refactor(auth): add some comments

auth/auth.ts

@@ -117,13 +117,14 @@ export class MockAuth implements firebase.auth.Auth {
   }
 
   private async signInWithSocial(provider: firebase.auth.AuthProvider) {
-    const data = await this.store.consumeSocialMock(provider);
-    let user = this.store.findByProviderAndEmail(data.email, provider.providerId);
+    const mockResponse = await this.store.consumeSocialMock(provider);
+    let user = this.store.findByProviderAndEmail(mockResponse.email, provider.providerId);
     if (user) {
       return this.signIn(user, { isNewUser: false });
     }
 
-    user = this.store.add({ ...data, providerId: provider.providerId });
+    // user didn't exist, so it's created and then signed in
+    user = this.store.add({ ...mockResponse, providerId: provider.providerId });
     return this.signIn(user, { isNewUser: true });
   }
 

auth/user-store.ts

@@ -6,11 +6,16 @@ export class UserStore {
   private store = new Map<string, UserSchema>();
   private readonly socialMocks: SocialSignInMock[] = [];
 
+  /**
+   * Adds a user to this store with the given data.
+   * The new user is assigned a new ID and is returned.
+   */
   add(data: Partial<UserSchema>): User {
     const uid = ++this.nextId + "";
     const user = new User(
       {
         ...data,
+        // If the user is being created with a provider ID, then its data is coming from that provider.
         providerData: data.providerId ? [new UserInfo(uid, data.providerId, data)] : [],
         uid,
       },
@@ -26,6 +31,12 @@ export class UserStore {
     this.socialMocks.push(mock);
   }
 
+  /**
+   * Finds the mock response for a given AuthProvider, removes it from the list of mocks
+   * and returns its response.
+   *
+   * If a mock for that AuthProvider is not set, then this method throws.
+   */
   consumeSocialMock(provider: firebase.auth.AuthProvider) {
     const index = this.socialMocks.findIndex((mock) => mock.type === provider.providerId);
     if (index === -1) {