/// One thing planned for a Meal on a day: a Recipe or a short note.
class PlanEntry {
  const PlanEntry({
    required this.id,
    required this.day,
    required this.mealId,
    this.recipeId,
    this.note,
    required this.position,
  }) : assert((recipeId == null) != (note == null), 'A Plan Entry is either a Recipe or a note');

  final String id;

  /// The calendar day, as a UTC midnight (see `day.dart`).
  final DateTime day;
  final String mealId;
  final String? recipeId;
  final String? note;

  /// Order within its Meal on its day.
  final int position;
}