UICollectionView vertical flow layout keep in collection bounds - ios

Question

I have a UICollectionView with vertical cells alignment, but I want also vertical section alignment, I also want to keep the sections inside the current frame of the UICollectionView, that means if a section reach the end and it's longer then the collection itself, then it will go to next line.
This is how it looks right now:
This is the final result I want to end up with:
This is my code so far:
class LettersCollectionTestViewController: UIViewController, UICollectionViewDelegate, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout {
#IBOutlet weak var collectionContainer: UIView!
var collectionView: UICollectionView?
private let ReuseIdentifierCollectionLetterCell = "LetterCollectionViewCell"
var collectionWords: NSArray?
var itemSize: CGFloat = 25.0
var itemSpacing: CGFloat = 5.0
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
let logoWord: String = "This is just this"
self.collectionWords = logoWord.componentsSeparatedByString(" ")
self.initializeCollection()
}
func initializeCollection() {
let collectionViewLayout: UICollectionViewFlowLayout = UICollectionViewFlowLayout()
collectionViewLayout.itemSize = CGSizeMake(self.itemSize, self.itemSize)
collectionViewLayout.minimumInteritemSpacing = 0
collectionViewLayout.minimumLineSpacing = self.itemSpacing
collectionViewLayout.scrollDirection = UICollectionViewScrollDirection.Vertical
let collectionView: UICollectionView = UICollectionView(frame: self.collectionContainer.bounds, collectionViewLayout: collectionViewLayout)
collectionView.delegate = self;
collectionView.dataSource = self;
collectionView.showsHorizontalScrollIndicator = false
collectionView.showsVerticalScrollIndicator = false
collectionView.registerClass(LetterCollectionViewCell.self, forCellWithReuseIdentifier: self.ReuseIdentifierCollectionLetterCell)
collectionView.registerNib(UINib(nibName: self.ReuseIdentifierCollectionLetterCell, bundle: nil), forCellWithReuseIdentifier: self.ReuseIdentifierCollectionLetterCell)
self.collectionView = collectionView
self.collectionContainer.addSubview(collectionView)
}
// MARK: UICollectionViewDelegate, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout
func collectionView(collectionView: UICollectionView, didSelectItemAtIndexPath indexPath: NSIndexPath) {
print("clicked item at index: \(indexPath.row)")
}
func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
let cell: LetterCollectionViewCell = collectionView.dequeueReusableCellWithReuseIdentifier(self.ReuseIdentifierCollectionLetterCell, forIndexPath: indexPath) as! LetterCollectionViewCell
let scalingTransform: CGAffineTransform = CGAffineTransformMakeScale(-1, 1)
cell.transform = scalingTransform
return cell
}
func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return (self.collectionWords?.objectAtIndex(section).length)!
}
func numberOfSectionsInCollectionView(collectionView: UICollectionView) -> Int {
return (self.collectionWords?.count)!
}
func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, insetForSectionAtIndex section: Int) -> UIEdgeInsets {
return UIEdgeInsets(top: self.itemSpacing, left: self.itemSpacing, bottom: self.itemSpacing, right: self.itemSpacing)
}
}
What do I need to do? I know I should create a custom FlowLayout, but where should I start? I never did it before.
Thanks in advance!