meld.js

/** @license MIT License (c) copyright 2011-2013 original author or authors */

/**
 * meld
 * Aspect Oriented Programming for Javascript
 *
 * meld is part of the cujo.js family of libraries (http://cujojs.com/)
 *
 * Licensed under the MIT License at:
 * http://www.opensource.org/licenses/mit-license.php
 *
 * @author Brian Cavalier
 * @author John Hann
 * @version 1.3.1
 */
(function (define) {
define(function () {

	//
	// Public API
	//

	// Add a single, specific type of advice
	// returns a function that will remove the newly-added advice
	meld.before =         adviceApi('before');
	meld.around =         adviceApi('around');
	meld.on =             adviceApi('on');
	meld.afterReturning = adviceApi('afterReturning');
	meld.afterThrowing =  adviceApi('afterThrowing');
	meld.after =          adviceApi('after');

	// Access to the current joinpoint in advices
	meld.joinpoint =      joinpoint;

	// DEPRECATED: meld.add(). Use meld() instead
	// Returns a function that will remove the newly-added aspect
	meld.add =            function() { return meld.apply(null, arguments); };

	/**
	 * Add an aspect to all matching methods of target, or to target itself if
	 * target is a function and no pointcut is provided.
	 * @param {object|function} target
	 * @param {string|array|RegExp|function} [pointcut]
	 * @param {object} aspect
	 * @param {function?} aspect.before
	 * @param {function?} aspect.on
	 * @param {function?} aspect.around
	 * @param {function?} aspect.afterReturning
	 * @param {function?} aspect.afterThrowing
	 * @param {function?} aspect.after
	 * @returns {{ remove: function }|function} if target is an object, returns a
	 *  remover { remove: function } whose remove method will remove the added
	 *  aspect. If target is a function, returns the newly advised function.
	 */
	function meld(target, pointcut, aspect) {
		var pointcutType, remove;

		if(arguments.length < 3) {
			return addAspectToFunction(target, pointcut);
		} else {
			if (isArray(pointcut)) {
				remove = addAspectToAll(target, pointcut, aspect);
			} else {
				pointcutType = typeof pointcut;

				if (pointcutType === 'string') {
					if (typeof target[pointcut] === 'function') {
						remove = addAspectToMethod(target, pointcut, aspect);
					}

				} else if (pointcutType === 'function') {
					remove = addAspectToAll(target, pointcut(target), aspect);

				} else {
					remove = addAspectToMatches(target, pointcut, aspect);
				}
			}

			return remove;
		}

	}

	function Advisor(target, func) {

		var orig, advisor, advised;

		this.target = target;
		this.func = func;
		this.aspects = {};

		orig = this.orig = target[func];
		advisor = this;

		advised = this.advised = function() {
			var context, joinpoint, args, callOrig, afterType;

			// If called as a constructor (i.e. using "new"), create a context
			// of the correct type, so that all advice types (including before!)
			// are called with the correct context.
			if(this instanceof advised) {
				// shamelessly derived from https://github.com/cujojs/wire/blob/c7c55fe50238ecb4afbb35f902058ab6b32beb8f/lib/component.js#L25
				context = objectCreate(orig.prototype);
				callOrig = function (args) {
					return applyConstructor(orig, context, args);
				};

			} else {
				context = this;
				callOrig = function(args) {
					return orig.apply(context, args);
				};

			}

			args = slice.call(arguments);
			afterType = 'afterReturning';

			// Save the previous joinpoint and set the current joinpoint
			joinpoint = pushJoinpoint({
				target: context,
				method: func,
				args: args
			});

			try {
				advisor._callSimpleAdvice('before', context, args);

				try {
					joinpoint.result = advisor._callAroundAdvice(context, func, args, callOrigAndOn);
				} catch(e) {
					joinpoint.result = joinpoint.exception = e;
					// Switch to afterThrowing
					afterType = 'afterThrowing';
				}

				args = [joinpoint.result];

				callAfter(afterType, args);
				callAfter('after', args);

				if(joinpoint.exception) {
					throw joinpoint.exception;
				}

				return joinpoint.result;

			} finally {
				// Restore the previous joinpoint, if necessary.
				popJoinpoint();
			}

			function callOrigAndOn(args) {
				var result = callOrig(args);
				advisor._callSimpleAdvice('on', context, args);

				return result;
			}

			function callAfter(afterType, args) {
				advisor._callSimpleAdvice(afterType, context, args);
			}
		};

		defineProperty(advised, '_advisor', { value: advisor, configurable: true });
	}

	Advisor.prototype = {

		/**
		 * Invoke all advice functions in the supplied context, with the supplied args
		 *
		 * @param adviceType
		 * @param context
		 * @param args
		 */
		_callSimpleAdvice: function(adviceType, context, args) {

			// before advice runs LIFO, from most-recently added to least-recently added.
			// All other advice is FIFO
			var iterator, advices;

			advices = this.aspects[adviceType];
			if(!advices) {
				return;
			}

			iterator = iterators[adviceType];

			iterator(this.aspects[adviceType], function(aspect) {
				var advice = aspect.advice;
				advice && advice.apply(context, args);
			});
		},

