Compositional.swift

Compositional.swift

enum Section: Int {
  case name
  case newFeature
  case preview
}

func compositionLayout() -> UICollectionViewLayout {
  let layout = UICollectionViewCompositionalLayout { index, environment in
    guard let section = Section(rawValue: index) else { return nil }
    let sectionLayout: NSCollectionLayoutSection
    switch section {
    case .name:
      let itemSize = NSCollectionLayoutSize(
        widthDimension: .fractionalWidth(1.0),
        heightDimension: .estimated(200)
      )

      let item = NSCollectionLayoutItem(
        layoutSize: itemSize
      )

      let groupSize = NSCollectionLayoutSize(
        widthDimension: .fractionalWidth(1.0),
        heightDimension: .estimated(100)
      )

      let group = NSCollectionLayoutGroup.vertical(
        layoutSize: groupSize,
        subitems: [item]
      )

      let headerSize = NSCollectionLayoutSize(
        widthDimension: .fractionalWidth(1.0),
        heightDimension: .absolute(44)
      )

      let header = NSCollectionLayoutBoundarySupplementaryItem(
        layoutSize: headerSize,
        elementKind: UICollectionView.elementKindSectionHeader,
        alignment: .top
      )

      let section = NSCollectionLayoutSection(group: group)
      section.boundarySupplementaryItems = [header]
      sectionLayout = section

    case .newFeature:
      let itemSize = NSCollectionLayoutSize(
        widthDimension: .fractionalWidth(1.0),
        heightDimension: .estimated(120)
      )

      let item = NSCollectionLayoutItem(
        layoutSize: itemSize
      )

      let groupSize = NSCollectionLayoutSize(
        widthDimension: .fractionalWidth(1.0),
        heightDimension: .estimated(100)
      )

      let group = NSCollectionLayoutGroup.vertical(
        layoutSize: groupSize,
        subitems: [item]
      )

      let headerSize = NSCollectionLayoutSize(
        widthDimension: .fractionalWidth(1.0),
        heightDimension: .absolute(44)
      )

      let header = NSCollectionLayoutBoundarySupplementaryItem(
        layoutSize: headerSize,
        elementKind: UICollectionView.elementKindSectionHeader,
        alignment: .top
      )

      let section = NSCollectionLayoutSection(group: group)
      section.boundarySupplementaryItems = [header]
      sectionLayout = section

    case .preview:
      let itemSize = NSCollectionLayoutSize(
        widthDimension: .fractionalWidth(1.0),
        heightDimension: .estimated(600)
      )

      let item = NSCollectionLayoutItem(
        layoutSize: itemSize
      )

      let groupSize = NSCollectionLayoutSize(
        widthDimension: .fractionalWidth(0.56),
        heightDimension: .fractionalWidth(1.0)
      )

      let group = NSCollectionLayoutGroup.horizontal(
        layoutSize: groupSize,
        subitems: [item]
      )

      let headerSize = NSCollectionLayoutSize(
        widthDimension: .fractionalWidth(1.0),
        heightDimension: .absolute(44)
      )

      let header = NSCollectionLayoutBoundarySupplementaryItem(
        layoutSize: headerSize,
        elementKind: UICollectionView.elementKindSectionHeader,
        alignment: .top
      )

      let section = NSCollectionLayoutSection(group: group)
      section.boundarySupplementaryItems = [header]
      section.orthogonalScrollingBehavior = .continuous
      sectionLayout = section
    }

    return sectionLayout
  }

  return layout
}