Infinite UIScrollView with dynamically added/removed views

InfiniteUIScrollView.m

//
//  RootViewController.m
//  ScrollTest
//
//  Created by Marcus Westin on 2/7/14.
//  Copyright (c) 2014 Marcus Westin. All rights reserved.
//

#import "RootViewController.h"

static CGFloat START_Y = 99999.0f;
static CGFloat MAX_Y = 9999999.0f;

@interface RootViewController ()
@property UIScrollView* scrollView;
@property CGFloat topY;
@property CGFloat bottomY;
@property CGFloat lastY;
@property BOOL purged;
@end
@implementation RootViewController

- (id)init {
    return [self initWithNibName:nil bundle:nil];
}

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        [self render];
    }
    return self;
}

- (void)render {
    _scrollView = [[UIScrollView alloc] initWithFrame:self.view.bounds];
    _scrollView.contentOffset = CGPointMake(0, START_Y);
    _scrollView.contentSize = CGSizeMake(self.view.frame.size.width, MAX_Y);
    [self.view addSubview:_scrollView];
    _topY = START_Y;
    _bottomY = START_Y;
    [self addNextViewDown];
    [self extendBottom];
    [self extendTop];
    _scrollView.delegate = self;
}

- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
    if (_lastY < scrollView.contentOffset.y) {
        [self extendBottom];
    } else {
        [self extendTop];
    }
    _lastY = scrollView.contentOffset.y;
}

- (void)extendBottom {
    CGFloat targetY = _scrollView.contentOffset.y + _scrollView.frame.size.height;
    while (_bottomY < targetY) {
        [self addNextViewDown];
    }
    [self cleanTop];
}

- (void)extendTop {
    CGFloat targetY = _scrollView.contentOffset.y;
    while (_topY > targetY) {
        [self addNextViewUp];
    }
    [self cleanBottom];
}

- (void)cleanTop {
    NSLog(@"CLEAN TOP");
    UIView* view;
    CGFloat targetY = _scrollView.contentOffset.y;
    while ((view = self.topView) && view.frame.origin.y + view.frame.size.height < targetY) {
        [view removeFromSuperview];
        _topY += view.frame.size.height;
    }
}

- (void)cleanBottom {
    NSLog(@"CLEAN BOTTOM");
    UIView* view;
    CGFloat targetY = _scrollView.contentOffset.y + _scrollView.frame.size.height;
    while ((view = self.bottomView) && view.frame.origin.y > targetY) {
        [view removeFromSuperview];
        _bottomY -= view.frame.size.height;
    }
}

- (void)addNextViewUp {
    CGFloat height = 40 + arc4random() % 40;
    _topY -= height;
    UIView* view = [self makeView:_topY height:height];
    [_scrollView insertSubview:view atIndex:0];
}

- (void)addNextViewDown {
    CGFloat height = 40 + arc4random() % 40;
    UIView* view = [self makeView:_bottomY height:height];
    _bottomY += view.frame.size.height;
    [_scrollView addSubview:view];
}

- (UIView*)makeView:(CGFloat)y height:(CGFloat)height {
    CGFloat hue = ( arc4random() % 256 / 256.0 );  //  0.0 to 1.0
    CGFloat saturation = ( arc4random() % 128 / 256.0 ) + 0.5;  //  0.5 to 1.0, away from white
    CGFloat brightness = ( arc4random() % 128 / 256.0 ) + 0.5;  //  0.5 to 1.0, away from black
    UIView* view = [[UIView alloc] initWithFrame:CGRectMake(0, y, _scrollView.frame.size.width, height)];
    view.backgroundColor = [UIColor colorWithHue:hue saturation:saturation brightness:brightness alpha:1];
    return view;
}

- (NSArray*)views {
    if (!_purged) {
        for (UIView* view in _scrollView.subviews) {
            if ([view isKindOfClass:[UIImageView class]]) {
                [view removeFromSuperview];
            }
        }
        _purged = YES;
    }
    return _scrollView.subviews ? _scrollView.subviews : @[];
}

- (UIView*)topView {
    return self.views.firstObject;
}

- (UIView*)bottomView {
    return self.views.lastObject;
}

@end

wondering if there is a Swift version?