use bevy::prelude::*;

#[derive(Clone)]
pub enum AppState {
    Loading,
}

fn main() {
    App::build()
        .add_plugins(DefaultPlugins)
        .add_resource(State::new(AppState::Loading))
        // uncomment the next line and 'enter_system' is not called
        // .add_stage_before(stage::UPDATE, "STAGE_1", StateStage::<AppState>::default())
        .add_stage_after(stage::UPDATE, "STAGE_2", StateStage::<AppState>::default()
            .with_enter_stage(
                AppState::Loading,
                SystemStage::parallel()
                    .with_system(enter_system.system()),
            )
            .with_update_stage(
                AppState::Loading,
                SystemStage::parallel()
                    .with_system(update_system.system()),
            ))
        .run();
}

pub fn enter_system() {
    println!("enter_system");
}

pub fn update_system() {
    println!("update_system");
}