library_server

import ballerina/grpc;
import ballerina/log;
import library.proto;

// Assuming library.proto defines the service
// consist of a stub//
const string ROOT_DESCRIPTOR = "library.BookService"; 
map<string> descriptorMap = {
  "library.BookService": ROOT_DESCRIPTOR
};

@grpc:ServiceDescriptor {
  descriptor: ROOT_DESCRIPTOR,
  descMap descriptorMap
}
service "BookService" on new grpc:Listener(9090) {

  remote function AddBook(Book request) returns BookId|error {

    if (bookExists(request.isbn)) {
      return error("Book already exists!");
    }

    var bookId = addBookToLibrary(request);
    if (bookId is error) {
      return bookId;
    }

    BookId response = {id: bookId};
    return response;

  }

}

// Utility function implementations
function bookExists(string isbn) returns boolean {
  // Check if book exists
  return false; 
}

function addBookToLibrary(Book book) returns int|error {
  // Logic to add book
  return 5;
}

// Similarly implement other utils like updateBook, 
// removeBook, getAvailability etc.