%%%-------------------------------------------------------------------
%%% File    : ibrowse_lb.erl
%%% Author  : chandru <chandrashekhar.mullaparthi@t-mobile.co.uk>
%%% Description : 
%%%
%%% Created :  6 Mar 2008 by chandru <chandrashekhar.mullaparthi@t-mobile.co.uk>
%%%-------------------------------------------------------------------
-module(ibrowse_lb).
-author(chandru).
-behaviour(gen_server).
%%--------------------------------------------------------------------
%% Include files
%%--------------------------------------------------------------------

%%--------------------------------------------------------------------
%% External exports
-export([
	 start_link/1,
	 spawn_connection/6,
         stop/1
	]).

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

-record(state, {parent_pid,
		ets_tid,
		host,
		port,
		max_sessions,
		max_pipeline_size,
                proc_state
               }).

-include("ibrowse.hrl").

%%====================================================================
%% External functions
%%====================================================================
%%--------------------------------------------------------------------
%% Function: start_link/0
%% Description: Starts the server
%%--------------------------------------------------------------------
start_link(Args) ->
    gen_server:start_link(?MODULE, Args, []).

%%====================================================================
%% Server functions
%%====================================================================

%%--------------------------------------------------------------------
%% Function: init/1
%% Description: Initiates the server
%% Returns: {ok, State}          |
%%          {ok, State, Timeout} |
%%          ignore               |
%%          {stop, Reason}
%%--------------------------------------------------------------------
init([Host, Port]) ->
    process_flag(trap_exit, true),
    Max_sessions = ibrowse:get_config_value({max_sessions, Host, Port}, 10),
    Max_pipe_sz = ibrowse:get_config_value({max_pipeline_size, Host, Port}, 10),
    put(my_trace_flag, ibrowse_lib:get_trace_status(Host, Port)),
    put(ibrowse_trace_token, ["LB: ", Host, $:, integer_to_list(Port)]),
    State = #state{parent_pid = whereis(ibrowse),
		host = Host,
		port = Port,
		max_pipeline_size = Max_pipe_sz,
	        max_sessions = Max_sessions},
    State_1 = maybe_create_ets(State),
    {ok, State_1}.

spawn_connection(Lb_pid, Url,
		 Max_sessions,
		 Max_pipeline_size,
		 SSL_options,
		 Process_options)
  when is_pid(Lb_pid),
       is_record(Url, url),
       is_integer(Max_pipeline_size),
       is_integer(Max_sessions) ->
    gen_server:call(Lb_pid,
		    {spawn_connection, Url, Max_sessions, Max_pipeline_size, SSL_options, Process_options}).

stop(Lb_pid) ->
    case catch gen_server:call(Lb_pid, stop) of
        {'EXIT', {timeout, _}} ->
            exit(Lb_pid, kill);
        ok ->
            ok
    end.
%%--------------------------------------------------------------------
%% Function: handle_call/3
%% Description: Handling call messages
%% Returns: {reply, Reply, State}          |
%%          {reply, Reply, State, Timeout} |
%%          {noreply, State}               |
%%          {noreply, State, Timeout}      |
%%          {stop, Reason, Reply, State}   | (terminate/2 is called)
%%          {stop, Reason, State}            (terminate/2 is called)
%%--------------------------------------------------------------------

handle_call(stop, _From, #state{ets_tid = undefined} = State) ->
    gen_server:reply(_From, ok),
    {stop, normal, State};

handle_call(stop, _From, #state{ets_tid = Tid} = State) ->
    stop_all_conn_procs(Tid),
    gen_server:reply(_From, ok),
    {stop, normal, State};

handle_call(_, _From, #state{proc_state = shutting_down} = State) ->
    {reply, {error, shutting_down}, State};

