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.util;
  
  import java.util.ArrayList;
  import java.util.List;
  import java.util.Map;
  import java.util.Set;
  import org.apache.arrow.memory.BufferAllocator;
  import org.apache.arrow.vector.FieldVector;
  import org.apache.arrow.vector.dictionary.Dictionary;
  import org.apache.arrow.vector.dictionary.DictionaryProvider;
  import org.apache.arrow.vector.types.pojo.ArrowType;
  import org.apache.arrow.vector.types.pojo.DictionaryEncoding;
  import org.apache.arrow.vector.types.pojo.Field;
  import org.apache.arrow.vector.types.pojo.FieldType;
  
  /** Utility methods for working with Dictionaries used in Dictionary encodings. */
  public class DictionaryUtility {
    private DictionaryUtility() {}
  
    /**
     * Convert field and child fields that have a dictionary encoding to message format, so fields
     * have the dictionary type.
     *
     * <p>NOTE: in the message format, fields have the dictionary type in the memory format, they have
     * the index type
     */
    public static Field toMessageFormat(
        Field field, DictionaryProvider provider, Set<Long> dictionaryIdsUsed) {
      if (!needConvertToMessageFormat(field)) {
        return field;
      }
      DictionaryEncoding encoding = field.getDictionary();
      List<Field> children;
  
      ArrowType type;
      if (encoding == null) {
        type = field.getType();
        children = field.getChildren();
      } else {
        long id = encoding.getId();
        Dictionary dictionary = provider.lookup(id);
        if (dictionary == null) {
          throw new IllegalArgumentException("Could not find dictionary with ID " + id);
        }
        type = dictionary.getVectorType();
        children = dictionary.getVector().getField().getChildren();
  
        dictionaryIdsUsed.add(id);
      }
  
      final List<Field> updatedChildren = new ArrayList<>(children.size());
      for (Field child : children) {
        updatedChildren.add(toMessageFormat(child, provider, dictionaryIdsUsed));
      }
  
      return new Field(
          field.getName(),
          new FieldType(field.isNullable(), type, encoding, field.getMetadata()),
          updatedChildren);
    }
  
    /**
     * Checks if it is required to convert the field to message format.
     *
     * @param field the field to check.
     * @return true if a conversion is required, and false otherwise.
     */
    public static boolean needConvertToMessageFormat(Field field) {
      DictionaryEncoding encoding = field.getDictionary();
  
      if (encoding != null) {
        // when encoding is not null, the type must be determined from the
        // dictionary, so conversion must be performed.
        return true;
      }
  
      List<Field> children = field.getChildren();
      for (Field child : children) {
        if (needConvertToMessageFormat(child)) {
          return true;
        }
      }
      return false;
    }
  
    /**
     * Convert field and child fields that have a dictionary encoding to memory format, so fields have
     * the index type.
     */
    public static Field toMemoryFormat(
        Field field, BufferAllocator allocator, Map<Long, Dictionary> dictionaries) {
      DictionaryEncoding encoding = field.getDictionary();
      List<Field> children = field.getChildren();
  
      if (encoding == null && children.isEmpty()) {
        return field;
      }
  
      List<Field> updatedChildren = new ArrayList<>(children.size());
      for (Field child : children) {
        updatedChildren.add(toMemoryFormat(child, allocator, dictionaries));
      }
  
      ArrowType type;
      List<Field> fieldChildren = null;
      if (encoding == null) {
        type = field.getType();
        fieldChildren = updatedChildren;
      } else {
        // re-type the field for in-memory format
        type = encoding.getIndexType();
        if (type == null) {
          type = new ArrowType.Int(32, true);
        }
        // get existing or create dictionary vector
        if (!dictionaries.containsKey(encoding.getId())) {
          // create a new dictionary vector for the values
          String dictName = "DICT" + encoding.getId();
          Field dictionaryField =
              new Field(
                  dictName,
                  new FieldType(field.isNullable(), field.getType(), null, null),
                  updatedChildren);
          FieldVector dictionaryVector = dictionaryField.createVector(allocator);
          dictionaries.put(encoding.getId(), new Dictionary(dictionaryVector, encoding));
        }
      }
  
      return new Field(
          field.getName(),
          new FieldType(field.isNullable(), type, encoding, field.getMetadata()),
          fieldChildren);
    }
  }
  