Support "Mutations"

[nicoburniske]

Add custom mutation helpers compatible with Server actions. Rough draft below

pub fn create_server_action_with_callbacks<S>(
    on_invoke: impl Fn(&S) + 'static,
    on_settled: impl Fn((S, &Result<S::Output, ServerFnError<S::Error>>)) + 'static,
) -> Action<S, Result<S::Output, ServerFnError<S::Error>>>
where
    S: Clone + server_fn::ServerFn,
    S::Error: Clone,
{
    let on_invoke = Rc::new(on_invoke);
    let on_settled = Rc::new(on_settled);

    // The server is able to call the function directly
    #[cfg(feature = "ssr")]
    let action_function = move |args: &S| {
        let args = args.clone();
        let on_invoke = on_invoke.clone();
        let on_settled = on_settled.clone();

        async move {
            on_invoke(&args);
            let result = S::run_body(args.clone()).await;
            on_settled((args, &result));
            result
        }
    };

    // When not on the server send a fetch to request the fn call.
    #[cfg(not(feature = "ssr"))]
    let action_function = move |args: &S| {
        let args = args.clone();
        let on_invoke = on_invoke.clone();
        let on_settled = on_settled.clone();

        async move {
            on_invoke(&args);
            let result = S::run_on_client(args.clone()).await;
            on_settled((args, &result));
            result
        }
    };

    // create the action
    Action::new(action_function).using_server_fn()
}

pub fn create_server_multi_action_with_callbacks<S>(
    on_invoke: impl Fn(&S) + 'static,
    on_settled: impl Fn((S, &Result<S::Output, ServerFnError<S::Error>>)) + 'static,
) -> MultiAction<S, Result<S::Output, ServerFnError<S::Error>>>
where
    S: Clone + server_fn::ServerFn,
{
    let on_invoke = Rc::new(on_invoke);
    let on_settled = Rc::new(on_settled);
    #[cfg(feature = "ssr")]
    let c = move |args: &S| {
        let args = args.clone();
        let on_invoke = on_invoke.clone();
        let on_settled = on_settled.clone();
        async move {
            on_invoke(&args);
            let result = S::run_body(args.clone()).await;
            on_settled((args, &result));
            result
        }
    };
    #[cfg(not(feature = "ssr"))]
    let c = move |args: &S| {
        let args = args.clone();
        let on_invoke = on_invoke.clone();
        let on_settled = on_settled.clone();
        async move {
            on_invoke(&args);
            let result = S::run_on_client(args.clone()).await;
            on_settled((args, &result));
            result
        }
    };

    create_multi_action(c).using_server_fn::<S>()
}