Flips/ImageLoader.swift at main · JaMata/Flips · GitHub

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//
//  ImageLoader.swift
//  AsyncImage
//
//  Created by Vadym Bulavin on 2/13/20.
//  Copyright © 2020 Vadym Bulavin. All rights reserved.
//

import Combine
import UIKit

class ImageLoader: ObservableObject {
		@Published var image: UIImage?

		private(set) var isLoading = false

		private let url: URL
		private var cache: ImageCache?
		private var cancellable: AnyCancellable?

		private static let imageProcessingQueue = DispatchQueue(label: "image-processing")

		init(url: URL, cache: ImageCache? = nil) {
				self.url = url
				self.cache = cache
		}

		deinit {
				cancel()
		}

		func load() {
				guard !isLoading else { return }

				if let image = cache?[url] {
						self.image = image
						return
				}

				cancellable = URLSession.shared.dataTaskPublisher(for: url)
						.map { UIImage(data: $0.data) }
						.replaceError(with: nil)
						.handleEvents(receiveSubscription: { [weak self] _ in self?.onStart() },
													receiveOutput: { [weak self] in self?.cache($0) },
													receiveCompletion: { [weak self] _ in self?.onFinish() },
													receiveCancel: { [weak self] in self?.onFinish() })
						.subscribe(on: Self.imageProcessingQueue)
						.receive(on: DispatchQueue.main)
						.sink { [weak self] in self?.image = $0 }
		}

		func cancel() {
				cancellable?.cancel()
		}

		private func onStart() {
				isLoading = true
		}

		private func onFinish() {
				isLoading = false
		}

		private func cache(_ image: UIImage?) {
				image.map { cache?[url] = $0 }
		}
}