cassandra-trunk/src/java/org/apache/cassandra/index/sasi/utils/trie/Cursor.java
/*
 * Copyright 2005-2010 Roger Kapsi, Sam Berlin
 *
 *   Licensed 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.cassandra.index.sasi.utils.trie;

import java.util.Map;
import java.util.Map.Entry;

/**
 * This class is taken from https://github.com/rkapsi/patricia-trie (v0.6), and slightly modified
 * to correspond to Cassandra code style, as the only Patricia Trie implementation,
 * which supports pluggable key comparators (e.g. commons-collections PatriciaTrie (which is based
 * on rkapsi/patricia-trie project) only supports String keys)
 * but unfortunately is not deployed to the maven central as a downloadable artifact.
 */

/**
 * A {@link Cursor} can be used to traverse a {@link Trie}, visit each node
 * step by step and make {@link Decision}s on each step how to continue with
 * traversing the {@link Trie}.
 */
public interface Cursor<K, V>
{

    /**
     * The {@link Decision} tells the {@link Cursor} what to do on each step
     * while traversing the {@link Trie}.
     *
     * NOTE: Not all operations that work with a {@link Cursor} support all
     * {@link Decision} types
     */
    enum Decision
    {

        /**
         * Exit the traverse operation
         */
        EXIT,

        /**
         * Continue with the traverse operation
         */
        CONTINUE,

        /**
         * Remove the previously returned element
         * from the {@link Trie} and continue
         */
        REMOVE,

        /**
         * Remove the previously returned element
         * from the {@link Trie} and exit from the
         * traverse operation
         */
        REMOVE_AND_EXIT
    }

    /**
     * Called for each {@link Entry} in the {@link Trie}. Return
     * {@link Decision#EXIT} to finish the {@link Trie} operation,
     * {@link Decision#CONTINUE} to go to the next {@link Entry},
     * {@link Decision#REMOVE} to remove the {@link Entry} and
     * continue iterating or {@link Decision#REMOVE_AND_EXIT} to
     * remove the {@link Entry} and stop iterating.
     *
     * Note: Not all operations support {@link Decision#REMOVE}.
     */
    Decision select(Map.Entry<? extends K, ? extends V> entry);
}
