source: Dev/trunk/src/client/dojox/lang/observable.js

dojo.provide("dojox.lang.observable");
// Used to create a wrapper object with monitored reads and writes
//
dojo.experimental("dojox.lang.observable");
// IMPORTANT DISCLAIMER:
// This is experimental and based on hideous hacks.
// There are severe limitations on the ability of wrapper objects:
// Only properties that have vbscript-legal names are accessible (similar to JavaScript, but they can't start with an underscore).
// The wrapper objects are not expando in IE, because they are built
// from VBScript objects. This means you can't add new properties after an object is created.
// The wrapper objects can not be used a prototype for other objects.
// Only properties with primitive values can be wrapped.
// This has performance implications as well.
dojox.lang.observable = function(/*Object*/wrapped,/*function*/onRead,/*function*/onWrite,/*function*/onInvoke){
        // summary:
        //              Creates a wrapper object, which can be observed. The wrapper object
        //              is a proxy to the wrapped object. If you will be making multiple wrapper
        //              objects with the same set of listeners, it is recommended that you
        //              use makeObservable, as it is more memory efficient.
        // wrapped:
        //              The object to be wrapped and monitored for property access and modification
        // onRead:
        //              See dojox.lang.makeObservable.onRead
        // onWrite:
        //              See dojox.lang.makeObservable.onWrite
        // onInvoke:
        //              See dojox.lang.makeObservable.onInvoke
        
        return dojox.lang.makeObservable(onRead,onWrite,onInvoke)(wrapped);
};
dojox.lang.makeObservable = function(/*function*/onRead,/*function*/onWrite,/*function*/onInvoke,/*Object*/hiddenFunctions){
                
        // summary:
        //              Creates and returns an observable creator function. All the objects that
        //              are created with the returned constructor will use the provided onRead and
        //              onWrite listeners.
        //              The created constructor should be called with a single argument,
        //              the object that will be wrapped to be observed. The constructor will
        //              return the wrapper object.
        // onRead:
        //              This is called whenever one of the wrapper objects created
        //              from the constructor has a property that is accessed. onRead
        //              will be called with two arguments, the first being the wrapped object,
        //              and the second is the name of property that is being accessed.
        //              The value that onRead returns will be used as the value returned
        //              by the property access
        // onWrite:
        //              This is called whenever one of the wrapper objects created
        //              from the constructor has a property that is modified. onWrite
        //              will be called with three arguments, the first being the wrapped object,
        //              the second is the name of property that is being modified, and the
        //              third is the value that is being set on the property.
        // onInvoke:
        //              This is called when a method on the object is invoked. The first
        //              argument is the wrapper object, the second is the original wrapped object,
        //              the third is the method name, and the fourth is the arguments.
        //
        // hiddenFunctions:
        //              allows you to define functions that should be delegated
        //              but may not be enumerable on the wrapped objects, so they must be
        //              explicitly included
        // example:
        //              The following could be used to create a wrapper that would
        //              prevent functions from being accessed on an object:
        //      |       function onRead(obj,prop){
        //      |               return typeof obj[prop] == 'function' ? null : obj[prop];
        //      |       }
        //      |       var observable = dojox.lang.makeObservable(onRead,onWrite);
        //      |       var obj = {foo:1,bar:function(){}};
        //      |       obj = observable(obj);
        //      |       obj.foo -> 1
        //      |       obj.bar -> null

        hiddenFunctions = hiddenFunctions || {};
        onInvoke = onInvoke || function(scope,obj,method,args){
                // default implementation for onInvoke, just passes the call through
                return obj[method].apply(scope,args);
        };
        function makeInvoker(scope,wrapped,i){
                return function(){
                        // this is function used for all methods in the wrapper object
                        return onInvoke(scope,wrapped,i,arguments);
                };
        }
        
        if(dojox.lang.lettableWin){ // create the vb class
                var factory = dojox.lang.makeObservable;
                factory.inc = (factory.inc || 0) + 1;
                // create globals for the getters and setters so they can be accessed from the vbscript
                var getName = "gettable_"+factory.inc;
                dojox.lang.lettableWin[getName] = onRead;
                var setName = "settable_"+factory.inc;
                dojox.lang.lettableWin[setName] = onWrite;
                var cache = {};
                return function(wrapped){
                        if(wrapped.__observable){ // if it already has an observable, use that
                                return wrapped.__observable;
                        }
                        if(wrapped.data__){
                                throw new Error("Can wrap an object that is already wrapped");
                        }
                        // create the class
                        var props = [], i, l;
                        for(i in hiddenFunctions){
                                props.push(i);
                        }
                        var vbReservedWords = {type:1,event:1};
                        // find the unique signature for the class so we can reuse it if possible
                        for(i in wrapped){
                                if(i.match(/^[a-zA-Z][\w\$_]*$/) && !(i in hiddenFunctions) && !(i in vbReservedWords)){ //can only do properties with valid vb names/tokens and primitive values
                                        props.push(i);
                                }
                        }
                        var signature = props.join(",");
                        var prop,clazz = cache[signature];
                        if(!clazz){
                                var tname = "dj_lettable_"+(factory.inc++);
                                var gtname = tname+"_dj_getter";
                                var cParts = [
                                        "Class "+tname,
                                        "       Public data__" // this our reference to the original object
                                ];
                                for(i=0, l=props.length; i<l; i++){
                                        prop = props[i];
                                        var type = typeof wrapped[prop];
                                        if(type == 'function' || hiddenFunctions[prop]){ // functions must go in regular properties for delegation:/
                                                cParts.push("  Public " + prop);
                                        }else if(type != 'object'){ // the getters/setters can only be applied to primitives
                                                cParts.push(
                                                        "       Public Property Let "+prop+"(val)",
                                                        "               Call "+setName+"(me.data__,\""+prop+"\",val)",
                                                        "       End Property",
                                                        "       Public Property Get "+prop,
                                                        "               "+prop+" = "+getName+"(me.data__,\""+prop+"\")",
                                                        "       End Property");
                                        }
                                }
                                cParts.push("End Class");
                                cParts.push(
                                        "Function "+gtname+"()",
                                        "       Dim tmp",
                                        "       Set tmp = New "+tname,
                                        "       Set "+gtname+" = tmp",
                                        "End Function");
                                dojox.lang.lettableWin.vbEval(cParts.join("\n"));
                                        
