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.causeway.applib.value.semantics;
  
  import java.time.LocalDateTime;
  import java.time.ZoneId;
  import java.time.ZoneOffset;
  import java.util.List;
  import java.util.stream.Collectors;
  
  /**
   * When implemented by a service {@link #getAvailableZoneIds()} 
   * can be customized to limit the time-zone choices 
   * as e.g. offered by the <i>Wicket Viewer<i> login page.
   * 
   * @since 2.1, 3.1
   */
  public interface TimeZoneChoiceProvider {
      
      /**
       * For temporal value editing, provides the list of available time zones to choose from.
       */
      default List<ZoneId> getAvailableZoneIds() {
          return ZoneId.getAvailableZoneIds().stream()
              .sorted()
              .map(ZoneId::of)
              .collect(Collectors.toList());
      }
  
      /**
       * For temporal value editing, provides the list of available offsets to choose from.
       */
      default List<ZoneOffset> getAvailableOffsets() {
          var now = LocalDateTime.now();
          return getAvailableZoneIds().stream()
              .map(ZoneId::getRules)
              .flatMap(zoneIdRules->zoneIdRules.getValidOffsets(now).stream())
              .sorted()
              .distinct()
              .collect(Collectors.toList());
      }
      
      /**
       * Returns the fallback implementation, which provides all ZoneIds known to the JVM.
       */
      static TimeZoneChoiceProvider fallback() {
          return new TimeZoneChoiceProvider() {};
      }
      
  }
  