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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.java.util.common.parsers;

import com.google.common.collect.Iterables;
import io.druid.java.util.common.IAE;
import io.druid.java.util.common.UOE;

import java.util.AbstractMap;
import java.util.Collection;
import java.util.LinkedHashMap;
import java.util.LinkedHashSet;
import java.util.Map;
import java.util.Set;
import java.util.function.Function;
import java.util.stream.Collectors;

public class ObjectFlatteners
{
  private ObjectFlatteners()
  {
    // No instantiation.
  }

  public static  ObjectFlattener create(
      final JSONPathSpec flattenSpec,
      final FlattenerMaker flattenerMaker
  )
  {
    final Map> extractors = new LinkedHashMap<>();

    for (final JSONPathFieldSpec fieldSpec : flattenSpec.getFields()) {
      final Function extractor;

      switch (fieldSpec.getType()) {
        case ROOT:
          extractor = obj -> flattenerMaker.getRootField(obj, fieldSpec.getExpr());
          break;
        case PATH:
          extractor = flattenerMaker.makeJsonPathExtractor(fieldSpec.getExpr());
          break;
        case JQ:
          extractor = flattenerMaker.makeJsonQueryExtractor(fieldSpec.getExpr());
          break;
        default:
          throw new UOE("Unsupported field type[%s]", fieldSpec.getType());
      }

      if (extractors.put(fieldSpec.getName(), extractor) != null) {
        throw new IAE("Cannot have duplicate field definition: %s", fieldSpec.getName());
      }
    }

    return new ObjectFlattener()
    {
      @Override
      public Map flatten(final T obj)
      {
        return new AbstractMap()
        {
          @Override
          public int size()
          {
            return keySet().size();
          }

          @Override
          public boolean isEmpty()
          {
            throw new UnsupportedOperationException();
          }

          @Override
          public boolean containsKey(final Object key)
          {
            if (key == null) {
              return false;
            }

            return keySet().contains(key.toString());
          }

          @Override
          public boolean containsValue(final Object value)
          {
            throw new UnsupportedOperationException();
          }

          @Override
          public Object get(final Object key)
          {
            final String keyString = key.toString();
            final Function extractor = extractors.get(keyString);
            if (extractor != null) {
              return extractor.apply(obj);
            } else {
              return flattenerMaker.getRootField(obj, keyString);
            }
          }

          @Override
          public Object put(final String key, final Object value)
          {
            throw new UnsupportedOperationException();
          }

          @Override
          public Object remove(final Object key)
          {
            throw new UnsupportedOperationException();
          }

          @Override
          public void putAll(final Map m)
          {
            throw new UnsupportedOperationException();
          }

          @Override
          public void clear()
          {
            throw new UnsupportedOperationException();
          }

          @Override
          public Set keySet()
          {
            if (flattenSpec.isUseFieldDiscovery()) {
              final Iterable rootFields = flattenerMaker.discoverRootFields(obj);
              if (extractors.isEmpty() && rootFields instanceof Set) {
                return (Set) rootFields;
              } else {
                final Set keys = new LinkedHashSet<>(extractors.keySet());
                Iterables.addAll(keys, rootFields);
                return keys;
              }
            } else {
              return extractors.keySet();
            }
          }

          @Override
          public Collection