SPIGOT-5553, #964: Add EntityKnockbackEvent

By: Jishuna <joshl5324@gmail.com>

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

@@ -0,0 +1,30 @@
+package org.bukkit.event.entity;
+
+import org.bukkit.entity.Entity;
+import org.bukkit.entity.LivingEntity;
+import org.bukkit.util.Vector;
+import org.jetbrains.annotations.NotNull;
+
+/**
+ * Called when an entity receives knockback from another entity.
+ */
+public class EntityKnockbackByEntityEvent extends EntityKnockbackEvent {
+
+    private final Entity source;
+
+    public EntityKnockbackByEntityEvent(@NotNull final LivingEntity entity, @NotNull final Entity source, @NotNull final KnockbackCause cause, final double force, @NotNull final Vector rawKnockback, @NotNull final Vector knockback) {
+        super(entity, cause, force, rawKnockback, knockback);
+
+        this.source = source;
+    }
+
+    /**
+     * Get the entity that has caused knockback to the defender.
+     *
+     * @return entity that caused knockback
+     */
+    @NotNull
+    public Entity getSourceEntity() {
+        return source;
+    }
+}

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

@@ -0,0 +1,153 @@
+package org.bukkit.event.entity;
+
+import com.google.common.base.Preconditions;
+import org.bukkit.attribute.Attribute;
+import org.bukkit.enchantments.Enchantment;
+import org.bukkit.entity.LivingEntity;
+import org.bukkit.event.Cancellable;
+import org.bukkit.event.HandlerList;
+import org.bukkit.util.Vector;
+import org.jetbrains.annotations.NotNull;
+
+/**
+ * Called when a living entity receives knockback.
+ */
+public class EntityKnockbackEvent extends EntityEvent implements Cancellable {
+
+    private static final HandlerList handlers = new HandlerList();
+    private final KnockbackCause cause;
+    private final double force;
+    private final Vector rawKnockback;
+    private Vector knockback;
+    private boolean cancelled;
+
+    public EntityKnockbackEvent(@NotNull final LivingEntity entity, @NotNull final KnockbackCause cause, final double force, @NotNull final Vector rawKnockback, @NotNull final Vector knockback) {
+        super(entity);
+
+        this.cause = cause;
+        this.force = force;
+        this.rawKnockback = rawKnockback;
+        this.knockback = knockback;
+    }
+
+    @NotNull
+    @Override
+    public LivingEntity getEntity() {
+        return (LivingEntity) entity;
+    }
+
+    /**
+     * Gets the cause of the knockback.
+     *
+     * @return the cause of the knockback
+     */
+    @NotNull
+    public KnockbackCause getCause() {
+        return cause;
+    }
+
+    /**
+     * Gets the raw force of the knockback. <br>
+     * This value is based on factors such as the {@link Enchantment#KNOCKBACK}
+     * level of an attacker and the
+     * {@link Attribute#GENERIC_KNOCKBACK_RESISTANCE} of the entity.
+     *
+     * @return the knockback force
+     */
+    public double getForce() {
+        return force;
+    }
+
+    /**
+     * Gets the raw knockback force that will be applied to the entity. <br>
+     * This value is read-only, changes made to it <b>will not</b> have any
+     * effect on the final knockback received.
+     *
+     * @return the raw knockback
+     * @see #getFinalKnockback()
+     */
+    @NotNull
+    public Vector getKnockback() {
+        return rawKnockback.clone();
+    }
+
+    /**
+     * Gets the force that will be applied to the entity. <br>
+     * In contrast to {@link EntityKnockbackEvent#getKnockback()} this value is
+     * affected by the entities current velocity and whether they are touching
+     * the ground.
+     * <p>
+     * <b>Note:</b> this method returns a copy, changes must be applied with
+     * {@link #setFinalKnockback(Vector)}.
+     *
+     * @return the final knockback
+     */
+    @NotNull
+    public Vector getFinalKnockback() {
+        return knockback.clone();
+    }
+
+    /**
+     * Sets the force that will be applied to the entity.
+     *
+     * @param knockback the force to apply
+     */
+    @NotNull
+    public void setFinalKnockback(@NotNull Vector knockback) {
+        Preconditions.checkArgument(knockback != null, "Knockback cannot be null");
+
+        this.knockback = knockback;
+    }
+
+    @Override
+    public boolean isCancelled() {
+        return cancelled;
+    }
+
+    @Override
+    public void setCancelled(boolean cancel) {
+        cancelled = cancel;
+    }
+
+    @NotNull
+    @Override
+    public HandlerList getHandlers() {
+        return handlers;
+    }
+
+    @NotNull
+    public static HandlerList getHandlerList() {
+        return handlers;
+    }
+
+    /**
+     * An enum to specify the cause of the knockback.
+     */
+    public enum KnockbackCause {
+
+        /**
+         * Knockback caused by non-entity damage.
+         */
+        DAMAGE,
+        /**
+         * Knockback caused by an attacking entity.
+         */
+        ENTITY_ATTACK,
+        /**
+         * Knockback caused by an explosion.
+         */
+        EXPLOSION,
+        /**
+         * Knockback caused by the target blocking with a shield.
+         */
+        SHIELD_BLOCK,
+        /**
+         * Knockback caused by a sweeping attack.
+         */
+        SWEEP_ATTACK,
+        /**
+         * Knockback with an unknown cause.
+         */
+        UNKNOWN;
+    }
+}