Add support for boss health bars.

Three different types of health bars are implemented behind a basic Strategy Pattern. A new per-arena setting, boss-health-bar, can be used to configure which one of the three types (if any) of health bar should be used for bosses in the given arena:

- `boss-bar` creates a boss bar at the top of the screen as if the players were fighting an ender dragon or a wither.
- `title` uses the Chapters/Titles API in Bukkit to display the health of the boss as a "subtitle" whenever it takes damage.
- `name` sets the entitiy's health along with an optional custom name above the entity's head.

src/main/java/com/garbagemule/MobArena/ArenaImpl.java

@@ -25,6 +25,7 @@ import com.garbagemule.MobArena.util.ClassChests;
 import com.garbagemule.MobArena.util.inventory.InventoryManager;
 import com.garbagemule.MobArena.util.timer.AutoStartTimer;
 import com.garbagemule.MobArena.util.timer.StartDelayTimer;
+import com.garbagemule.MobArena.waves.MABoss;
 import com.garbagemule.MobArena.waves.SheepBouncer;
 import com.garbagemule.MobArena.waves.WaveManager;
 import org.bukkit.Bukkit;
@@ -1118,6 +1119,14 @@ public class ArenaImpl implements Arena
     
     private void clearPlayer(Player p)
     {
+        // Remove from boss health bar
+        monsterManager.getBossMonsters().forEach(entity -> {
+            MABoss boss = monsterManager.getBoss(entity);
+            if (boss != null) {
+                boss.getHealthBar().removePlayer(p);
+            }
+        });
+        
         // Remove pets.
         monsterManager.removePets(p);
         

src/main/java/com/garbagemule/MobArena/ArenaListener.java

@@ -635,6 +635,7 @@ public class ArenaListener
                 event.getDrops().addAll(drops);
             }
             boss.setDead(true);
+            boss.getHealthBar().setProgress(0);
         }
 
         List<ItemStack> loot = monsters.getLoot(damagee);
@@ -685,6 +686,10 @@ public class ArenaListener
             }
         }
 
+        MABoss boss = (damagee instanceof LivingEntity)
+            ? monsters.getBoss((LivingEntity) damagee)
+            : null;
+
         // Pet wolf
         if (damagee instanceof Wolf && arena.hasPet(damagee)) {
             onPetDamage(event, (Wolf) damagee, damager);
@@ -701,6 +706,10 @@ public class ArenaListener
         else if (damagee instanceof Snowman && event.getCause() == DamageCause.MELTING) {
             event.setCancelled(true);
         }
+        // Boss monster
+        else if (boss != null) {
+            onBossDamage(event, boss, damager);
+        }
         // Regular monster
         else if (monsters.getMonsters().contains(damagee)) {
             onMonsterDamage(event, damagee, damager);
@@ -739,6 +748,16 @@ public class ArenaListener
     private void onMountDamage(EntityDamageEvent event, Horse mount, Entity damager) {
         event.setCancelled(true);
     }
+
+    private void onBossDamage(EntityDamageEvent event, MABoss boss, Entity damager) {
+        onMonsterDamage(event, boss.getEntity(), damager);
+        if (event.isCancelled()) {
+            return;
+        }
+
+        double progress = boss.getHealth() / boss.getMaxHealth();
+        boss.getHealthBar().setProgress(progress);
+    }
     
     private void onMonsterDamage(EntityDamageEvent event, Entity monster, Entity damager) {
         if (damager instanceof Player) {

src/main/java/com/garbagemule/MobArena/MASpawnThread.java

@@ -3,6 +3,8 @@ package com.garbagemule.MobArena;
 import com.garbagemule.MobArena.events.ArenaCompleteEvent;
 import com.garbagemule.MobArena.events.NewWaveEvent;
 import com.garbagemule.MobArena.framework.Arena;
+import com.garbagemule.MobArena.healthbar.CreatesHealthBar;
+import com.garbagemule.MobArena.healthbar.HealthBar;
 import com.garbagemule.MobArena.region.ArenaRegion;
 import com.garbagemule.MobArena.things.Thing;
 import com.garbagemule.MobArena.waves.MABoss;
@@ -31,6 +33,7 @@ public class MASpawnThread implements Runnable
     private RewardManager rewardManager;
     private WaveManager waveManager;
     private MonsterManager monsterManager;
+    private CreatesHealthBar createsHealthBar;
 
     private int playerCount, monsterLimit;
     private boolean waveClear, bossClear, preBossClear, wavesAsLevel;
@@ -48,6 +51,7 @@ public class MASpawnThread implements Runnable
         this.rewardManager = arena.getRewardManager();
         this.waveManager = arena.getWaveManager();
         this.monsterManager = arena.getMonsterManager();
+        this.createsHealthBar = new CreatesHealthBar(arena.getSettings().getString("boss-health-bar", "none"));
 
