96 lines
3.3 KiB
Swift
96 lines
3.3 KiB
Swift
//
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// Copyright 2022 Google LLC
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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import Foundation
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#if SWIFT_PACKAGE
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@_implementationOnly import GoogleUtilities_UserDefaults
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#else
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@_implementationOnly import GoogleUtilities
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#endif // SWIFT_PACKAGE
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/// CacheKey is like a "key" to a "safe". It provides necessary metadata about the current cache to
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/// know if it should be expired.
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struct CacheKey: Codable {
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var createdAt: Date
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var googleAppID: String
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var appVersion: String
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}
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/// SettingsCacheClient is responsible for accessing the cache that Settings are stored in.
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protocol SettingsCacheClient {
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/// Returns in-memory cache content in O(1) time. Returns empty dictionary if it does not exist in
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/// cache.
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var cacheContent: [String: Any] { get set }
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/// Returns in-memory cache-key, no performance guarantee because type-casting depends on size of
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/// CacheKey
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var cacheKey: CacheKey? { get set }
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/// Removes all cache content and cache-key
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func removeCache()
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}
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/// SettingsCache uses UserDefaults to store Settings on-disk, but also directly query UserDefaults
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/// when accessing Settings values during run-time. This is because UserDefaults encapsulates both
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/// in-memory and persisted-on-disk storage, allowing fast synchronous access in-app while hiding
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/// away the complexity of managing persistence asynchronously.
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class SettingsCache: SettingsCacheClient {
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private static let settingsVersion: Int = 1
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private enum UserDefaultsKeys {
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static let forContent = "firebase-sessions-settings"
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static let forCacheKey = "firebase-sessions-cache-key"
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}
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/// UserDefaults holds values in memory, making access O(1) and synchronous within the app, while
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/// abstracting away async disk IO.
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private let cache: GULUserDefaults = .standard()
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/// Converting to dictionary is O(1) because object conversion is O(1)
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var cacheContent: [String: Any] {
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get {
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return (cache.object(forKey: UserDefaultsKeys.forContent) as? [String: Any]) ?? [:]
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}
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set {
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cache.setObject(newValue, forKey: UserDefaultsKeys.forContent)
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}
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}
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/// Casting to Codable from Data is O(n)
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var cacheKey: CacheKey? {
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get {
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if let data = cache.object(forKey: UserDefaultsKeys.forCacheKey) as? Data {
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do {
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return try JSONDecoder().decode(CacheKey.self, from: data)
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} catch {
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Logger.logError("[Settings] Decoding CacheKey failed with error: \(error)")
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}
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}
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return nil
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}
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set {
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do {
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try cache.setObject(JSONEncoder().encode(newValue), forKey: UserDefaultsKeys.forCacheKey)
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} catch {
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Logger.logError("[Settings] Encoding CacheKey failed with error: \(error)")
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}
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}
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}
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/// Removes stored cache
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func removeCache() {
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cache.setObject(nil, forKey: UserDefaultsKeys.forContent)
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cache.setObject(nil, forKey: UserDefaultsKeys.forCacheKey)
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}
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}
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