Start implementing backends and authentication

src/backends/backend.js

@@ -0,0 +1,49 @@
+import TestRepoBackend from './test-repo/Implementation';
+
+export function resolveBackend(config) {
+  const name = config.getIn(['backend', 'name']);
+  if (name == null) {
+    throw 'No backend defined in configuration';
+  }
+
+  switch (name) {
+    case 'test-repo':
+      return new Backend(new TestRepoBackend(config));
+    default:
+      throw `Backend not found: ${name}`;
+  }
+}
+
+class Backend {
+  constructor(implementation, authStore = null) {
+    this.implementation = implementation;
+    this.authStore = authStore;
+    if (this.implementation == null) {
+      throw 'Cannot instantiate a Backend with no implementation';
+    }
+  }
+
+  currentUser() {
+    if (this.user) { return this.user; }
+    return this.authStore && this.authStore.retrieve();
+  }
+
+  authComponent() {
+    return this.implementation.authComponent();
+  }
+
+  authenticate(state) {
+    return this.implementation.authenticate(state);
+  }
+}
+
+export const currentBackend = (function() {
+  let backend = null;
+
+  return (config) => {
+    if (backend) { return backend; }
+    if (config.get('backend')) {
+      return backend = resolveBackend(config);
+    }
+  };
+})();