Add CustomCodablePreferenceKey

Packages/TuskerPreferences/Sources/TuskerPreferences/Preference.swift

@@ -27,17 +27,26 @@ final class Preference<Key: PreferenceKey>: Codable {
     }
     
     init(from decoder: any Decoder) throws {
-        if let container = try? decoder.singleValueContainer() {
+        if let keyType = Key.self as? any CustomCodablePreferenceKey.Type {
+            self.storedValue = try keyType.decode(from: decoder) as! Key.Value?
+        } else if let container = try? decoder.singleValueContainer() {
             self.storedValue = try? container.decode(Key.Value.self)
         }
     }
     
     func encode(to encoder: any Encoder) throws {
         if let storedValue {
+            if let keyType = Key.self as? any CustomCodablePreferenceKey.Type {
+                func encode<K: CustomCodablePreferenceKey>(_: K.Type) throws {
+                    try K.encode(value: storedValue as! K.Value, to: encoder)
+                }
+                return try _openExistential(keyType, do: encode)
+            } else {
                 var container = encoder.singleValueContainer()
                 try container.encode(storedValue)
             }
         }
+    }
     
     static subscript(
         _enclosingInstance instance: PreferenceStore,

Packages/TuskerPreferences/Sources/TuskerPreferences/PreferenceKey.swift

@@ -28,3 +28,8 @@ extension MigratablePreferenceKey {
         oldValue != defaultValue
     }
 }
+
+protocol CustomCodablePreferenceKey: PreferenceKey {
+    static func encode(value: Value, to encoder: any Encoder) throws
+    static func decode(from decoder: any Decoder) throws -> Value?
+}

Packages/TuskerPreferences/Tests/TuskerPreferencesTests/PreferenceStoreTests.swift

@@ -15,11 +15,11 @@ final class PreferenceStoreTests: XCTestCase {
         static let defaultValue = false
     }
     
-    final class TestStore: Codable, ObservableObject {
+    final class TestStore<Key: PreferenceKey>: Codable, ObservableObject {
-        private var _test = Preference<TestKey>()
+        private var _test = Preference<Key>()
         
         // the acutal subscript expects the enclosingInstance to be a PreferenceStore, so do it manually
-        var test: Bool {
+        var test: Key.Value {
             get {
                 Preference.get(enclosingInstance: self, storage: \._test)
             }
@@ -28,7 +28,7 @@ final class PreferenceStoreTests: XCTestCase {
             }
         }
         
-        var testPublisher: some Publisher<TestKey.Value, Never> {
+        var testPublisher: some Publisher<Key.Value, Never> {
             _test.projectedValue
         }
         
@@ -37,7 +37,7 @@ final class PreferenceStoreTests: XCTestCase {
         
         init(from decoder: any Decoder) throws {
             let container = try decoder.container(keyedBy: CodingKeys.self)
-            self._test = try container.decode(Preference<TestKey>.self, forKey: .test)
+            self._test = try container.decode(Preference<Key>.self, forKey: .test)
         }
         
         enum CodingKeys: CodingKey {
@@ -52,18 +52,18 @@ final class PreferenceStoreTests: XCTestCase {
 
     func testDecoding() throws {
         let decoder = JSONDecoder()
-        let present = try decoder.decode(PreferenceCoding<TestStore>.self, from: Data("""
+        let present = try decoder.decode(PreferenceCoding<TestStore<TestKey>>.self, from: Data("""
 {"test": true}
 """.utf8)).wrapped
         XCTAssertEqual(present.test, true)
-        let absent = try decoder.decode(PreferenceCoding<TestStore>.self, from: Data("""
+        let absent = try decoder.decode(PreferenceCoding<TestStore<TestKey>>.self, from: Data("""
 {}
 """.utf8)).wrapped
         XCTAssertEqual(absent.test, false)
     }
     
     func testEncoding() throws {
-        let store = TestStore()
+        let store = TestStore<TestKey>()
         let encoder = JSONEncoder()
         XCTAssertEqual(String(data: try encoder.encode(PreferenceCoding(wrapped: store)), encoding: .utf8)!, """
 {}
@@ -83,7 +83,7 @@ final class PreferenceStoreTests: XCTestCase {
         let specificPref = expectation(description: "preference publisher")
         // initial and on change
         specificPref.expectedFulfillmentCount = 2
-        let store = TestStore()
+        let store = TestStore<TestKey>()
         var cancellables = Set<AnyCancellable>()
         store.objectWillChange.sink {
             topLevel.fulfill()
@@ -97,4 +97,32 @@ final class PreferenceStoreTests: XCTestCase {
         wait(for: [topLevel, specificPref])
     }
     
+    func testCustomCodable() throws {
+        struct Key: CustomCodablePreferenceKey {
+            static let defaultValue = 1
+            static func encode(value: Int, to encoder: any Encoder) throws {
+                var container = encoder.singleValueContainer()
+                try container.encode(2)
+            }
+            static func decode(from decoder: any Decoder) throws -> Int? {
+                3
+            }
+        }
+        let store = TestStore<Key>()
+        store.test = 123
+        let encoder = JSONEncoder()
+        XCTAssertEqual(String(data: try encoder.encode(PreferenceCoding(wrapped: store)), encoding: .utf8)!, """
+{"test":2}
+""")
+        let decoder = JSONDecoder()
+        let present = try decoder.decode(PreferenceCoding<TestStore<Key>>.self, from: Data("""
+{"test":2}
+""".utf8)).wrapped
+        XCTAssertEqual(present.test, 3)
+        let absent = try decoder.decode(PreferenceCoding<TestStore<Key>>.self, from: Data("""
+{}
+""".utf8)).wrapped
+        XCTAssertEqual(absent.test, 1)
+    }
+
 }