Generalize cache storage to allow using any hashable key parameter

Author: nerdsupremacist

Source/Shared/Storage/AsyncStorage.swift

@@ -3,18 +3,18 @@ import Dispatch
 
 /// Manipulate storage in a "all async" manner.
 /// The completion closure will be called when operation completes.
-public class AsyncStorage<T> {
-  public let innerStorage: HybridStorage<T>
+public class AsyncStorage<Key: Hashable, Value> {
+  public let innerStorage: HybridStorage<Key, Value>
   public let serialQueue: DispatchQueue
 
-  public init(storage: HybridStorage<T>, serialQueue: DispatchQueue) {
+  public init(storage: HybridStorage<Key, Value>, serialQueue: DispatchQueue) {
     self.innerStorage = storage
     self.serialQueue = serialQueue
   }
 }
 
 extension AsyncStorage {
-  public func entry(forKey key: String, completion: @escaping (Result<Entry<T>>) -> Void) {
+  public func entry(forKey key: Key, completion: @escaping (Result<Entry<Value>>) -> Void) {
     serialQueue.async { [weak self] in
       guard let `self` = self else {
         completion(Result.error(StorageError.deallocated))
@@ -30,7 +30,7 @@ extension AsyncStorage {
     }
   }
 
-  public func removeObject(forKey key: String, completion: @escaping (Result<()>) -> Void) {
+  public func removeObject(forKey key: Key, completion: @escaping (Result<()>) -> Void) {
     serialQueue.async { [weak self] in
       guard let `self` = self else {
         completion(Result.error(StorageError.deallocated))
@@ -47,8 +47,8 @@ extension AsyncStorage {
   }
 
   public func setObject(
-    _ object: T,
-    forKey key: String,
+    _ object: Value,
+    forKey key: Key,
     expiry: Expiry? = nil,
     completion: @escaping (Result<()>) -> Void) {
     serialQueue.async { [weak self] in
@@ -98,18 +98,18 @@ extension AsyncStorage {
     }
   }
 
-  public func object(forKey key: String, completion: @escaping (Result<T>) -> Void) {
-    entry(forKey: key, completion: { (result: Result<Entry<T>>) in
+  public func object(forKey key: Key, completion: @escaping (Result<Value>) -> Void) {
+    entry(forKey: key, completion: { (result: Result<Entry<Value>>) in
       completion(result.map({ entry in
         return entry.object
       }))
     })
   }
 
   public func existsObject(
-    forKey key: String,
+    forKey key: Key,
     completion: @escaping (Result<Bool>) -> Void) {
-    object(forKey: key, completion: { (result: Result<T>) in
+    object(forKey: key, completion: { (result: Result<Value>) in
       completion(result.map({ _ in
         return true
       }))
@@ -118,8 +118,8 @@ extension AsyncStorage {
 }
 
 public extension AsyncStorage {
-  func transform<U>(transformer: Transformer<U>) -> AsyncStorage<U> {
-    let storage = AsyncStorage<U>(
+  func transform<U>(transformer: Transformer<U>) -> AsyncStorage<Key, U> {
+    let storage = AsyncStorage<Key, U>(
       storage: innerStorage.transform(transformer: transformer),
       serialQueue: serialQueue
     )

Source/Shared/Storage/DiskStorage.swift

@@ -1,7 +1,7 @@
 import Foundation
 
 /// Save objects to file on disk
-final public class DiskStorage<T> {
+final public class DiskStorage<Key: Hashable, Value> {
   enum Error: Swift.Error {
     case fileEnumeratorFailed
   }
@@ -15,10 +15,11 @@ final public class DiskStorage<T> {
   /// The closure to be called when single file has been removed
   var onRemove: ((String) -> Void)?
 
-  private let transformer: Transformer<T>
+  private let transformer: Transformer<Value>
+  private let hasher = Hasher.constantAccrossExecutions()
 
   // MARK: - Initialization
-  public convenience init(config: DiskConfig, fileManager: FileManager = FileManager.default, transformer: Transformer<T>) throws {
+  public convenience init(config: DiskConfig, fileManager: FileManager = FileManager.default, transformer: Transformer<Value>) throws {
     let url: URL
     if let directory = config.directory {
       url = directory
@@ -48,7 +49,7 @@ final public class DiskStorage<T> {
     #endif
   }
 
