Implement observations in HybridStorage

Cache.xcodeproj/project.pbxproj

@@ -141,6 +141,9 @@
 		D5A9D1BB211345D4005DBD3F /* Dictionary+Extensions.swift in Sources */ = {isa = PBXBuildFile; fileRef = D5A9D1BA211345D4005DBD3F /* Dictionary+Extensions.swift */; };
 		D5A9D1BC211345D4005DBD3F /* Dictionary+Extensions.swift in Sources */ = {isa = PBXBuildFile; fileRef = D5A9D1BA211345D4005DBD3F /* Dictionary+Extensions.swift */; };
 		D5A9D1BD211345D4005DBD3F /* Dictionary+Extensions.swift in Sources */ = {isa = PBXBuildFile; fileRef = D5A9D1BA211345D4005DBD3F /* Dictionary+Extensions.swift */; };
+		D5A9D1BF21134776005DBD3F /* StoreChange.swift in Sources */ = {isa = PBXBuildFile; fileRef = D5A9D1BE21134776005DBD3F /* StoreChange.swift */; };
+		D5A9D1C021134776005DBD3F /* StoreChange.swift in Sources */ = {isa = PBXBuildFile; fileRef = D5A9D1BE21134776005DBD3F /* StoreChange.swift */; };
+		D5A9D1C121134776005DBD3F /* StoreChange.swift in Sources */ = {isa = PBXBuildFile; fileRef = D5A9D1BE21134776005DBD3F /* StoreChange.swift */; };
 /* End PBXBuildFile section */
 
 /* Begin PBXContainerItemProxy section */
@@ -230,6 +233,7 @@
 		D5A138C31EB29C2100881A20 /* NSImage+Extensions.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = "NSImage+Extensions.swift"; sourceTree = "<group>"; };
 		D5A9D1B621134547005DBD3F /* ObservationToken.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ObservationToken.swift; sourceTree = "<group>"; };
 		D5A9D1BA211345D4005DBD3F /* Dictionary+Extensions.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = "Dictionary+Extensions.swift"; sourceTree = "<group>"; };
+		D5A9D1BE21134776005DBD3F /* StoreChange.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = StoreChange.swift; sourceTree = "<group>"; };
 		D5DC59E01C20593E003BD79B /* Cache.framework */ = {isa = PBXFileReference; explicitFileType = wrapper.framework; includeInIndex = 0; path = Cache.framework; sourceTree = BUILT_PRODUCTS_DIR; };
 		EBAACA991FBC369300FA206E /* SimpleStorage.playground */ = {isa = PBXFileReference; lastKnownFileType = file.playground; path = SimpleStorage.playground; sourceTree = "<group>"; xcLanguageSpecificationIdentifier = xcode.lang.swift; };
 /* End PBXFileReference section */
@@ -358,6 +362,7 @@
 				D270147F20D10982003B45C7 /* Storage.swift */,
 				D270148320D10E76003B45C7 /* AsyncStorage.swift */,
 				D270148720D11040003B45C7 /* Storage+Transform.swift */,
+				D5A9D1BE21134776005DBD3F /* StoreChange.swift */,
 			);
 			path = Storage;
 			sourceTree = "<group>";
@@ -833,6 +838,7 @@
 				D28897071F8B79B300C61DEE /* JSONDecoder+Extensions.swift in Sources */,
 				D270148220D10982003B45C7 /* Storage.swift in Sources */,
 				D221E5C220D00DCC00BC940E /* Entry.swift in Sources */,
+				D5A9D1C121134776005DBD3F /* StoreChange.swift in Sources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 		};
@@ -916,6 +922,7 @@
 				D28897061F8B79B300C61DEE /* JSONDecoder+Extensions.swift in Sources */,
 				D270148120D10982003B45C7 /* Storage.swift in Sources */,
 				D221E5C120D00DCC00BC940E /* Entry.swift in Sources */,
+				D5A9D1C021134776005DBD3F /* StoreChange.swift in Sources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 		};
@@ -968,6 +975,7 @@
 				D2CF98611F694FFA00CE8F68 /* MemoryConfig.swift in Sources */,
 				D2CF98661F694FFA00CE8F68 /* ExpirationMode.swift in Sources */,
 				D221E5C020D00DCC00BC940E /* Entry.swift in Sources */,
+				D5A9D1BF21134776005DBD3F /* StoreChange.swift in Sources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 		};

Source/Shared/Storage/HybridStorage.swift

@@ -5,6 +5,8 @@ public class HybridStorage<T> {
   public let memoryStorage: MemoryStorage<T>
   public let diskStorage: DiskStorage<T>
 
