/*
 * 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;
import java.util.stream.StreamSupport;

import org.apache.arrow.util.Preconditions;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import io.netty.util.collection.IntObjectHashMap;
import io.netty.util.collection.IntObjectMap;

/**
 * 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 static final Logger logger = LoggerFactory.getLogger(MapWithOrdinalImpl.class);

  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();
    }

    public boolean put(K key, V value, boolean override) {
      return put(key, value) != null;
    }

    @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 StreamSupport.stream(secondary.entries().spliterator(), false)
          .map((IntObjectMap.PrimitiveEntry<V> t) -> Preconditions.checkNotNull(t).value())
          .collect(Collectors.toList());
    }

    @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
   */
  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
   */
  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();
  }

}