-  public required init(config: DiskConfig, fileManager: FileManager = FileManager.default, path: String, transformer: Transformer<T>) {
+  public required init(config: DiskConfig, fileManager: FileManager = FileManager.default, path: String, transformer: Transformer<Value>) {
     self.config = config
     self.fileManager = fileManager
     self.path = path
@@ -57,7 +58,7 @@ final public class DiskStorage<T> {
 }
 
 extension DiskStorage: StorageAware {
-  public func entry(forKey key: String) throws -> Entry<T> {
+  public func entry(forKey key: Key) throws -> Entry<Value> {
     let filePath = makeFilePath(for: key)
     let data = try Data(contentsOf: URL(fileURLWithPath: filePath))
     let attributes = try fileManager.attributesOfItem(atPath: filePath)
@@ -74,15 +75,15 @@ extension DiskStorage: StorageAware {
     )
   }
 
-  public func setObject(_ object: T, forKey key: String, expiry: Expiry? = nil) throws {
+  public func setObject(_ object: Value, forKey key: Key, expiry: Expiry? = nil) throws {
     let expiry = expiry ?? config.expiry
     let data = try transformer.toData(object)
     let filePath = makeFilePath(for: key)
     _ = fileManager.createFile(atPath: filePath, contents: data, attributes: nil)
     try fileManager.setAttributes([.modificationDate: expiry.date], ofItemAtPath: filePath)
   }
 
-  public func removeObject(forKey key: String) throws {
+  public func removeObject(forKey key: Key) throws {
     let filePath = makeFilePath(for: key)
     try fileManager.removeItem(atPath: filePath)
     onRemove?(filePath)
@@ -160,24 +161,30 @@ extension DiskStorage {
    - Parameter key: Unique key to identify the object in the cache
    - Returns: A md5 string
    */
-  func makeFileName(for key: String) -> String {
-    let fileExtension = URL(fileURLWithPath: key).pathExtension
-    let fileName = MD5(key)
-
-    switch fileExtension.isEmpty {
-    case true:
-      return fileName
-    case false:
-      return "\(fileName).\(fileExtension)"
+  func makeFileName(for key: Key) -> String {
+    if let key = key as? String {
+        let fileExtension = URL(fileURLWithPath: key).pathExtension
+        let fileName = MD5(key)
+
+        switch fileExtension.isEmpty {
+        case true:
+          return fileName
+        case false:
+          return "\(fileName).\(fileExtension)"
+        }
     }
+
+    var hasher = self.hasher
+    key.hash(into: &hasher)
+    return String(hasher.finalize())
   }
 
   /**
    Builds file path from the key.
    - Parameter key: Unique key to identify the object in the cache
    - Returns: A string path based on key
    */
-  func makeFilePath(for key: String) -> String {
+  func makeFilePath(for key: Key) -> String {
     return "\(path)/\(makeFileName(for: key))"
   }
 
@@ -244,7 +251,7 @@ extension DiskStorage {
    Removes the object from the cache if it's expired.
    - Parameter key: Unique key to identify the object in the cache
    */
-  func removeObjectIfExpired(forKey key: String) throws {
+  func removeObjectIfExpired(forKey key: Key) throws {
     let filePath = makeFilePath(for: key)
     let attributes = try fileManager.attributesOfItem(atPath: filePath)
     if let expiryDate = attributes[.modificationDate] as? Date, expiryDate.inThePast {
@@ -255,8 +262,8 @@ extension DiskStorage {
 }
 
 public extension DiskStorage {
-  func transform<U>(transformer: Transformer<U>) -> DiskStorage<U> {
-    let storage = DiskStorage<U>(
+  func transform<U>(transformer: Transformer<U>) -> DiskStorage<Key, U> {
+    let storage = DiskStorage<Key, U>(
       config: config,
       fileManager: fileManager,
       path: path,

Source/Shared/Storage/HybridStorage.swift

@@ -1,14 +1,14 @@
 import Foundation
 
 /// Use both memory and disk storage. Try on memory first.
-public final class HybridStorage<T> {
-  public let memoryStorage: MemoryStorage<T>
-  public let diskStorage: DiskStorage<T>
+public final class HybridStorage<Key: Hashable, Value> {
+  public let memoryStorage: MemoryStorage<Key, Value>
+  public let diskStorage: DiskStorage<Key, Value>
 
-  private(set) var storageObservations = [UUID: (HybridStorage, StorageChange) -> Void]()
-  private(set) var keyObservations = [String: (HybridStorage, KeyChange<T>) -> Void]()
+  private(set) var storageObservations = [UUID: (HybridStorage, StorageChange<Key>) -> Void]()
+  private(set) var keyObservations = [Key: (HybridStorage, KeyChange<Value>) -> Void]()
 
-  public init(memoryStorage: MemoryStorage<T>, diskStorage: DiskStorage<T>) {
+  public init(memoryStorage: MemoryStorage<Key, Value>, diskStorage: DiskStorage<Key, Value>) {
     self.memoryStorage = memoryStorage
     self.diskStorage = diskStorage
 
