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/*
 * Copyright 2021 Google LLC
 *
 * 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
 *
 *     https://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 com.google.appengine.api.datastore;

import com.google.appengine.api.datastore.CompositeIndexManager.IndexSource;
import com.google.apphosting.api.AppEngineInternal;
import com.google.storage.onestore.v3.OnestoreEntity.Index;
import com.google.storage.onestore.v3.OnestoreEntity.Index.Property;
import com.google.storage.onestore.v3.OnestoreEntity.Index.Property.Direction;
import com.google.storage.onestore.v3.OnestoreEntity.Index.Property.Mode;

/** Static utilities for working with composite indexes. */
@AppEngineInternal
public final class CompositeIndexUtils {

  /** The format of a datastore-index XML element when it has properties. */
  private static final String DATASTORE_INDEX_WITH_PROPERTIES_XML_FORMAT =
      "    \n%s" + "    \n\n";

  private static final String ANCESTOR_ATTRIBUTE_FORMAT = "ancestor=\"%s\"";

  /** The format of a datastore-index XML element when it does not have properties. */
  private static final String DATASTORE_INDEX_NO_PROPERTIES_XML_FORMAT =
      "    \n\n";

  /** The format of a property XML element. */
  // This of course only works because "direction" and "mode" are mutually exclusive.
  // TODO: revisit if we ever need the ability to add more than one extra attribute.
  private static final String PROPERTY_XML_FORMAT = "        \n";

  private static final String ASC_ATTRIBUTE = "direction=\"asc\"";
  private static final String DESC_ATTRIBUTE = "direction=\"desc\"";
  private static final String GEOSPATIAL_ATTRIBUTE = "mode=\"geospatial\"";

  private CompositeIndexUtils() {}

  /**
   * Generate an xml representation of the provided {@link Index}.
   *
   * {@code
   * 
   *     
   *         
   *         
   *     
   * 
   * }
   *
   * @param index The index for which we want an xml representation.
   * @param source The source of the provided index.
   * @return The xml representation of the provided index.
   */
  public static String generateXmlForIndex(Index index, IndexSource source) {
    // Careful with pb method names - index.hasAncestor just returns whether or not
    // the ancestor was set, not the value of the field itself.  We always provide
    // a value for this field, so we just want the value.
    boolean isAncestor = index.isAncestor();
    if (index.propertySize() == 0) {
      return String.format(
          DATASTORE_INDEX_NO_PROPERTIES_XML_FORMAT, index.getEntityType(), isAncestor, source);
    }
    boolean isSearchIndex = false;
    StringBuilder sb = new StringBuilder();
    for (Property prop : index.propertys()) {
      String extraAttribute;
      if (prop.getDirectionEnum() == Direction.ASCENDING) {
        extraAttribute = ASC_ATTRIBUTE;
      } else if (prop.getDirectionEnum() == Direction.DESCENDING) {
        extraAttribute = DESC_ATTRIBUTE;
      } else if (prop.getModeEnum() == Mode.GEOSPATIAL) {
        isSearchIndex = true;
        extraAttribute = GEOSPATIAL_ATTRIBUTE;
      } else {
        extraAttribute = "";
      }
      sb.append(String.format(PROPERTY_XML_FORMAT, prop.getName(), extraAttribute));
    }
    String ancestorAttribute =
        isSearchIndex ? "" : String.format(ANCESTOR_ATTRIBUTE_FORMAT, isAncestor);
    return String.format(
        DATASTORE_INDEX_WITH_PROPERTIES_XML_FORMAT,
        index.getEntityType(),
        ancestorAttribute,
        source,
        sb.toString());
  }
}