fix(spectator): rebuild the overview instead of showing an empty grid

game/src/main/java/net/onelitefeather/cygnus/spectator/SpectatorInventory.java

@@ -23,6 +23,13 @@
 import java.util.function.BiConsumer;
 import java.util.function.Consumer;
 
+/**
+ * The overview a spectator uses to jump to a player who is still in the round.
+ *
+ * @author theEvilReaper
+ * @version 1.1.0
+ * @since 2.7.0
+ */
 public class SpectatorInventory extends GlobalInventoryBuilder {
 
     private static final ItemStack DECORATION_PANE = ItemStack.builder(Material.BLACK_STAINED_GLASS_PANE)
@@ -114,10 +121,29 @@ void handleClick(Player player, int slot, Click click, ItemStack stack, Consumer
 
     /**
      * Opens the inventory for a specific {@link Player}.
+     * <p>
+     * Refreshes first, so the spectator always sees the survivors that are alive right now.
      *
      * @param player who should get it
      */
     public void open(Player player) {
+        this.refresh();
         player.openInventory(getInventory());
     }
+
+    /**
+     * Marks both layouts as stale so the next inventory update rebuilds the head list from the survivor team.
+     * <p>
+     * Invalidating the data layout alone is not enough for two reasons. The inventory is built once, at
+     * server start, when the survivor team is still empty, and {@code invalidateDataLayout} only clears the
+     * valid flag while nobody is looking at the inventory - the following {@code getInventory} then skips the
+     * rebuild, because it only retrieves a data layout while it is applying the design layout as well. The
+     * head list therefore stayed at the empty one from server start for the whole round. Invalidating the
+     * design layout too is also what clears the inventory: a data layout can only write items, so the head of
+     * a player who left the round would otherwise stay in place.
+     */
+    public void refresh() {
+        this.invalidateLayout();
+        this.invalidateDataLayout();
+    }
 }

game/src/main/java/net/onelitefeather/cygnus/spectator/SpectatorService.java

@@ -24,7 +24,7 @@
  * the spectate-overview GUI, and leaving spectator mode.
  *
  * @author theEvilReaper
- * @version 1.0.0
+ * @version 1.1.0
  * @since 2.7.0
  */
 public final class SpectatorService {
@@ -110,9 +110,9 @@ public boolean isSpectator(Player player) {
     }
 
     /**
-     * Invalidates the spectator inventory's data layout.
+     * Rebuilds the spectator inventory so its head list matches the players still in the round.
      */
     public void updateInventory() {
-        this.spectatorInventory.invalidateDataLayout();
+        this.spectatorInventory.refresh();
     }
 }

game/src/test/java/net/onelitefeather/cygnus/spectator/SpectatorInventoryTest.java

@@ -98,4 +98,50 @@ void testOpenPopulatesPlayerHeadsEvenWhenSkinIsNull(@NotNull Env env) {
 
         env.destroyInstance(instance, true);
     }
+
+    @Test
+    void testOpenPicksUpSurvivorsThatJoinedAfterTheInventoryWasBuilt(@NotNull Env env) {
+        Instance instance = env.createFlatInstance();
+        Player spectator = env.createPlayer(instance);
+        Team survivorTeam = Team.of(GameConfig.SURVIVOR_KEY, 5);
+
+        // The production instance is built at server start, when nobody is on the survivor team yet.
+        SpectatorInventory inventory = new SpectatorInventory(survivorTeam, (_, _) -> {});
+        env.tick();
+
+        Player survivor = env.createPlayer(instance);
+        survivorTeam.addPlayer(survivor);
+
+        inventory.open(spectator);
+        env.tick();
+
+        ItemStack item = inventory.getInventory().getItemStack(9);
+        assertEquals(Material.PLAYER_HEAD, item.material());
+        assertEquals(survivor.getUuid(), item.getTag(SpectatorInventory.TARGET_TAG));
+
+        env.destroyInstance(instance, true);
+    }
+
+    @Test
+    void testOpenDropsHeadsOfPlayersThatLeftTheSurvivorTeam(@NotNull Env env) {
+        Instance instance = env.createFlatInstance();
+        Player spectator = env.createPlayer(instance);
+        Player survivor = env.createPlayer(instance);
+        Team survivorTeam = Team.of(GameConfig.SURVIVOR_KEY, 5);
+        survivorTeam.addPlayer(survivor);
+
+        SpectatorInventory inventory = new SpectatorInventory(survivorTeam, (_, _) -> {});
+        inventory.open(spectator);
+        env.tick();
+        assertEquals(Material.PLAYER_HEAD, inventory.getInventory().getItemStack(9).material());
+
+        survivorTeam.removePlayer(survivor);
+
+        inventory.open(spectator);
+        env.tick();
+
+        assertTrue(inventory.getInventory().getItemStack(9).isAir(), "a player who left the round must not stay listed");
+
+        env.destroyInstance(instance, true);
+    }
 }