Fixes #367 - Refactor AppSettings usage patterns

ElementX/Sources/Other/UserSettingPropertyWrapper.swift

@@ -0,0 +1,127 @@
+//
+// Copyright 2022 New Vector Ltd
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+// Taken from https://www.swiftbysundell.com/articles/property-wrappers-in-swift/
+
+import Combine
+import Foundation
+
+/// Property wrapper that allows transparent access to user defaults and exposes
+/// a combine publisher for listening to value changes
+///
+/// Please use `UserSettingRawRepresentable` for storing RawRepresentable values
+@propertyWrapper
+struct UserSetting<Value: Equatable> {
+    private let key: String
+    private let defaultValue: Value
+    private let storage: UserDefaults
+    private let publisher: CurrentValueSubject<Value, Never>
+    
+    init(key: String, defaultValue: Value, storage: UserDefaults = .standard) {
+        self.key = key
+        self.defaultValue = defaultValue
+        self.storage = storage
+        
+        let value = storage.value(forKey: key) as? Value ?? defaultValue
+        publisher = CurrentValueSubject<Value, Never>(value)
+    }
+    
+    var wrappedValue: Value {
+        get {
+            let value = storage.value(forKey: key) as? Value
+            return value ?? defaultValue
+        }
+        set {
+            if let optional = newValue as? AnyOptional, optional.isNil {
+                storage.removeObject(forKey: key)
+                publisher.send(defaultValue)
+            } else {
+                storage.setValue(newValue, forKey: key)
+                publisher.send(newValue)
+            }
+        }
+    }
+    
+    var projectedValue: AnyPublisher<Value, Never> {
+        publisher.removeDuplicates(by: { $0 == $1 }).eraseToAnyPublisher()
+    }
+}
+
+extension UserSetting where Value: ExpressibleByNilLiteral {
+    init(key: String, storage: UserDefaults = .standard) {
+        self.init(key: key, defaultValue: nil, storage: storage)
+    }
+}
+
+/// Property wrapper that allows transparent access to user defaults for RawRepresentable types
+/// and exposes a combine publisher for listening to value changes
+///
+/// Tried extending UserSetting with RawRepresentable conformance but in that case the non-restricted
+/// method takes precedence. Decided to go with with the simple solution instead of fighting the system
+@propertyWrapper
+struct UserSettingRawRepresentable<Value: RawRepresentable & Equatable> {
+    private let key: String
+    private let defaultValue: Value
+    private let storage: UserDefaults
+    private let publisher: CurrentValueSubject<Value, Never>
+    
+    init(key: String, defaultValue: Value, storage: UserDefaults = .standard) {
+        self.key = key
+        self.defaultValue = defaultValue
+        self.storage = storage
+        
+        let value = (storage.value(forKey: key) as? Value.RawValue).flatMap { Value(rawValue: $0) } ?? defaultValue
+        publisher = CurrentValueSubject<Value, Never>(value)
+    }
+    
+    var wrappedValue: Value {
+        get {
+            guard let value = storage.value(forKey: key) as? Value.RawValue else {
+                return defaultValue
+            }
+            
+            return Value(rawValue: value) ?? defaultValue
+        }
+        set {
+            if let optional = newValue as? AnyOptional, optional.isNil {
+                storage.removeObject(forKey: key)
+                publisher.send(newValue)
+            } else {
+                storage.setValue(newValue.rawValue, forKey: key)
+                publisher.send(newValue)
+            }
+        }
+    }
+    
+    var projectedValue: AnyPublisher<Value, Never> {
+        publisher.removeDuplicates(by: { $0 == $1 }).eraseToAnyPublisher()
+    }
+}
+
+extension UserSettingRawRepresentable where Value: ExpressibleByNilLiteral {
+    init(key: String, storage: UserDefaults = .standard) {
+        self.init(key: key, defaultValue: nil, storage: storage)
+    }
+}
+
+// Casting to AnyOptional will fail for any types that are not Optional (below)
+private protocol AnyOptional {
+    var isNil: Bool { get }
+}
+
+extension Optional: AnyOptional {
+    var isNil: Bool { self == nil }
+}