SPIGOT-1934: Expand EnderDragon API - adds dragon phases

By: Matthew <stteg@hotmail.com>

paper-api/src/main/java/org/bukkit/entity/EnderDragon.java

@@ -5,4 +5,74 @@ package org.bukkit.entity;
  */
 public interface EnderDragon extends ComplexLivingEntity {
 
+    /**
+     * Represents a phase or action that an Ender Dragon can perform.
+     */
+    enum Phase {
+        /**
+         * The dragon will circle outside the ring of pillars if ender
+         * crystals remain or inside the ring if not.
+         */
+        CIRCLING,
+        /**
+         * The dragon will fly towards a targetted player and shoot a
+         * fireball when within 64 blocks.
+         */
+        STRAFING,
+        /**
+         * The dragon will fly towards the empty portal (approaching
+         * from the other side, if applicable).
+         */
+        FLY_TO_PORTAL,
+        /**
+         * The dragon will land on on the portal. If the dragon is not near
+         * the portal, it will fly to it before mounting.
+         */
+        LAND_ON_PORTAL,
+        /**
+         * The dragon will leave the portal.
+         */
+        LEAVE_PORTAL,
+        /**
+         * The dragon will attack with dragon breath at its current location.
+         */
+        BREATH_ATTACK,
+        /**
+         * The dragon will search for a player to attack with dragon breath.
+         * If no player is close enough to the dragon for 5 seconds, the 
+         * dragon will charge at a player within 150 blocks or will take off 
+         * and begin circling if no player is found.
+         */
+        SEARCH_FOR_BREATH_ATTACK_TARGET,
+        /**
+         * The dragon will roar before performing a breath attack.
+         */
+        ROAR_BEFORE_ATTACK,
+        /**
+         * The dragon will charge a player.
+         */
+        CHARGE_PLAYER,
+        /**
+         * The dragon will fly to the vicinity of the portal and die.
+         */
+        DYING,
+        /**
+         * The dragon will hover at its current location, not performing any actions.
+         */
+        HOVER
+    }
+
+    /**
+     * Gets the current phase that the dragon is performing.
+     *
+     * @return the current phase
+     */
+    Phase getPhase();
+
+    /**
+     * Sets the next phase for the dragon to perform.
+     *
+     * @param phase the next phase
+     */
+    void setPhase(Phase phase);
 }