syntax = "proto3";

package library.domain;

enum Genre {
  UNKNOWN = 0;
  FICTION = 1;
  NON_FICTION = 2;
  SCI_FI = 3;
  HISTORY = 4;
}

message Publisher {
  string id = 1;
  string name = 2;
  string address = 3;
}

// Represents a Book in the collection.
message Book {
  string isbn = 1;
  string title = 2;
  
  // Circular Dependency: Book references Author (valid since they are in the same file)
  Author author = 3;
  
  Publisher publisher = 4;
  
  Genre genre = 5;
}

message Author {
  string id = 1;
  string full_name = 2;
  
  // Circular Dependency: Author references Book
  repeated Book bibliography = 3;
}