Add support for 1.8 boss bars

Automatically converts legacy boss bars to 1.9 ones using ViaVersions's
boss API.

I suggest you add a config option
Note: also fixed crash on wither/dragon spawn

src/main/java/us/myles/ViaVersion/metadata/MetaIndex.java

@@ -91,6 +91,7 @@ public enum MetaIndex {
     WITHER_TARGET2(Wither.class, 18, Type.Int, 12, NewType.VarInt),
     WITHER_TARGET3(Wither.class, 19, Type.Int, 13, NewType.VarInt),
     WITHER_INVULN_TIME(Wither.class, 20, Type.Int, 14, NewType.VarInt),
+    WITHER_PROPERTIES(Wither.class, 10, Type.Byte, NewType.Byte),
     // wither skull
     WITHERSKULL_INVULN(WitherSkull.class, 10, Type.Byte, 5, NewType.Boolean),
     // guardian
@@ -123,7 +124,10 @@ public enum MetaIndex {
     ITEMFRAME_ITEM(ItemFrame.class, 8, Type.Slot, 5, NewType.Slot),
     ITEMFRAME_ROTATION(ItemFrame.class, 9, Type.Byte, 6, NewType.VarInt),
     // ender crystal
-    ENDERCRYSTAL_HEALTH(EnderCrystal.class, 8, Type.Int, NewType.Discontinued),;
+    ENDERCRYSTAL_HEALTH(EnderCrystal.class, 8, Type.Int, NewType.Discontinued),
+    // Ender dragon
+    ENDERDRAGON_FLAG(EnderDragon.class, 15, Type.Byte, NewType.Discontinued),
+    ENDERDRAGON_PHASE(EnderDragon.class, 11, Type.Int, NewType.VarInt);
 
     private Class<?> clazz;
     private int newIndex;

src/main/java/us/myles/ViaVersion/metadata/MetadataRewriter.java

@@ -207,7 +207,7 @@ public class MetadataRewriter {
         private MetaIndex index;
         private Object value;
 
-        private Entry(MetaIndex index, Object value, int id) {
+        public Entry(MetaIndex index, Object value, int id) {
             this.index = index;
             this.value = value;
             this.oldID = id;

src/main/java/us/myles/ViaVersion/transformers/OutgoingTransformer.java

@@ -15,7 +15,12 @@ import us.myles.ViaVersion.CancelException;
 import us.myles.ViaVersion.ConnectionInfo;
 import us.myles.ViaVersion.ViaVersionPlugin;
 import us.myles.ViaVersion.api.ViaVersion;
+import us.myles.ViaVersion.api.boss.BossBar;
+import us.myles.ViaVersion.api.boss.BossColor;
+import us.myles.ViaVersion.api.boss.BossStyle;
+import us.myles.ViaVersion.metadata.MetaIndex;
 import us.myles.ViaVersion.metadata.MetadataRewriter;
+import us.myles.ViaVersion.metadata.MetadataRewriter.Entry;
 import us.myles.ViaVersion.packets.PacketType;
 import us.myles.ViaVersion.packets.State;
 import us.myles.ViaVersion.slot.ItemSlotRewriter;
@@ -40,6 +45,7 @@ public class OutgoingTransformer {
     private final Map<Integer, Integer> vehicleMap = new HashMap<>();
     private final Set<Integer> validBlocking = new HashSet<>();
     private final Set<Integer> knownHolograms = new HashSet<>();
+    private final Map<Integer, BossBar> bossBarMap = new HashMap<>();
     private boolean autoTeam = false;
 
     public OutgoingTransformer(ConnectionInfo info) {
@@ -384,6 +390,12 @@ public class OutgoingTransformer {
                 clientEntityTypes.remove(entityID);
                 knownHolograms.remove(entityID);
                 PacketUtil.writeVarInt(entityID, output);
+
+                // Remvoe boss bar
+                BossBar bar = bossBarMap.remove(entityID);
+                if(bar != null) {
+                    bar.hide();
+                }
             }
             return;
         }
@@ -832,6 +844,14 @@ public class OutgoingTransformer {
         for (MetadataRewriter.Entry entry : list) {
             handleMetadata(entityID, entry, type);
         }
+        // Fix: wither (crash fix)
+        if(type == EntityType.WITHER) {
+            list.add(new Entry(MetaIndex.WITHER_PROPERTIES, (byte) 0, 10));
+        }
+        // Fix: Dragon (crash fix)
+        if(type == EntityType.ENDER_DRAGON) {
+            list.add(new Entry(MetaIndex.ENDERDRAGON_PHASE, 0, 11));
+        }
         MetadataRewriter.writeMetadata1_9(type, list, output);
     }
 
@@ -875,6 +895,39 @@ public class OutgoingTransformer {
                 }
             }
         }
+
+        // TODO: Add config option
+        // Boss bar
+        if(type == EntityType.ENDER_DRAGON || type == EntityType.WITHER) {
+            if(entry.getOldID() == 2) {
+                BossBar bar = bossBarMap.get(entityID);
+                String title = (String) entry.getValue();
+                title = title.isEmpty() ? (type == EntityType.ENDER_DRAGON ? "Ender Dragon" : "Wither") : title;
+                if(bar == null) {
+                    bar = ViaVersion.getInstance().createBossBar(title, BossColor.PURPLE, BossStyle.SOLID);
+                    bossBarMap.put(entityID, bar);
+                    bar.addPlayer(info.getPlayer());
+                    bar.show();
+                } else {
+                    bar.setTitle((String) entry.getValue());
+                }
+            } else if(entry.getOldID() == 6) {
+                BossBar bar = bossBarMap.get(entityID);
+                // Make health range between 0 and 1
+                float maxHealth = type == EntityType.ENDER_DRAGON ? 200.0f : 300.0f;
+                float health = Math.max(0.0f, Math.min(((float) entry.getValue()) / maxHealth, 1.0f));
+                System.out.println(health + " " + entry.getValue());
+                if(bar == null) {
+                    String title = type == EntityType.ENDER_DRAGON ? "Ender Dragon" : "Wither";
+                    bar = ViaVersion.getInstance().createBossBar(title, health, BossColor.PURPLE, BossStyle.SOLID);
+                    bossBarMap.put(entityID, bar);
+                    bar.addPlayer(info.getPlayer());
+                    bar.show();
+                } else {
+                    bar.setHealth(health);
+                }
+            }
+        }
     }