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This nifi-utils module should be a general purpose place to store widely and generally useful functions that any component might want to leverage. NO DEPENDENCIES should be added. This module is likely to be leveraged by every extension and should not bring along any other dependencies. The only dependency intended is the nifi-api and even this is expected to be already provided in any case where it would be used. The typical place this util would be found is within a nar and all nars already have nifi-api as a parent dependency. The nifi-api can be thought of as a NiFi Application Container level dependency.

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/*
 * 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.nifi.util;

/**
 * Fluent api for checking one or more strings and selecting the first non-empty one.
 * 


 * {@link #toString()} returns the first encountered non-empty string or "".
 * 
 * Optimized so that no intermediary objects are created, only one, once the first non-empty string is found.
 */
public interface StringSelector {
    /**
     * Starts the fluent expression by checking the first string(s).
     *
     * @param strings The first string(s) to check if empty.
     * @return a {@link StringSelector} that checked the first string.
     */
    static StringSelector of(String... strings) {
        return EMPTY_STRING_SELECTOR.or(strings);
    }

    /**
     * Check the next string(s).
     *
     * @param strings The next string(s) to check if empty.
     * @return a {@link StringSelector} that checked all strings so far.
     */
    StringSelector or(String... strings);

    /**
     * May be used to stop processing subsequent inputs when a result is already available.
     *
     * @return true if a non-empty string has been found, false otherwise.
     */
    boolean found();

    StringSelector EMPTY_STRING_SELECTOR = new StringSelector() {
        @Override
        public String toString() {
            return "";
        }

        @Override
        public StringSelector or(String... strings) {
            for (String string : strings) {
                if (string != null && string.length() > 0) {
                    return new StringSelector() {
                        @Override
                        public StringSelector or(String... string) {
                            return this;
                        }

                        @Override
                        public String toString() {
                            return string;
                        }

                        @Override
                        public boolean found() {
                            return true;
                        }
                    };
                }
            }

            return EMPTY_STRING_SELECTOR;
        }

        @Override
        public boolean found() {
            return false;
        }
    };
}