Add utilities for bundle creation

Summary: Adds utilities needed for bundle creation: `completeModuleWrapper` appends numeric IDs for the module itself and its dependencies to a module wrapped. `createGetModuleId` returns a function that returns sequential numeric IDs for strings, and is idempotent.

Reviewed By: cpojer

Differential Revision: D4240334

fbshipit-source-id: c165482ebcf0e81ebb83ba6ff634de095ffb6bf0

packager/react-packager/src/ModuleGraph/output/util.js

@@ -0,0 +1,52 @@
+/**
+ * Copyright (c) 2016-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *
+ * @flow
+ */
+'use strict';
+
+import type {Module} from '../types.flow';
+
+// Transformed modules have the form
+//   __d(function(require, module, global, exports, dependencyMap) {
+//       /* code */
+//   });
+//
+// This function adds the numeric module ID, and an array with dependencies of
+// the dependencies of the module before the closing parenthesis.
+exports.addModuleIdsToModuleWrapper = (
+  module: Module,
+  idForPath: {path: string} => number,
+): string => {
+  const {dependencies, file} = module;
+  const {code} = file;
+  const index = code.lastIndexOf(')');
+  const depencyIds =
+    dependencies.length ? `, [${dependencies.map(idForPath).join(', ')}]` : '';
+  return (
+    code.slice(0, index) +
+    `, ${idForPath(file)}` +
+    depencyIds +
+    code.slice(index)
+  );
+};
+
+// Creates an idempotent function that returns numeric IDs for objects based
+// on their `path` property.
+exports.createIdForPathFn = (): ({path: string} => number) => {
+  const seen = new Map();
+  let next = 0;
+  return ({path}) => {
+    let id = seen.get(path);
+    if (id == null) {
+      id = next++;
+      seen.set(path, id);
+    }
+    return id;
+  };
+};