Add leash API. Adds BUKKIT-4459 and BUKKIT-4583

By: T00thpick1 <t00thpick1dirko@gmail.com>

paper-api/src/main/java/org/bukkit/event/entity/EntityUnleashEvent.java

@@ -0,0 +1,52 @@
+package org.bukkit.event.entity;
+
+import org.bukkit.entity.Entity;
+import org.bukkit.event.HandlerList;
+
+/**
+ * Called immediately prior to an entity being unleashed.
+ */
+public class EntityUnleashEvent extends EntityEvent {
+    private static final HandlerList handlers = new HandlerList();
+    private final UnleashReason reason;
+
+    public EntityUnleashEvent(Entity entity, UnleashReason reason) {
+        super(entity);
+        this.reason = reason;
+    }
+
+    /**
+     * Returns the reason for the unleashing.
+     *
+     * @return The reason
+     */
+    public UnleashReason getReason() {
+        return reason;
+    }
+
+    @Override
+    public HandlerList getHandlers() {
+        return handlers;
+    }
+
+    public static HandlerList getHandlerList() {
+        return handlers;
+    }
+
+    public enum UnleashReason {
+        /**
+         * When the entity's leashholder has died or logged out, and so is
+         * unleashed
+         */
+        HOLDER_GONE,
+        /**
+         * When the entity's leashholder attempts to unleash it
+         */
+        PLAYER_UNLEASH,
+        /**
+         * When the entity's leashholder is more than 10 blocks away
+         */
+        DISTANCE,
+        UNKNOWN;
+    }
+}

paper-api/src/main/java/org/bukkit/event/entity/PlayerLeashEntityEvent.java

@@ -0,0 +1,68 @@
+package org.bukkit.event.entity;
+
+import org.bukkit.entity.Entity;
+import org.bukkit.entity.Player;
+import org.bukkit.event.Cancellable;
+import org.bukkit.event.Event;
+import org.bukkit.event.HandlerList;
+
+/**
+ * Called immediately prior to a creature being leashed by a player.
+ */
+public class PlayerLeashEntityEvent extends Event implements Cancellable {
+    private static final HandlerList handlers = new HandlerList();
+    private final Entity leashHolder;
+    private final Entity entity;
+    private boolean cancelled = false;
+    private final Player player;
+
+    public PlayerLeashEntityEvent(Entity what, Entity leashHolder, Player leasher) {
+        this.leashHolder = leashHolder;
+        this.entity = what;
+        this.player = leasher;
+    }
+
+    /**
+     * Returns the entity that is holding the leash.
+     *
+     * @return The leash holder
+     */
+    public Entity getLeashHolder() {
+        return leashHolder;
+    }
+
+    /**
+     * Returns the entity being leashed.
+     *
+     * @return The entity
+     */
+    public Entity getEntity() {
+        return entity;
+    }
+
+    /**
+     * Returns the player involved in this event
+     *
+     * @return Player who is involved in this event
+     */
+    public final Player getPlayer() {
+        return player;
+    }
+
+    @Override
+    public HandlerList getHandlers() {
+        return handlers;
+    }
+
+    public static HandlerList getHandlerList() {
+        return handlers;
+    }
+
+    public boolean isCancelled() {
+        return this.cancelled;
+    }
+
+    public void setCancelled(boolean cancel) {
+        this.cancelled  = cancel;
+    }
+}

paper-api/src/main/java/org/bukkit/event/player/PlayerUnleashEntityEvent.java

@@ -0,0 +1,36 @@
+package org.bukkit.event.player;
+
+import org.bukkit.entity.Entity;
+import org.bukkit.entity.Player;
+import org.bukkit.event.Cancellable;
+import org.bukkit.event.entity.EntityUnleashEvent;
+
+/**
+ * Called prior to an entity being unleashed due to a player's action.
+ */
+public class PlayerUnleashEntityEvent extends EntityUnleashEvent implements Cancellable {
+    private final Player player;
+    private boolean cancelled = false;
+
+    public PlayerUnleashEntityEvent(Entity entity, Player player) {
+        super(entity, UnleashReason.PLAYER_UNLEASH);
+        this.player = player;
+    }
+
+    /**
+     * Returns the player who is unleashing the entity.
+     *
+     * @return The player
+     */
+    public Player getPlayer() {
+        return player;
+    }
+
+    public boolean isCancelled() {
+        return cancelled;
+    }
+
+    public void setCancelled(boolean cancel) {
+        this.cancelled = cancel;
+    }
+}