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Extension to rename Druid dimension values using namespaces

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/*
 * Licensed to Metamarkets Group Inc. (Metamarkets) under one
 * or more contributor license agreements. See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership. Metamarkets 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 io.druid.server.lookup.namespace;

import io.druid.query.lookup.namespace.CacheGenerator;
import io.druid.query.lookup.namespace.StaticMapExtractionNamespace;
import io.druid.server.lookup.namespace.cache.CacheScheduler;

import javax.annotation.Nullable;
import java.util.UUID;

public final class StaticMapCacheGenerator implements CacheGenerator
{
  private final String version = UUID.randomUUID().toString();

  @Override
  @Nullable
  public CacheScheduler.VersionedCache generateCache(
      final StaticMapExtractionNamespace namespace,
      final CacheScheduler.EntryImpl id,
      final String lastVersion,
      final CacheScheduler scheduler
  )
  {
    if (lastVersion != null) {
      // Throwing AssertionError, because CacheScheduler doesn't suppress Errors and will stop trying to update
      // the cache periodically.
      throw new AssertionError(
          "StaticMapCacheGenerator could only be configured for a namespace which is scheduled "
          + "to be updated once, not periodically. Last version: `" + lastVersion + "`");
    }
    CacheScheduler.VersionedCache versionedCache = scheduler.createVersionedCache(id, version);
    try {
      versionedCache.getCache().putAll(namespace.getMap());
      return versionedCache;
    }
    catch (Throwable t) {
      try {
        versionedCache.close();
      }
      catch (Exception e) {
        t.addSuppressed(e);
      }
      throw t;
    }
  }

  String getVersion()
  {
    return version;
  }
}