import Combine
import SwiftUI

final class ImageCacheManager {
  // MARK: - Singleton
  static let shared = ImageCacheManager()

  // MARK: - Private Properties
  private let cache = URLCache(
    memoryCapacity: 100 * 1_024 * 1_024,  // 100 MB
    diskCapacity: 500 * 1_024 * 1_024,  // 500 MB
    directory: FileManager.default.urls(for: .cachesDirectory, in: .userDomainMask).first?
      .appendingPathComponent("SoraImageCache", isDirectory: true)
  )
  private var cancellables = Set<AnyCancellable>()
  private let cancellablesQueue = DispatchQueue(
    label: "\(Bundle.main.bundleIdentifier!).ImageCacheManager.cancellablesQueue"
  )
  private let downloadQueue = OperationQueue()

  // MARK: - Initialisation
  private init() {
    downloadQueue.maxConcurrentOperationCount = 5
  }

  // MARK: - Public Methods
  func preloadImages(_ urls: [URL]) {
    urls.forEach { url in
      downloadQueue.addOperation {
        self.cancellablesQueue.sync {
          URLSession.shared.dataTaskPublisher(for: url)
            .map { CachedURLResponse(response: $0.response, data: $0.data) }
            .sink(
              receiveCompletion: { _ in () },
              receiveValue: { [self] in cache.storeCachedResponse($0, for: URLRequest(url: url)) }
            )
            .store(in: &self.cancellables)
        }
      }
    }
  }
}