/*
 * Copyright (C) 2008 The Guava Authors
 *
 * Licensed 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 com.google.common.collect;

import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkPositionIndex;
import static com.google.common.collect.CollectPreconditions.checkEntryNotNull;
import static com.google.common.collect.ImmutableMapEntry.createEntryArray;

import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.annotations.VisibleForTesting;
import com.google.common.collect.ImmutableMapEntry.NonTerminalImmutableMapEntry;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.io.Serializable;
import java.util.function.BiConsumer;
import org.checkerframework.checker.nullness.qual.Nullable;

Implementation of ImmutableMap with two or more entries. 
Author:
Jesse Wilson, Kevin Bourrillion, Gregory Kick/**
 * Implementation of {@link ImmutableMap} with two or more entries.
 *
 * @author Jesse Wilson
 * @author Kevin Bourrillion
 * @author Gregory Kick
 */
@GwtCompatible(serializable = true, emulated = true)
final class RegularImmutableMap<K, V> extends ImmutableMap<K, V> {
  @SuppressWarnings("unchecked")
  static final ImmutableMap<Object, Object> EMPTY =
      new RegularImmutableMap<>((Entry<Object, Object>[]) ImmutableMap.EMPTY_ENTRY_ARRAY, null, 0);

  
Closed addressing tends to perform well even with high load factors. Being conservative here
ensures that the table is still likely to be relatively sparse (hence it misses fast) while
saving space.
/**
   * Closed addressing tends to perform well even with high load factors. Being conservative here
   * ensures that the table is still likely to be relatively sparse (hence it misses fast) while
   * saving space.
   */
  @VisibleForTesting static final double MAX_LOAD_FACTOR = 1.2;

  
Maximum allowed false positive probability of detecting a hash flooding attack given random
input.
/**
   * Maximum allowed false positive probability of detecting a hash flooding attack given random
   * input.
   */
  @VisibleForTesting static final double HASH_FLOODING_FPP = 0.001;

  
Maximum allowed length of a hash table bucket before falling back to a j.u.HashMap based
implementation. Experimentally determined.
/**
   * Maximum allowed length of a hash table bucket before falling back to a j.u.HashMap based
   * implementation. Experimentally determined.
   */
  @VisibleForTesting static final int MAX_HASH_BUCKET_LENGTH = 8;

  // entries in insertion order
  @VisibleForTesting final transient Entry<K, V>[] entries;
  // array of linked lists of entries
  private final transient ImmutableMapEntry<K, V>[] table;
  // 'and' with an int to get a table index
  private final transient int mask;

  static <K, V> ImmutableMap<K, V> fromEntries(Entry<K, V>... entries) {
    return fromEntryArray(entries.length, entries);
  }

  
Creates an ImmutableMap from the first n entries in entryArray. This implementation may replace
the entries in entryArray with its own entry objects (though they will have the same key/value
contents), and may take ownership of entryArray.
/**
   * Creates an ImmutableMap from the first n entries in entryArray. This implementation may replace
   * the entries in entryArray with its own entry objects (though they will have the same key/value
   * contents), and may take ownership of entryArray.
   */
  static <K, V> ImmutableMap<K, V> fromEntryArray(int n, Entry<K, V>[] entryArray) {
    checkPositionIndex(n, entryArray.length);
    if (n == 0) {
      return (RegularImmutableMap<K, V>) EMPTY;
    }
    Entry<K, V>[] entries;
    if (n == entryArray.length) {
      entries = entryArray;
    } else {
      entries = createEntryArray(n);
    }
    int tableSize = Hashing.closedTableSize(n, MAX_LOAD_FACTOR);
    ImmutableMapEntry<K, V>[] table = createEntryArray(tableSize);
    int mask = tableSize - 1;
    for (int entryIndex = 0; entryIndex < n; entryIndex++) {
      Entry<K, V> entry = entryArray[entryIndex];
      K key = entry.getKey();
      V value = entry.getValue();
      checkEntryNotNull(key, value);
      int tableIndex = Hashing.smear(key.hashCode()) & mask;
      @Nullable ImmutableMapEntry<K, V> existing = table[tableIndex];
      // prepend, not append, so the entries can be immutable
      ImmutableMapEntry<K, V> newEntry =
          (existing == null)
              ? makeImmutable(entry, key, value)
              : new NonTerminalImmutableMapEntry<K, V>(key, value, existing);
      table[tableIndex] = newEntry;
      entries[entryIndex] = newEntry;
      int bucketSize = checkNoConflictInKeyBucket(key, newEntry, existing);
      if (bucketSize > MAX_HASH_BUCKET_LENGTH) {
        // probable hash flooding attack, fall back to j.u.HM based implementation and use its
        // implementation of hash flooding protection
        return JdkBackedImmutableMap.create(n, entryArray);
      }
    }
    return new RegularImmutableMap<>(entries, table, mask);
  }

