Property wrapper for firebase remote config

RemoteConfigPropertyWrapper.swift

//
//  FCRemoteConfig.swift
//  Brut
//
//  Created by Hugo Saynac on 25/11/2020.
//
import FirebaseRemoteConfig

private let remoteConfigDecoder = JSONDecoder()
@propertyWrapper struct FCRemoteConfig<Value: Decodable> {
    let key: String
    let defaultValue: Value

    var wrappedValue: Value {
        get {
            do {
                let data = RemoteConfig.remoteConfig()
                    .configValue(forKey: key).dataValue
                return try remoteConfigDecoder.decode(Value.self, from: data)
            } catch {
                Log(.firebase, .error, "Error fetching remote config\n\(error)")
                return defaultValue
            }
        }
        set {
            fatalError("Cannot set a remote config value")
        }
    }
}

protocol FeatureFlag {
    static var `default`: Self { get }
    static var key: String { get }
}

extension FCRemoteConfig where Value: FeatureFlag {
    init() {
        self.key = Value.key
        self.defaultValue = Value.default
    }
}