MainBackgroundMainUtility.swift

func onMainDo<T>(_ firstMainBlock: @escaping () -> Void, onBackgroundDo backgroundBlock: @escaping () -> T, thenOnMainDo mainBlock: @escaping (T) -> Void) {
    DispatchQueue.main.async {
        firstMainBlock()
        DispatchQueue.global(qos: .background).async {
            let result = backgroundBlock()
            DispatchQueue.main.async {
                mainBlock(result)
            }
        }
    }
}