Prevent mobs targeting mobs in their friends group.

New/changed mob type properties:

 * Comma- or space-separated lists of tag strings are now merged
   into sorted sets with case-insensitive string comparison, for
   properties `tags`, `groups` (new) and `friend-groups` (new).
 * `groups` is the set of groups a mob type belongs to.
 * `friend-groups` is the set of groups that the mob type
   refuses to target.

src/nu/nerd/beastmaster/BeastMaster.java

@@ -1,7 +1,9 @@
 package nu.nerd.beastmaster;
 
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.List;
+import java.util.Set;
 import java.util.stream.Collectors;
 
 import org.bukkit.Bukkit;
@@ -29,6 +31,7 @@
 import org.bukkit.event.entity.EntityDamageEvent;
 import org.bukkit.event.entity.EntityDamageEvent.DamageCause;
 import org.bukkit.event.entity.EntityDeathEvent;
+import org.bukkit.event.entity.EntityTargetLivingEntityEvent;
 import org.bukkit.event.entity.EntityTeleportEvent;
 import org.bukkit.event.entity.ProjectileHitEvent;
 import org.bukkit.event.entity.ProjectileLaunchEvent;
@@ -742,6 +745,44 @@ protected void onEntityDeath(EntityDeathEvent event) {
 
     } // onEntityDeath
 
+    // ------------------------------------------------------------------------
+    /**
+     * Prevent a mob from targeting any other mob whose "groups" set includes a
+     * name that is in the targeting mob's "friend-groups".
+     */
+    @SuppressWarnings("unchecked")
+    @EventHandler(ignoreCancelled = true, priority = EventPriority.LOWEST)
+    protected void onEntityTargetLivingEntity(EntityTargetLivingEntityEvent event) {
+        Entity targetter = event.getEntity();
+        LivingEntity target = event.getTarget();
+        if (!(targetter instanceof LivingEntity)) {
+            return;
+        }
+
+        // If the targeting mob is not friendly to any groups, no action needed.
+        MobType mobType = getMobType(targetter);
+        if (mobType == null) {
+            return;
+        }
+        Set<String> friendGroups = (Set<String>) mobType.getDerivedProperty("friend-groups").getValue();
+        if (friendGroups == null || friendGroups.isEmpty()) {
+            return;
+        }
+
+        // Targeted mob.
+        MobType targetType = getMobType(target);
+        Set<String> targetGroups = targetType == null ? Collections.EMPTY_SET
+                                                      : (Set<String>) targetType.getDerivedProperty("groups").getValue();
+
+        // If the targeted mob is a friend, don't target.
+        for (String friend : friendGroups) {
+            if (targetGroups.contains(friend)) {
+                event.setCancelled(true);
+                return;
+            }
+        }
+    }
+
     // ------------------------------------------------------------------------
     /**
      * Play the teleport-sound, if configured for the mob.

src/nu/nerd/beastmaster/mobs/DataType.java

@@ -2,6 +2,10 @@
 
 import java.lang.reflect.InvocationTargetException;
 import java.util.Arrays;
+import java.util.List;
+import java.util.Set;
+import java.util.TreeSet;
+import java.util.stream.Collectors;
 
 import org.bukkit.Bukkit;
 import org.bukkit.ChatColor;
@@ -103,17 +107,15 @@ public int compare(Object o1, Object o2) {
 
     // ------------------------------------------------------------------------
     /**
-     * Comma separated list of Strings assumed to be scoreboard tags.
+     * Comma separated ordered set of case-insensitive Strings.
      * 
      * Spaces are treated as equivalent to commas.
-     * 
-     * Tags are compared case-sensitively. I assume that it might occasionally
-     * matter for scoreboard tags.
      */
-    public static final IDataType TAG_LIST = new IDataType() {
+    public static final IDataType TAG_SET = new IDataType() {
+        @SuppressWarnings("unchecked")
         @Override
         public String format(Object value) {
-            return String.join(",", (String[]) value);
+            return ((Set<String>) value).stream().collect(Collectors.joining(","));
         }
 
         @Override
@@ -128,15 +130,19 @@ public String serialise(Object value) {
 
         @Override
         public Object deserialise(String value) throws IllegalArgumentException {
-            // Sort to account for hand-edited configs.
-            String[] tags = value.split(",");
-            Arrays.sort(tags);
-            return tags;
+            Set<String> set = new TreeSet<>(String.CASE_INSENSITIVE_ORDER);
+            // Handle input like: "," by removing empty tags.
+            List<String> tags = Arrays.asList(value.split(",")).stream()
+            .filter(tag -> !tag.isEmpty())
+            .sorted(String.CASE_INSENSITIVE_ORDER)
+            .collect(Collectors.toList());
+            set.addAll(tags);
+            return set;
         }
 
         @Override
         public int compare(Object o1, Object o2) {
-            return serialise(o1).compareTo(serialise(o2));
+            return serialise(o1).compareToIgnoreCase(serialise(o2));
         }
     };
 

src/nu/nerd/beastmaster/mobs/MobType.java

@@ -622,6 +622,14 @@ protected void addProperties() {
 
         // Behaviour ----------------------------------------------------------
 
+        addProperty(new MobProperty("groups", DataType.TAG_SET, null));
+        addProperty(new MobProperty("friend-groups", DataType.TAG_SET, null));
+        addProperty(new MobProperty("tags", DataType.TAG_SET, (mob, logger) -> {
+            @SuppressWarnings("unchecked")
+            Set<String> tags = (Set<String>) getDerivedProperty("tags").getValue();
+            mob.getScoreboardTags().addAll(tags);
+        }));
+
         addProperty(new MobProperty("anger-ticks", DataType.INTEGER, (mob, logger) -> {
             int ticks = (Integer) getDerivedProperty("anger-ticks").getValue();
             if (mob instanceof Bee) {
@@ -641,11 +649,6 @@ protected void addProperties() {
                 boolean canDespawn = (Boolean) getDerivedProperty("can-despawn").getValue();
                 mob.setRemoveWhenFarAway(canDespawn);
             }));
-        addProperty(new MobProperty("tags", DataType.TAG_LIST, (mob, logger) -> {
-            String[] tags = (String[]) getDerivedProperty("tags").getValue();
-            mob.getScoreboardTags().addAll(Arrays.asList(tags));
-        }));
-
         // projectile-... properties are enforced in ProjectileLaunchEvent and
         // ProectileHitEvent handlers.
         addProperty(new MobProperty("projectile-mobs", DataType.LOOT_OR_MOB, null));