FetchedResultList.swift

@MainActor final class FetchedResultList<Result: NSManagedObject> {
  private let fetchedResultsController: NSFetchedResultsController<Result>
  private let observer: FetchedResultsObserver<Result>
    
  init(context: NSManagedObjectContext, filter: NSPredicate? = nil, sortDescriptors: [NSSortDescriptor]) {
    let request = NSFetchRequest<Result>(entityName: Result.entity().name ?? "<not set>")
    request.predicate = filter
    request.sortDescriptors = sortDescriptors.isEmpty ? nil : sortDescriptors
    fetchedResultsController = NSFetchedResultsController(fetchRequest: request, managedObjectContext: context, sectionNameKeyPath: nil, cacheName: nil)
    observer = FetchedResultsObserver(controller: fetchedResultsController)
    observer.willChange = { [unowned self] in self.willChange?() }
    observer.didChange = { [unowned self] in self.didChange?() }
    refresh()
  }
    
  private func refresh() {
    do {
      try fetchedResultsController.performFetch()
    }
    catch {
      Logger().error("Failed to load results")
    }
  }
    
  var items: [Result] {
    fetchedResultsController.fetchedObjects ?? []
  }
    
  var predicate: NSPredicate? {
    get {
      fetchedResultsController.fetchRequest.predicate
    }
    set {
      fetchedResultsController.fetchRequest.predicate = newValue
      refresh()
    }
  }
    
  var sortDescriptors: [NSSortDescriptor] {
    get {
      fetchedResultsController.fetchRequest.sortDescriptors ?? []
    }
    set {
      fetchedResultsController.fetchRequest.sortDescriptors = newValue.isEmpty ? nil : newValue
      refresh()
    }
  }
    
  var willChange: (() -> Void)?
  var didChange: (() -> Void)?
}