Merge pull request #13 from cuth/feature/function-dest

Allow dest path and map to be functions returning a string,
prevent creating empty file.

index.js

@@ -21,6 +21,9 @@ function plugin (opts) {
 
 	return function (css, result) {
 
+		opts.from = result.opts.from;
+		opts.to = result.opts.to;
+
 		if (opts.dest !== false) {
 			generateDataFile(css, opts);
 		}
@@ -175,10 +178,12 @@ function generateDataFile (css, opts) {
 	};
 
 	var data = dataCSS.toResult({
-		to: opts.dest.path,
-		map: opts.dest.map
+		to: (typeof opts.dest.path === 'function') ? opts.dest.path(opts) : opts.dest.path,
+		map: (typeof opts.dest.map === 'function') ? opts.dest.map(opts) : opts.dest.map
 	});
 
+	if (!data.css.length) return;
+
 	fsExtra.outputFileSync(data.opts.to, data.css);
 
 	if (data.map) {