Update config to act as subscribable data store

lib/config.js

@@ -1,8 +1,53 @@
 "use strict";
 
-module.exports = {
-  logging: {},
+var _ = require("./utils/helpers");
 
-  // are we in TDR test mode? Used to stub out adaptors/drivers.
-  testMode: false
+var config = module.exports = {},
+    callbacks = [];
+
+// default data
+config.logging = {};
+config.testMode = false;
+
+/**
+ * Updates the Config, and triggers handler callbacks
+ *
+ * @param {Object} data new configuration information to set
+ * @return {void}
+ */
+config.update = function update(data) {
+  var forbidden = ["update", "subscribe", "unsubscribe"];
+
+  Object.keys(data).forEach(function(key) {
+    if (~forbidden.indexOf(key)) { delete data[key]; }
+  });
+
+  if (!Object.keys(data).length) {
+    return;
+  }
+
+  _.extend(config, data);
+
+  callbacks.forEach(function(callback) { callback(data); });
+};
+
+/**
+ * Subscribes a function to be called whenever the config is updated
+ *
+ * @param {Function} callback function to be called with updated data
+ * @return {void}
+ */
+config.subscribe = function subscribe(callback) {
+  callbacks.push(callback);
+};
+
+/**
+ * Unsubscribes a callback from configuration changes
+ *
+ * @param {Function} callback function to unsubscribe from changes
+ * @return {void}
+ */
+config.unsubscribe = function unsubscribe(callback) {
+  var idx = callbacks.indexOf(callback);
+  if (idx >= 0) { callbacks.splice(idx, 1); }
 };

spec/lib/config.spec.js

@@ -0,0 +1,85 @@
+"use strict";
+
+var config = lib("config");
+
+describe("config", function() {
+  it("contains configuration options", function() {
+    expect(config.logging).to.be.an("object");
+    expect(config.testMode).to.be.eql(false);
+  });
+
+  describe("#update", function() {
+    var callback;
+
+    beforeEach(function() {
+      callback = spy();
+      config.subscribe(callback);
+    });
+
+    afterEach(function() {
+      config.unsubscribe(callback);
+      delete config.newValue;
+    });
+
+    it("updates the configuration", function() {
+      expect(config.newValue).to.be.eql(undefined);
+      config.update({ newValue: "value" });
+      expect(config.newValue).to.be.eql("value");
+    });
+
+    it("notifies subscribers of changes", function() {
+      var update = { newValue: "value" };
+      expect(callback).to.not.be.called;
+      config.update(update);
+      expect(callback).to.be.calledWith(update);
+    });
+
+    it("rejects changes that conflict with config functions", function() {
+      config.update({ update: null });
+      expect(config.update).to.be.a("function");
+    });
+
+    it("does nothing with empty changesets", function() {
+      config.update({});
+      expect(callback).to.not.be.called;
+    });
+  });
+
+  describe("#subscribe", function() {
+    var callback = spy();
+
+    afterEach(function() {
+      delete config.test;
+      config.unsubscribe(callback);
+    });
+
+    it("subscribes a callback to change updates", function() {
+      config.subscribe(callback);
+      config.update({ test: true });
+      expect(callback).to.be.calledWith({ test: true });
+    });
+  });
+
+  describe("#unsubscribe", function() {
+    var callback;
+
+    beforeEach(function() {
+      callback = spy();
+      config.subscribe(callback);
+    });
+
+    afterEach(function() {
+      delete config.test;
+    });
+
+    it("unsubscribes a callback from change updates", function() {
+      config.update({ test: true });
+      expect(callback).to.be.called;
+
+      config.unsubscribe(callback);
+
+      config.update({ test: false });
+      expect(callback).to.be.calledOnce;
+    });
+  });
+});