ImageGrid/ui (gen4)/lib/actions.js

/**********************************************************************
* 
*
*
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//var DEBUG = DEBUG != null ? DEBUG : true

define(function(require){ var module = {}


/*********************************************************************/
// Actions
//
// Actions are an extension to the JavaScript object model tailored for
// a set of specific tasks.
//
// The action system consists of these parts:
//
// 1) documentation generation and introspection
// 	XXX not all helpers are defined at this point...
// 	
//
// 2) event-like callbacks for actions
//
// 		MyActions.on('action', function(){ ... })
// 		MyActions.on('action.post', function(){ ... })
//
// 		MyActions.on('action.pre', function(){ ... })
//
//
// 3) a mechanism to extend already defined actions
// 	This replaces / complements the standard JavaScript overloading 
// 	mechanisms, here is a direct comparison:
//
//
// 		// Native...
// 		var X = {
// 			m: function(){ console.log('m') }
// 		}
// 		var O = {
// 			m: function(){
// 				console.log('pre')
// 				B.__proto__.m.call(this)
// 				console.log('post')
// 			}
// 		}
// 		O.__proto__ = X
//
//
// 		// Actions...
// 		var X = Actions({
// 			m: [function(){ console.log('m') }]
// 		})
// 		var O = Actions(X, {
// 			m: [function(){
// 				console.log('pre')
// 				return function(){
// 					console.log('post')
// 				}
// 			}]
// 		})
//
//
// Comparing to the native system:
// 	+ no need to chain overloaded calls by hand (automatic)
// 	+/- more restrictive -- no way to prevent original actions from 
// 	  running, i.e. no way to shadow.
// 	+/- hidden the internals (.__proto__ assignment)
// 	- more structural code (returning a callback vs. B.__proto__.m.call)
// 		NOTE: that the Actions(..) call and lists containing functions
// 			is not added complexity as they are mainly used for docs.
//
//
//
/*********************************************************************/
// helpers...

// XXX
function args2array(args){
	return Array.apply(null, args)
}


// collect all the handlers from the inheritance chain and arrange
// them up-down, first defined to last...
var _collect_handlers =
module._collect_handlers =
function _collect_handlers(obj, name){
	var handlers = []
	var cur = obj
	while(cur.__proto__ != null){
		// get action "event" handlers...
		if(cur.hasOwnProperty('_action_handlers') 
				&& name in cur._action_handlers){
			handlers.splice.apply(handlers,
					[handlers.length, 0].concat(cur._action_handlers[name]))
		}

		// get the overloading action...
		// NOTE: this will get all the handlers including the root 
		// 		and the current handlers...
		// NOTE: this will ignore "shadows" that are not actions...
		if(cur.hasOwnProperty(name) && cur[name] instanceof Action){
			handlers.push(cur[name].func)
		}

		cur = cur.__proto__
	}
	return handlers
}



/*********************************************************************/

// Construct an action object...
//
// Action function format:
//
// 		// pre event code...
// 		function(){
//			... // pre code
// 		}
//
// 		// pre/post event code...
// 		function(){
//			... // pre code
//			return function(){
//				... // post code
//			}
// 		}
//
// 		// same as above but using a deferred instead of a callback...
// 		function(){
//			... // pre code
//			return $.Deferred()
//				.done(function(){
//					... // post code
//				})
// 		}
//
//
var Action =
module.Action =
function Action(name, doc, ldoc, func){
	// we got called without a 'new'...
	if(this == null || this.constructor !== Action){
		// XXX using something like .apply(.., arguemnts) would be more
		// 		generel but have no time to figure out how to pass it 
		// 		to new without the later complaining...
		return new Action(name, doc, ldoc, func)
	}

	// prevent action overloading...
	if(this[name] != null){
		throw 'action "'+name+'" already exists.'
	}

	// create the actual instance we will be returning...
	var meth = function(){
		var that = this
		var args = args2array(arguments)

		// get and call handlers -- pre phase...
		//
		// NOTE: using CLASS.__proto__[name].call(this, ...) here is not
		// 		possible as there is no reliable way to get the "class" 
		// 		the current method is referenced from.
		// 		...searching the inheritance chain is not reliable as a
		// 		method can be referenced more than once, both with the 
		// 		same as well as under different names...
		var handlers = _collect_handlers(this, name)
			.map(function(h){ return h.apply(that, args) })

		// NOTE: this action will get included and called by the code 
		// 		above and below...

