ImageLoader TCA

public enum ImageLoaderError: Error, Equatable {
	case invalidData
	case imageLoadingFailed
	case message(String)
}

public struct ImageState: Equatable {
	public var image: UIImage?
}

public enum ImageLoaderAction: Equatable {
	case downloadImage(url: URL?)
	case imageLoadingFailed
	case imageLoaded(Result<UIImage, ImageLoaderError>)
}

public struct ImageLoaderEnvironment {
	public var fetchImage: (URL?) -> Effect<UIImage, ImageLoaderError>

	public init(fetchImage: @escaping (URL?) -> Effect<UIImage, ImageLoaderError>) {
		self.fetchImage = fetchImage
	}
}

extension ImageLoaderEnvironment {
	public static var live: ImageLoaderEnvironment = ImageLoaderEnvironment { url in

		guard let url = url else {
			return Effect(error: ImageLoaderError.imageLoadingFailed)
		}

		return URLSession.shared.dataTaskPublisher(for: url)
			.receive(on: RunLoop.main)
			.map(\.data)
			.tryMap({ data -> UIImage in
				guard let newImage = UIImage(data: data) else {
					throw ImageLoaderError.invalidData
				}
				return newImage
			})
			.mapError({ ImageLoaderError.message($0.localizedDescription) })
			.eraseToEffect()
	}

	public static var mock: ImageLoaderEnvironment = ImageLoaderEnvironment { url in

		guard let url = url,
			  let localImage: UIImage = .init(named: "demo", in: .module, with: nil)
		else {
			return Effect(error: ImageLoaderError.imageLoadingFailed)
		}

		return Effect(value: localImage)
	}
}

struct ImageView: View {
	let store: Store<ImageState, ImageLoaderAction> = .init(
		initialState: ImageState(),
		reducer: imageLoaderReducer.debug(),
		environment: ImageLoaderEnvironment.mock
	)

	var body: some View {
		WithViewStore(store) { viewStore in
			Image(uiImage: viewStore.image ?? UIImage(systemName: "person")!)
				.onAppear() {
					DispatchQueue.main.asyncAfter(deadline: .now() + .seconds(2)) {
						viewStore.send(.downloadImage(url: URL(string: "https://example.com")))
					}
				}
		}
	}
}

struct ImageView_Previews: PreviewProvider {
	static var previews: some View {
		ImageView()
	}
}

public let imageLoaderReducer: Reducer<ImageState, ImageLoaderAction, ImageLoaderEnvironment> =
	.init { state, action, environment in
		switch action {

		case let .downloadImage(url):
			return environment.fetchImage(url)
				.catchToEffect()
				.map(ImageLoaderAction.imageLoaded)

		case .imageLoadingFailed:

			return .none

		case .imageLoaded(.success(let image)):

			state.image = image

			return .none

		case .imageLoaded(.failure(let error)):

			state.image = UIImage(systemName: "exclamationmark.triangle.fill")

			return .none
		}
	}