/*
   Assume self has a property 'tableView' -- as is the case for an instance of a UITableViewController
   subclass -- and a method configureCell:atIndexPath: which updates the contents of a given cell
   with information from a managed object at the given index path in the fetched results controller.
 */
 
- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller
{
    [self.tableView beginUpdates];
}
 
- (void)controller:(NSFetchedResultsController *)controller didChangeSection:(id )sectionInfo
    atIndex:(NSUInteger)sectionIndex forChangeType:(NSFetchedResultsChangeType)type
{
    switch (type) {
        case NSFetchedResultsChangeInsert:
            [self.tableView insertSections:[NSIndexSet indexSetWithIndex:sectionIndex] withRowAnimation:UITableViewRowAnimationFade];
            break;
        case NSFetchedResultsChangeDelete:
            [self.tableView deleteSections:[NSIndexSet indexSetWithIndex:sectionIndex] withRowAnimation:UITableViewRowAnimationFade];
            break;
    }
}
 
- (void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject atIndexPath:(NSIndexPath *)indexPath 
          forChangeType:(NSFetchedResultsChangeType)type newIndexPath:(NSIndexPath *)newIndexPath
{
    UITableView *tableView = self.tableView;
 
    switch (type) {
        case NSFetchedResultsChangeInsert:
            [tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath] withRowAnimation:UITableViewRowAnimationFade];
            break;
        case NSFetchedResultsChangeDelete:
            [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
            break;
 
        case NSFetchedResultsChangeUpdate:
            [self configureCell:[tableView cellForRowAtIndexPath:indexPath] atIndexPath:indexPath];
            break;
 
        case NSFetchedResultsChangeMove:
            [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
            [tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath] withRowAnimation:UITableViewRowAnimationFade];
            break;
    }
}
 
- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller
{
    [self.tableView endUpdates];
}

@interface SomeViewController ()
 
// Declare some collection properties to hold the various updates we might get from the NSFetchedResultsControllerDelegate
@property (nonatomic, strong) NSMutableIndexSet *deletedSectionIndexes;
@property (nonatomic, strong) NSMutableIndexSet *insertedSectionIndexes;
@property (nonatomic, strong) NSMutableArray *deletedRowIndexPaths;
@property (nonatomic, strong) NSMutableArray *insertedRowIndexPaths;
@property (nonatomic, strong) NSMutableArray *updatedRowIndexPaths;
 
@end
 
@implementation SomeViewController
 
#pragma mark - NSFetchedResultsControllerDelegate methods
 
- (void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject atIndexPath:(NSIndexPath *)indexPath
          forChangeType:(NSFetchedResultsChangeType)type newIndexPath:(NSIndexPath *)newIndexPath
{
    if (type == NSFetchedResultsChangeInsert) {
        if ([self.insertedSectionIndexes containsIndex:newIndexPath.section]) {
            // If we've already been told that we're adding a section for this inserted row we skip it since it will handled by the section insertion.
            return;
        }
 
        [self.insertedRowIndexPaths addObject:newIndexPath];
    } else if (type == NSFetchedResultsChangeDelete) {
        if ([self.deletedSectionIndexes containsIndex:indexPath.section]) {
            // If we've already been told that we're deleting a section for this deleted row we skip it since it will handled by the section deletion.
            return;
        }
 
        [self.deletedRowIndexPaths addObject:indexPath];
    } else if (type == NSFetchedResultsChangeMove) {
        if ([self.insertedSectionIndexes containsIndex:newIndexPath.section] == NO) {
            [self.insertedRowIndexPaths addObject:newIndexPath];
        }
 
        if ([self.deletedSectionIndexes containsIndex:indexPath.section] == NO) {
            [self.deletedRowIndexPaths addObject:indexPath];
        }
    } else if (type == NSFetchedResultsChangeUpdate) {
        [self.updatedRowIndexPaths addObject:indexPath];
    }
}
 
- (void)controller:(NSFetchedResultsController *)controller didChangeSection:(id )sectionInfo atIndex:(NSUInteger)sectionIndex
          forChangeType:(NSFetchedResultsChangeType)type
{
    switch (type) {
        case NSFetchedResultsChangeInsert:
            [self.insertedSectionIndexes addIndex:sectionIndex];
            break;
        case NSFetchedResultsChangeDelete:
            [self.deletedSectionIndexes addIndex:sectionIndex];
            break;
        default:
            ; // Shouldn't have a default
            break;
    }
}
 
- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller
{
    [self.tableView beginUpdates];
 
    [self.tableView deleteSections:self.deletedSectionIndexes withRowAnimation:UITableViewRowAnimationAutomatic];
    [self.tableView insertSections:self.insertedSectionIndexes withRowAnimation:UITableViewRowAnimationAutomatic];
 
