protocol StorageItem: AnyObject {

    associatedtype Data: Equatable

    var savedData: Data? { get set }

    var data: Data { get }

    func saveToDisk(_ data: Data) -> Bool
}

extension StorageItem {

    /**
     Get the data to save, if the object has changed
     */
    func dataToSave() -> Data? {
        guard let savedData else {
            return data
        }
        if savedData != data {
            return data
        }
        return nil
    }

    func saveIfNeeded() -> Bool? {
        guard let data = dataToSave() else {
            return nil
        }
        guard saveToDisk(data) else {
            return false
        }
        savedData = data
        return true
    }
}