		/**
		 * Invoke all around advice and then the original method
		 *
		 * @param context
		 * @param method
		 * @param args
		 * @param applyOriginal
		 */
		_callAroundAdvice: function (context, method, args, applyOriginal) {
			var len, aspects;

			aspects = this.aspects.around;
			len = aspects ? aspects.length : 0;

			/**
			 * Call the next function in the around chain, which will either be another around
			 * advice, or the orig method.
			 * @param i {Number} index of the around advice
			 * @param args {Array} arguments with with to call the next around advice
			 */
			function callNext(i, args) {
				// If we exhausted all aspects, finally call the original
				// Otherwise, if we found another around, call it
				return i < 0
					? applyOriginal(args)
					: callAround(aspects[i].advice, i, args);
			}

			function callAround(around, i, args) {
				var proceedCalled, joinpoint;

				proceedCalled = 0;

				// Joinpoint is immutable
				// TODO: Use Object.freeze once v8 perf problem is fixed
				joinpoint = pushJoinpoint({
					target: context,
					method: method,
					args: args,
					proceed: proceedCall,
					proceedApply: proceedApply,
					proceedCount: proceedCount
				});

				try {
					// Call supplied around advice function
					return around.call(context, joinpoint);
				} finally {
					popJoinpoint();
				}

				/**
				 * The number of times proceed() has been called
				 * @return {Number}
				 */
				function proceedCount() {
					return proceedCalled;
				}

				/**
				 * Proceed to the original method/function or the next around
				 * advice using original arguments or new argument list if
				 * arguments.length > 0
				 * @return {*} result of original method/function or next around advice
				 */
				function proceedCall(/* newArg1, newArg2... */) {
					return proceed(arguments.length > 0 ? slice.call(arguments) : args);
				}

				/**
				 * Proceed to the original method/function or the next around
				 * advice using original arguments or new argument list if
				 * newArgs is supplied
				 * @param [newArgs] {Array} new arguments with which to proceed
				 * @return {*} result of original method/function or next around advice
				 */
				function proceedApply(newArgs) {
					return proceed(newArgs || args);
				}

				/**
				 * Create proceed function that calls the next around advice, or
				 * the original.  May be called multiple times, for example, in retry
				 * scenarios
				 * @param [args] {Array} optional arguments to use instead of the
				 * original arguments
				 */
				function proceed(args) {
					proceedCalled++;
					return callNext(i - 1, args);
				}

			}

			return callNext(len - 1, args);
		},

		/**
		 * Adds the supplied aspect to the advised target method
		 *
		 * @param aspect
		 */
		add: function(aspect) {

			var advisor, aspects;

			advisor = this;
			aspects = advisor.aspects;

			insertAspect(aspects, aspect);

			return {
				remove: function () {
					var remaining = removeAspect(aspects, aspect);

					// If there are no aspects left, restore the original method
					if (!remaining) {
						advisor.remove();
					}
				}
			};
		},

		/**
		 * Removes the Advisor and thus, all aspects from the advised target method, and
		 * restores the original target method, copying back all properties that may have
		 * been added or updated on the advised function.
		 */
		remove: function () {
			delete this.advised._advisor;
			this.target[this.func] = this.orig;
		}
	};

	/**
	 * Returns the advisor for the target object-function pair.  A new advisor
	 * will be created if one does not already exist.
	 * @param target {*} target containing a method with the supplied methodName
	 * @param methodName {String} name of method on target for which to get an advisor
	 * @return {Object|undefined} existing or newly created advisor for the supplied method
	 */
	Advisor.get = function(target, methodName) {
		if(!(methodName in target)) {
			return;
		}

		var advisor, advised;

		advised = target[methodName];

		if(typeof advised !== 'function') {
			throw new Error('Advice can only be applied to functions: ' + methodName);
		}

		advisor = advised._advisor;
		if(!advisor) {
			advisor = new Advisor(target, methodName);
			target[methodName] = advisor.advised;
		}

		return advisor;
	};

	/**
	 * Add an aspect to a pure function, returning an advised version of it.
	 * NOTE: *only the returned function* is advised.  The original (input) function
	 * is not modified in any way.
	 * @param func {Function} function to advise
	 * @param aspect {Object} aspect to add
	 * @return {Function} advised function
	 */
	function addAspectToFunction(func, aspect) {
		var name, placeholderTarget;

		name = func.name || '_';

		placeholderTarget = {};
		placeholderTarget[name] = func;

		addAspectToMethod(placeholderTarget, name, aspect);

		return placeholderTarget[name];