         reset();
     }
@@ -195,6 +199,10 @@ public class MASpawnThread implements Runnable
                         BossWave bw = (BossWave) w;
                         double maxHealth = bw.getMaxHealth(playerCount);
                         MABoss boss = monsterManager.addBoss(e, maxHealth);
+                        HealthBar healthbar = createsHealthBar.create(e, bw.getBossName());
+                        arena.getPlayersInArena().forEach(healthbar::addPlayer);
+                        healthbar.setProgress(1);
+                        boss.setHealthBar(healthbar);
                         boss.setReward(bw.getReward());
                         boss.setDrops(bw.getDrops());
                         bw.addMABoss(boss);

src/main/java/com/garbagemule/MobArena/healthbar/BossHealthBar.java

@@ -0,0 +1,49 @@
+package com.garbagemule.MobArena.healthbar;
+
+import org.bukkit.Bukkit;
+import org.bukkit.boss.BarColor;
+import org.bukkit.boss.BarFlag;
+import org.bukkit.boss.BarStyle;
+import org.bukkit.boss.BossBar;
+import org.bukkit.entity.Player;
+
+class BossHealthBar implements HealthBar {
+
+    private static final double LOW_HEALTH = 0.25;
+
+    private final BossBar bar;
+
+    BossHealthBar(String title) {
+        bar = Bukkit.createBossBar(
+            title.isEmpty() ? "Boss" : title,
+            BarColor.GREEN,
+            BarStyle.SOLID,
+            BarFlag.PLAY_BOSS_MUSIC,
+            BarFlag.DARKEN_SKY
+        );
+    }
+
+    @Override
+    public void setProgress(double progress) {
+        if (progress <= LOW_HEALTH && bar.getColor() != BarColor.RED) {
+            bar.setColor(BarColor.RED);
+        }
+        bar.setProgress(progress);
+    }
+
+    @Override
+    public void addPlayer(Player player) {
+        bar.addPlayer(player);
+    }
+
+    @Override
+    public void removePlayer(Player player) {
+        bar.removePlayer(player);
+    }
+
+    @Override
+    public void removeAll() {
+        bar.removeAll();
+    }
+
+}

src/main/java/com/garbagemule/MobArena/healthbar/CreatesHealthBar.java

@@ -0,0 +1,30 @@
+package com.garbagemule.MobArena.healthbar;
+
+import org.bukkit.entity.Entity;
+
+public class CreatesHealthBar {
+
+    private final String type;
+    private final CreatesHealthString createsHealthString;
+
+    public CreatesHealthBar(String type) {
+        this.type = type;
+        this.createsHealthString = new CreatesHealthString();
+    }
+
+    public HealthBar create(Entity entity, String title) {
+        String name = (title != null) ? title : "";
+
+        switch (type) {
+            case "boss-bar":
+                return new BossHealthBar(name);
+            case "title":
+                return new TitleHealthBar(name, createsHealthString);
+            case "name":
+                return new NameHealthBar(entity, name, createsHealthString);
+            default:
+                return new NullHealthBar();
+        }
+    }
+
+}

src/main/java/com/garbagemule/MobArena/healthbar/CreatesHealthString.java

@@ -0,0 +1,29 @@
+package com.garbagemule.MobArena.healthbar;
+
+import org.bukkit.ChatColor;
+
+import java.util.stream.Collectors;
+import java.util.stream.IntStream;
+
+class CreatesHealthString {
+
+    private static final int TOTAL_BARS = 20;
+    private static final int LOW_BARS = TOTAL_BARS / 4;
+
+    String create(double progress) {
+        int bars = (int) (progress * TOTAL_BARS);
+
+        String current = IntStream.range(0, bars)
+            .mapToObj(i -> "|")
+            .collect(Collectors.joining());
+
+        String lost = IntStream.range(bars, TOTAL_BARS)
+            .mapToObj(i -> "|")
+            .collect(Collectors.joining());
+
+        ChatColor color = (bars <= LOW_BARS) ? ChatColor.RED : ChatColor.GREEN;
+
+        return color + current + ChatColor.GRAY + lost;
+    }
+
+}

src/main/java/com/garbagemule/MobArena/healthbar/HealthBar.java

@@ -0,0 +1,15 @@
+package com.garbagemule.MobArena.healthbar;
+
+import org.bukkit.entity.Player;
+
+public interface HealthBar {
+
+    void setProgress(double progress);
+
+    void addPlayer(Player player);
+
+    void removePlayer(Player player);
+
+    void removeAll();
+
+}

