Merge the UserDefaultsStorage helpers into UserDefaultsProtocol.

ElementX/Sources/Application/Settings/UserDefaultsProtocol.swift

@@ -16,3 +16,66 @@ public nonisolated protocol UserDefaultsProtocol: AnyObject {
     
     func reset()
 }
+
+// MARK: - Codable handling
+
+nonisolated extension UserDefaultsProtocol {
+    /// Reads and writes a `Codable` value stored under `key`, used by the `@UserPreference` macro.
+    ///
+    /// When `Value` conforms to `PlistRepresentable` the Codable encode/decode phase is skipped and
+    /// the value is stored natively in the plist.
+    subscript<Value: Codable>(key: String) -> Value? {
+        get {
+            if Value.self is PlistRepresentable.Type {
+                object(forKey: key) as? Value
+            } else {
+                data(forKey: key).flatMap { try? JSONDecoder().decode(Value.self, from: $0) }
+            }
+        }
+        set {
+            // Detects correctly double optionals like this: String?? = .some(nil)
+            if newValue.isNil {
+                removeObject(forKey: key)
+            } else if Value.self is PlistRepresentable.Type {
+                set(newValue, forKey: key)
+            } else {
+                set(try? JSONEncoder().encode(newValue), forKey: key)
+            }
+        }
+    }
+}
+
+private nonisolated protocol Nullable {
+    var isNil: Bool { get }
+}
+
+nonisolated extension Optional: Nullable {
+    var isNil: Bool {
+        switch self {
+        case .none:
+            return true
+        case .some(let nullable as Nullable):
+            return nullable.isNil
+        case .some:
+            return false
+        }
+    }
+}
+
+// MARK: - PlistRepresentable
+
+/// A protocol to mark types as being plist compliant.
+/// The `UserDefaultsProtocol` storage subscript uses this to avoid encoding/decoding plist compliant values with Codable.
+nonisolated protocol PlistRepresentable { }
+
+extension Bool: PlistRepresentable { }
+extension String: PlistRepresentable { }
+extension Int: PlistRepresentable { }
+extension Float: PlistRepresentable { }
+extension Double: PlistRepresentable { }
+extension Date: PlistRepresentable { }
+extension Data: PlistRepresentable { }
+
+extension Array: PlistRepresentable where Element: PlistRepresentable { }
+extension Dictionary: PlistRepresentable where Key == String, Value: PlistRepresentable { }
+extension Optional: PlistRepresentable where Wrapped: PlistRepresentable { }