/*******************************************************************************
 * Copyright 2011 See AUTHORS file.
 * 
 * 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.esotericsoftware.kryo.util;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.NoSuchElementException;

/** An unordered map that uses identity comparison for keys. This implementation is a cuckoo hash map using 3 hashes, random
 * walking, and a small stash for problematic keys. Null keys are not allowed. Null values are allowed. No allocation is done
 * except when growing the table size. <br>
 * <br>
 * This map performs very fast get, containsKey, and remove (typically O(1), worst case O(log(n))). Put may be a bit slower,
 * depending on hash collisions. Load factors greater than 0.91 greatly increase the chances the map will have to rehash to the
 * next higher POT size.
 * @author Nathan Sweet */
public class IdentityMap<K, V> {
	private static final int PRIME1 = 0xbe1f14b1;
	private static final int PRIME2 = 0xb4b82e39;
	private static final int PRIME3 = 0xced1c241;

	public int size;

	K[] keyTable;
	V[] valueTable;
	int capacity, stashSize;

	private float loadFactor;
	private int hashShift, mask, threshold;
	private int stashCapacity;
	private int pushIterations;

	private Entries entries;
	private Values values;
	private Keys keys;

	/** Creates a new map with an initial capacity of 32 and a load factor of 0.8. This map will hold 25 items before growing the
	 * backing table. */
	public IdentityMap () {
		this(32, 0.8f);
	}

	/** Creates a new map with a load factor of 0.8. This map will hold initialCapacity * 0.8 items before growing the backing
	 * table. */
	public IdentityMap (int initialCapacity) {
		this(initialCapacity, 0.8f);
	}

	/** Creates a new map with the specified initial capacity and load factor. This map will hold initialCapacity * loadFactor items
	 * before growing the backing table. */
	public IdentityMap (int initialCapacity, float loadFactor) {
		if (initialCapacity < 0) throw new IllegalArgumentException("initialCapacity must be >= 0: " + initialCapacity);
		if (capacity > 1 << 30) throw new IllegalArgumentException("initialCapacity is too large: " + initialCapacity);
		capacity = ObjectMap.nextPowerOfTwo(initialCapacity);

		if (loadFactor <= 0) throw new IllegalArgumentException("loadFactor must be > 0: " + loadFactor);
		this.loadFactor = loadFactor;

		threshold = (int)(capacity * loadFactor);
		mask = capacity - 1;
		hashShift = 31 - Integer.numberOfTrailingZeros(capacity);
		stashCapacity = Math.max(3, (int)Math.ceil(Math.log(capacity)) * 2);
		pushIterations = Math.max(Math.min(capacity, 8), (int)Math.sqrt(capacity) / 8);

		keyTable = (K[])new Object[capacity + stashCapacity];
		valueTable = (V[])new Object[keyTable.length];
	}

	public V put (K key, V value) {
		if (key == null) throw new IllegalArgumentException("key cannot be null.");
		K[] keyTable = this.keyTable;

		// Check for existing keys.
		int hashCode = System.identityHashCode(key);
		int index1 = hashCode & mask;
		K key1 = keyTable[index1];
		if (key1 == key) {
			V oldValue = valueTable[index1];
			valueTable[index1] = value;
			return oldValue;
		}

		int index2 = hash2(hashCode);
		K key2 = keyTable[index2];
		if (key2 == key) {
			V oldValue = valueTable[index2];
			valueTable[index2] = value;
			return oldValue;
		}

		int index3 = hash3(hashCode);
		K key3 = keyTable[index3];
		if (key3 == key) {
			V oldValue = valueTable[index3];
			valueTable[index3] = value;
			return oldValue;
		}

		// Update key in the stash.
		for (int i = capacity, n = i + stashSize; i < n; i++) {
			if (keyTable[i] == key) {
				V oldValue = valueTable[i];
				valueTable[i] = value;
				return oldValue;
			}
		}

		// Check for empty buckets.
		if (key1 == null) {
			keyTable[index1] = key;
			valueTable[index1] = value;
			if (size++ >= threshold) resize(capacity << 1);
			return null;
		}

		if (key2 == null) {
			keyTable[index2] = key;
			valueTable[index2] = value;
			if (size++ >= threshold) resize(capacity << 1);
			return null;
		}

		if (key3 == null) {
			keyTable[index3] = key;
			valueTable[index3] = value;
			if (size++ >= threshold) resize(capacity << 1);
			return null;
		}

		push(key, value, index1, key1, index2, key2, index3, key3);
		return null;
	}

	/** Skips checks for existing keys. */
	private void putResize (K key, V value) {
		// Check for empty buckets.
		int hashCode = System.identityHashCode(key);
		int index1 = hashCode & mask;
		K key1 = keyTable[index1];
		if (key1 == null) {
			keyTable[index1] = key;
			valueTable[index1] = value;
			if (size++ >= threshold) resize(capacity << 1);
			return;
		}