                                // Put the new class in the cache
                                cache[signature] = clazz = function(){
                                        return dojox.lang.lettableWin.construct(gtname); // the class can't be accessed, only called, so we have to wrap it with a function
                                };
                        }
                        console.log("starting5");
                        var newObj = clazz();
                        newObj.data__ = wrapped;
                        console.log("starting6");
                        try {
                                wrapped.__observable = newObj;
                        } catch(e){ // some objects are not expando
                        }
                        for(i = 0,  l = props.length; i < l; i++){
                                prop = props[i];
                                try {
                                var val = wrapped[prop];
                                }
                                catch(e){
                                        console.log("error ",prop,e);
                                }
                                if(typeof val == 'function' || hiddenFunctions[prop]){ // we can make a delegate function here
                                        newObj[prop] = makeInvoker(newObj,wrapped,prop);
                                }
                        }
                        return newObj;
                };
        }else{
                return function(wrapped){ // do it with getters and setters
                        if(wrapped.__observable){ // if it already has an observable, use that
                                return wrapped.__observable;
                        }
                        var newObj = wrapped instanceof Array ? [] : {};
                        newObj.data__ = wrapped;
                        for(var i in wrapped){
                                if(i.charAt(0) != '_'){
                                        if(typeof wrapped[i] == 'function'){
                                                newObj[i] = makeInvoker(newObj,wrapped,i); // TODO: setup getters and setters so we can detect when this changes
                                        }else if(typeof wrapped[i] != 'object'){
                                                (function(i){
                                                        newObj.__defineGetter__(i,function(){
                                                                return onRead(wrapped,i);
                                                        });
                                                        newObj.__defineSetter__(i,function(value){
                                                                return onWrite(wrapped,i,value);
                                                        });
                                                })(i);
                                        }
                                }
                        }
                        for(i in hiddenFunctions){
                                newObj[i] = makeInvoker(newObj,wrapped,i);
                        }
                        wrapped.__observable = newObj;
                        return newObj;
                };
        }
};
if(!{}.__defineGetter__){
        if(dojo.isIE){
                // to setup the crazy lettable hack we need to
                // introduce vb script eval
                // the only way that seems to work for adding a VBScript to the page is with a document.write
                // document.write is not always available, so we use an iframe to do the document.write
                // the iframe also provides a good hiding place for all the global variables that we must
                // create in order for JScript and VBScript to interact.
                var frame;
                if(document.body){ // if the DOM is ready we can add it
                        frame = document.createElement("iframe");
                        document.body.appendChild(frame);
                }else{ // other we have to write it out
                        document.write("<iframe id='dj_vb_eval_frame'></iframe>");
                        frame = document.getElementById("dj_vb_eval_frame");
                }
                frame.style.display="none";
                var doc = frame.contentWindow.document;
                dojox.lang.lettableWin = frame.contentWindow;
                doc.write('<html><head><script language="VBScript" type="text/VBScript">' +
                        'Function vb_global_eval(code)' +
                                'ExecuteGlobal(code)' +
                        'End Function' +
                        '</script>' +
                        '<script type="text/javascript">' +
                        'function vbEval(code){ \n' + // this has to be here to call it from another frame
                                'return vb_global_eval(code);' +
                        '}' +
                        'function construct(name){ \n' + // and this too
                                'return window[name]();' +
                        '}' +
                        '</script>' +
                        '</head><body>vb-eval</body></html>');
                doc.close();
        }else{
                throw new Error("This browser does not support getters and setters");
        }
}

dojox.lang.ReadOnlyProxy =
// summary:
//              Provides a read only proxy to another object, this can be
//              very useful in object-capability systems
// example:
//      |       var obj = {foo:"bar"};
//      |       var readonlyObj = dojox.lang.ReadOnlyProxy(obj);
//      |       readonlyObj.foo = "test" // throws an error
//      |       obj.foo = "new bar";
//      |       readonlyObj.foo -> returns "new bar", always reflects the current value of the original (it is not just a copy)
dojox.lang.makeObservable(function(obj,i){
                return obj[i];
        },function(obj,i,value){
                // just ignore, exceptions don't seem to propagate through the VB stack.
});