  
Makes an entry usable internally by a new ImmutableMap without rereading its contents. /** Makes an entry usable internally by a new ImmutableMap without rereading its contents. */
  static <K, V> ImmutableMapEntry<K, V> makeImmutable(Entry<K, V> entry, K key, V value) {
    boolean reusable =
        entry instanceof ImmutableMapEntry && ((ImmutableMapEntry<K, V>) entry).isReusable();
    return reusable ? (ImmutableMapEntry<K, V>) entry : new ImmutableMapEntry<K, V>(key, value);
  }

  
Makes an entry usable internally by a new ImmutableMap. /** Makes an entry usable internally by a new ImmutableMap. */
  static <K, V> ImmutableMapEntry<K, V> makeImmutable(Entry<K, V> entry) {
    return makeImmutable(entry, entry.getKey(), entry.getValue());
  }

  private RegularImmutableMap(Entry<K, V>[] entries, ImmutableMapEntry<K, V>[] table, int mask) {
    this.entries = entries;
    this.table = table;
    this.mask = mask;
  }

  
Throws:
IllegalArgumentException – if another entry in the bucket has the same key
Returns:
number of entries in this bucket/**
   * @return number of entries in this bucket
   * @throws IllegalArgumentException if another entry in the bucket has the same key
   */
  @CanIgnoreReturnValue
  static int checkNoConflictInKeyBucket(
      Object key, Entry<?, ?> entry, @Nullable ImmutableMapEntry<?, ?> keyBucketHead) {
    int bucketSize = 0;
    for (; keyBucketHead != null; keyBucketHead = keyBucketHead.getNextInKeyBucket()) {
      checkNoConflict(!key.equals(keyBucketHead.getKey()), "key", entry, keyBucketHead);
      bucketSize++;
    }
    return bucketSize;
  }

  @Override
  public V get(@Nullable Object key) {
    return get(key, table, mask);
  }

  static <V> @Nullable V get(
      @Nullable Object key, ImmutableMapEntry<?, V> @Nullable [] keyTable, int mask) {
    if (key == null || keyTable == null) {
      return null;
    }
    int index = Hashing.smear(key.hashCode()) & mask;
    for (ImmutableMapEntry<?, V> entry = keyTable[index];
        entry != null;
        entry = entry.getNextInKeyBucket()) {
      Object candidateKey = entry.getKey();

      /*
       * Assume that equals uses the == optimization when appropriate, and that
       * it would check hash codes as an optimization when appropriate. If we
       * did these things, it would just make things worse for the most
       * performance-conscious users.
       */
      if (key.equals(candidateKey)) {
        return entry.getValue();
      }
    }
    return null;
  }

  @Override
  public void forEach(BiConsumer<? super K, ? super V> action) {
    checkNotNull(action);
    for (Entry<K, V> entry : entries) {
      action.accept(entry.getKey(), entry.getValue());
    }
  }

  @Override
  public int size() {
    return entries.length;
  }

  @Override
  boolean isPartialView() {
    return false;
  }

  @Override
  ImmutableSet<Entry<K, V>> createEntrySet() {
    return new ImmutableMapEntrySet.RegularEntrySet<>(this, entries);
  }

  @Override
  ImmutableSet<K> createKeySet() {
    return new KeySet<>(this);
  }

  @GwtCompatible(emulated = true)
  private static final class KeySet<K, V> extends IndexedImmutableSet<K> {
    private final RegularImmutableMap<K, V> map;

    KeySet(RegularImmutableMap<K, V> map) {
      this.map = map;
    }

    @Override
    K get(int index) {
      return map.entries[index].getKey();
    }

    @Override
    public boolean contains(Object object) {
      return map.containsKey(object);
    }

    @Override
    boolean isPartialView() {
      return true;
    }

    @Override
    public int size() {
      return map.size();
    }

    @GwtIncompatible // serialization
    @Override
    Object writeReplace() {
      return new SerializedForm<K>(map);
    }

    @GwtIncompatible // serialization
    private static class SerializedForm<K> implements Serializable {
      final ImmutableMap<K, ?> map;

      SerializedForm(ImmutableMap<K, ?> map) {
        this.map = map;
      }

      Object readResolve() {
        return map.keySet();
      }

      private static final long serialVersionUID = 0;
    }
  }

  @Override
  ImmutableCollection<V> createValues() {
    return new Values<>(this);
  }

  @GwtCompatible(emulated = true)
  private static final class Values<K, V> extends ImmutableList<V> {
    final RegularImmutableMap<K, V> map;

    Values(RegularImmutableMap<K, V> map) {
      this.map = map;
    }

    @Override
    public V get(int index) {
      return map.entries[index].getValue();
    }

    @Override
    public int size() {
      return map.size();
    }

    @Override
    boolean isPartialView() {
      return true;
    }

    @GwtIncompatible // serialization
    @Override
    Object writeReplace() {
      return new SerializedForm<V>(map);
    }

    @GwtIncompatible // serialization
    private static class SerializedForm<V> implements Serializable {
      final ImmutableMap<?, V> map;

      SerializedForm(ImmutableMap<?, V> map) {
        this.map = map;
      }

      Object readResolve() {
        return map.values();
      }

      private static final long serialVersionUID = 0;
    }
  }

  // This class is never actually serialized directly, but we have to make the
  // warning go away (and suppressing would suppress for all nested classes too)
  private static final long serialVersionUID = 0;
}