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use super::{Prefab, PrefabData, PrefabTag};
use amethyst_core::specs::{
    BitSet, Entities, Entity, InsertedFlag, Join, Read, ReadExpect, ReadStorage, ReaderId,
    Resources, System, Write, WriteStorage,
};
use amethyst_core::{ArcThreadPool, Parent, Time};
use std::marker::PhantomData;
use std::ops::Deref;
use {AssetStorage, Completion, Handle, HotReloadStrategy, ProcessingState, ResultExt};

/// System that load `Prefab`s for `PrefabData` `T`.
///
/// ### Type parameters:
///
/// - `T`: `PrefabData`
pub struct PrefabLoaderSystem<T> {
    _m: PhantomData<T>,
    entities: Vec<Entity>,
    finished: Vec<Entity>,
    to_process: BitSet,
    insert_reader: Option<ReaderId<InsertedFlag>>,
    next_tag: u64,
}

impl<T> Default for PrefabLoaderSystem<T> {
    fn default() -> Self {
        PrefabLoaderSystem {
            _m: PhantomData,
            entities: Vec::default(),
            finished: Vec::default(),
            to_process: BitSet::default(),
            insert_reader: None,
            next_tag: 0,
        }
    }
}

impl<'a, T> System<'a> for PrefabLoaderSystem<T>
where
    T: PrefabData<'a> + Send + Sync + 'static,
{
    type SystemData = (
        Entities<'a>,
        Write<'a, AssetStorage<Prefab<T>>>,
        ReadStorage<'a, Handle<Prefab<T>>>,
        Read<'a, Time>,
        ReadExpect<'a, ArcThreadPool>,
        Option<Read<'a, HotReloadStrategy>>,
        WriteStorage<'a, Parent>,
        WriteStorage<'a, PrefabTag<T>>,
        T::SystemData,
    );

    fn run(&mut self, data: Self::SystemData) {
        let (
            entities,
            mut prefab_storage,
            prefab_handles,
            time,
            pool,
            strategy,
            mut parents,
            mut tags,
            mut prefab_system_data,
        ) = data;
        let strategy = strategy.as_ref().map(Deref::deref);
        prefab_storage.process(
            |mut d| {
                d.tag = Some(self.next_tag);
                self.next_tag += 1;
                if !d.loading() {
                    if !d
                        .load_sub_assets(&mut prefab_system_data)
                        .chain_err(|| "Failed starting sub asset loading")?
                    {
                        return Ok(ProcessingState::Loaded(d));
                    }
                }
                match d.progress().complete() {
                    Completion::Complete => Ok(ProcessingState::Loaded(d)),
                    Completion::Failed => {
                        error!("Failed loading sub asset: {:?}", d.progress().errors());
                        Err("Failed loading sub asset")?
                    }
                    Completion::Loading => Ok(ProcessingState::Loading(d)),
                }
            },
            time.frame_number(),
            &**pool,
            strategy,
        );
        prefab_handles
            .populate_inserted(self.insert_reader.as_mut().unwrap(), &mut self.to_process);
        self.finished.clear();
        for (root_entity, handle, _) in (&*entities, &prefab_handles, &self.to_process).join() {
            if let Some(prefab) = prefab_storage.get(handle) {
                self.finished.push(root_entity);
                // create entities
                self.entities.clear();
                self.entities.push(root_entity);
                for entity_data in prefab.entities.iter().skip(1) {
                    let new_entity = entities.create();
                    self.entities.push(new_entity);
                    if let Some(parent) = entity_data.parent {
                        parents
                            .insert(
                                new_entity,
                                Parent {
                                    entity: self.entities[parent],
                                },
                            ).unwrap();
                    }
                    tags.insert(new_entity, PrefabTag::new(prefab.tag.unwrap()))
                        .unwrap();
                }
                // create components
                for (index, entity_data) in prefab.entities.iter().enumerate() {
                    if let Some(ref prefab_data) = &entity_data.data {
                        prefab_data
                            .add_to_entity(
                                self.entities[index],
                                &mut prefab_system_data,
                                &self.entities,
                            ).unwrap();
                    }
                }
            }
        }

        for entity in &self.finished {
            self.to_process.remove(entity.id());
        }
    }

    fn setup(&mut self, res: &mut Resources) {
        use amethyst_core::specs::prelude::SystemData;
        Self::SystemData::setup(res);
        self.insert_reader = Some(WriteStorage::<Handle<Prefab<T>>>::fetch(&res).track_inserted());
    }
}