CoreStore/Sources/Internals.FetchedDiffableDataSourceSnapshotDelegate.swift

//
//  Internals.FetchedDiffableDataSourceSnapshotDelegate.swift
//  CoreStore
//
//  Copyright © 2018 John Rommel Estropia
//
//  Permission is hereby granted, free of charge, to any person obtaining a copy
//  of this software and associated documentation files (the "Software"), to deal
//  in the Software without restriction, including without limitation the rights
//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
//  copies of the Software, and to permit persons to whom the Software is
//  furnished to do so, subject to the following conditions:
//
//  The above copyright notice and this permission notice shall be included in all
//  copies or substantial portions of the Software.
//
//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
//  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
//  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
//  SOFTWARE.
//

import Foundation
import CoreData

#if canImport(UIKit)

import UIKit

#elseif canImport(AppKit)

import AppKit

#endif


// MARK: - FetchedDiffableDataSourceSnapshot

internal protocol FetchedDiffableDataSourceSnapshotHandler: AnyObject {

    func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChangContentWith snapshot: Internals.DiffableDataSourceSnapshot)
}


// MARK: - Internal

extension Internals {

    // MARK: - FetchedDiffableDataSourceSnapshotDelegate

    internal final class FetchedDiffableDataSourceSnapshotDelegate: NSObject, NSFetchedResultsControllerDelegate {

        // MARK: Internal

        @nonobjc
        internal weak var handler: FetchedDiffableDataSourceSnapshotHandler?

        @nonobjc
        internal weak var fetchedResultsController: Internals.CoreStoreFetchedResultsController? {

            didSet {

                oldValue?.delegate = nil
                self.fetchedResultsController?.delegate = self
            }
        }

        deinit {

            self.fetchedResultsController?.delegate = nil
        }

        internal func initialFetch() {

//            #if canImport(UIKit) || canImport(AppKit)
//
//            if #available(iOS 13.0, tvOS 13.0, watchOS 6.0, macOS 15.0, *) {
//
//                return
//            }
//
//            #endif

            guard let fetchedResultsController = self.fetchedResultsController else {

                return
            }
            self.controllerDidChangeContent(fetchedResultsController.dynamicCast())
        }


        // MARK: NSFetchedResultsControllerDelegate

//        #if canImport(UIKit) || canImport(AppKit)
//
//        @available(iOS 13.0, tvOS 13.0, watchOS 6.0, macOS 15.0, *)
//        @objc
//        dynamic func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChangeContentWith snapshot: NSDiffableDataSourceSnapshotReference) {
//
//            self.handler?.controller(
//                controller,
//                didChangContentWith: snapshot as NSDiffableDataSourceSnapshot<NSString, NSManagedObjectID>
//            )
//        }
//
//        #endif
        
        @objc
        dynamic func controllerDidChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {

            let nextStateTag: UUID = .init()
            var dataSourceSnapshot = Internals.DiffableDataSourceSnapshot(
                sections: controller.sections ?? [],
                previousStateTag: self.previousStateTag,
                nextStateTag: nextStateTag
            )
            dataSourceSnapshot.reloadItems(self.reloadedItemIDs, nextStateTag: nextStateTag)
            dataSourceSnapshot.reloadSections(self.reloadedSectionIDs, nextStateTag: nextStateTag)

            self.handler?.controller(
                controller,
                didChangContentWith: dataSourceSnapshot
            )
            self.previousStateTag = nextStateTag
        }

        @objc
        dynamic func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChange anObject: Any, at indexPath: IndexPath?, for type: NSFetchedResultsChangeType, newIndexPath: IndexPath?) {

            let managedObject = anObject as! NSManagedObject
            self.reloadedItemIDs.insert(managedObject.objectID)
        }

        @objc
        dynamic func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChange sectionInfo: NSFetchedResultsSectionInfo, atSectionIndex sectionIndex: Int, for type: NSFetchedResultsChangeType) {

            self.reloadedSectionIDs.insert(sectionInfo.name)
        }


        // MARK: Private

        private var previousStateTag: UUID = .init() {

            didSet {

                self.reloadedItemIDs = []
                self.reloadedSectionIDs = []
            }
        }

        private var reloadedItemIDs: Set<NSManagedObjectID> = []
        private var reloadedSectionIDs: Set<String> = []
    }
}