Add preference computed property

README.md

@@ -7,3 +7,8 @@
 2. Inject the service on all routes, controllers and components
   * create preferences mixin
   * create initializer and inject mixin to Route, Controller and Component
+3. Computed property
+  * read from preferences
+  * read default value
+  * write to preferences
+  * return value from `set` operation to update de cp

app/utils/preference.js

@@ -0,0 +1,25 @@
+import Ember from 'ember';
+
+export default function preference(dependentKey, options = {}) {
+  var key = `preferences.${dependentKey}`;
+
+  return Ember.computed(key, {
+    get() {
+      var value = this.get(key);
+
+      if (typeof value === 'undefined' || value === null) {
+        if (typeof options.defaultValue === 'function') {
+          return options.defaultValue();
+        } else {
+          return options.defaultValue;
+        }
+      }
+
+      return value;
+    },
+
+    set(_, value) {
+      return this.set(key, value);
+    }
+  });
+}

tests/unit/utils/preference-test.js

@@ -0,0 +1,89 @@
+import Ember from 'ember';
+import preference from 'ember-preferences/utils/preference';
+import { module, test } from 'qunit';
+
+module('Unit | Utility | preference');
+
+function createInstance(options = {}) {
+  let Class = Ember.Object.extend({
+    foo: preference('foo', options.cpOptions)
+  });
+
+  let preferences = options.preferences || { foo: 'bar' };
+
+  let instance = Class.create({ preferences });
+
+  return instance;
+}
+
+test('returns values from "preference" property', function(assert) {
+  let instance = createInstance();
+
+  assert.equal(instance.get('foo'), 'bar');
+});
+
+test('updates value when the preference changes', function(assert) {
+  let instance = createInstance();
+
+  assert.equal(instance.get('foo'), 'bar');
+
+  instance.set('preferences.foo', 'baz');
+
+  assert.equal(instance.get('foo'), 'baz');
+});
+
+test('returns default value when preference is null', function(assert) {
+  let instance = createInstance({
+    cpOptions: {
+      defaultValue: 'qux'
+    },
+
+    preferences: { foo: null }
+  });
+
+  assert.equal(instance.get('foo'), 'qux');
+});
+
+test('returns default value when preference is undefined', function(assert) {
+  let instance = createInstance({
+    cpOptions: {
+      defaultValue: 'qux'
+    },
+
+    preferences: { }
+  });
+
+  assert.equal(instance.get('foo'), 'qux');
+});
+
+test('evaluates default value when it is a function', function(assert) {
+  let instance = createInstance({
+    cpOptions: {
+      defaultValue() {
+        return 'qux';
+      }
+    },
+
+    preferences: { }
+  });
+
+  assert.equal(instance.get('foo'), 'qux');
+});
+
+test('writes configuration to preference object', function(assert) {
+  let instance = createInstance();
+
+  instance.set('foo', 'baz');
+
+  assert.equal(instance.get('preferences.foo'), 'baz');
+});
+
+test('updates value when the property changes', function(assert) {
+  let instance = createInstance();
+
+  assert.equal(instance.get('foo'), 'bar');
+
+  instance.set('foo', 'baz');
+
+  assert.equal(instance.get('foo'), 'baz');
+});