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<div class="header">
The NakedMud Tutorial :: Events
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<div class="head">Events</div>
<div class="info">
NakedMud provides support for delayed events. These are simply functions that
are called after a pre-specified amount of time. They are not to be confused
with Events in, say, Java, which refer to specific things that take place
(such as someone clicking on a mouse) which have a set of 'listeners' that
execute some function once the event occurs. NakedMud supports this sort of
behavior as well, in the form of hooks.
<p></p>
Events have three parameters. An owner, data, and a string argument, each of
which might possibly be None. The owner is the person, place, or thing the event
belongs to. If the owner ever leaves the game, the event is canceled. The
owner can be None. For instance, you may want to write a combat update event 
that iterates across all characters and make them perform an attack every
second. To do this, you could start the event up without an owner when your 
module is initialized, and have the event do its work, and re-start itself 
whenever it is called.
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<div class="head">Delayed Commands</div>
<div class="info">
The most basic thing that could be done with events is creating a command that
delays another command for a specified amount of time. Here is how something
like that would be written:

<pre class="code">
import mudsys, event, mud

def delayed_cmd_event(owner, data, arg):
    ch.act(arg)

def cmd_delay(ch, cmd, arg):
    '''attempt to delay a command by a specified amount of time.'''
    try:
        # take two arguments: the delay time, and the command to execute
        time, todo = mud.parse_args(ch, True, cmd, arg, "int(time) string(cmd)")
    except: return

    # notify the character that their command has been delayed,
    # and start the event handler
    ch.send("In %d seconds you will perform '%s'." % (time, todo))
    event.start_event(ch, time, delayed_cmd_event, None, todo)

mudsys.add_cmd("delay", None, cmd_delay, "player", False)
</pre>

<p></p>
Data can be anything you want it to be. Suppose you want to implement a delayed
fireball spell that hurts everyone in the room except for the person who set it
up. The owner would be the room, and the data might be the character. You could
possibly do it as the owner being the character and the data being None, but
think what might happen if the character decided to move before the event went
off! Here is one way to do a delayed fireball event

<pre class="code">
import mudsys, event

def delayed_fireball_event(room, caster, arg):
    '''do the delayed fireball event. Hurt everyone in the room except the
       caster. arg is None.'''
    room.send("With violent force, a delayed fireball explodes in the room!")
    for ch in room:
        if ch != caster:
            # do something mean here
            ############
            # FINISH ME
            ############

def cmd_delayed_fireball(ch, cmd, arg):
    '''cast a delayed fireball.'''
    ch.send("You set up a delayed fireball to go off in 5 seconds!")
    event.start_event(ch.room, 5, delayed_fireball_event, ch, None)

mudsys.add_cmd("df", None, cmd_delayed_fireball, "player", False)
</pre>
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<div class="head">Writing Handlers</div>
<div class="info">
Suppose you want some sort of handler to run on a periodic basis. Maybe you want
everyone in combat to attack each second, or maybe you want to extract linkdead
characters every five minutes. Periodic handlers can be created with events that
requeue theirselves. Here is an example of an event that saves characters every
5 minutes, and extracts those that are linkdead:

<pre class="code">
'''
autosave.py

automatically save all existing PCs, every 5 mins. Extract those that are
linkdead.
'''
import mudsys, event, mud
import char as mudchar

__autosave_delay__ = 5 * 60

def autosave_event(owner, data, arg):
    '''go through all our characters and save them. Then, force-quit them if
       they are linkdead.'''
    try:
        for ch in mudchar.char_list():
            if ch.is_pc:
                mudsys.do_save(ch)
                if ch.socket == None:
                    mudsys.do_quit(ch)
    except: pass

    # make sure we requeue the event outside the body of the try block.
    # this is just so that if something goes wrong with the event, the event
    # is still requeued.
    event.start_event(None, __autosave_delay__, autosave_event)

event.start_event(None, __autosave_delay__, autosave_event)
</pre>
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<div class="head">Starting and Stopping</div>
<div class="info">
Once an event is started, it cannot be canceled unless its owner is removed
from the game, so be certain to design your events with this in mind.
<p></p>
Events are started with a call to start_event. This function takes three
mandatory arguments, and two optional ones. The first argument is the owner,
the second is the time to delay the event, and the third is the event itself.
The fourth and fifth are the data and the string argument, respectively.
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<!--div class="footer">Edit Date: Nov 15, 2008. By Geoff Hollis</div-->
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