%%
%% Licensed to the Apache Software Foundation (ASF) under one
%% or more contributor license agreements. See the NOTICE file
%% distributed with this work for additional information
%% regarding copyright ownership. The ASF licenses this file
%% to you 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(thrift_reconnecting_client).

-behaviour(gen_server).

%% API
-export([
    call/3,
    get_stats/1,
    get_and_reset_stats/1
]).

-export([start_link/6]).

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

-record(state, {
    client = nil,
    host,
    port,
    thrift_svc,
    thrift_opts,
    reconn_min,
    reconn_max,
    reconn_time = 0,
    op_cnt_dict,
    op_time_dict
}).

%%====================================================================
%% API
%%====================================================================
%%--------------------------------------------------------------------
%% Function: start_link() -> {ok,Pid} | ignore | {error,Error}
%% Description: Starts the server
%%--------------------------------------------------------------------
start_link(
    Host,
    Port,
    ThriftSvc,
    ThriftOpts,
    ReconnMin,
    ReconnMax
) ->
    gen_server:start_link(
        ?MODULE,
        [
            Host,
            Port,
            ThriftSvc,
            ThriftOpts,
            ReconnMin,
            ReconnMax
        ],
        []
    ).

call(Pid, Op, Args) ->
    gen_server:call(Pid, {call, Op, Args}).

get_stats(Pid) ->
    gen_server:call(Pid, get_stats).

get_and_reset_stats(Pid) ->
    gen_server:call(Pid, get_and_reset_stats).

%%====================================================================
%% gen_server callbacks
%%====================================================================

%%--------------------------------------------------------------------
%% Function: init(Args) -> {ok, State} |
%%                         {ok, State, Timeout} |
%%                         ignore               |
%%                         {stop, Reason}
%% Description: Start the server.
%%--------------------------------------------------------------------
init([Host, Port, TSvc, TOpts, ReconnMin, ReconnMax]) ->
    process_flag(trap_exit, true),

    State = #state{
        host = Host,
        port = Port,
        thrift_svc = TSvc,
        thrift_opts = TOpts,
        reconn_min = ReconnMin,
        reconn_max = ReconnMax,
        op_cnt_dict = dict:new(),
        op_time_dict = dict:new()
    },

    {ok, try_connect(State)}.

%%--------------------------------------------------------------------
%% Function: %% handle_call(Request, From, State) -> {reply, Reply, State} |
%%                                                   {reply, Reply, State, Timeout} |
%%                                                   {noreply, State} |
%%                                                   {noreply, State, Timeout} |
%%                                                   {stop, Reason, Reply, State} |
%%                                                   {stop, Reason, State}
%% Description: Handling call messages
%%--------------------------------------------------------------------
handle_call(
    {call, Op, _},
    _From,
    State = #state{client = nil}
) ->
    {reply, {error, noconn}, incr_stats(Op, "failfast", 1, State)};
handle_call(
    {call, Op, Args},
    _From,
    State = #state{client = Client}
) ->
    Timer = timer_fun(),
    Result = (catch thrift_client:call(Client, Op, Args)),
    Time = Timer(),

    case Result of
        {C, {ok, Reply}} ->
            S = incr_stats(Op, "success", Time, State#state{client = C}),
            {reply, {ok, Reply}, S};
        {_, {E, Msg}} when E == error; E == exception ->
            S = incr_stats(Op, "error", Time, try_connect(State)),
            {reply, {E, Msg}, S};
        Other ->
            S = incr_stats(Op, "error", Time, try_connect(State)),
            {reply, Other, S}
    end;
handle_call(
    get_stats,
    _From,
    State = #state{}
) ->
    {reply, stats(State), State};
handle_call(
    get_and_reset_stats,
    _From,
    State = #state{}
) ->
    {reply, stats(State), reset_stats(State)}.

%%--------------------------------------------------------------------
%% Function: handle_cast(Msg, State) -> {noreply, State} |
%%                                      {noreply, State, Timeout} |
%%                                      {stop, Reason, State}
%% Description: Handling cast messages
%%--------------------------------------------------------------------
handle_cast(_Msg, State) ->
    {noreply, State}.

