->
    [Rule#{id => Id} || {Id, Rule} <- ets:tab2list(Tab)].

maps_foreach(Fun, Map) ->
    lists:foreach(Fun, maps:to_list(Map)).

now_ms() ->
    erlang:system_time(millisecond).

bin(A) when is_atom(A) -> atom_to_binary(A, utf8);
bin(B) when is_binary(B) -> B.

binary_to_module(ModName) ->
    try
        binary_to_existing_atom(ModName, utf8)
    catch
        error:badarg ->
            not_exist_mod
    end.

contains_actions(Actions, Mod0, Func0) ->
    lists:any(
        fun
            (#{mod := Mod, func := Func}) when Mod =:= Mod0; Func =:= Func0 -> true;
            (_) -> false
        end,
        Actions
    ).