Feature/image feed/cache feed use case

EssentialFeed/EssentialFeed.xcodeproj/project.pbxproj

@@ -11,6 +11,8 @@
 		080EDF0C21B6DAE800813479 /* FeedImage.swift in Sources */ = {isa = PBXBuildFile; fileRef = 080EDF0B21B6DAE800813479 /* FeedImage.swift */; };
 		080EDF0E21B6DCB600813479 /* FeedLoader.swift in Sources */ = {isa = PBXBuildFile; fileRef = 080EDF0D21B6DCB600813479 /* FeedLoader.swift */; };
 		231DA90C2D28B3AE00A50156 /* RemoteFeedLoader.swift in Sources */ = {isa = PBXBuildFile; fileRef = 231DA90B2D28B3AB00A50156 /* RemoteFeedLoader.swift */; };
+		234EE2712F1FE49200817225 /* FeedImageCell.swift in Sources */ = {isa = PBXBuildFile; fileRef = 234EE2702F1FE49000817225 /* FeedImageCell.swift */; };
+		234EE2752F21394A00817225 /* UIView+Shimmering.swift in Sources */ = {isa = PBXBuildFile; fileRef = 234EE2742F21394800817225 /* UIView+Shimmering.swift */; };
 		2370B4092EEC68FE00737DAC /* HTTPClient.swift in Sources */ = {isa = PBXBuildFile; fileRef = 2370B4082EEC68FE00737DAC /* HTTPClient.swift */; };
 		2370B40B2EEC6BE200737DAC /* FeedItemsMapper.swift in Sources */ = {isa = PBXBuildFile; fileRef = 2370B40A2EEC6BE200737DAC /* FeedItemsMapper.swift */; };
 		2377131E2F199AAF00D1122A /* FeedViewControllerTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 2377131D2F199AAF00D1122A /* FeedViewControllerTests.swift */; };
@@ -116,6 +118,8 @@
 		080EDF0B21B6DAE800813479 /* FeedImage.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = FeedImage.swift; sourceTree = "<group>"; };
 		080EDF0D21B6DCB600813479 /* FeedLoader.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = FeedLoader.swift; sourceTree = "<group>"; };
 		231DA90B2D28B3AB00A50156 /* RemoteFeedLoader.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = RemoteFeedLoader.swift; sourceTree = "<group>"; };
+		234EE2702F1FE49000817225 /* FeedImageCell.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = FeedImageCell.swift; sourceTree = "<group>"; };
+		234EE2742F21394800817225 /* UIView+Shimmering.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = "UIView+Shimmering.swift"; sourceTree = "<group>"; };
 		2370B4082EEC68FE00737DAC /* HTTPClient.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = HTTPClient.swift; sourceTree = "<group>"; };
 		2370B40A2EEC6BE200737DAC /* FeedItemsMapper.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = FeedItemsMapper.swift; sourceTree = "<group>"; };
 		2377131D2F199AAF00D1122A /* FeedViewControllerTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = FeedViewControllerTests.swift; sourceTree = "<group>"; };
@@ -312,6 +316,8 @@
 		23F5D6F02F182E5600AC7D9F /* EssentialFeediOS */ = {
 			isa = PBXGroup;
 			children = (
+				234EE2742F21394800817225 /* UIView+Shimmering.swift */,
+				234EE2702F1FE49000817225 /* FeedImageCell.swift */,
 				2377132C2F1EC94D00D1122A /* FeedViewController.swift */,
 				23F5D6FA2F18345C00AC7D9F /* CI_iOS.xctestplan */,
 			);
@@ -698,7 +704,9 @@
 			isa = PBXSourcesBuildPhase;
 			buildActionMask = 2147483647;
 			files = (
+				234EE2752F21394A00817225 /* UIView+Shimmering.swift in Sources */,
 				2377132D2F1EC9D800D1122A /* FeedViewController.swift in Sources */,
+				234EE2712F1FE49200817225 /* FeedImageCell.swift in Sources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 		};

EssentialFeed/EssentialFeediOS/FeedImageCell.swift

@@ -0,0 +1,28 @@
+//
+//  FeedImageCell.swift
+//  EssentialFeed
+//
+//  Created by Andres Sanchez on 20/1/26.
+//
+
+import UIKit
+
+public final class FeedImageCell: UITableViewCell {
+    public let locationContainer = UIView()
+    public let locationLabel = UILabel()
+    public let descriptionLabel = UILabel()
+    public let feedImageContainer = UIView()
+    public let feedImageView = UIImageView()
+
+    private(set) public lazy var feedImageRetryButton: UIButton = {
+        let button = UIButton()
+        button.addTarget(self, action: #selector(retryButtonTapped), for: .touchUpInside)
+        return button
+    }()
+
+    var onRetry: (() -> Void)?
+
+    @objc private func retryButtonTapped() {
+        onRetry?()
+    }
+}

EssentialFeed/EssentialFeediOS/FeedViewController.swift

@@ -8,20 +8,36 @@
 import UIKit
 import EssentialFeed
 
-final public class FeedViewController: UITableViewController {
-    private var loader: FeedLoader?
+public protocol FeedImageDataLoaderTask {
+    func cancel()
+}
+
+public protocol FeedImageDataLoader {
+    typealias Result = Swift.Result<Data, Error>
+
+    func loadImageData(from url: URL, completion: @escaping (Result) -> Void) -> FeedImageDataLoaderTask
+}
+
+final public class FeedViewController: UITableViewController, UITableViewDataSourcePrefetching {
+    private var feedLoader: FeedLoader?
+    private var imageLoader: FeedImageDataLoader?
+    private var tableModel = [FeedImage]()
+    private var tasks = [IndexPath: FeedImageDataLoaderTask]()
+
     private var onViewIsAppearing: ((FeedViewController) -> Void)?
 