    [self.tableView deleteRowsAtIndexPaths:self.deletedRowIndexPaths withRowAnimation:UITableViewRowAnimationLeft];
    [self.tableView insertRowsAtIndexPaths:self.insertedRowIndexPaths withRowAnimation:UITableViewRowAnimationRight];
    [self.tableView reloadRowsAtIndexPaths:self.updatedRowIndexPaths withRowAnimation:UITableViewRowAnimationAutomatic];
 
    [self.tableView endUpdates];
 
    // nil out the collections so they are ready for their next use.
    self.insertedSectionIndexes = nil;
    self.deletedSectionIndexes = nil;
    self.deletedRowIndexPaths = nil;
    self.insertedRowIndexPaths = nil;
    self.updatedRowIndexPaths = nil;
}
 
#pragma mark - Overridden getters
 
/**
 * Lazily instantiate these collections.
 */
 
- (NSMutableIndexSet *)deletedSectionIndexes
{
    if (_deletedSectionIndexes == nil) {
        _deletedSectionIndexes = [[NSMutableIndexSet alloc] init];
    }
 
    return _deletedSectionIndexes;
}
 
- (NSMutableIndexSet *)insertedSectionIndexes
{
    if (_insertedSectionIndexes == nil) {
        _insertedSectionIndexes = [[NSMutableIndexSet alloc] init];
    }
 
    return _insertedSectionIndexes;
}
 
- (NSMutableArray *)deletedRowIndexPaths
{
    if (_deletedRowIndexPaths == nil) {
        _deletedRowIndexPaths = [[NSMutableArray alloc] init];
    }
 
    return _deletedRowIndexPaths;
}
 
- (NSMutableArray *)insertedRowIndexPaths
{
    if (_insertedRowIndexPaths == nil) {
        _insertedRowIndexPaths = [[NSMutableArray alloc] init];
    }
 
    return _insertedRowIndexPaths;
}
 
- (NSMutableArray *)updatedRowIndexPaths
{
    if (_updatedRowIndexPaths == nil) {
        _updatedRowIndexPaths = [[NSMutableArray alloc] init];
    }
 
    return _updatedRowIndexPaths;
}
 
@end

- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller
{
    NSInteger totalChanges = [self.deletedSectionIndexes count] + 
                             [self.insertedSectionIndexes count] + 
                             [self.deletedRowIndexPaths count] + 
                             [self.insertedRowIndexPaths count] + 
                             [self.updatedRowIndexPaths count];
    if (totalChanges > 50) {
        self.insertedSectionIndexes = nil;
        self.deletedSectionIndexes = nil;
        self.deletedRowIndexPaths = nil;
        self.insertedRowIndexPaths = nil;
        self.updatedRowIndexPaths = nil;
 
        [self.tableView reloadData];
        return;
    }
 
    [self.tableView beginUpdates];
 
    [self.tableView deleteSections:self.deletedSectionIndexes withRowAnimation:UITableViewRowAnimationAutomatic];
    [self.tableView insertSections:self.insertedSectionIndexes withRowAnimation:UITableViewRowAnimationAutomatic];
 
    [self.tableView deleteRowsAtIndexPaths:self.deletedRowIndexPaths withRowAnimation:UITableViewRowAnimationLeft];
    [self.tableView insertRowsAtIndexPaths:self.insertedRowIndexPaths withRowAnimation:UITableViewRowAnimationRight];
    [self.tableView reloadRowsAtIndexPaths:self.updatedRowIndexPaths withRowAnimation:UITableViewRowAnimationAutomatic];
 
    [self.tableView endUpdates];
 
    self.insertedSectionIndexes = nil;
    self.deletedSectionIndexes = nil;
    self.deletedRowIndexPaths = nil;
    self.insertedRowIndexPaths = nil;
    self.updatedRowIndexPaths = nil;
}

- (void)awakeFromNib
{
    NSDictionary *viewsDictionary = @{ @"view":self.view };
 
    NSArray *horizontalMaximizingConstraints = [NSLayoutConstraint constraintsWithVisualFormat:@"|[view]|"
                                                                                       options:0 
                                                                                       metrics:nil 
                                                                                         views:viewsDictionary];
 
    NSArray *verticalMaximizingConstraints = [NSLayoutConstraint constraintsWithVisualFormat:@"V:|[view]|" 
                                                                                     options:0 
                                                                                     metrics:nil 
                                                                                       views:viewsDictionary];
    [self.view addConstraints:horizontalMaximizingConstraints];
    [self.view addConstraints:verticalMaximizingConstraints];
}