Add save methond

lib/index.js

@@ -8,5 +8,6 @@ module.exports = {
     parse: require('./parse'),
     assign: require('./assign'),
     load: require('./load'),
-    stringify: require('./stringify')
+    stringify: require('./stringify'),
+    save: require('./save')
 };

lib/save.js

@@ -0,0 +1,32 @@
+'use strict';
+
+const fs = require('fs');
+const stringify = require('javascript-stringify');
+const converter = require('./convert');
+
+/**
+ * Save normalized declaration to target format
+ *
+ * @param  {String} filename    Filename for save declaration
+ * @param  {Object} decl        Normalized declaraions
+ * @param  {Object} opts        Addtional options
+ * @param  {String} opts.format Format for save declaration
+ * @return {Promise}            Success or Error
+ */
+module.exports = (filename, decl, opts) => {
+    opts = Object.assign({ format: 'v2' }, opts);
+    decl = converter(decl, opts);
+
+    let data = [
+        'exports.format = ' + stringify(opts.format),
+        'exports.decl = ' + stringify(decl, null, '    '),
+        ''
+    ].join(';\n');
+
+    return new Promise((resolve, reject) => {
+        fs.writeFile(filename, data, (err) => {
+            if (err) { reject(err); }
+            resolve()
+        });
+    });
+}

package.json

@@ -28,6 +28,7 @@
     "@bem/entity-name": "1.1.0",
     "es6-promisify": "5.0.0",
     "graceful-fs": "4.1.11",
+    "javascript-stringify": "^1.5.0",
     "node-eval": "1.0.4"
   },
   "devDependencies": {