Animate NSFetchedResultsController changes when setting the fetch request's predicate or sortDescriptors property

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The MIT License (MIT)

Copyright (c) 2016 Fueled

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NSFetchedResultsController+AnimateChanges.swift

import CoreData

extension NSFetchedResultsController {
	var predicate: NSPredicate? {
		get {
			return self.fetchRequest.predicate
		}
		set {
			try! self.setPredicate(newValue)
		}
	}
	
	var sortDescriptors: [NSSortDescriptor]? {
		get {
			return self.fetchRequest.sortDescriptors
		}
		set {
			try! self.setSortDescriptors(newValue)
		}
	}
	
	func setPredicate(predicate: NSPredicate?) throws {
		try self.setPredicate(predicate, sortDescriptors: self.sortDescriptors)
	}
	
	func setSortDescriptors(sortDescriptors: [NSSortDescriptor]?) throws {
		try self.setPredicate(self.predicate, sortDescriptors: sortDescriptors)
	}
	
	func setPredicate(predicate: NSPredicate?, sortDescriptors: [NSSortDescriptor]?) throws {
		func updateProperties() throws {
			if let cacheName = cacheName {
				NSFetchedResultsController.deleteCacheWithName(cacheName)
			}
			
			self.fetchRequest.predicate = predicate
			self.fetchRequest.sortDescriptors = sortDescriptors
			try self.performFetch()
		}
		
		guard let delegate = self.delegate else {
			try updateProperties()
			return
		}
		
		let previousSections = self.sections ?? []
		let previousSectionsCount = previousSections.count
		var previousObjects = Set(self.fetchedObjects as? [NSManagedObject] ?? [])
		var previousIndexPaths: [NSManagedObject: NSIndexPath] = [:]
		previousObjects.forEach {
			previousIndexPaths[$0] = self.indexPathForObject($0)
		}
		try updateProperties()
		let newSections = self.sections ?? []
		let newSectionsCount = newSections.count
		var newObjects = Set(self.fetchedObjects as? [NSManagedObject] ?? [])
		var newIndexPaths: [NSManagedObject: NSIndexPath] = [:]
		newObjects.forEach {
			newIndexPaths[$0] = self.indexPathForObject($0)
		}
		
		let updatedObjects = newObjects.intersect(previousObjects)
		previousObjects.subtractInPlace(updatedObjects)
		newObjects.subtractInPlace(updatedObjects)
		
		var moves: [(object: NSManagedObject, fromIndexPath: NSIndexPath, toIndexPath: NSIndexPath)] = []
		updatedObjects.forEach { updatedObject in
			if let previousIndexPath = previousIndexPaths[updatedObject],
				let newIndexPath = newIndexPaths[updatedObject]
			{
				if previousIndexPath != newIndexPath {
					moves.append((updatedObject, previousIndexPath, newIndexPath))
				}
			}
		}
		
		if moves.isEmpty && previousObjects.isEmpty && newObjects.isEmpty {
			// Nothing really changed
			return
		}
		
		delegate.controllerWillChangeContent?(self)
		
		moves.forEach {
			delegate.controller?(self, didChangeObject: $0.object, atIndexPath: $0.fromIndexPath, forChangeType: .Move, newIndexPath: $0.toIndexPath)
		}
		
		let sectionDifference = newSectionsCount - previousSectionsCount
		if sectionDifference < 0 {
			(newSectionsCount..<previousSectionsCount).forEach {
				delegate.controller?(self, didChangeSection: previousSections[$0], atIndex: $0, forChangeType: .Delete)
			}
		} else if sectionDifference > 0 {
			(previousSectionsCount..<newSectionsCount).forEach {
				delegate.controller?(self, didChangeSection: newSections[$0], atIndex: $0, forChangeType: .Insert)
			}
		}
		
		previousObjects.forEach {
			delegate.controller?(self, didChangeObject: $0, atIndexPath: previousIndexPaths[$0], forChangeType: .Delete, newIndexPath: nil)
		}
		newObjects.forEach {
			delegate.controller?(self, didChangeObject: $0, atIndexPath: nil, forChangeType: .Insert, newIndexPath: newIndexPaths[$0])
		}
		
		delegate.controllerDidChangeContent?(self)
	}
}