handle_call({spawn_connection, Url, Max_sess, Max_pipe, SSL_options, Process_options}, _From,
	    State) ->
    State_1   = maybe_create_ets(State),
    Tid       = State_1#state.ets_tid,
    Tid_size  = ets:info(Tid, size),
    case Tid_size >= Max_sess of
        true ->
            Reply = find_best_connection(Tid, Max_pipe),
            {reply, Reply, State_1#state{max_sessions      = Max_sess,
                                         max_pipeline_size = Max_pipe}};
        false ->
            {ok, Pid} = ibrowse_http_client:start({Tid, Url, SSL_options}, Process_options),
            Ts = os:timestamp(),
            ets:insert(Tid, {{1, Ts, Pid}, []}),
            {reply, {ok, {1, Ts, Pid}}, State_1#state{max_sessions      = Max_sess,
						      max_pipeline_size = Max_pipe}}
    end;

handle_call(Request, _From, State) ->
    Reply = {unknown_request, Request},
    {reply, Reply, State}.

%%--------------------------------------------------------------------
%% Function: handle_cast/2
%% Description: Handling cast messages
%% Returns: {noreply, State}          |
%%          {noreply, State, Timeout} |
%%          {stop, Reason, State}            (terminate/2 is called)
%%--------------------------------------------------------------------
handle_cast(_Msg, State) ->
    {noreply, State}.

%%--------------------------------------------------------------------
%% Function: handle_info/2
%% Description: Handling all non call/cast messages
%% Returns: {noreply, State}          |
%%          {noreply, State, Timeout} |
%%          {stop, Reason, State}            (terminate/2 is called)
%%--------------------------------------------------------------------

handle_info({trace, Bool}, #state{ets_tid = undefined} = State) ->
    put(my_trace_flag, Bool),
    {noreply, State};

handle_info({trace, Bool}, #state{ets_tid = Tid} = State) ->
    ets:foldl(fun({{_, Pid}, _}, Acc) when is_pid(Pid) ->
		      catch Pid ! {trace, Bool},
		      Acc;
		 (_, Acc) ->
		      Acc
	      end, undefined, Tid),
    put(my_trace_flag, Bool),
    {noreply, State};

handle_info(timeout, State) ->
    %% We can't shutdown the process immediately because a request
    %% might be in flight. So we first remove the entry from the
    %% ibrowse_lb ets table, and then shutdown a couple of seconds
    %% later
    ets:delete(ibrowse_lb, {State#state.host, State#state.port}),
    erlang:send_after(2000, self(), shutdown),
    {noreply, State#state{proc_state = shutting_down}};

handle_info(shutdown, State) ->
    {stop, normal, State};

handle_info(_Info, State) ->
    {noreply, State}.

%%--------------------------------------------------------------------
%% Function: terminate/2
%% Description: Shutdown the server
%% Returns: any (ignored by gen_server)
%%--------------------------------------------------------------------
terminate(_Reason, #state{host = Host, port = Port, ets_tid = Tid} = _State) ->
    catch ets:delete(ibrowse_lb, {Host, Port}),
    stop_all_conn_procs(Tid),
    ok.

stop_all_conn_procs(Tid) ->
    ets:foldl(fun({{_, _, Pid}, _}, Acc) ->
                      ibrowse_http_client:stop(Pid),
                      Acc
              end, [], Tid).

%%--------------------------------------------------------------------
%% Func: code_change/3
%% Purpose: Convert process state when code is changed
%% Returns: {ok, NewState}
%%--------------------------------------------------------------------
code_change(_OldVsn, State, _Extra) ->
    {ok, State}.

%%--------------------------------------------------------------------
%%% Internal functions
%%--------------------------------------------------------------------
find_best_connection(Tid, Max_pipe) ->
    case ets:first(Tid) of
        {Spec_size, Ts, Pid} = First when Spec_size < Max_pipe ->
	    ets:delete(Tid, First),
	    ets:insert(Tid, {{Spec_size + 1, Ts, Pid}, []}),
	    {ok, First};
        _ ->
            {error, retry_later}
    end.

maybe_create_ets(#state{ets_tid = undefined, host = Host, port = Port} = State) ->
    Tid = ets:new(ibrowse_lb, [public, ordered_set]),
    ets:insert(ibrowse_lb, #lb_pid{host_port = {Host, Port}, pid = self(), ets_tid = Tid}),
    State#state{ets_tid = Tid};
maybe_create_ets(State) ->
    State.