%% Author: hillqand
%% Created: 5 dec 2007
%% Description: TODO: Add description to priority_queue
-module(priority_queue).

-define(EMPTY, []).

%%
%% Exported Functions
%%
-export([start_link/0,
         push/3,
         pull/1]).

-export([init/1,
         write_debug/3,
         system_continue/3,
         system_terminate/4]).

%%
%% API Functions
%%
start_link() ->
    proc_lib:start_link(?MODULE, init, [self()]).

push(Pid, Priority, Message) when is_integer(Priority) ->
    Pid ! {push, Priority, Message},
    ok.

pull(Pid) ->
    Ref = make_ref(),
    Pid ! {pull, self(), Ref},
    receive
    	{Ref, Message} ->
            Message
    end.


init(Parent) ->
    Deb = sys:debug_options([]),
    proc_lib:init_ack(Parent, {ok, self()}),    
    loop(Parent, Deb, ?EMPTY).
%%    proc_lib:hibernate(?MODULE, loop, [Parent, Deb, ?EMPTY]).

write_debug(Dev, Event, Name) ->
    io:format(Dev, "~p event = ~p~n", [Name, Event]).

system_continue(Parent, Deb, Queue) ->
    loop(Parent, Deb, Queue).

system_terminate(Reason, Parent, Deb, Queue) ->
    exit(Reason).

%%
%% Local Functions
%%
loop(Parent, Deb, ?EMPTY) ->
    receive
       {push, NewPriority, NewMessage} = Msg ->
           NewDeb = handle_debug(Deb, {in, Msg}),
                                     
           NewQueue = [{NewPriority, NewMessage}],
           loop(Parent, NewDeb, NewQueue);
       {system, From, Request} ->
           sys:handle_system_msg(Request, From, Parent, ?MODULE, Deb, ?EMPTY)
   	end;
loop(Parent, Deb, [{Priority, _} | _] = Queue) ->
    receive
       {push, NewPriority, NewMessage} = Msg when NewPriority > Priority ->
           NewDeb = handle_debug(Deb, {in, Msg}),
           
           NewQueue = [{NewPriority, NewMessage} | Queue],
           loop(Parent, NewDeb, NewQueue);
       {pull, From, Ref} = Msg ->
           Deb2 = handle_debug(Deb, {in, Msg, From}),
                      
           [{_, Message} | NewQueue] = Queue,
           Reply = {Ref, Message},
           From ! Reply,
           
           Deb3 = handle_debug(Deb, {out, Reply, From}),

           loop(Parent, Deb3, NewQueue);
%%            case NewQueue of
%%                [] ->
%%                    proc_lib:hibernate(?MODULE, loop, [Parent, Deb3, ?EMPTY]);
%%                [{NewPriority, _}| _] ->
%%                    loop(Parent, Deb3, NewQueue)
%%            end;
       {system, From, Request} ->
            sys:handle_system_msg(Request, From, Parent, ?MODULE, Deb, Queue)
   	end.

handle_debug(Deb, Event) ->
	sys:handle_debug(Deb, {?MODULE, write_debug}, ok, Event).