dojo.provide("dojo.data.util.sorter");

dojo.data.util.sorter.basicComparator = function(	/*anything*/ a, 
													/*anything*/ b){
	//	summary:  
	//		Basic comparision function that compares if an item is greater or less than another item
	//	description:  
	//		returns 1 if a > b, -1 if a < b, 0 if equal.
	//		'null' values (null, undefined) are treated as larger values so that they're pushed to the end of the list.
	//		And compared to each other, null is equivalent to undefined.
	
	//null is a problematic compare, so if null, we set to undefined.
	//Makes the check logic simple, compact, and consistent
	//And (null == undefined) === true, so the check later against null
	//works for undefined and is less bytes.
	var r = -1;
	if(a === null){
		a = undefined;
	}
	if(b === null){
		b = undefined;
	}
	if(a == b){
		r = 0; 
	}else if(a > b || a == null){
		r = 1; 
	}
	return r; //int {-1,0,1}
};

dojo.data.util.sorter.createSortFunction = function(	/* attributes array */sortSpec,
														/*dojo.data.core.Read*/ store){
	//	summary:  
	//		Helper function to generate the sorting function based off the list of sort attributes.
	//	description:  
	//		The sort function creation will look for a property on the store called 'comparatorMap'.  If it exists
	//		it will look in the mapping for comparisons function for the attributes.  If one is found, it will
	//		use it instead of the basic comparator, which is typically used for strings, ints, booleans, and dates.
	//		Returns the sorting function for this particular list of attributes and sorting directions.
	//
	//	sortSpec: array
	//		A JS object that array that defines out what attribute names to sort on and whether it should be descenting or asending.
	//		The objects should be formatted as follows:
	//		{
	//			attribute: "attributeName-string" || attribute,
	//			descending: true|false;   // Default is false.
	//		}
	//	store: object
	//		The datastore object to look up item values from.
	//
	var sortFunctions=[];

	function createSortFunction(attr, dir, comp, s){
		//Passing in comp and s (comparator and store), makes this
		//function much faster.
		return function(itemA, itemB){
			var a = s.getValue(itemA, attr);
			var b = s.getValue(itemB, attr);
			return dir * comp(a,b); //int
		};
	}
	var sortAttribute;
	var map = store.comparatorMap;
	var bc = dojo.data.util.sorter.basicComparator;
	for(var i = 0; i < sortSpec.length; i++){
		sortAttribute = sortSpec[i];
		var attr = sortAttribute.attribute;
		if(attr){
			var dir = (sortAttribute.descending) ? -1 : 1;
			var comp = bc;
			if(map){
				if(typeof attr !== "string" && ("toString" in attr)){
					 attr = attr.toString();
				}
				comp = map[attr] || bc;
			}
			sortFunctions.push(createSortFunction(attr, 
				dir, comp, store));
		}
	}
	return function(rowA, rowB){
		var i=0;
		while(i < sortFunctions.length){
			var ret = sortFunctions[i++](rowA, rowB);
			if(ret !== 0){
				return ret;//int
			}
		}
		return 0; //int  
	}; // Function
};