+  private var observations = [UUID : (HybridStorage, StoreChange) -> Void]()
+
   public init(memoryStorage: MemoryStorage<T>, diskStorage: DiskStorage<T>) {
     self.memoryStorage = memoryStorage
     self.diskStorage = diskStorage
@@ -26,21 +28,25 @@ extension HybridStorage: StorageAware {
   public func removeObject(forKey key: String) throws {
     memoryStorage.removeObject(forKey: key)
     try diskStorage.removeObject(forKey: key)
+    notifyObservers(of: .singleDeletion)
   }
 
   public func setObject(_ object: T, forKey key: String, expiry: Expiry? = nil) throws {
     memoryStorage.setObject(object, forKey: key, expiry: expiry)
     try diskStorage.setObject(object, forKey: key, expiry: expiry)
+    notifyObservers(of: .addition)
   }
 
   public func removeAll() throws {
     memoryStorage.removeAll()
     try diskStorage.removeAll()
+    notifyObservers(of: .allDeletion)
   }
 
   public func removeExpiredObjects() throws {
     memoryStorage.removeExpiredObjects()
     try diskStorage.removeExpiredObjects()
+    notifyObservers(of: .expiredDeletion)
   }
 }
 
@@ -54,3 +60,25 @@ public extension HybridStorage {
     return storage
   }
 }
+
+// MARK: - Observations
+
+extension HybridStorage {
+  @discardableResult
+  func observeChanges(using closure: @escaping (HybridStorage, StoreChange) -> Void) -> ObservationToken {
+    let id = observations.insert(closure)
+
+    return ObservationToken { [weak self] in
+      self?.observations.removeValue(forKey: id)
+    }
+  }
+
+  private func notifyObservers(of change: StoreChange) {
+    observations.values.forEach { [weak self] closure in
+      guard let strongSelf = self else {
+        return
+      }
+      closure(strongSelf, change)
+    }
+  }
+}

Source/Shared/Storage/Storage.swift

@@ -1,13 +1,6 @@
 import Foundation
 import Dispatch
 
-enum StoreChange {
-  case addition
-  case singleDeletion
-  case allDeletion
-  case expiredDeletion
-}
-
 /// Manage storage. Use memory storage if specified.
 /// Synchronous by default. Use `async` for asynchronous operations.
 public class Storage<T> {
@@ -41,7 +34,6 @@ public class Storage<T> {
       storage: hybridStorage,
       serialQueue: DispatchQueue(label: "Cache.SyncStorage.SerialQueue")
     )
-
     let asyncStorage = AsyncStorage(
       storage: hybridStorage,
       serialQueue: DispatchQueue(label: "Cache.AsyncStorage.SerialQueue")
@@ -57,10 +49,29 @@ public class Storage<T> {
   public required init(syncStorage: SyncStorage<T>, asyncStorage: AsyncStorage<T>) {
     self.syncStorage = syncStorage
     self.asyncStorage = asyncStorage
+    subscribeToChanges()
   }
 
   /// Used for async operations
   public lazy var async = self.asyncStorage
+
+  private func subscribeToChanges() {
+    subscribeToChanges(in: syncStorage.innerStorage)
+    if syncStorage !== asyncStorage {
+      subscribeToChanges(in: asyncStorage.innerStorage)
+    }
+  }
+
+  private func subscribeToChanges(in storage: HybridStorage<T>) {
+    storage.observeChanges { [weak self] _, change in
+      self?.observations.values.forEach { [weak self] closure in
+        guard let strongSelf = self else {
+          return
+        }
+        closure(strongSelf, change)
+      }
+    }
+  }
 }
 
 extension Storage: StorageAware {
@@ -74,26 +85,14 @@ extension Storage: StorageAware {
 
   public func setObject(_ object: T, forKey key: String, expiry: Expiry? = nil) throws {
     try self.syncStorage.setObject(object, forKey: key, expiry: expiry)
-    notifyObservers(of: .addition)
   }
 
   public func removeAll() throws {
     try self.syncStorage.removeAll()
-    notifyObservers(of: .allDeletion)
   }
 
   public func removeExpiredObjects() throws {
     try self.syncStorage.removeExpiredObjects()
-    notifyObservers(of: .expiredDeletion)
-  }
-
-  private func notifyObservers(of change: StoreChange) {
-    observations.values.forEach { [weak self] closure in
-      guard let strongSelf = self else {
-        return
-      }
-      closure(strongSelf, change)
-    }
   }
 }
 

Source/Shared/Storage/StoreChange.swift

@@ -0,0 +1,6 @@
+public enum StoreChange {
+  case addition
+  case singleDeletion
+  case allDeletion
+  case expiredDeletion
+}

Tests/iOS/Tests/Storage/StorageTests.swift

@@ -96,4 +96,8 @@ final class StorageTests: XCTestCase {
     let cachedObject = try! alienStorage.object(forKey: "person")
     XCTAssertEqual(cachedObject.firstName, "John")
   }
+
+  func testObserveAddition() {
+
+  }
 }