ImageCache.swift

final class ImageCache {

    // 1st level cache, that contains encoded images
    private lazy var imageCache: NSCache<AnyObject, AnyObject> = {
        let cache = NSCache<AnyObject, AnyObject>()
        cache.countLimit = config.countLimit
        return cache
    }()
    // 2nd level cache, that contains decoded images
    private lazy var decodedImageCache: NSCache<AnyObject, AnyObject> = {
        let cache = NSCache<AnyObject, AnyObject>()
        cache.totalCostLimit = config.memoryLimit
        return cache
    }()
    private let lock = NSLock()
    private let config: Config

    struct Config {
        let countLimit: Int
        let memoryLimit: Int

        static let defaultConfig = Config(countLimit: 100, memoryLimit: 1024 * 1024 * 100) // 100 MB
    }

    init(config: Config = Config.defaultConfig) {
        self.config = config
    }
}