		// call handlers -- post phase...
		// NOTE: post handlers need to get called last run pre first run post...
		handlers.reverse().forEach(function(h){ 
			// function...
			if(h instanceof Function){
				//h.call(that, res)
				h.call(that)

			// deferred...
			} else if(h != null && h.resolve instanceof Function){
				//h.resolve(res)
				h.resolve()
			} 
		})

		//return res
		return this
	}
	meth.__proto__ = this.__proto__

	// populate the action attributes...
	meth.name = name
	meth.doc = doc
	meth.long_doc = ldoc

	meth.func = func

	return meth
}


// XXX .off(...) needs more work...
var MetaActions =
module.MetaActions = {
	// List actions...
	//
	// NOTE: this will only list all actions except the ones defined in 
	// 		MetaActions, unless 'all' is set...
	actions: function(all){
		var res = []
		for(var k in this){
			// get only actions...
			if(this[k] instanceof Action 
					// if all is true, get all actions...
					&& !all 
					// if all is false, skip actions defined in MetaActions...
					|| MetaActions.hasOwnProperty(k)){
				res.push(k)
			}
		}
		return res
	},

	// Number of defined actions...
	get length(){
		return this.actions.length
	},

	// Register an action callback...
	//
	//	Register a post action callback
	// 	.on('action', <function>)
	// 	.on('action.post', <function>)
	// 		-> <action-set>
	//
	// 	Register a pre action callback
	// 	.on('action.pre', <function>)
	// 		-> <action-set>
	//
	// Modes:
	// 	'pre'		- the handler is fired before the action is triggered,
	// 					and if the handler returns a deferred or a function
	// 					then that will get resolved, called resp. after
	// 					the action is done.
	// 	'post'		- the handler is fired after the action is finished.
	// 					this is the default.
	//
	// NOTE: 'post' mode is the default.
	on: function(action, handler){
		// prepare the handler...
		var mode = action.split('.')
		action = mode[0]
		mode = mode[1]

		// a post handler (default)...
		if(mode == null || mode == 'post'){
			var old_handler = handler
			handler = function(){ return old_handler }
			// NOTE: this is set so as to identify the handler for removal
			// 		via. .off(..)
			handler.orig_handler = old_handler

		// mot pre mode...
		} else if(mode != 'pre') {
			throw 'Unknown action mode: '+action+'.'+mode
		}

		// register handlers locally only...
		if(!this.hasOwnProperty('_action_handlers')){
			this._action_handlers = {}
		}
		if(!(action in this._action_handlers)){
			this._action_handlers[action] = []
		}
		// register a handler only once...
		if(this._action_handlers[action].indexOf(handler) < 0){
			// NOTE: last registered is first...
			this._action_handlers[action].splice(0, 0, handler)
		}
		return this
	},

	// Remove an action callback...
	//
	// XXX this will not work for explicit <action>.post...
	off: function(action, handler){
		if(this.hasOwnProperty('_action_handlers')){
			var mode = action.split('.')
			action = mode[0]
			mode = mode[1]

			// get the handlers...
			var h = this._action_handlers[action]

			var i = -1
			if(mode == null || mode == 'post'){
				// XXX find via e.orig_handler == handler && e.mode == 'post'
				h.forEach(function(e, j){
					// NOTE: we will only get the first match...
					if(e.orig_handler == handler && i == -1){
						i = j
					}
				})

			} else if(mode == 'pre'){
				i = h.indexOf(handler)
			}

			// NOTE: unknown modes are skipped...
			if(i >= 0){
				h.splice(i, 1)
			}
		}
		return this
	},
}



