feat(tamer): limit custody to one mob

src/main/java/games/dmg/spigottyrant/CapturedMobCustodyRelease.java

@@ -2,7 +2,8 @@ package games.dmg.spigottyrant;
 
 import org.bukkit.entity.Player;
 
-@FunctionalInterface
 public interface CapturedMobCustodyRelease {
     PlayerState releaseAll(Player player, PlayerState state);
+
+    PlayerState releaseExcess(Player player, PlayerState state, int custodyLimit);
 }

src/main/java/games/dmg/spigottyrant/CapturedMobService.java

@@ -16,6 +16,11 @@ public final class CapturedMobService {
         if (player.tyrantClass() != TyrantClass.TAMER) {
             throw new IllegalStateException("only a Tamer can capture mobs");
         }
+        if (!player.capturedMobs().isEmpty()) {
+            throw new IllegalStateException(
+                "release the currently captured mob before capturing another"
+            );
+        }
         if ("ENDER_DRAGON".equalsIgnoreCase(entityType)) {
             throw new IllegalArgumentException("Ender Dragons cannot be captured");
         }

src/main/java/games/dmg/spigottyrant/DefaultCapturedMobCustodyRelease.java

@@ -13,13 +13,27 @@ public final class DefaultCapturedMobCustodyRelease implements CapturedMobCustod
 
     @Override
     public PlayerState releaseAll(Player player, PlayerState state) {
+        return releaseExcess(player, state, 0);
+    }
+
+    @Override
+    public PlayerState releaseExcess(
+        Player player,
+        PlayerState state,
+        int custodyLimit
+    ) {
+        if (custodyLimit < 0) {
+            throw new IllegalArgumentException("custodyLimit must not be negative");
+        }
         List<CapturedMob> retained = new ArrayList<>();
-        for (CapturedMob mob : state.capturedMobs()) {
-            if (!spawner.spawn(player, mob)) {
+        List<CapturedMob> custody = state.capturedMobs();
+        for (int index = 0; index < custody.size(); index++) {
+            CapturedMob mob = custody.get(index);
+            if (index < custodyLimit || !spawner.spawn(player, mob)) {
                 retained.add(mob);
             }
         }
-        if (retained.size() == state.capturedMobs().size()) {
+        if (retained.equals(custody)) {
             return state;
         }
         return new PlayerState(

src/main/java/games/dmg/spigottyrant/FormerTamerReleaseTask.java

@@ -37,14 +37,18 @@ public final class FormerTamerReleaseTask implements Runnable {
         Map<UUID, Player> online = server.getOnlinePlayers().stream()
             .collect(Collectors.toMap(Player::getUniqueId, player -> player));
         for (PlayerState state : stateManager.players().values()) {
-            if (state.tyrantClass() == TyrantClass.TAMER || state.capturedMobs().isEmpty()) {
+            if (state.capturedMobs().isEmpty()
+                    || state.tyrantClass() == TyrantClass.TAMER
+                        && state.capturedMobs().size() == 1) {
                 continue;
             }
             Player player = online.get(state.playerId());
             if (player == null || player.isDead()) {
                 continue;
             }
-            PlayerState released = release.releaseAll(player, state);
+            PlayerState released = state.tyrantClass() == TyrantClass.TAMER
+                ? release.releaseExcess(player, state, 1)
+                : release.releaseAll(player, state);
             if (released.equals(state)) {
                 continue;
             }

src/main/java/games/dmg/spigottyrant/TamerListener.java

@@ -63,6 +63,11 @@ public final class TamerListener implements Listener {
             return;
         }
         PlayerState state = stateManager.player(player.getUniqueId(), player.getName());
+        if (!state.capturedMobs().isEmpty()) {
+            player.sendMessage(ChatColor.RED
+                + "Release the currently captured mob before capturing another.");
+            return;
+        }
         Entity target = event.getRightClicked();
         if (!canCapture(state, target)) {
             player.sendMessage(ChatColor.RED + "That mob cannot be captured.");