source: Dev/branches/rest-dojo-ui/client/dojo/aspect.js @ 256

define([], function(){

// TODOC: after/before/around return object
// TODOC: after/before/around param types. 

/*=====
        dojo.aspect = {
                // summary: provides aspect oriented programming functionality, allowing for
                //              one to add before, around, or after advice on existing methods.
                //
                // example:
                //      |       define(["dojo/aspect"], function(aspect){
                //      |               var signal = aspect.after(targetObject, "methodName", function(someArgument){
                //      |                       this will be called when targetObject.methodName() is called, after the original function is called
                //      |               });
                //
                // example:
                //      The returned signal object can be used to cancel the advice.
                //      |       signal.remove(); // this will stop the advice from being executed anymore
                //      |       aspect.before(targetObject, "methodName", function(someArgument){
                //      |               // this will be called when targetObject.methodName() is called, before the original function is called
                //      |        });
                
                after: function(target, methodName, advice, receiveArguments){
                        // summary: The "after" export of the aspect module is a function that can be used to attach
                        //              "after" advice to a method. This function will be executed after the original method
                        //              is executed. By default the function will be called with a single argument, the return
                        //              value of the original method, or the the return value of the last executed advice (if a previous one exists).
                        //              The fourth (optional) argument can be set to true to so the function receives the original
                        //              arguments (from when the original method was called) rather than the return value.
                        //              If there are multiple "after" advisors, they are executed in the order they were registered.
                        // target: Object
                        //              This is the target object
                        // methodName: String
                        //              This is the name of the method to attach to.
                        // advice: Function
                        //              This is function to be called after the original method
                        // receiveArguments: Boolean?
                        //              If this is set to true, the advice function receives the original arguments (from when the original mehtod
                        //              was called) rather than the return value of the original/previous method.
                        // returns:
                        //              A signal object that can be used to cancel the advice. If remove() is called on this signal object, it will
                        //              stop the advice function from being executed.
                },
                
                before: function(target, methodName, advice){
                        // summary: The "before" export of the aspect module is a function that can be used to attach
                        //              "before" advice to a method. This function will be executed before the original method
                        //              is executed. This function will be called with the arguments used to call the method.
                        //              This function may optionally return an array as the new arguments to use to call
                        //              the original method (or the previous, next-to-execute before advice, if one exists).
                        //              If the before method doesn't return anything (returns undefined) the original arguments
                        //              will be preserved.
                        //              If there are multiple "before" advisors, they are executed in the reverse order they were registered.
                        //
                        // target: Object
                        //              This is the target object
                        // methodName: String
                        //              This is the name of the method to attach to.
                        // advice: Function
                        //              This is function to be called before the original method         
                },

                around: function(target, methodName, advice){
                        // summary: The "around" export of the aspect module is a function that can be used to attach
                        //              "around" advice to a method. The advisor function is immediately executed when
                        //              the around() is called, is passed a single argument that is a function that can be
                        //              called to continue execution of the original method (or the next around advisor).
                        //              The advisor function should return a function, and this function will be called whenever
                        //              the method is called. It will be called with the arguments used to call the method.
                        //              Whatever this function returns will be returned as the result of the method call (unless after advise changes it).
                        //
                        // example:
                        //              If there are multiple "around" advisors, the most recent one is executed first,
                        //              which can then delegate to the next one and so on. For example:
                        //              |       around(obj, "foo", function(originalFoo){
                        //              |               return function(){
                        //              |                       var start = new Date().getTime();
                        //              |                       var results = originalFoo.apply(this, arguments); // call the original
                        //              |                       var end = new Date().getTime();
                        //              |                       console.log("foo execution took " + (end - start) + " ms");
                        //              |                       return results;
                        //              |               };
                        //              |       });
                        //
                        // target: Object
                        //              This is the target object
                        // methodName: String
                        //              This is the name of the method to attach to.
                        // advice: Function
                        //              This is function to be called around the original method
                }

        };
=====*/

        "use strict";
        function advise(dispatcher, type, advice, receiveArguments){
                var previous = dispatcher[type];
                var around = type == "around";
                var signal;
                if(around){
                        var advised = advice(function(){
                                return previous.advice(this, arguments);
                        });
                        signal = {
                                remove: function(){
                                        signal.cancelled = true;
                                },
                                advice: function(target, args){
                                        return signal.cancelled ?
                                                previous.advice(target, args) : // cancelled, skip to next one
                                                advised.apply(target, args);    // called the advised function
                                }
                        };
                }else{
                        // create the remove handler
                        signal = {
                                remove: function(){
                                        var previous = signal.previous;
                                        var next = signal.next;
                                        if(!next && !previous){
                                                delete dispatcher[type];
                                        }else{
                                                if(previous){
                                                        previous.next = next;
                                                }else{
                                                        dispatcher[type] = next;
                                                }
                                                if(next){
                                                        next.previous = previous;
                                                }
                                        }
                                },
                                advice: advice,
                                receiveArguments: receiveArguments
                        };
                }
                if(previous && !around){
                        if(type == "after"){
                                // add the listener to the end of the list
                                var next = previous;
                                while(next){
                                        previous = next;
                                        next = next.next;
                                }
                                previous.next = signal;
                                signal.previous = previous;
                        }else if(type == "before"){
                                // add to beginning
                                dispatcher[type] = signal;
                                signal.next = previous;
                                previous.previous = signal;
                        }
                }else{
                        // around or first one just replaces
                        dispatcher[type] = signal;
                }
                return signal;
        }
        function aspect(type){
                return function(target, methodName, advice, receiveArguments){
                        var existing = target[methodName], dispatcher;
                        if(!existing || existing.target != target){
                                // no dispatcher in place
                                dispatcher = target[methodName] = function(){
                                        // before advice
                                        var args = arguments;
                                        var before = dispatcher.before;
                                        while(before){
                                                args = before.advice.apply(this, args) || args;
                                                before = before.next;
                                        }
                                        // around advice
                                        if(dispatcher.around){
                                                var results = dispatcher.around.advice(this, args);
                                        }
                                        // after advice
                                        var after = dispatcher.after;
                                        while(after){
                                                results = after.receiveArguments ? after.advice.apply(this, args) || results :
                                                                after.advice.call(this, results);
                                                after = after.next;
                                        }
                                        return results;
                                };
                                if(existing){
                                        dispatcher.around = {advice: function(target, args){
                                                return existing.apply(target, args);
                                        }};
                                }
                                dispatcher.target = target;
                        }
                        var results = advise((dispatcher || existing), type, advice, receiveArguments);
                        advice = null;
                        return results;
                };
        }
        return {
                before: aspect("before"),
                around: aspect("around"),
                after: aspect("after")
        };
});