src/main/java/com/garbagemule/MobArena/healthbar/NameHealthBar.java

@@ -0,0 +1,43 @@
+package com.garbagemule.MobArena.healthbar;
+
+import org.bukkit.entity.Entity;
+import org.bukkit.entity.Player;
+
+class NameHealthBar implements HealthBar {
+
+    private final Entity entity;
+    private final String title;
+    private final CreatesHealthString createsHealthString;
+
+    NameHealthBar(Entity entity, String title, CreatesHealthString createsHealthString) {
+        this.entity = entity;
+        this.title = title;
+        this.createsHealthString = createsHealthString;
+
+        entity.setCustomNameVisible(true);
+    }
+
+    @Override
+    public void setProgress(double progress) {
+        String health = createsHealthString.create(progress);
+        String name = title.isEmpty() ? health : title + " " + health;
+
+        entity.setCustomName(name);
+    }
+
+    @Override
+    public void addPlayer(Player player) {
+        // OK BOSS
+    }
+
+    @Override
+    public void removePlayer(Player player) {
+        // OK BOSS
+    }
+
+    @Override
+    public void removeAll() {
+        // OK BOSS
+    }
+
+}

src/main/java/com/garbagemule/MobArena/healthbar/NullHealthBar.java

@@ -0,0 +1,27 @@
+package com.garbagemule.MobArena.healthbar;
+
+import org.bukkit.entity.Player;
+
+class NullHealthBar implements HealthBar {
+
+    @Override
+    public void setProgress(double progress) {
+        // OK BOSS
+    }
+
+    @Override
+    public void addPlayer(Player player) {
+        // OK BOSS
+    }
+
+    @Override
+    public void removePlayer(Player player) {
+        // OK BOSS
+    }
+
+    @Override
+    public void removeAll() {
+        // OK BOSS
+    }
+
+}

src/main/java/com/garbagemule/MobArena/healthbar/TitleHealthBar.java

@@ -0,0 +1,53 @@
+package com.garbagemule.MobArena.healthbar;
+
+import org.bukkit.entity.Player;
+
+import java.util.HashSet;
+import java.util.Set;
+
+class TitleHealthBar implements HealthBar {
+
+    private static final int FADE_IN_TICKS = 5;
+    private static final int STAY_TICKS = 40;
+    private static final int FADE_OUT_TICKS = 10;
+
+    private final String title;
+    private final CreatesHealthString createsHealthString;
+    private final Set<Player> players;
+
+    TitleHealthBar(String title, CreatesHealthString createsHealthString) {
+        this.title = title;
+        this.createsHealthString = createsHealthString;
+        this.players = new HashSet<>();
+    }
+
+    @Override
+    public void setProgress(double progress) {
+        String health = createsHealthString.create(progress);
+        String message = title.isEmpty() ? health : title + " " + health;
+
+        players.forEach(player -> player.sendTitle(
+            "",
+            message,
+            FADE_IN_TICKS,
+            STAY_TICKS,
+            FADE_OUT_TICKS
+        ));
+    }
+
+    @Override
+    public void addPlayer(Player player) {
+        players.add(player);
+    }
+
+    @Override
+    public void removePlayer(Player player) {
+        players.remove(player);
+    }
+
+    @Override
+    public void removeAll() {
+        players.clear();
+    }
+
+}

src/main/java/com/garbagemule/MobArena/waves/MABoss.java

@@ -1,5 +1,6 @@
 package com.garbagemule.MobArena.waves;
 
+import com.garbagemule.MobArena.healthbar.HealthBar;
 import com.garbagemule.MobArena.things.Thing;
 import org.bukkit.Bukkit;
 import org.bukkit.entity.LivingEntity;
@@ -13,6 +14,7 @@ public class MABoss
     private boolean dead;
     private Thing reward;
     private List<ItemStack> drops;
+    private HealthBar healthbar;
     
     /**
      * Create an MABoss from the given entity with the given max health.
@@ -73,6 +75,7 @@ public class MABoss
      */
     public void setDead(boolean dead) {
         this.dead = dead;
+        healthbar.removeAll();
     }
     
     public void setReward(Thing reward) {
@@ -90,4 +93,12 @@ public class MABoss
     public List<ItemStack> getDrops() {
         return drops;
     }
+
+    public HealthBar getHealthBar() {
+        return healthbar;
+    }
+
+    public void setHealthBar(HealthBar healthbar) {
+        this.healthbar = healthbar;
+    }
 }

src/main/resources/res/settings.yml

@@ -34,6 +34,7 @@ auto-start-timer: 0
 start-delay-timer: 0
 auto-ready: false
 use-class-chests: false
+boss-health-bar: boss-bar
 display-waves-as-level: false
 display-timer-as-level: false
 use-scoreboards: true