FirstLaunch.swift

public final class FirstLaunchHelper {
    
    let wasLaunchedBefore: Bool
    var isFirstLaunch: Bool {
        return !wasLaunchedBefore
    }
    
    init(getWasLaunchedBefore: () -> Bool,
         setWasLaunchedBefore: (Bool) -> ()) {
        let wasLaunchedBefore = getWasLaunchedBefore()
        self.wasLaunchedBefore = wasLaunchedBefore
        if !wasLaunchedBefore {
            setWasLaunchedBefore(true)
        }
    }
    
    convenience init(userDefaults: UserDefaults, key: String) {
        self.init(getWasLaunchedBefore: { userDefaults.bool(forKey: key) },
                  setWasLaunchedBefore: { userDefaults.set($0, forKey: key) })
    }
}

extension FirstLaunchHelper {
    
    static func alwaysFirst() -> FirstLaunchHelper {
        return FirstLaunchHelper(getWasLaunchedBefore: { return false }, setWasLaunchedBefore: { _ in })
    }
}