-    public convenience init(loader: FeedLoader) {
+    public convenience init(feedLoader: FeedLoader, imageLoader: FeedImageDataLoader) {
         self.init()
-        self.loader = loader
+        self.feedLoader = feedLoader
+        self.imageLoader = imageLoader
     }
 
     public override func viewDidLoad() {
         super.viewDidLoad()
 
         refreshControl = UIRefreshControl()
         refreshControl?.addTarget(self, action: #selector(load), for: .valueChanged)
+        tableView.prefetchDataSource = self
         onViewIsAppearing = { vc in
             vc.onViewIsAppearing = nil
             vc.load()
@@ -35,8 +51,64 @@ final public class FeedViewController: UITableViewController {
 
     @objc private func load() {
         refreshControl?.beginRefreshing()
-        loader?.load { [weak self] _ in
+        feedLoader?.load { [weak self] result in
+            if let feed = try? result.get() {
+                self?.tableModel = feed
+                self?.tableView.reloadData()
+            }
             self?.refreshControl?.endRefreshing()
         }
     }
+
+    public override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
+        return tableModel.count
+    }
+
+    public override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
+        let cellModel = tableModel[indexPath.row]
+        let cell = FeedImageCell()
+        cell.locationContainer.isHidden = (cellModel.location == nil)
+        cell.locationLabel.text = cellModel.location
+        cell.descriptionLabel.text = cellModel.description
+        cell.feedImageView.image = nil
+        cell.feedImageRetryButton.isHidden = true
+        cell.feedImageContainer.startShimmering()
+
+        let loadImage = { [weak self, weak cell] in
+            guard let self = self else { return }
+
+            self.tasks[indexPath] = self.imageLoader?.loadImageData(from: cellModel.url) { [weak cell] result in
+                let data = try? result.get()
+                let image = data.map(UIImage.init) ?? nil
+                cell?.feedImageView.image = image
+                cell?.feedImageRetryButton.isHidden = (image != nil)
+                cell?.feedImageContainer.stopShimmering()
+            }
+        }
+
+        cell.onRetry = loadImage
+        loadImage()
+
+        return cell
+    }
+
+    public override func tableView(_ tableView: UITableView, didEndDisplaying cell: UITableViewCell, forRowAt indexPath: IndexPath) {
+        cancelTask(forRowAt: indexPath)
+    }
+
+    public func tableView(_ tableView: UITableView, prefetchRowsAt indexPaths: [IndexPath]) {
+        indexPaths.forEach { indexPath in
+            let cellModel = tableModel[indexPath.row]
+            tasks[indexPath] = imageLoader?.loadImageData(from: cellModel.url) { _ in }
+        }
+    }
+
+    public func tableView(_ tableView: UITableView, cancelPrefetchingForRowsAt indexPaths: [IndexPath]) {
+        indexPaths.forEach(cancelTask)
+    }
+
+    private func cancelTask(forRowAt indexPath: IndexPath) {
+        tasks[indexPath]?.cancel()
+        tasks[indexPath] = nil
+    }
 }

EssentialFeed/EssentialFeediOS/UIView+Shimmering.swift

@@ -0,0 +1,60 @@
+//
+//  UIView+Shimmering.swift
+//  EssentialFeed
+//
+//  Created by Andres Sanchez on 21/1/26.
+//
+
+import UIKit
+
+extension UIView {
+    public var isShimmering: Bool {
+        set {
+            if newValue {
+                startShimmering()
+            } else {
+                stopShimmering()
+            }
+        }
+
+        get {
+            layer.mask is ShimmeringLayer
+        }
+    }
+
+    func startShimmering() {
+        layer.mask = ShimmeringLayer(size: bounds.size)
+    }
+
+    func stopShimmering() {
+        layer.mask = nil
+    }
+
+    private class ShimmeringLayer: CAGradientLayer {
+        private var observer: Any?
+
+        convenience init(size: CGSize) {
+            self.init()
+
+            let white = UIColor.white.cgColor
+            let alpha = UIColor.white.withAlphaComponent(0.75).cgColor
+
+            colors = [alpha, white, alpha]
+            startPoint = CGPoint(x: 0.0, y: 0.4)
+            endPoint = CGPoint(x: 1.0, y: 0.6)
+            locations = [0.4, 0.5, 0.6]
+            frame = CGRect(x: -size.width, y: 0, width: size.width*3, height: size.height)
+
+            let animation = CABasicAnimation(keyPath: #keyPath(CAGradientLayer.locations))
+            animation.fromValue = [0.0, 0.1, 0.2]
+            animation.toValue = [0.8, 0.9, 1.0]
+            animation.duration = 1.25
+            animation.repeatCount = .infinity
+            add(animation, forKey: "shimmer")
+
+            observer = NotificationCenter.default.addObserver(forName: UIApplication.willEnterForegroundNotification, object: nil, queue: nil) { [weak self] _ in
+                self?.add(animation, forKey: "shimmer")
+            }
+        }
+    }
+}