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.AbstractMap;
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.LinkedHashMap;
  import java.util.List;
  import java.util.Map;
  import java.util.Set;
  import java.util.stream.Collectors;
  
  /**
   * An implementation of map that supports constant time look-up by a generic key or an ordinal.
   *
   * <p>This class extends the functionality a regular {@link Map} with ordinal lookup support. Upon
   * insertion an unused ordinal is assigned to the inserted (key, value) tuple. Upon update the same
   * ordinal id is re-used while value is replaced. Upon deletion of an existing item, its
   * corresponding ordinal is recycled and could be used by another item.
   *
   * <p>For any instance with N items, this implementation guarantees that ordinals are in the range
   * of [0, N). However, the ordinal assignment is dynamic and may change after an insertion or
   * deletion. Consumers of this class are responsible for explicitly checking the ordinal
   * corresponding to a key via {@link MapWithOrdinalImpl#getOrdinal(Object)} before attempting to
   * execute a lookup with an ordinal.
   *
   * @param <K> key type
   * @param <V> value type
   */
  public class MapWithOrdinalImpl<K, V> implements MapWithOrdinal<K, V> {
  
    private final Map<K, Map.Entry<Integer, V>> primary = new LinkedHashMap<>();
    private final IntObjectHashMap<V> secondary = new IntObjectHashMap<>();
  
    private final Map<K, V> delegate =
        new Map<K, V>() {
          @Override
          public boolean isEmpty() {
            return size() == 0;
          }
  
          @Override
          public int size() {
            return primary.size();
          }
  
          @Override
          public boolean containsKey(Object key) {
            return primary.containsKey(key);
          }
  
          @Override
          public boolean containsValue(Object value) {
            return primary.containsValue(value);
          }
  
          @Override
          public V get(Object key) {
            Entry<Integer, V> pair = primary.get(key);
            if (pair != null) {
              return pair.getValue();
            }
            return null;
          }
  
          @Override
          public V put(K key, V value) {
            final Entry<Integer, V> oldPair = primary.get(key);
            // if key exists try replacing otherwise, assign a new ordinal identifier
            final int ordinal = oldPair == null ? primary.size() : oldPair.getKey();
            primary.put(key, new AbstractMap.SimpleImmutableEntry<>(ordinal, value));
            secondary.put(ordinal, value);
            return oldPair == null ? null : oldPair.getValue();
          }
  
          @Override
          public V remove(Object key) {
            final Entry<Integer, V> oldPair = primary.remove(key);
            if (oldPair != null) {
              final int lastOrdinal = secondary.size();
              final V last = secondary.get(lastOrdinal);
              // normalize mappings so that all numbers until primary.size() is assigned
              // swap the last element with the deleted one
              secondary.put(oldPair.getKey(), last);
              primary.put((K) key, new AbstractMap.SimpleImmutableEntry<>(oldPair.getKey(), last));
            }
            return oldPair == null ? null : oldPair.getValue();
          }
  
          @Override
          public void putAll(Map<? extends K, ? extends V> m) {
            throw new UnsupportedOperationException();
          }
  
          @Override
          public void clear() {
            primary.clear();
            secondary.clear();
          }
  
          @Override
          public Set<K> keySet() {
            return primary.keySet();
          }
  
          @Override
          public Collection<V> values() {
            return secondary.values();
          }
  
          @Override
          public Set<Entry<K, V>> entrySet() {
            return primary.entrySet().stream()
                .map(
                    entry ->
                        new AbstractMap.SimpleImmutableEntry<>(
                            entry.getKey(), entry.getValue().getValue()))
                .collect(Collectors.toSet());
          }
        };
  
    /**
     * Returns the value corresponding to the given ordinal.
     *
     * @param id ordinal value for lookup
     * @return an instance of V
     */
    @Override
    public V getByOrdinal(int id) {
      return secondary.get(id);
    }
  
    /**
     * Returns the ordinal corresponding to the given key.
     *
     * @param key key for ordinal lookup
     * @return ordinal value corresponding to key if it exists or -1
     */
    @Override
    public int getOrdinal(K key) {
      Map.Entry<Integer, V> pair = primary.get(key);
      if (pair != null) {
        return pair.getKey();
      }
      return -1;
    }
  
    @Override
    public int size() {
      return delegate.size();
    }
  
    @Override
    public boolean isEmpty() {
      return delegate.isEmpty();
    }
  
    @Override
    public Collection<V> getAll(K key) {
      if (delegate.containsKey(key)) {
        List<V> list = new ArrayList<>(1);
        list.add(get(key));
        return list;
      }
      return null;
    }
  
    @Override
    public V get(K key) {
      return delegate.get(key);
    }
  
    /**
     * Inserts the tuple (key, value) into the map extending the semantics of {@link Map#put} with
     * automatic ordinal assignment. A new ordinal is assigned if key does not exists. Otherwise the
     * same ordinal is re-used but the value is replaced.
     *
     * @see java.util.Map#put
     */
    @Override
    public boolean put(K key, V value, boolean overwrite) {
      return delegate.put(key, value) != null;
    }
  
    @Override
    public Collection<V> values() {
      return delegate.values();
    }
  
    @Override
    public boolean remove(K key, V value) {
      return false;
    }
  
    @Override
    public boolean containsKey(Object key) {
      return delegate.containsKey(key);
    }
  
    /**
     * Removes the element corresponding to the key if exists extending the semantics of {@link
     * java.util.Map#remove} with ordinal re-cycling. The ordinal corresponding to the given key may
     * be re-assigned to another tuple. It is important that consumer checks the ordinal value via
     * {@link MapWithOrdinalImpl#getOrdinal(Object)} before attempting to look-up by ordinal.
     *
     * @see java.util.Map#remove
     */
    @Override
    public boolean removeAll(K key) {
      return delegate.remove(key) != null;
    }
  
    @Override
    public void clear() {
      delegate.clear();
    }
  
    @Override
    public Set<K> keys() {
      return delegate.keySet();
    }
  }
  