% The MasterKey Widget Set developer's guide
% Mike Taylor
% 11 August 2014


Introduction
============

Development with MKWS consists primarily of defining new types of
widgets. These can interact with the core functionality is several
defined ways.

You create a new widget type by calling the `mkws.registerWidgetType`
function, passing in the widget name and a function. The name is used
to recognise HTML elements as being widgets of this type -- for
example, if you register a `Foo` widget, elements like
`<div class="mkwsFoo">` will be widgets of this type.

The function promotes a bare widget object (passed as `this`) into a
widget of the appropriate type. MKWS doesn't use classes or explicit
prototypes: it just makes objects that have the necessary
behaviours. There are _no_ behaviours that Widgets are obliged to
provide: you can make a doesn't-do-anything-at-all widget if you like:

	mkws.registerWidgetType('Sluggard', function() {});

More commonly, widgets will subscribe to one or more events, so that
they're notified when something interesting happens. For example, the
`Log` widget asks to be notified when a `log` event happens, and
appends the logged message to its node, as follows:

	mkws.registerWidgetType('Log', function() {
	  var that = this;

	  this.team.queue("log").subscribe(function(teamName, timestamp, message) {
	    $(that.node).append(teamName + ": " + timestamp + message + "<br/>");
	  });
	});

This simple widget illustrates several important points:

* The base widget object (`this`) has several baked-in properties and
  methods that are available to individual widgets. These include
  `this.team` (the team that this widget is a part of) and `this.node`
  (the DOM element of the widget). See below for a full list.

* The team object (`this.team`) also has baked-in properties and
  methods. These include the `queue` function, which takes an event-name
  as its argument. See below for a full list.

* You can add functionality to a widget by subscribing it to an
  event's queue using `this.team.queue("EVENT").subscribe`. The
  argument is a function which is called whenever the event is
  published. The arguments to the function are different for different
  events.

* As with so much JavaScript programming, the value of the special
  variable `this` is lost inside the `subscribez` callback function,
  so it must be saved if it's to be used inside that callback
  (typically as a local variable named `that`).


Widget specialisation (inheritance)
===================================

Many widgets are simple specialisations of existing widgets. For
example, the `Record` widget is the same as the `Records` widget
except that it defaults to displaying a single record. It's defined as
follows:

	mkws.registerWidgetType('Record', function() {
	  mkws.promotionFunction('Records').call(this);
	  if (!this.config.maxrecs) this.config.maxrecs = 1;
	});

Remember that when a promotion function is called, it's passed a base
widget object that's not specialised for any particular task. To make
a specialised widget, first promote that base widget into the type
that you want to specialise from -- in this case, "Records" -- using
the promotion function that's been registered for that type.

Once this has been done, the specialisations can be introduced. In
this case, it's a very simple matter of changing the "maxrecs"
configuration setting to 1 unless it's already been given an explicit
value. (That would occur if the HTML used an element like <div
class="mkwsRecord" maxrecs="2">, though it's not obvious why anyone
would do that.)


Widget Properties and Methods
=============================

String this.type
	A string containing the type of the widget.

Team this.team
	The team object to which this widget belongs. The team has
	several additional important properties and methods, described
	below.

DOMElement this.node
	The DOM element of the widget

Hash this.config
	A table of configuration values for the widget. This table
	inherits missing values from the team's configuration, which
	in turn inherits from the top-level MKWS configuration, which
	inherits from the default configuration. Instances of widgets
	in HTML can set configuration items as HTML attributes, as in
	<div class="mkwsRecords" maxrecs="2">.

String this.toString()
	A function returning a string that briefly names this
	widget. Can be useful in logging.

Void this.log(string)
	A function to log a string for debugging purposes. The string
	is written on the browser console, and also published to any
	"log" subcribers.

String this.value()
	A function returning the value of the widget's HTML element.


Team methods
============

Since the team object is supposed to be opaque to widgets, all access
is via the following API methods rather than direct access to
properties.

String team.name()
Bool team.submitted()
Num team.perpage()
Num team.totalRecordCount()
Num team.currentPage();
String team.currentRecordId()
String team.currentRecordData()
	Simple accessor functions that provide the ability to read
	properties of the team.

Array team.filters()
	Another accessor function, providing access to the array of
	prevailing filters (which narrow the search results by means
	of Pazpar2 filters and limits). This is really too complicated
	an object for the widgets to be given access to, but it's
	convenient to do it this way. See the "Navi" widget, which is
	the only place it's used.

Hash team.config()
	Access to the team's configuration settings. There is almost
	certainly no reason to use this: the settings that haven't
	been overridden are accessible via this.config.

Void team.set_sortOrder(string)
Void team.set_perpage(number)
	"Setter" functions for the team's sortOrder and perpage
	functions. Unlikely to be needed outside of the "Sort" and
	"Perpage" widgets.

Queue team.queue(eventName)
	Returns the queue associated with the named event: this can be
	used to subscribe to the event (or more rarely to publish it).

Bool team.targetFiltered(targetId)
	Indicates whether the specified target has been filtered by
	selection as a facet.

Void team.newSearch(query, sortOrder, maxrecs, perpage, limit, targets, targetfilter)
	Starts a new search with the specified parameters. All but the
	query may be omitted, in which case the prevailing defaults
	are used.

Void team.reShow()
	Using the existing search, re-shows the result records after a
	change in sort-order, per-page count, etc.

String team.recordElementId(recordId)
	Utility function for converting a record identifer (returned
	from Pazpar2) into a version suitable for use as an HTML
	element ID.

String team.renderDetails(recordData)
	Utility function returns an HTML rendering of the record
	represented by the specified data.

Template team.loadTemplate(templateName)
	Loads (or retrieves from cache) the named Handlebars template,
	and returns it in a form that can be invoked as a function,
	passed a data-set.

Some of these methods either (A) are really too low-level and should
not be exposed, or (B) should be widget-level methods. The present
infelicities reflect the fact that some code that rightly belongs in
widgets is still in the team. When we finish migrating it, the widget
API should get simpler.

- - -

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