Leashable API

paper-server/src/main/java/io/papermc/paper/entity/PaperLeashable.java

@@ -0,0 +1,50 @@
+package io.papermc.paper.entity;
+
+import com.google.common.base.Preconditions;
+import net.minecraft.world.entity.Leashable;
+import org.bukkit.craftbukkit.entity.CraftEntity;
+import org.bukkit.entity.Entity;
+
+public interface PaperLeashable extends io.papermc.paper.entity.Leashable {
+
+    Leashable getHandle();
+
+    @Override
+    default boolean isLeashed() {
+        return this.getHandle().getLeashHolder() != null;
+    }
+
+    @Override
+    default Entity getLeashHolder() throws IllegalStateException {
+        Preconditions.checkState(this.isLeashed(), "Entity not leashed");
+        return this.getHandle().getLeashHolder().getBukkitEntity();
+    }
+
+    private boolean unleash() {
+        if (!this.isLeashed()) {
+            return false;
+        }
+
+        this.getHandle().removeLeash();
+        return true;
+    }
+
+    @Override
+    default boolean setLeashHolder(Entity holder) {
+        if (this.getHandle() instanceof net.minecraft.world.entity.Entity entity && entity.generation) {
+            return false;
+        }
+
+        if (holder == null) {
+            return this.unleash();
+        }
+
+        if (holder.isDead()) {
+            return false;
+        }
+
+        this.unleash();
+        this.getHandle().setLeashedTo(((CraftEntity) holder).getHandle(), true);
+        return true;
+    }
+}