/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
package org.apache.tinkerpop.gremlin.structure.util;

import org.apache.tinkerpop.gremlin.structure.Edge;
import org.apache.tinkerpop.gremlin.structure.Property;
import org.apache.tinkerpop.gremlin.structure.Vertex;

/**
 * A marker interface that identifies an object as something that an {@link Attachable} can connect to.
 *
 * @author Stephen Mallette (http://stephen.genoprime.com)
 */
public interface Host {

    /**
     * Extracts the {@link Vertex} that is holding the specified object.
     *
     * @throws IllegalStateException if the object is not a graph element type
     */
    public static Vertex getHostingVertex(final Object object) {
        Object obj = object;
        while (true) {
            if (obj instanceof Vertex)
                return (Vertex) obj;
            else if (obj instanceof Edge)
                return ((Edge) obj).outVertex();
            else if (obj instanceof Property)
                obj = ((Property) obj).element();
            else
                throw new IllegalStateException("The host of the object is unknown: " + obj.toString() + ':' + obj.getClass().getCanonicalName());
        }
    }
}
