=head1 NAME

JavaScript_Guide for Apache::UploadMeter

=head1 SYNOPSIS

    // Register a global callback
    UploadMeter.Responders.register({
        onCreate: function (meter) {
            Element.update(meter.desc, "Please wait...");
        }
    });
    
    // Create a new UploadMeter
    var um = new UploadMeter(el, meter_id, meter_url, {
        // Callback to be executed every time we get a status update
        onUpdate: function (status, last) {
            Element.update('file', "Now uploading: " + status.filename);
            Element.update('bytes', status.seen + "/" + status.total + "  bytes transfered (" + Util.formatDec(status.currentrate) + " bytes/sec)");
            Element.update('time', Util.formatTime(status.elapsed) + " elapsed (" + Util.formatTime(status.remaining) + " remaining)"); 
        },
        onFinished: function(status, last) {
        // Callback to be executed when we've detected a complete upload and stop the meter
            Element.show('closeme');
        }
    });
    
    // Start our uploadmeter - only do this once the corresponding upload has started (or is about to start)
    um.start();
    
    // Stop (or pause) a previouslky start()ed meter
    um.stop();
    
    // Un-register the default pop-up window behavior 
    Event.stopObserving(aum_el, 'submit', aum_popup);

=head1 DESCRIPTION

Apache::UploadMeter includes several JavaScript objects to help quickly create
a customized GUI interface for Apache::UploadMeter using the JSON meter type

=head1 DOM, JavaScript and Cascading StyleSheet rules

Although we aim to give maximum customizability, in order to keep a balance between
ease of initial set-up and basic usage, and customizability, the built-in UploadMeter
includes JS code and CSS rules for a simple graphical progress-bar.  At the
current moment, the constructor for the UploadMeter object requires a reference
to a DOM node as one of the parameters, to be used as the base for creating this
progress bar.  If you don't want to use the built-in progress-bar, but also don't
want to muck with the UploadMeter object to get around this, just create an empty
DIV on your page, set the style to hidden (eg, display: none), and pass that to
the UploadMeter object.  If you do wish to use this built-in object, ensure that
the CSS class of this div is "uploadmeter" (and don't hide it!)

Also, it is worth noting that the default behavior looks for an element class
named "uploadform" and attempts to add to the onSubmit code for it, to trigger
the bundled default pop-up window.  If you don't want this to happen, just run:

C<Event.stopObserving(aum_el, 'submit', aum_popup);>


=head1 API Documentation

=head3 UploadMeter Object

This is where most of the action happens.  The public interface to this object
consists of a constructor, start and stop methods, and some callbacks that can 
be used to do extra stuff at various key points in the UploadMeter's lifetime.

=over

=item *
UploadMeter(I<Element>, I<Meter-Id>, I<Meter-URL>, I<options>)

This is the default constructor for a new UploadMeter instance.  It accepts 3
mandatory parameters and a hash of additional options.  The first parameter,
I<Element> is a DIV element under which to create a graphical progress-bar (see
L<DOM, JavaScript and Cascading StyleSheet rules> above).  The second parameter
is the unique identifier of the uploadmeter data you wish to use.  If you're using
MeterType JSON, this will be embedded in your JavaScript as I<meter_id>.  The
third parameter is the URL of the meter-status URL.  If you're using
MeterType JSON, this will be embedded in your JavaScript as I<meter_url>.

The final parameter is a hash of additional optional configuration directives and
callback routines.

=over

=item *
Parameters

=over

=item *
delay

The delay (in seconds or partial seconds) between meter updates.  The default
value (3) should probably be good enough for you.  As a warning, if you set this
too high, your users will not have a good feel for what's happening.  Too low and
(besided the extra traffic to your server), the animation for the progress-bar
may garble (this is known to happen if 2 animation requests happen simultaniously.
While this will likely eventually be fixed, as of the time of writing, it's not.

=back

=item *
Callback routines

The callback routines all contain zero, one or two parameters.  The parameter
order will always be I<status>, I<last>.

I<status> contains the current status of the upload.  I<last> always contains
the B<previous> status of the uploadmeter, such that on a repeating callback
such as onUpdate, the value of any given request's I<last> will always be the
same as the previous callback's I<status>.

The parameters contain the following information:

=over

=item *
meter_id

Contains the meter_id for the current upload

=item *
filename

Contains the filename (as supplied by the client) of the currently uploading file

=item *
finished

Contains a boolean value which will be set to 1 once the upload is complete

=item *
status

=over

=item *
timestamp

Current timestamp from server, as seconds since the epoch

=item * 
start

Timestamp (as seconds since the epoch) when upload was started

=item *
received

Number of bytes received so far

=item *
total

Total number of bytes in the upload (more accurately, of the upload B<request>
including other form information)

=back

=item *
total

This is a shortcut for C<status.total>

=item *
seen

This is a shortcut for C<status.received>

=item *
progress

A value between 0 and 100, representing the percentage of the upload that has
been completed.

=item *
currentrate

The approximate current upload rate (in bytes/second)

=item *
elapsed

The time (in seconds) which has elapsed since the upload started

=item *
remaining

The approximate time (in seconds) remaining in the upload

=back

The callbacks currently available are:

=over

=item *
onCreate(I<>)

This callback is called once just before the first AJAX call is made.  As such,
it doesn't happen on construction; it happens after um.start(), but before the
initial AJAX request is made.  I know it's not really well named, but you're
welcom to suggest something better.

=item *
onInitialize(I<status>, I<last>)

This callback is called once after the initial AJAX response is received and
parsed.  While I<last> is generally useless at this point (it's a subset of
I<status> right now), it's provided in case you want to change the value of
anything in it.

=item *
onUpdate(I<status>, I<last>)

This callback is called every time data is updated from meter URL.  It can be
utilized to update other GUI elements, such as is done in the default pop-up.

=item *
onFinished(I<status>, I<last>)

This callback is called after onUpdate if the upload is determined to be complete
(eg, C<tatus.finished == 1>)

=back

=back

=back

=head3 UploadMeter.Responders

In addition to adding handlers to individual UploadMeter objects, as described
above, you can also add global callbacks which will be called for *every* uploadmeter
on the page.  This might be useful, for example, for Web 2.0 applications that
allow for multiple asynchronous uploads in separate requests.  In such a case,
rather than registering identical handlers for each UploadMeter instance,
you can register a single function globally and it will be called for the appropriate
callback for all UploadMeter instances running on the page.

Callbacks that are registered this way will receive, as the first parameter,
the UploadMeter object of the instance which is currently calling into it.

=head3 Util

The Util namespace is not an object, but rather a namespace to group some helper
utility functions that may make your life a bit easier when creating your custom
user interface.

=over

=item *
Util.formatTime(I<timestamp>)

This function takes a single parameter, I<timestamp> which is a numeric value
corresponding to a number of seconds.  This is not necessarily a "unix timestamp"
(the number of seconds since the epoch) but rather an arbitrary number of seconds.

The function will return a formatted string returning the number of seconds in
HH:mm:ss format

=item *
Util.formatDec(I<value>)

This function takes a numeric (decimal/floating point) value as a parameter
and returns a string containing the number and 2 decimal points.

=back

=head1 AUTHOR AND COPYRIGHT

Copyright (c) 2001-2007 Issac Goldstand E<lt>margol@beamartyr.netE<gt> - All rights reserved.

This library is free software. It can be redistributed and/or modified
under the same terms as Perl itself.

This software contains third-party components licensed under BSD and MIT style
open-source licenses.

=head1 SEE ALSO

L<Apache::UploadMeter>

=cut