UserDefaultsManagedWrapper.swift

//
//  UserDefaultsManagedWrapper.swift
//  Yoga
//
//  Created by Maxim Kotliar on 11.12.2019.
//  Copyright © 2019 Wikrgroup. All rights reserved.
//

import Foundation
import Bindy

@propertyWrapper
class UserDefaultsManaged<T: Codable> {
    let key: String
    let defaultValue: T
    let userDefaults: UserDefaults

    let projectedValue: Observable<T>

    private var notificationToken: NSObjectProtocol?

    init(key: String, defaultValue: T, userDefaults: UserDefaults = .standard) {

        func currentValue() -> T {
            userDefaults.value(for: key) ?? defaultValue
        }

        self.key = key
        self.defaultValue = defaultValue
        self.userDefaults = userDefaults
        self.projectedValue = Observable(currentValue())

        var skipNextChange: Bool = false
        projectedValue.observe(self) { value in
            guard !skipNextChange else { return }
            userDefaults.set(value: value, forKey: key)
        }

        notificationToken =
            NotificationCenter.default.addObserver(forName: UserDefaults.didChangeNotification,
                                                   object: nil,
                                                   queue: nil) { [weak self] _ in
                                                    skipNextChange = true
                                                    self?.projectedValue.value = currentValue()
                                                    skipNextChange = false
            }
    }

    var wrappedValue: T {
        get {
            return self.projectedValue.value
        }
        set {
            projectedValue.value = newValue
        }
    }
}

extension UserDefaults {

    private struct CodableWrapper<T: Codable>: Codable {
        let value: T
    }

    func value<T: Codable>(for key: String) -> T? {
        do {
            guard let data = self.data(forKey: key) else { return nil }
            return try JSONDecoder.fromLocalStorage.decode(CodableWrapper<T>.self, from: data).value
        } catch {
            return nil
        }
    }

    func set<T: Codable>(value: T?, forKey key: String) {
        do {
            guard let value = value else {
                removeObject(forKey: key)
                return
            }
            let data = try JSONEncoder.toLocalStorage.encode(CodableWrapper(value: value))
            set(data, forKey: key)
        } catch {
            assertionFailure("Fail to store \(T.self) in keychain, reason: \(error.localizedDescription)")
        }
    }
}