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use std::marker::PhantomData;

use shred::SetupHandler;
use specs::{Resources, SystemData, Tracked, WriteStorage};

use super::{Parent, SceneGraph};

#[derive(Debug, Default)]
pub struct SceneGraphSetupHandler<P>(PhantomData<P>);

impl<P> SetupHandler<SceneGraph<P>> for SceneGraphSetupHandler<P>
where
    P: Parent,
    P::Storage: Default + Tracked,
{
    #[inline]
    fn setup(res: &mut Resources) {
        if !res.has_value::<SceneGraph<P>>() {
            let scene_graph = {
                let mut storage: WriteStorage<P> = SystemData::fetch(&res);
                SceneGraph::<P>::new(storage.register_reader())
            };

            res.insert(scene_graph);
        }
    }
}