@@ -26,7 +26,7 @@ public final class HybridStorage<T> {
 }
 
 extension HybridStorage: StorageAware {
-  public func entry(forKey key: String) throws -> Entry<T> {
+  public func entry(forKey key: Key) throws -> Entry<Value> {
     do {
       return try memoryStorage.entry(forKey: key)
     } catch {
@@ -37,15 +37,15 @@ extension HybridStorage: StorageAware {
     }
   }
 
-  public func removeObject(forKey key: String) throws {
+  public func removeObject(forKey key: Key) throws {
     memoryStorage.removeObject(forKey: key)
     try diskStorage.removeObject(forKey: key)
 
     notifyStorageObservers(about: .remove(key: key))
   }
 
-  public func setObject(_ object: T, forKey key: String, expiry: Expiry? = nil) throws {
-    var keyChange: KeyChange<T>?
+  public func setObject(_ object: Value, forKey key: Key, expiry: Expiry? = nil) throws {
+    var keyChange: KeyChange<Value>?
 
     if keyObservations[key] != nil {
       keyChange = .edit(before: try? self.object(forKey: key), after: object)
@@ -78,8 +78,8 @@ extension HybridStorage: StorageAware {
 }
 
 public extension HybridStorage {
-  func transform<U>(transformer: Transformer<U>) -> HybridStorage<U> {
-    let storage = HybridStorage<U>(
+  func transform<U>(transformer: Transformer<U>) -> HybridStorage<Key, U> {
+    let storage = HybridStorage<Key, U>(
       memoryStorage: memoryStorage.transform(),
       diskStorage: diskStorage.transform(transformer: transformer)
     )
@@ -92,7 +92,7 @@ extension HybridStorage: StorageObservationRegistry {
   @discardableResult
   public func addStorageObserver<O: AnyObject>(
     _ observer: O,
-    closure: @escaping (O, HybridStorage, StorageChange) -> Void
+    closure: @escaping (O, HybridStorage, StorageChange<Key>) -> Void
   ) -> ObservationToken {
     let id = UUID()
 
@@ -114,7 +114,7 @@ extension HybridStorage: StorageObservationRegistry {
     storageObservations.removeAll()
   }
 
-  private func notifyStorageObservers(about change: StorageChange) {
+  private func notifyStorageObservers(about change: StorageChange<Key>) {
     storageObservations.values.forEach { closure in
       closure(self, change)
     }
@@ -125,8 +125,8 @@ extension HybridStorage: KeyObservationRegistry {
   @discardableResult
   public func addObserver<O: AnyObject>(
     _ observer: O,
-    forKey key: String,
-    closure: @escaping (O, HybridStorage, KeyChange<T>) -> Void
+    forKey key: Key,
+    closure: @escaping (O, HybridStorage, KeyChange<Value>) -> Void
   ) -> ObservationToken {
     keyObservations[key] = { [weak self, weak observer] storage, change in
       guard let observer = observer else {
@@ -142,24 +142,24 @@ extension HybridStorage: KeyObservationRegistry {
     }
   }
 
-  public func removeObserver(forKey key: String) {
+  public func removeObserver(forKey key: Key) {
     keyObservations.removeValue(forKey: key)
   }
 
   public func removeAllKeyObservers() {
     keyObservations.removeAll()
   }
 
-  private func notifyObserver(forKey key: String, about change: KeyChange<T>) {
+  private func notifyObserver(forKey key: Key, about change: KeyChange<Value>) {
     keyObservations[key]?(self, change)
   }
 
-  private func notifyObserver(about change: KeyChange<T>, whereKey closure: ((String) -> Bool)) {
+  private func notifyObserver(about change: KeyChange<Value>, whereKey closure: ((Key) -> Bool)) {
     let observation = keyObservations.first { key, _ in closure(key) }?.value
     observation?(self, change)
   }
 
-  private func notifyKeyObservers(about change: KeyChange<T>) {
+  private func notifyKeyObservers(about change: KeyChange<Value>) {
     keyObservations.values.forEach { closure in
       closure(self, change)
     }

Source/Shared/Storage/KeyObservationRegistry.swift

@@ -15,15 +15,15 @@ public protocol KeyObservationRegistry {
   @discardableResult
   func addObserver<O: AnyObject>(
     _ observer: O,
-    forKey key: String,
-    closure: @escaping (O, S, KeyChange<S.T>) -> Void
+    forKey key: S.Key,
+    closure: @escaping (O, S, KeyChange<S.Value>) -> Void
   ) -> ObservationToken
 
   /**
    Removes observer by the given key.
    - Parameter key: Unique key to identify the object in the cache
    */
-  func removeObserver(forKey key: String)
+  func removeObserver(forKey key: S.Key)
 
   /// Removes all registered key observers
   func removeAllKeyObservers()