content: /*
   * 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.arrow.vector.validate;
  
  import java.io.IOException;
  import java.util.Iterator;
  import org.apache.arrow.vector.types.MetadataVersion;
  import org.apache.arrow.vector.types.pojo.ArrowType;
  import org.apache.arrow.vector.types.pojo.Field;
  import org.apache.arrow.vector.types.pojo.Schema;
  
  /**
   * Given a field, checks that no Union fields are present.
   *
   * <p>This is intended to be used to prevent unions from being read/written with V4 metadata.
   */
  public final class MetadataV4UnionChecker {
    static boolean isUnion(Field field) {
      return field.getType().getTypeID() == ArrowType.ArrowTypeID.Union;
    }
  
    static Field check(Field field) {
      if (isUnion(field)) {
        return field;
      }
      // Naive recursive DFS
      for (final Field child : field.getChildren()) {
        final Field result = check(child);
        if (result != null) {
          return result;
        }
      }
      return null;
    }
  
    /**
     * Check the schema, raising an error if an unsupported feature is used (e.g. unions with < V5
     * metadata).
     */
    public static void checkForUnion(Iterator<Field> fields, MetadataVersion metadataVersion) {
      if (metadataVersion.toFlatbufID() >= MetadataVersion.V5.toFlatbufID()) {
        return;
      }
      while (fields.hasNext()) {
        Field union = check(fields.next());
        if (union != null) {
          throw new IllegalArgumentException(
              "Cannot write union with V4 metadata version, use V5 instead. Found field: " + union);
        }
      }
    }
  
    /**
     * Check the schema, raising an error if an unsupported feature is used (e.g. unions with < V5
     * metadata).
     */
    public static void checkRead(Schema schema, MetadataVersion metadataVersion) throws IOException {
      if (metadataVersion.toFlatbufID() >= MetadataVersion.V5.toFlatbufID()) {
        return;
      }
      for (final Field field : schema.getFields()) {
        Field union = check(field);
        if (union != null) {
          throw new IOException("Cannot read union with V4 metadata version. Found field: " + union);
        }
      }
    }
  }
  