//! This example illustrates scrolling in Bevy UI.

use games::*;

fn main() {
    let mut app = App::new();
    app.add_plugins(BaseGamePlugin::default())
        .add_systems(Startup, setup);
    app.run();
}

const LINE_HEIGHT: f32 = 21.;

fn setup(mut commands: Commands) {
    // Scrolling list
    commands
        .spawn((
            Node {
                flex_direction: FlexDirection::Column,
                // If height is not set, we need both align_self: Stetch and overflow: scroll()
                height: Val::Percent(50.0),
                // align_self: AlignSelf::Stretch,
                overflow: Overflow::scroll(),
                ..default()
            },
            BackgroundColor(Color::srgb(0.10, 0.10, 0.10)),
        ))
        .with_children(|parent| {
            // List items
            (0..250).for_each(|i| {
                parent.spawn(Text(format!("Item {i}")));
            });
        })
        .observe(scroll);
}

/// Updates the scroll position of scrollable nodes in response to mouse input
pub fn scroll(
    trigger: Trigger<Pointer<Scroll>>,
    mut scrollers: Query<&mut ScrollPosition>,
) {
    let Pointer { event: Scroll { unit, x, y, .. }, .. } = trigger.event();

    let (dx, dy) = match unit {
        MouseScrollUnit::Line => (x * LINE_HEIGHT, y * LINE_HEIGHT),
        MouseScrollUnit::Pixel => (x * 1., y * 1.),
    };

    if let Ok(mut pos) = scrollers.get_mut(trigger.target()) {
        pos.offset_x -= dx;
        pos.offset_y -= dy;
    }
}