	}

	function addAspectToMethod(target, method, aspect) {
		var advisor = Advisor.get(target, method);

		return advisor && advisor.add(aspect);
	}

	function addAspectToAll(target, methodArray, aspect) {
		var removers, added, f, i;

		removers = [];
		i = 0;

		while((f = methodArray[i++])) {
			added = addAspectToMethod(target, f, aspect);
			added && removers.push(added);
		}

		return createRemover(removers);
	}

	function addAspectToMatches(target, pointcut, aspect) {
		var removers = [];
		// Assume the pointcut is a an object with a .test() method
		for (var p in target) {
			// TODO: Decide whether hasOwnProperty is correct here
			// Only apply to own properties that are functions, and match the pointcut regexp
			if (typeof target[p] == 'function' && pointcut.test(p)) {
				// if(object.hasOwnProperty(p) && typeof object[p] === 'function' && pointcut.test(p)) {
				removers.push(addAspectToMethod(target, p, aspect));
			}
		}

		return createRemover(removers);
	}

	function createRemover(removers) {
		return {
			remove: function() {
				for (var i = removers.length - 1; i >= 0; --i) {
					removers[i].remove();
				}
			}
		};
	}

	// Create an API function for the specified advice type
	function adviceApi(type) {
		return function(target, method, adviceFunc) {
			var aspect = {};

			if(arguments.length === 2) {
				aspect[type] = method;
				return meld(target, aspect);
			} else {
				aspect[type] = adviceFunc;
				return meld(target, method, aspect);
			}
		};
	}

	/**
	 * Insert the supplied aspect into aspectList
	 * @param aspectList {Object} list of aspects, categorized by advice type
	 * @param aspect {Object} aspect containing one or more supported advice types
	 */
	function insertAspect(aspectList, aspect) {
		var adviceType, advice, advices;

		for(adviceType in iterators) {
			advice = aspect[adviceType];

			if(advice) {
				advices = aspectList[adviceType];
				if(!advices) {
					aspectList[adviceType] = advices = [];
				}

				advices.push({
					aspect: aspect,
					advice: advice
				});
			}
		}
	}

	/**
	 * Remove the supplied aspect from aspectList
	 * @param aspectList {Object} list of aspects, categorized by advice type
	 * @param aspect {Object} aspect containing one or more supported advice types
	 * @return {Number} Number of *advices* left on the advised function.  If
	 *  this returns zero, then it is safe to remove the advisor completely.
	 */
	function removeAspect(aspectList, aspect) {
		var adviceType, advices, remaining;

		remaining = 0;

		for(adviceType in iterators) {
			advices = aspectList[adviceType];
			if(advices) {
				remaining += advices.length;

				for (var i = advices.length - 1; i >= 0; --i) {
					if (advices[i].aspect === aspect) {
						advices.splice(i, 1);
						--remaining;
						break;
					}
				}
			}
		}

		return remaining;
	}

	function applyConstructor(C, instance, args) {
		try {
			// Try to define a constructor, but don't care if it fails
			defineProperty(instance, 'constructor', {
				value: C,
				enumerable: false
			});
		} catch(e) {
			// ignore
		}

		C.apply(instance, args);

		return instance;
	}

	var currentJoinpoint, joinpointStack,
		ap, prepend, append, iterators, slice, isArray, defineProperty, objectCreate;

	// TOOD: Freeze joinpoints when v8 perf problems are resolved
//	freeze = Object.freeze || function (o) { return o; };

	joinpointStack = [];

	ap      = Array.prototype;
	prepend = ap.unshift;
	append  = ap.push;
	slice   = ap.slice;

	isArray = Array.isArray || function(it) {
		return Object.prototype.toString.call(it) == '[object Array]';
	};

	// Check for a *working* Object.defineProperty, fallback to
	// simple assignment.
	defineProperty = definePropertyWorks()
		? Object.defineProperty
		: function(obj, prop, descriptor) {
		obj[prop] = descriptor.value;
	};

	objectCreate = Object.create ||
		(function() {
			function F() {}
			return function(proto) {
				F.prototype = proto;
				var instance = new F();
				F.prototype = null;
				return instance;
			};
		}());

	iterators = {
		// Before uses reverse iteration
		before: forEachReverse,
		around: false
	};

	// All other advice types use forward iteration
	// Around is a special case that uses recursion rather than
	// iteration.  See Advisor._callAroundAdvice
	iterators.on
		= iterators.afterReturning
		= iterators.afterThrowing
		= iterators.after
		= forEach;

	function forEach(array, func) {
		for (var i = 0, len = array.length; i < len; i++) {
			func(array[i]);
		}
	}

	function forEachReverse(array, func) {
		for (var i = array.length - 1; i >= 0; --i) {
			func(array[i]);
		}
	}

	function joinpoint() {
		return currentJoinpoint;
	}

	function pushJoinpoint(newJoinpoint) {
		joinpointStack.push(currentJoinpoint);
		return currentJoinpoint = newJoinpoint;
	}

	function popJoinpoint() {
		return currentJoinpoint = joinpointStack.pop();
	}

	function definePropertyWorks() {
		try {
			return 'x' in Object.defineProperty({}, 'x', {});
		} catch (e) { /* return falsey */ }
	}

	return meld;

});
})(typeof define == 'function' && define.amd ? define : function (factory) { module.exports = factory(); }
);