CoreStore/Sources/FetchedResultsControllerDelegate.swift

//
//  FetchedResultsControllerDelegate.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


// MARK: - FetchedResultsControllerHandler

@available(macOS 10.12, *)
internal protocol FetchedResultsControllerHandler: class {
    
    func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChangeObject anObject: Any, atIndexPath indexPath: IndexPath?, forChangeType type: NSFetchedResultsChangeType, newIndexPath: IndexPath?)
    
    func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChangeSection sectionInfo: NSFetchedResultsSectionInfo, atIndex sectionIndex: Int, forChangeType type: NSFetchedResultsChangeType)
    
    func controllerWillChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>)
    
    func controllerDidChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>)
    
    func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, sectionIndexTitleForSectionName sectionName: String?) -> String?
}


// MARK: - FetchedResultsControllerDelegate

@available(macOS 10.12, *)
internal final class FetchedResultsControllerDelegate: NSObject, NSFetchedResultsControllerDelegate {
    
    // MARK: Internal
    
    @nonobjc
    internal var enabled = true
    
    @nonobjc
    internal let taskGroup = DispatchGroup()
    
    @nonobjc
    internal weak var handler: FetchedResultsControllerHandler?
    
    @nonobjc
    internal weak var fetchedResultsController: CoreStoreFetchedResultsController? {
        
        didSet {
            
            oldValue?.delegate = nil
            self.fetchedResultsController?.delegate = self
        }
    }
    
    deinit {
        
        self.fetchedResultsController?.delegate = nil
    }
    
    
    // MARK: NSFetchedResultsControllerDelegate
    
    @objc
    dynamic func controllerWillChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
        
        self.taskGroup.enter()
        guard self.enabled else {
            
            return
        }
        self.handler?.controllerWillChangeContent(controller)
    }
    
    @objc
    dynamic func controllerDidChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
        
        defer {
            
            self.taskGroup.leave()
        }
        guard self.enabled else {
            
            return
        }
        self.handler?.controllerDidChangeContent(controller)
    }
    
    @objc
    dynamic func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChange anObject: Any, at indexPath: IndexPath?, for type: NSFetchedResultsChangeType, newIndexPath: IndexPath?) {
        
        guard self.enabled else {
            
            return
        }
        self.handler?.controller(
            controller,
            didChangeObject: anObject,
            atIndexPath: indexPath,
            forChangeType: type,
            newIndexPath: newIndexPath
        )
    }
    
    @objc
    dynamic func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChange sectionInfo: NSFetchedResultsSectionInfo, atSectionIndex sectionIndex: Int, for type: NSFetchedResultsChangeType) {
        
        guard self.enabled else {
            
            return
        }
        self.handler?.controller(
            controller,
            didChangeSection: sectionInfo,
            atIndex: sectionIndex,
            forChangeType: type
        )
    }
    
    @objc
    dynamic func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, sectionIndexTitleForSectionName sectionName: String) -> String? {
        
        return self.handler?.controller(
            controller,
            sectionIndexTitleForSectionName: sectionName
        )
    }
}