Impressia/Vernissage/Cache/MemoryCache.swift

91 lines
2.4 KiB
Swift

//
// https://mczachurski.dev
// Copyright © 2023 Marcin Czachurski and the repository contributors.
// Licensed under the MIT License.
//
import Foundation
/// Memory cache based on article: https://www.swiftbysundell.com/articles/caching-in-swift/
final class MemoryCache<Key: Hashable, Value> {
private let wrapped = NSCache<WrappedKey, Entry>()
private let dateProvider: () -> Date
private let entryLifetime: TimeInterval
init(dateProvider: @escaping () -> Date = Date.init,
entryLifetime: TimeInterval = 12 * 60 * 60) {
self.dateProvider = dateProvider
self.entryLifetime = entryLifetime
}
func insert(_ value: Value, forKey key: Key) {
let date = dateProvider().addingTimeInterval(entryLifetime)
let entry = Entry(value: value, expirationDate: date)
wrapped.setObject(entry, forKey: WrappedKey(key))
}
func value(forKey key: Key) -> Value? {
guard let entry = wrapped.object(forKey: WrappedKey(key)) else {
return nil
}
guard dateProvider() < entry.expirationDate else {
// Discard values that have expired
removeValue(forKey: key)
return nil
}
return entry.value
}
func removeValue(forKey key: Key) {
wrapped.removeObject(forKey: WrappedKey(key))
}
}
private extension MemoryCache {
final class WrappedKey: NSObject {
let key: Key
init(_ key: Key) { self.key = key }
override var hash: Int { return key.hashValue }
override func isEqual(_ object: Any?) -> Bool {
guard let value = object as? WrappedKey else {
return false
}
return value.key == key
}
}
}
private extension MemoryCache {
final class Entry {
let value: Value
let expirationDate: Date
init(value: Value, expirationDate: Date) {
self.value = value
self.expirationDate = expirationDate
}
}
}
extension MemoryCache {
subscript(key: Key) -> Value? {
get { return value(forKey: key) }
set {
guard let value = newValue else {
// If nil was assigned using our subscript,
// then we remove any value for that key:
removeValue(forKey: key)
return
}
insert(value, forKey: key)
}
}
}