Refactor into a Intl format memoizer

**This is a major-version level refactor.** This refactor proposes a shift in the role of this package in the overall FormatJS system to a memoizer of `Intl*` format instances.

These change mean that this package no longer has dependencies on the `intl-*` packages, as the template/component integration layers should be the packages with those dependencies.

Gruntfile.js

@@ -15,7 +15,7 @@ module.exports = function (grunt) {
             tmp: {
                 expand : true,
                 flatten: true,
-                src    : 'tmp/src/*.*',
+                src    : 'tmp/src/*.js',
                 dest   : 'lib/'
             }
         }

README.md

@@ -9,7 +9,7 @@ Produces instances of JavaScript `Intl` formats, and caches them for reuse.
 Overview
 --------
 
-This is an helper package used within [Yahoo's IntlJS suite][IntlJS]. It provides a cache layer for creating [`Intl`][Intl] format instances: [`IntlNumberFormat`][Intl-NF], [`Intl.DateTimeFormat`][Intl-DTF], and [`IntlMessageFormat`][Intl-MF].
+This is an helper package used within [Yahoo's IntlJS suite][IntlJS]. It provides a cache/memoize layer for creating [`Intl`][Intl] format instances: [`IntlNumberFormat`][Intl-NF], [`Intl.DateTimeFormat`][Intl-DTF], and [`IntlMessageFormat`][Intl-MF].
 
 
 License

index.js

@@ -1 +1,2 @@
-module.exports = require('./lib/formats');
+exports = module.exports = require('./lib/memoizer').default;
+Object.defineProperty(exports, 'default', {value: exports});

package.json

@@ -3,7 +3,7 @@
   "version": "1.0.0",
   "description": "Produces instances of JavaScript `Intl` formats, and caches them for reuse.",
   "main": "index.js",
-  "jsnext:main": "src/formats.js",
+  "jsnext:main": "src/memoizer.js",
   "scripts": {
     "prepublish": "grunt",
     "test": "echo \"Error: no test specified\" && exit 1"
@@ -22,15 +22,12 @@
     "url": "https://github.com/yahoo/intl-format-cache/issues"
   },
   "homepage": "https://github.com/yahoo/intl-format-cache",
-  "dependencies": {
-    "intl-messageformat": "^1.0.0-rc-2"
-  },
+  "dependencies": {},
   "devDependencies": {
     "grunt": "^0.4.5",
     "grunt-bundle-jsnext-lib": "^0.2.1",
     "grunt-cli": "^0.1.13",
     "grunt-contrib-clean": "^0.6.0",
-    "grunt-contrib-copy": "^0.5.0",
-    "intl": "^0.1.4"
+    "grunt-contrib-copy": "^0.6.0"
   }
 }

src/es5.js

@@ -0,0 +1,30 @@
+/*
+Copyright (c) 2014, Yahoo! Inc. All rights reserved.
+Copyrights licensed under the New BSD License.
+See the accompanying LICENSE file for terms.
+*/
+
+/* jslint esnext: true */
+
+export {objCreate};
+
+// Purposely using the same implementation as the Intl.js `Intl` polyfill.
+// Copyright 2013 Andy Earnshaw, MIT License
+
+var hop = Object.prototype.hasOwnProperty;
+
+var objCreate = Object.create || function (proto, props) {
+    var obj, k;
+
+    function F() {}
+    F.prototype = proto;
+    obj = new F();
+
+    for (k in props) {
+        if (hop.call(props, k)) {
+            defineProperty(obj, k, props[k]);
+        }
+    }
+
+    return obj;
+};

src/memoizer.js

@@ -0,0 +1,82 @@
+/*
+Copyright (c) 2014, Yahoo! Inc. All rights reserved.
+Copyrights licensed under the New BSD License.
+See the accompanying LICENSE file for terms.
+*/
+
+/* jshint esnext: true */
+
+import {objCreate} from './es5';
+
+export default createFormatCache;
+
+// -----------------------------------------------------------------------------
+
+function createFormatCache(FormatConstructor) {
+    var cache = objCreate(null);
+
+    return function () {
+        var args    = Array.prototype.slice.call(arguments);
+        var cacheId = getCacheId(args);
+        var format  = cache[cacheId];
+
+        if (!format) {
+            format = objCreate(FormatConstructor.prototype);
+            FormatConstructor.apply(format, args);
+
+            if (cacheId) {
+                cache[cacheId] = format;
+            }
+        }
+
+        return format;
+    };
+}
+
+// -- Utilities ----------------------------------------------------------------
+
+function getCacheId(inputs) {
+    // When JSON is not available in the runtime, we will not create a cache id.
+    if (!JSON) { return; }
+
+    var cacheId = [];
+
+    var i, len, input;
+
+    for (i = 0, len = inputs.length; i < len; i += 1) {
+        input = inputs[i];
+
+        if (input && typeof input === 'object') {
+            cacheId.push(orderedProps(input));
+        } else {
+            cacheId.push(input);
+        }
+    }
+
+    return JSON.stringify(cacheId);
+}
+
+function orderedProps(obj) {
+    var props = [],
+        keys  = [];
+
+    var key, i, len, prop;
+
+    for (key in obj) {
+        if (obj.hasOwnProperty(key)) {
+            keys.push(key);
+        }
+    }
+
+    var orderedKeys = keys.sort();
+
+    for (i = 0, len = orderedKeys.length; i < len; i += 1) {
+        key  = orderedKeys[i];
+        prop = {};
+
+        prop[key] = obj[key];
+        props[i]  = prop;
+    }
+
+    return props;
+}