%%--------------------------------------------------------------------
%% Function: handle_info(Info, State) -> {noreply, State} |
%%                                       {noreply, State, Timeout} |
%%                                       {stop, Reason, State}
%% Description: Handling all non call/cast messages
%%--------------------------------------------------------------------
handle_info(try_connect, State) ->
    {noreply, try_connect(State)};
handle_info(_Info, State) ->
    {noreply, State}.

%%--------------------------------------------------------------------
%% Function: terminate(Reason, State) -> void()
%% Description: This function is called by a gen_server when it is about to
%% terminate. It should be the opposite of Module:init/1 and do any necessary
%% cleaning up. When it returns, the gen_server terminates with Reason.
%% The return value is ignored.
%%--------------------------------------------------------------------
terminate(_Reason, #state{client = Client}) ->
    thrift_client:close(Client),
    ok.

%%--------------------------------------------------------------------
%% Func: code_change(OldVsn, State, Extra) -> {ok, NewState}
%% Description: Convert process state when code is changed
%%--------------------------------------------------------------------
code_change(_OldVsn, State, _Extra) ->
    {ok, State}.

%%--------------------------------------------------------------------
%%% Internal functions
%%--------------------------------------------------------------------
try_connect(
    State = #state{
        client = OldClient,
        host = Host,
        port = Port,
        thrift_svc = TSvc,
        thrift_opts = TOpts
    }
) ->
    case OldClient of
        nil -> ok;
        _ -> (catch thrift_client:close(OldClient))
    end,

    case catch thrift_client_util:new(Host, Port, TSvc, TOpts) of
        {ok, Client} ->
            State#state{client = Client, reconn_time = 0};
        {E, Msg} when E == error; E == exception ->
            ReconnTime = reconn_time(State),
            error_logger:error_msg(
                "[~w] ~w connect failed (~w), trying again in ~w ms~n",
                [self(), TSvc, Msg, ReconnTime]
            ),
            erlang:send_after(ReconnTime, self(), try_connect),
            State#state{client = nil, reconn_time = ReconnTime}
    end.

reconn_time(#state{reconn_min = ReconnMin, reconn_time = 0}) ->
    ReconnMin;
reconn_time(#state{reconn_max = ReconnMax, reconn_time = ReconnMax}) ->
    ReconnMax;
reconn_time(#state{reconn_max = ReconnMax, reconn_time = R}) ->
    Backoff = 2 * R,
    case Backoff > ReconnMax of
        true -> ReconnMax;
        false -> Backoff
    end.

-ifdef(time_correction).
timer_fun() ->
    T1 = erlang:monotonic_time(),
    fun() ->
        T2 = erlang:monotonic_time(),
        erlang:convert_time_unit(T2 - T1, native, micro_seconds)
    end.
-else.
timer_fun() ->
    T1 = erlang:timestamp(),
    fun() ->
        T2 = erlang:timestamp(),
        timer:now_diff(T2, T1)
    end.
-endif.

incr_stats(
    Op,
    Result,
    Time,
    State = #state{
        op_cnt_dict = OpCntDict,
        op_time_dict = OpTimeDict
    }
) ->
    Key = lists:flatten([atom_to_list(Op), ["_" | Result]]),
    State#state{
        op_cnt_dict = dict:update_counter(Key, 1, OpCntDict),
        op_time_dict = dict:update_counter(Key, Time, OpTimeDict)
    }.

stats(#state{
    thrift_svc = TSvc,
    op_cnt_dict = OpCntDict,
    op_time_dict = OpTimeDict
}) ->
    Svc = atom_to_list(TSvc),

    F = fun(Key, Count, Stats) ->
        Name = lists:flatten([Svc, ["_" | Key]]),
        Micros = dict:fetch(Key, OpTimeDict),
        [{Name, Count, Micros} | Stats]
    end,

    dict:fold(F, [], OpCntDict).

reset_stats(State = #state{}) ->
    State#state{op_cnt_dict = dict:new(), op_time_dict = dict:new()}.