4 files changed, 142 insertions, 0 deletions
diff --git a/src/preload/events.rs b/src/preload/events.rs
new file mode 100644
index 0000000..7167d73
--- /dev/null
+++ b/src/preload/events.rs
@@ -0,0 +1,12 @@
+use bevy::prelude::*;
+
+/// Event used to trigger preload callbacks after the asset file has been pre-processed to extract
+/// the payload
+#[derive(Debug, Event, Clone)]
+pub struct DirworldPreload {
+    /// Entity with the `[DirworldEntity]` component corresponding to the entity being preloaded
+    pub entity: Entity,
+    /// The data portion of the file after being pre-processed
+    pub data: Option<Vec<u8>>,
+}
+
diff --git a/src/preload/mod.rs b/src/preload/mod.rs
new file mode 100644
index 0000000..b90db38
--- /dev/null
+++ b/src/preload/mod.rs
@@ -0,0 +1,82 @@
+use crate::cache::DirworldCache;
+use crate::{
+    components::DirworldEntity,
+    resources::{DirworldCodecs, DirworldObservers, EntryType},
+    utils::extract_entity_payload,
+    Extensions,
+};
+use bevy::prelude::*;
+use std::{collections::HashMap, path::PathBuf};
+
+mod systems;
+
+mod resources;
+pub use resources::*;
+
+mod events;
+pub use events::DirworldPreload;
+
+pub(crate) struct DirworldPreloadPlugin;
+
+impl Plugin for DirworldPreloadPlugin {
+    fn build(&self, app: &mut App) {
+        app.add_systems(
+            PostUpdate,
+            systems::handle_preload.run_if(in_state(PreloadState::Loading)),
+        )
+        .add_systems(OnEnter(PreloadState::Done), systems::handle_spawn)
+        .init_resource::<RoomAssets>()
+        .init_state::<PreloadState>();
+    }
+}
+
+/// State of asset preloading
+#[derive(States, Debug, Clone, PartialEq, Eq, Hash, Default)]
+pub enum PreloadState {
+    /// Indicates assets are in the process of loading
+    #[default]
+    Loading,
+    /// Indicates all room assets are finished loading, i.e. all assets are loaded with
+    /// dependencies
+    Done,
+}
+
+/// Initiates loading of an asset
+// TODO: Make into a command extension
+pub fn load_entity(
+    entry: &PathBuf,
+    cache: &mut DirworldCache,
+    codecs: &DirworldCodecs,
+    observers: &DirworldObservers,
+    commands: &mut Commands,
+    preload_state: &mut NextState<PreloadState>,
+    room_assets: &mut RoomAssets,
+) {
+    let (mut payload, data) = extract_entity_payload(&entry, &codecs);
+    payload = payload.map(|p| cache.get_entity_cache(&entry).unwrap_or(p));
+    let entry_type = if entry.is_dir() {
+        EntryType::Folder
+    } else {
+        EntryType::File(entry.extensions())
+    };
+    let transform = payload
+        .as_ref()
+        .map(|payload| payload.transform.clone())
+        .unwrap_or_default();
+    let entity = commands
+        .spawn((
+            *transform,
+            Visibility::Inherited,
+            DirworldEntity {
+                path: entry.clone(),
+                payload,
+            },
+        ))
+        .id();
+    if let Some(observer) = observers.get(&entry_type) {
+        preload_state.set(PreloadState::Loading);
+        room_assets.insert(entry.clone(), HashMap::default());
+        commands.trigger_targets(DirworldPreload { entity, data }, observer.clone());
+        info!("Triggered preload for {entry:?}");
+    }
+}
diff --git a/src/preload/resources.rs b/src/preload/resources.rs
new file mode 100644
index 0000000..4060c10
--- /dev/null
+++ b/src/preload/resources.rs
@@ -0,0 +1,7 @@
+use std::{collections::HashMap, path::PathBuf};
+
+use bevy::prelude::*;
+
+/// A map of asset handles required by each entry in a room, indexed by their paths
+#[derive(Resource, Default, Debug, Deref, DerefMut)]
+pub struct RoomAssets(pub HashMap<PathBuf, HashMap<String, UntypedHandle>>);
diff --git a/src/preload/systems.rs b/src/preload/systems.rs
new file mode 100644
index 0000000..ec867ae
--- /dev/null
+++ b/src/preload/systems.rs
@@ -0,0 +1,41 @@
+use bevy::prelude::*;
+
+use crate::{components::DirworldEntity, events::DirworldSpawn, resources::{DirworldObservers, EntryType}, Extensions};
+
+use super::{PreloadState, RoomAssets};
+
+pub fn handle_preload(
+    asset_server: Res<AssetServer>,
+    room_assets: Res<RoomAssets>,
+    mut next_state: ResMut<NextState<PreloadState>>,
+) {
+    if room_assets.is_empty()
+        || room_assets
+            .values()
+            .flat_map(|v| v.values())
+            .all(|a| asset_server.is_loaded_with_dependencies(a))
+    {
+        info!("Preload Done.");
+        next_state.set(PreloadState::Done);
+    }
+}
+
+pub fn handle_spawn(
+    dirworld_entity_query: Query<(Entity, &DirworldEntity)>,
+    mut commands: Commands,
+    observers: Res<DirworldObservers>,
+) {
+    info!("Spawning");
+    for (entity, DirworldEntity { path, .. }) in dirworld_entity_query.iter() {
+        let entry_type = if path.is_dir() {
+            EntryType::Folder
+        } else {
+            EntryType::File(path.extensions())
+        };
+        if let Some(observer) = observers.get(&entry_type) {
+            info!("Found observer {observer:?} for {entry_type:?}");
+            commands.trigger_targets(DirworldSpawn(entity), observer.clone());
+        }
+    }
+}
+