use bevy::prelude::*;
use bevy_mod_picking::prelude::*;

fn main() {
	App::new()
		.add_plugins((
			DefaultPlugins,
			DefaultPickingPlugins,
		))
		.add_systems(Startup, init_ui)
		.run();
}

fn init_ui(
	mut commands: Commands,
) {
	commands.spawn(Camera3dBundle { ..default() });

	commands.spawn((
		NodeBundle {
			style: Style {
				width: Val::Px(100.0),
				height: Val::Px(100.0),
				top: Val::Px(0.0),
				left: Val::Px(0.0),
				position_type: PositionType::Absolute,
				..default()
			},
			background_color: Color::WHITE.into(),
			..default()
		},
		PickableBundle::default(),
		On::<Pointer<Drag>>::target_component_mut::<Style>(|drag, style| {
			match style.left {
				Val::Px(curr) => style.left = Val::Px(curr + drag.delta.x),
				_ => panic!("Drag UI only applies to Val::Px"),
			}
			match style.top {
				Val::Px(curr) => style.top = Val::Px(curr + drag.delta.y),
				_ => panic!("Drag UI only applies to Val::Px"),
			}
		}),
	));
}