statefun-flink/statefun-flink-common/src/main/java/org/apache/flink/statefun/flink/common/protopath/ProtobufPath.java

/*
 * 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.flink.statefun.flink.common.protopath;

import com.google.protobuf.Descriptors;
import com.google.protobuf.Message;
import java.util.List;
import java.util.function.Function;

public final class ProtobufPath {

  /**
   * Compile a (limited) {@code ProtocolBuffer}'s path expression.
   *
   * <p>A {@code ProtocolBuffer}'s path expression applied to a {@link com.google.protobuf.Message}
   * and can be one of the following:
   *
   * <ul>
   *   <li>Field selector - donated by a {@code .field} expression.
   *   <li>A repeated filed index - donated by {@code .field[index]} expression.
   * </ul>
   *
   * <p>Each path expression starts with a {@code $} symbol to donate the root message. For example,
   * with this message type:
   *
   * <pre>{@code
   * message Foo {
   *     string baz = 1;
   * }
   * }</pre>
   *
   * The following expression can select the field {@code baz}: {@code $.baz}.
   *
   * @param pathString an {@code ProtocolBuffer}'s path expression.
   * @return an ordered list of path fragments.
   */
  public static Function<Message, ?> protobufPath(
      Descriptors.Descriptor messageDescriptor, String pathString) {
    List<PathFragment> fields = ProtobufPathParser.parse(pathString);
    List<PathFragmentDescriptor> pathFragments =
        ProtobufPathCompiler.compile(messageDescriptor, fields);
    return new ProtobufDynamicMessageLens(pathFragments);
  }
}