Handle player ship destruction... some of it...

The player will be respawned, their lives decreased, and the board
cleared. The UI doesn't update, and the sudden snap to a freshly reset
board is quite jarring. The state transition to GameOver stops the game,
but there isn't anything else running in that state so it just looks
frozen.

Basically, there's a ton left to do, but technically I have handled
player ship destruction!

src/lib.rs

@@ -57,6 +57,7 @@ impl Plugin for AsteroidPlugin {
                 asteroids::spawn_asteroid.after(asteroids::tick_asteroid_manager),
                 asteroids::split_asteroids,
                 ship::bullet_impact_listener,
+                ship::ship_impact_listener,
                 collision_listener,
                 // TODO: Remove debug printing
                 debug_collision_event_printer,

src/ship.rs

@@ -1,6 +1,7 @@
 use crate::{
-    AngularVelocity, GameAssets,
+    AngularVelocity, GameAssets, GameState, Lives,
-    event::BulletDestroy,
+    asteroids::Asteroid,
+    event::{BulletDestroy, ShipDestroy},
     physics::{Velocity, Wrapping},
 };
 
@@ -44,3 +45,38 @@ pub fn bullet_impact_listener(mut commands: Commands, mut events: EventReader<Bu
         commands.entity(event.0).despawn();
     }
 }
+
+/// Watch for [`ShipDestroy`] events and update game state accordingly.
+///
+/// - Subtract a life
+/// - Check life count. If 0, go to game-over state
+/// - Clear all asteroids
+/// - Respawn player
+pub fn ship_impact_listener(
+    mut events: EventReader<ShipDestroy>,
+    mut commands: Commands,
+    mut lives: ResMut<Lives>,
+    rocks: Query<Entity, With<Asteroid>>,
+    mut player: Single<(&mut Transform, &mut Velocity), With<Ship>>,
+    mut next_state: ResMut<NextState<GameState>>,
+) {
+    for _ in events.read() {
+        // STEP 1: Decrement lives (and maybe go to game over)
+        if lives.0 == 0 {
+            // If already at 0, game is over.
+            next_state.set(GameState::GameOver);
+        } else {
+            // Decrease life count.
+            lives.0 -= 1;
+        }
+
+        // STEP 2: Clear asteroids
+        for rock in rocks {
+            commands.entity(rock).despawn();
+        }
+
+        // STEP 3: Respawn player (teleport them to the origin)
+        player.0.translation = Vec3::ZERO;
+        player.1.0 = Vec2::ZERO;
+    }
+}