function bookShelf(input) {
  let shelvesList = new Map();
  let bookList = new Map();
  for (const line of input) {
    if (line.includes('->')) {
      let [id, genre] = line.split('->').map(str => str.trim());
      if (![...shelvesList.values()].includes(id)) {
        shelvesList.set(genre, id);
        bookList.set(genre, []);
      }
    } else {
      let [bookTitle, bookAuthor, genre] = line.split(/[:,]+/).map(str => str.trim());
      if (bookList.has(genre)) {
        bookList.get(genre).push({bookTitle: bookTitle, bookAuthor: bookAuthor});
      }
    }
  }

  [...bookList.entries()]
    .sort((a, b) => b[1].length - a[1].length)
    .forEach((shelf) => {
      let [genre, books] = shelf;
      books.sort((a, b) => a.bookTitle.localeCompare(b.bookTitle));
      console.log(`${shelvesList.get(genre)} ${genre}: ${books.length}`);
      for (const book of books) {
        console.log(`--> ${book.bookTitle}: ${book.bookAuthor}`);
      }
    });
}