import Combine
import SwiftUI

@MainActor
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 downloadQueue = OperationQueue()
  private var preloadingURLs = Set<URL>()

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

  // MARK: - Public Methods
  func preloadImages(_ urls: [URL]) {
    let newURLs = urls.filter { !preloadingURLs.contains($0) }

    for url in newURLs {
      preloadingURLs.insert(url)

      downloadQueue.addOperation {
        let cancellable = URLSession.shared.dataTaskPublisher(for: url)
          .map { CachedURLResponse(response: $0.response, data: $0.data) }
          .sink(
            receiveCompletion: { _ in
              DispatchQueue.main.async { [weak self] in
                self?.preloadingURLs.remove(url)
              }
            },
            receiveValue: { [weak self] cachedResponse in
              self?.cache.storeCachedResponse(cachedResponse, for: URLRequest(url: url))
            }
          )

        DispatchQueue.main.async { [weak self] in
          self?.cancellables.insert(cancellable)
        }
      }
    }
  }

  func clearCache() {
    cache.removeAllCachedResponses()
    cancellables.removeAll()
    preloadingURLs.removeAll()
  }

  func getCachedResponse(for url: URL) -> CachedURLResponse? {
    cache.cachedResponse(for: URLRequest(url: url))
  }
}