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

define(["../_base/kernel", "../_base/lang", "../_base/Deferred", "../_base/array"
], function(kernel, lang, Deferred, array) {
        // module:
        //              dojo/store/Observable
        // summary:
        //              TODOC

var ds = lang.getObject("dojo.store", true);

return ds.Observable = function(store){
        // summary:
        //              The Observable store wrapper takes a store and sets an observe method on query()
        //              results that can be used to monitor results for changes.
        //
        // description:
        //              Observable wraps an existing store so that notifications can be made when a query
        //              is performed.
        //
        // example:
        //              Create a Memory store that returns an observable query, and then log some
        //              information about that query.
        //
        //      |       var store = dojo.store.Observable(new dojo.store.Memory({
        //      |               data: [
        //      |                       {id: 1, name: "one", prime: false},
        //      |                       {id: 2, name: "two", even: true, prime: true},
        //      |                       {id: 3, name: "three", prime: true},
        //      |                       {id: 4, name: "four", even: true, prime: false},
        //      |                       {id: 5, name: "five", prime: true}
        //      |               ]
        //      |       }));
        //      |       var changes = [], results = store.query({ prime: true });
        //      |       var observer = results.observe(function(object, previousIndex, newIndex){
        //      |               changes.push({previousIndex:previousIndex, newIndex:newIndex, object:object});
        //      |       });
        //
        //              See the Observable tests for more information.

        var undef, queryUpdaters = [], revision = 0;
        // a Comet driven store could directly call notify to notify observers when data has
        // changed on the backend
        store.notify = function(object, existingId){
                revision++;
                var updaters = queryUpdaters.slice();
                for(var i = 0, l = updaters.length; i < l; i++){
                        updaters[i](object, existingId);
                }
        };
        var originalQuery = store.query;
        store.query = function(query, options){
                options = options || {};
                var results = originalQuery.apply(this, arguments);
                if(results && results.forEach){
                        var nonPagedOptions = lang.mixin({}, options);
                        delete nonPagedOptions.start;
                        delete nonPagedOptions.count;

                        var queryExecutor = store.queryEngine && store.queryEngine(query, nonPagedOptions);
                        var queryRevision = revision;
                        var listeners = [], queryUpdater;
                        results.observe = function(listener, includeObjectUpdates){
                                if(listeners.push(listener) == 1){
                                        // first listener was added, create the query checker and updater
                                        queryUpdaters.push(queryUpdater = function(changed, existingId){
                                                Deferred.when(results, function(resultsArray){
                                                        var atEnd = resultsArray.length != options.count;
                                                        var i, l, listener;
                                                        if(++queryRevision != revision){
                                                                throw new Error("Query is out of date, you must observe() the query prior to any data modifications");
                                                        }
                                                        var removedObject, removedFrom = -1, insertedInto = -1;
                                                        if(existingId !== undef){
                                                                // remove the old one
                                                                for(i = 0, l = resultsArray.length; i < l; i++){
                                                                        var object = resultsArray[i];
                                                                        if(store.getIdentity(object) == existingId){
                                                                                removedObject = object;
                                                                                removedFrom = i;
                                                                                if(queryExecutor || !changed){// if it was changed and we don't have a queryExecutor, we shouldn't remove it because updated objects would be eliminated
                                                                                        resultsArray.splice(i, 1);
                                                                                }
                                                                                break;
                                                                        }
                                                                }
                                                        }
                                                        if(queryExecutor){
                                                                // add the new one
                                                                if(changed &&
                                                                                // if a matches function exists, use that (probably more efficient)
                                                                                (queryExecutor.matches ? queryExecutor.matches(changed) : queryExecutor([changed]).length)){

                                                                        var firstInsertedInto = removedFrom > -1 ? 
                                                                                removedFrom : // put back in the original slot so it doesn't move unless it needs to (relying on a stable sort below)
                                                                                resultsArray.length;
                                                                        resultsArray.splice(firstInsertedInto, 0, changed); // add the new item
                                                                        insertedInto = array.indexOf(queryExecutor(resultsArray), changed); // sort it
                                                                        // we now need to push the chagne back into the original results array
                                                                        resultsArray.splice(firstInsertedInto, 1); // remove the inserted item from the previous index
                                                                        
                                                                        if((options.start && insertedInto == 0) ||
                                                                                (!atEnd && insertedInto == resultsArray.length)){
                                                                                // if it is at the end of the page, assume it goes into the prev or next page
                                                                                insertedInto = -1;
                                                                        }else{
                                                                                resultsArray.splice(insertedInto, 0, changed); // and insert into the results array with the correct index
                                                                        }
                                                                }
                                                        }else if(changed && !options.start){
                                                                // we don't have a queryEngine, so we can't provide any information
                                                                // about where it was inserted, but we can at least indicate a new object
                                                                insertedInto = removedFrom >= 0 ? removedFrom : (store.defaultIndex || 0);
                                                        }
                                                        if((removedFrom > -1 || insertedInto > -1) &&
                                                                        (includeObjectUpdates || !queryExecutor || (removedFrom != insertedInto))){
                                                                var copyListeners = listeners.slice();
                                                                for(i = 0;listener = copyListeners[i]; i++){
                                                                        listener(changed || removedObject, removedFrom, insertedInto);
                                                                }
                                                        }
                                                });
                                        });
                                }
                                return {
                                        cancel: function(){
                                                // remove this listener
                                                var index = array.indexOf(listeners, listener);
                                                if(index > -1){ // check to make sure we haven't already called cancel
                                                        listeners.splice(index, 1);
                                                        if(!listeners.length){
                                                                // no more listeners, remove the query updater too
                                                                queryUpdaters.splice(array.indexOf(queryUpdaters, queryUpdater), 1);
                                                        }
                                                }                                               
                                        }
                                };
                        };
                }
                return results;
        };
        var inMethod;
        function whenFinished(method, action){
                var original = store[method];
                if(original){
                        store[method] = function(value){
                                if(inMethod){
                                        // if one method calls another (like add() calling put()) we don't want two events
                                        return original.apply(this, arguments);
                                }
                                inMethod = true;
                                try{
                                        var results = original.apply(this, arguments);
                                        Deferred.when(results, function(results){
                                                action((typeof results == "object" && results) || value);
                                        });
                                        return results;
                                }finally{
                                        inMethod = false;
                                }
                        };
                }
        }
        // monitor for updates by listening to these methods
        whenFinished("put", function(object){
                store.notify(object, store.getIdentity(object));
        });
        whenFinished("add", function(object){
                store.notify(object);
        });
        whenFinished("remove", function(id){
                store.notify(undefined, id);
        });

        return store;
};
});