fix todo: decouple spawning from eating

Signed-off-by: Agustín Ramiro Díaz <agustin.ramiro.diaz@gmail.com>

src/apple.rs

@@ -8,20 +8,22 @@ use super::{
     coordinate::Coordinate,
     game_state::AppState,
     schedule::InGameSet,
-    snake::{Depth, MyColor, Snake, SnakeSegment},
+    snake::{Depth, Snake},
     HALF_LEN,
 };
 
 pub(crate) struct ApplePlugin;
 
 impl Plugin for ApplePlugin {
     fn build(&self, app: &mut App) {
-        app.add_systems(Startup, setup).add_systems(
-            Update,
-            eat_apple
-                .in_set(InGameSet::SpawnDespawnEntities)
-                .run_if(in_state(AppState::InGame)),
-        );
+        app.add_event::<AppleEaten>()
+            .add_systems(Startup, setup)
+            .add_systems(
+                Update,
+                eat_apple
+                    .in_set(InGameSet::SpawnDespawnEntities)
+                    .run_if(in_state(AppState::InGame)),
+            );
     }
 }
 
@@ -48,31 +50,29 @@ fn spawn_apple(commands: &mut Commands, assets: &Res<SceneAssets>) {
 #[derive(Component)]
 pub(crate) struct Apple;
 
+#[derive(Event)]
+pub(crate) struct AppleEaten(pub(crate) Entity);
+
 // TODO: decouple this logic into smaller units
-// TODO: decouple spawning from eating
 fn eat_apple(
     mut commands: Commands,
-    mut snakes: Query<(&mut Snake, &MyColor)>,
+    mut snakes: Query<(Entity, &mut Snake)>,
     coordinates: Query<&Coordinate>,
     apples: Query<(Entity, &Coordinate), With<Apple>>,
     assets: Res<SceneAssets>,
+    mut apple_eaten: EventWriter<AppleEaten>,
 ) {
     let get_head = |snake: &Snake| {
         let &head = snake.segments.front()?;
         coordinates.get(head).ok()
     };
 
-    for (mut snake, &color) in snakes.iter_mut() {
+    for (entity, snake) in snakes.iter_mut() {
         for (apple, coord) in apples.iter() {
-            if coord == get_head(&snake).unwrap() {
+            if Some(coord) == get_head(&snake) {
                 commands.entity(apple).despawn();
                 spawn_apple(&mut commands, &assets);
-
-                let tail = commands
-                    .spawn((color, SnakeSegment, snake.trail.clone(), Tile))
-                    .id();
-
-                snake.segments.push_back(tail);
+                apple_eaten.send(AppleEaten(entity));
                 return;
             }
         }

src/snake.rs

@@ -3,7 +3,7 @@ use std::collections::VecDeque;
 use bevy::prelude::*;
 
 use crate::{
-    coordinate::Coordinate, direction::Direction, game_state::AppState,
+    apple::AppleEaten, coordinate::Coordinate, direction::Direction, game_state::AppState,
     main_menu::NumberOfPlayersSelected, schedule::InGameSet, BOARD_VIEWPORT_IN_WORLD_UNITS,
     HALF_LEN, SIZE,
 };
@@ -18,10 +18,11 @@ impl Plugin for SnakePlugin {
             .add_systems(
                 Update,
                 (
+                    grow_snake,
+                    apply_deferred,
                     toroid_coordinates,
                     add_sprite_bundles,
-                    // This is needed in order to render the sprites correctly, we need to flush the sprites into the world and then update their transforms
-                    apply_deferred,
+                    apply_deferred, // This is needed in order to render the sprites correctly, we need to flush the sprites into the world and then update their transforms
                     set_sprite_size,
                     update_local_coordinates_to_world_transforms,
                 )
@@ -158,6 +159,22 @@ pub(crate) struct Id(pub(crate) u8);
 #[derive(Component)]
 pub(crate) struct SnakeSegment;
 
+fn grow_snake(
+    mut commands: Commands,
+    mut query: Query<(&mut Snake, &MyColor)>,
+    mut apple_eaten: EventReader<AppleEaten>,
+) {
+    for AppleEaten(entity) in apple_eaten.read() {
+        if let Ok((mut snake, &color)) = query.get_mut(*entity) {
+            let tail = commands
+                .spawn((color, SnakeSegment, snake.trail.clone(), Tile))
+                .id();
+
+            snake.segments.push_back(tail);
+        }
+    }
+}
+
 fn toroid_coordinates(
     mut query: Query<&mut Coordinate, (With<SnakeSegment>, Changed<Coordinate>)>,
 ) {
@@ -198,7 +215,6 @@ fn add_sprite_bundles(
     for (entity, color) in query.iter() {
         commands.entity(entity).insert(SpriteBundle {
             sprite: Sprite {
-                // custom_size: Some(Vec2 { x: SIZE, y: SIZE }),
                 color: color.0,
                 ..Default::default()
             },