90 lines
2.4 KiB
Swift
90 lines
2.4 KiB
Swift
//
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// https://mczachurski.dev
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// Copyright © 2023 Marcin Czachurski and the repository contributors.
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// Licensed under the Apache License 2.0.
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//
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import Foundation
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/// Memory cache based on article: https://www.swiftbysundell.com/articles/caching-in-swift/
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public final class MemoryCache<Key: Hashable, Value> {
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private let wrapped = NSCache<WrappedKey, Entry>()
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private let dateProvider: () -> Date
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private let entryLifetime: TimeInterval
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public init(dateProvider: @escaping () -> Date = Date.init, entryLifetime: TimeInterval = 12 * 60 * 60) {
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self.dateProvider = dateProvider
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self.entryLifetime = entryLifetime
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}
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public func insert(_ value: Value, forKey key: Key) {
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let date = dateProvider().addingTimeInterval(entryLifetime)
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let entry = Entry(value: value, expirationDate: date)
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wrapped.setObject(entry, forKey: WrappedKey(key))
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}
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public func value(forKey key: Key) -> Value? {
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guard let entry = wrapped.object(forKey: WrappedKey(key)) else {
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return nil
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}
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guard dateProvider() < entry.expirationDate else {
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// Discard values that have expired
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removeValue(forKey: key)
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return nil
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}
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return entry.value
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}
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public func removeValue(forKey key: Key) {
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wrapped.removeObject(forKey: WrappedKey(key))
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}
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}
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private extension MemoryCache {
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final class WrappedKey: NSObject {
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let key: Key
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init(_ key: Key) { self.key = key }
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override var hash: Int { return key.hashValue }
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override func isEqual(_ object: Any?) -> Bool {
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guard let value = object as? WrappedKey else {
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return false
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}
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return value.key == key
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}
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}
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}
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private extension MemoryCache {
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final class Entry {
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let value: Value
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let expirationDate: Date
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init(value: Value, expirationDate: Date) {
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self.value = value
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self.expirationDate = expirationDate
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}
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}
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}
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public extension MemoryCache {
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subscript(key: Key) -> Value? {
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get { return value(forKey: key) }
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set {
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guard let value = newValue else {
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// If nil was assigned using our subscript,
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// then we remove any value for that key:
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removeValue(forKey: key)
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return
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}
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insert(value, forKey: key)
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}
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}
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}
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