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/** @namespace util/handler-registry */
define('util/handler-registry', [
'jquery',
'underscore'
],
/**
* @example
* var registry = new require('util/handler-registry');
*
* // The consumer determines the options _and_ the expected type of the result
* registry._handle({type: 'foo'}).done(function(result) {
* console.log(result.toUpperCase());
* });
*
* // Register one instance of a handler that conforms to _this_ registry API ('type' on options and returns a string)
* registry.register({
* weight: 200,
* handle: function(options) {
* return options.type === 'foo' ? "hello" : null;
* }
* });
*
* @exports util/handler-registry
*/
function(
$,
_
) {
'use strict';
/**
* Callback to handle a specific type of this type of registry, be it file rendering or something else.
*
* @callback HandleCallback
* @memberOf util/handler-registry
*
* @param {util/handler-registry.HandleCallbackOptions} options - Options data provided to handle callback.
* @return {Promise} A promise object which will hopefully be resolved with a per-registry specific object.
* Returning falsey here is the same as a rejected promise.
*/
/**
* @typedef {Object} Handler
* @memberOf util/handler-registry
*
* @property {number} [weight=1000] - Weight of handler determining the order it is tried.
* @property {util/handler-registry.HandleCallback} handle - Function called to handle file
*/
/**
* The properties of this object are purely determined by the API of the specific registry in use.
*
* @typedef {Object} HandleCallbackOptions
* @memberOf util/handler-registry
*/
/**
* An object that can 'register' objects to 'handle' a single request, using promises to either
* resolve or reject, which then passes to the next handler in order (determined by a specified weight).
*
* This registry may itself need to be namespaced depending on the requirements. For example there might be a single
* registry for all the file handlers on a given page, or there might be a registry just for image files.
*
* @constructor
*/
function HandlerRegistry() {
// List of handlers in this specific registry
this.handlers = [];
}
/**
* Registers a {@linkcode Handler} for processing requests to the registry.
*
* @param {Handler} handler - Handler to register.
* @returns {Function} A function to unregister the given {@linkcode Handler}.
*/
HandlerRegistry.prototype.register = function(handler) {
if (!_.isFunction(handler.handle)) {
throw new Error('Handler must have a handle function');
}
handler.weight = typeof handler.weight === 'number' && !isNaN(handler.weight) ? handler.weight : 1000;
this.handlers.push(handler);
this.handlers = _.sortBy(this.handlers, function (handler) {
return handler.weight;
});
var that = this;
return function unregister() {
var index = that.handlers.indexOf(handler);
if (index >= 0) {
that.handlers.splice(index, 1);
}
};
};
/**
* Handles a request by calling registered handlers in order of their weight until the request is handled.
* @param {HandleCallbackOptions} options - See parameters passed into {@link HandleCallback}.
* @returns {Promise} Resolved with an object or rejected if no handler could be found.
*/
HandlerRegistry.prototype._handle = function(options) {
var deferred = $.Deferred();
var aborted;
var currentResult;
var handlers = this.handlers;
var errors = [];
function next(depth) {
if (aborted) {
return deferred.reject(new Error('Handling aborted.'));
}
if (depth < handlers.length) {
// Falsey is handled as reject
currentResult = handlers[depth].handle(options) || $.Deferred().reject();
return $.when(currentResult).done(function (data) {
deferred.resolve(data || {}, errors);
}).fail(function(error) {
error && errors.push(error);
next(depth + 1);
});
} else {
deferred.reject(new Error('No registered handlers were able to handle file'));
}
}
next(0);
return deferred.promise({
abort: function() {
if (!aborted && currentResult && currentResult.abort) {
currentResult.abort();
}
aborted = true;
}
});
};
/**
* Unregisters all handlers.
*/
HandlerRegistry.prototype._clear = function() {
this.handlers = [];
};
return HandlerRegistry;
});
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