IGListKit/Examples/Examples-iOS/IGListKitExamples/SectionControllers/WorkingRangeSectionController.swift

/**
 Copyright (c) Facebook, Inc. and its affiliates.

 The examples provided by Facebook are for non-commercial testing and evaluation
 purposes only. Facebook reserves all rights not expressly granted.

 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
 FACEBOOK BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
 ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */

import IGListKit
import UIKit

final class WorkingRangeSectionController: ListSectionController, ListWorkingRangeDelegate {

    private var height: Int?
    private var downloadedImage: UIImage?
    private var task: URLSessionDataTask?

    private var urlString: String? {
        guard let height = height,
            let width = collectionContext?.containerSize.width
            else { return nil }
        return "https://unsplash.it/" + width.description + "/" + height.description
    }

    deinit {
        task?.cancel()
    }

    override init() {
        super.init()
        workingRangeDelegate = self
    }

    override func numberOfItems() -> Int {
        return 2
    }

    override func sizeForItem(at index: Int) -> CGSize {
        let width: CGFloat = collectionContext?.containerSize.width ?? 0
        let height: CGFloat = CGFloat(index == 0 ? 55 : (self.height ?? 0))
        return CGSize(width: width, height: height)
    }

    override func cellForItem(at index: Int) -> UICollectionViewCell {
        let cellClass: AnyClass = index == 0 ? LabelCell.self : ImageCell.self
        let cell = collectionContext!.dequeueReusableCell(of: cellClass, for: self, at: index)
        if let cell = cell as? LabelCell {
            cell.text = urlString
        } else if let cell = cell as? ImageCell {
            cell.setImage(image: downloadedImage)
        }
        return cell
    }

    override func didUpdate(to object: Any) {
        self.height = object as? Int
    }

    // MARK: ListWorkingRangeDelegate

    func listAdapter(_ listAdapter: ListAdapter, sectionControllerWillEnterWorkingRange sectionController: ListSectionController) {
        guard downloadedImage == nil,
            task == nil,
            let urlString = urlString,
            let url = URL(string: urlString)
            else { return }

        print("Downloading image \(urlString) for section \(self.section)")

        task = URLSession.shared.dataTask(with: url) { data, _, error in
            guard let data = data, let image = UIImage(data: data) else {
                return print("Error downloading \(urlString): " + String(describing: error))
            }
            DispatchQueue.main.async {
                self.downloadedImage = image
                if let cell = self.collectionContext?.cellForItem(at: 1, sectionController: self) as? ImageCell {
                    cell.setImage(image: image)
                }
            }
        }
        task?.resume()
    }

    func listAdapter(_ listAdapter: ListAdapter, sectionControllerDidExitWorkingRange sectionController: ListSectionController) {}

}