// Define an action set...
//
//	Actions(<object>)
//	Actions(<prototype>, <object>)
//		-> actions
//
// This will pre-process an object to setup the action mechanics.
//
//
// The action format:
// 	{
// 		// full format...
// 		<name> : [
// 			<doc>,
// 			<long-doc>,
// 			<function>
// 		],
//
// 		// short doc only...
// 		<name> : [
// 			<doc>,
// 			<function>
// 		],
//
// 		// only the code...
// 		<name> : [
// 			<function>
// 		],
// 		...
// 	}
//
//
// An action definition can be processed in two different ways:
//
// 	1) when no actions with <name> exist in the inheritance chain.
// 		A new <name> action will be created.
//
// 		The action object will get .name, .doc and .long_doc attributes
// 		set to the respective fields if they are defined and null if 
// 		they are not.
//
// 	2) when action <name> is already defined in the inheritance chain.
// 		A new <name> action callback will be registered in the current
// 		action context (set).
//
// 		Documentation fields will be ignored (this might change in the 
// 		future)
//
// 		This callback is called before the action (pre-callback).
//
// 		If the callback returns a deferred object or a function 
// 		(post-callback) then it will get resolved, called respectively 
// 		when the action is done.
//
// NOTE: the action, action pre-callback and post-callbacks will be 
// 		called with the same context (this) as the original callback 
// 		and the action, i.e. the action set.
//
//
var Actions =
module.Actions =
function Actions(a, b){
	var obj = b == null ? a : b
	var proto = b == null ? MetaActions : a

	// NOTE: this is intentionally done only for own attributes...
	Object.keys(obj).forEach(function(k){
		var args = obj[k]

		// skip non-arrays...
		if(args.constructor !== Array 
				// and arrays the last element of which is not a function...
				|| !(args[args.length-1] instanceof Function)){
			return
		}

		var func = args.pop()

		// create a new action...
		obj[k] = new Action(k, args[0], args[1], func)
	})

	if(proto != null){
		obj.__proto__ = proto
	}

	return obj
}



/*********************************************************************/

var test =
module.test =
function test(){
	var TestActions = 
	module.TestActions = 
	Actions({
		testActionGen1: ['baisc test action...',
			'some extra info',
			function(){
				console.log('  test 1!')
				return function(){
					console.log('  test 2!')
				}
			}],

		testActionGen2: ['baisc 2\'nd gen test action...',
			// no extra info...
			function(){
				console.log('  test gen 2!')
				this.testActionGen1()
			}],
	})

	var TestActions2 = 
	module.TestActions2 = 
	Actions(TestActions, {
		// NOTE: this looks like an action and feels like an action but 
		// 		actually this is a callback as an action with this name 
		// 		already exists...
		testActionGen1: [function(){
			console.log('  pre callback!')
			return function(){
				console.log('  post callback!')
			}
		}],

	})

	// XXX the main question here is that there is no way to know if a 
	// 		particular action is going to be a root action or an action
	// 		callback because we do not know if the action in the parent 
	// 		will be available at mix time or not, and the two models 
	// 		are different...
	// 		XXX one way to do this is to make all code a callback and 
	// 			just use the root as an event trigger...
	//
	// 			...but this effectively means we are implementing 
	// 			inheritance ourselves as the traditional name resolution
	// 			will no longer be used, and as in the case we implement
	// 			MRO why not go the whole way and implement multiple 
	// 			inheritance in the first place...
	//
	// 			...let's try and avoid this...
	/*
	var TestActionMixin =
	module.TestActionMixin = 
	ActionMixin({
		// XXX
	})
	*/


	console.log('TestActions.testActionGen1()')
	TestActions.testActionGen1()
	console.log('TestActions.testActionGen2()')
	TestActions.testActionGen2()

		
	// both of these should cet a callback...
	console.log('TestActions2.testActionGen1()')
	TestActions2.testActionGen1()
	console.log('TestActions2.testActionGen2()')
	TestActions2.testActionGen2()

	// and an event-like handler...
	TestActions2.on('testActionGen1.post', 
			function(){ console.log('  post handler! (first defined)') })
	TestActions2.on('testActionGen1', 
			function(){ console.log('  post handler! (last defined)') })

	console.log('TestActions2.testActionGen1()')
	TestActions2.testActionGen1()

	TestActions2.on('testActionGen2.pre', 
			function(){ console.log('  pre handler! (first defined)') })
	TestActions2.on('testActionGen2.pre', 
			function(){ console.log('  pre handler! (last defined)') })

	console.log('TestActions2.testActionGen2()')
	TestActions2.testActionGen2()
}



/**********************************************************************
* vim:set ts=4 sw=4 :                                                */
return module })