fix(revision-service): fix count of duplicate authors

`getRevisionUserInfo` returned an incorrect list of usernames,
as users who edited a note at multiple places appeared multiple times.

 This commit fixes this behaviour by deduplicating the author
  objects using a Set.

  Closes #2180

Signed-off-by: David Mehren <git@herrmehren.de>

src/revisions/revisions.service.spec.ts

@@ -163,4 +163,26 @@ describe('RevisionsService', () => {
       expect(revisions).toEqual(updatedRevisions);
     });
   });
+
+  describe('getRevisionUserInfo', () => {
+    it('counts users correctly', async () => {
+      const user = User.create('test', 'test') as User;
+      const author = Author.create(123) as Author;
+      author.user = Promise.resolve(user);
+      const anonAuthor = Author.create(123) as Author;
+      const anonAuthor2 = Author.create(123) as Author;
+      const edits = [Edit.create(author, 12, 15) as Edit];
+      edits.push(Edit.create(author, 16, 18) as Edit);
+      edits.push(Edit.create(author, 29, 20) as Edit);
+      edits.push(Edit.create(anonAuthor, 29, 20) as Edit);
+      edits.push(Edit.create(anonAuthor, 29, 20) as Edit);
+      edits.push(Edit.create(anonAuthor2, 29, 20) as Edit);
+      const revision = Revision.create('', '', {} as Note) as Revision;
+      revision.edits = Promise.resolve(edits);
+
+      const userInfo = await service.getRevisionUserInfo(revision);
+      expect(userInfo.usernames.length).toEqual(1);
+      expect(userInfo.anonymousUserCount).toEqual(2);
+    });
+  });
 });

src/revisions/revisions.service.ts

@@ -109,16 +109,21 @@ export class RevisionsService {
   }
 
   async getRevisionUserInfo(revision: Revision): Promise<RevisionUserInfo> {
-    const users = await Promise.all(
+    // get a deduplicated list of all authors
-      (
+    let authors = await Promise.all(
-        await revision.edits
+      (await revision.edits).map(async (edit) => await edit.author),
-      ).map(async (edit) => await (await edit.author).user),
     );
+    authors = [...new Set(authors)]; // remove duplicates with Set
+
+    // retrieve user objects of the authors
+    const users = await Promise.all(
+      authors.map(async (author) => await author.user),
+    );
+    // collect usernames of the users
     const usernames = users.flatMap((user) => (user ? [user.username] : []));
-    const anonymousUserCount = users.filter((user) => user === null).length;
     return {
       usernames: usernames,
-      anonymousUserCount: anonymousUserCount,
+      anonymousUserCount: users.length - usernames.length,
     };
   }