using { AdminService, sap.capire.bookshop as my } from './admin-service';

extend service AdminService with {

  // entity Books.drafts as projection on AdminService.Books;
  // @cds.api.ignore view Books.drafts.constraints as select from AdminService.Books.drafts mixin {
  //   before: Association to my.Books on before.ID = $self.ID;
  //   base: Association to my.Books on base.ID = $self.ID;
  // } into { ID, // FIXME: compiler should resolve Books without AdminService prefix
  //   case
  //     when title is null  then 'is missing'
  //     when trim(title)='' then 'must not be empty'
  //   end as title,
  //   ...
  // }

  /**
   * Validation constraints for Books
   */
  @cds.api.ignore view Books.constraints as select from AdminService.Books mixin {
    base: Association to my.Books on base.ID = $self.ID;
  } into { ID, // FIXME: compiler should resolve Books without AdminService prefix

    // two-step mandatory check
    case
      when title is null  then 'is missing'
      when trim(title)='' then 'must not be empty'
    end as title,
    // the above is equivalent to:
    // title is null ? 'is missing' : trim(title)='' ? 'must not be empty' :

    // range check
    stock < 0 ? 'must not be negative' :
    null as stock,

    // range check
    price < 0 ? 'must not be negative' :
    null as price,

    // assert target check
    genre.ID is not null and not exists genre ? 'does not exist' :
    null as genre,

    // multiple constraints: mandatory + assert target + special
    author.ID is null ? 'is missing' : // FIXME: 1) // TODO: 2)
    not exists author ? 'Author does not exist: ' || author.ID :
    count(base.author.books.ID) -1 > 1 ? author.name || ' already wrote too many books' : // TODO: 3)
    null as author,

  } group by ID;

  // 1) FIXME: expected author.ID to refer to foreign key,
  // apparently that is not the case -> move one line up
  // and run test to see the erroneous impact.

  // 2) TODO: we should allow to write author is null instead of author.ID is null

  // 3) TODO: we should support count(author.books)


  /**
   * Validation constraints for Authors
   */
  view Authors.constraints as select from AdminService.Authors { ID, // FIXME: compiler should resolve Authors without AdminService prefix

    // two-step mandatory check
    name = null ? 'is missing' : trim(name)='' ? 'must not be empty' :
    null as name,

    // constraint related to two fields
    dateOfDeath > dateOfBirth ? 'we must be born before we die' : null as _born_before_death,
    $self._born_before_death as dateOfBirth,
    $self._born_before_death as dateOfDeath,

  }
}