import AppKit

class ImageCache {
  static let shared = ImageCache()
  private let cache = NSCache<NSString, NSImage>()
  private let session: URLSession

  init(session: URLSession = .shared) {
    self.session = session
  }

  func image(for url: URL) -> NSImage? {
    return cache.object(forKey: url.absoluteString as NSString)
  }

  func insertImage(_ image: NSImage, for url: URL) {
    cache.setObject(image, forKey: url.absoluteString as NSString)
  }

  func fetchImage(url: URL) async throws -> NSImage {
    if let cached = image(for: url) {
      return cached
    }

    let (data, response) = try await session.data(from: url)
    guard let response = response as? HTTPURLResponse,
      (200...299).contains(response.statusCode)
    else {
      throw WallhavenError.apiError("Image download failed")
    }
    guard let image = NSImage(data: data) else {
      throw WallhavenError.decodingError(NSError(domain: "ImageCache", code: -1, userInfo: nil))
    }

    insertImage(image, for: url)
    return image
  }
}