		int index2 = hash2(hashCode);
		K key2 = keyTable[index2];
		if (key2 == null) {
			keyTable[index2] = key;
			valueTable[index2] = value;
			if (size++ >= threshold) resize(capacity << 1);
			return;
		}

		int index3 = hash3(hashCode);
		K key3 = keyTable[index3];
		if (key3 == null) {
			keyTable[index3] = key;
			valueTable[index3] = value;
			if (size++ >= threshold) resize(capacity << 1);
			return;
		}

		push(key, value, index1, key1, index2, key2, index3, key3);
	}

	private void push (K insertKey, V insertValue, int index1, K key1, int index2, K key2, int index3, K key3) {
		K[] keyTable = this.keyTable;
		V[] valueTable = this.valueTable;
		int mask = this.mask;

		// Push keys until an empty bucket is found.
		K evictedKey;
		V evictedValue;
		int i = 0, pushIterations = this.pushIterations;
		do {
			// Replace the key and value for one of the hashes.
			switch (ObjectMap.random.nextInt(3)) {
			case 0:
				evictedKey = key1;
				evictedValue = valueTable[index1];
				keyTable[index1] = insertKey;
				valueTable[index1] = insertValue;
				break;
			case 1:
				evictedKey = key2;
				evictedValue = valueTable[index2];
				keyTable[index2] = insertKey;
				valueTable[index2] = insertValue;
				break;
			default:
				evictedKey = key3;
				evictedValue = valueTable[index3];
				keyTable[index3] = insertKey;
				valueTable[index3] = insertValue;
				break;
			}

			// If the evicted key hashes to an empty bucket, put it there and stop.
			int hashCode = System.identityHashCode(evictedKey);
			index1 = hashCode & mask;
			key1 = keyTable[index1];
			if (key1 == null) {
				keyTable[index1] = evictedKey;
				valueTable[index1] = evictedValue;
				if (size++ >= threshold) resize(capacity << 1);
				return;
			}

			index2 = hash2(hashCode);
			key2 = keyTable[index2];
			if (key2 == null) {
				keyTable[index2] = evictedKey;
				valueTable[index2] = evictedValue;
				if (size++ >= threshold) resize(capacity << 1);
				return;
			}

			index3 = hash3(hashCode);
			key3 = keyTable[index3];
			if (key3 == null) {
				keyTable[index3] = evictedKey;
				valueTable[index3] = evictedValue;
				if (size++ >= threshold) resize(capacity << 1);
				return;
			}

			if (++i == pushIterations) break;

			insertKey = evictedKey;
			insertValue = evictedValue;
		} while (true);

		putStash(evictedKey, evictedValue);
	}

	private void putStash (K key, V value) {
		if (stashSize == stashCapacity) {
			// Too many pushes occurred and the stash is full, increase the table size.
			resize(capacity << 1);
			put(key, value);
			return;
		}
		// Store key in the stash.
		int index = capacity + stashSize;
		keyTable[index] = key;
		valueTable[index] = value;
		stashSize++;
		size++;
	}

	public V get (K key) {
		int hashCode = System.identityHashCode(key);
		int index = hashCode & mask;
		if (key != keyTable[index]) {
			index = hash2(hashCode);
			if (key != keyTable[index]) {
				index = hash3(hashCode);
				if (key != keyTable[index]) return getStash(key, null);
			}
		}
		return valueTable[index];
	}

	public V get (K key, V defaultValue) {
		int hashCode = System.identityHashCode(key);
		int index = hashCode & mask;
		if (key != keyTable[index]) {
			index = hash2(hashCode);
			if (key != keyTable[index]) {
				index = hash3(hashCode);
				if (key != keyTable[index]) return getStash(key, defaultValue);
			}
		}
		return valueTable[index];
	}

	private V getStash (K key, V defaultValue) {
		K[] keyTable = this.keyTable;
		for (int i = capacity, n = i + stashSize; i < n; i++)
			if (keyTable[i] == key) return valueTable[i];
		return defaultValue;
	}

	public V remove (K key) {
		int hashCode = System.identityHashCode(key);
		int index = hashCode & mask;
		if (keyTable[index] == key) {
			keyTable[index] = null;
			V oldValue = valueTable[index];
			valueTable[index] = null;
			size--;
			return oldValue;
		}

		index = hash2(hashCode);
		if (keyTable[index] == key) {
			keyTable[index] = null;
			V oldValue = valueTable[index];
			valueTable[index] = null;
			size--;
			return oldValue;
		}

		index = hash3(hashCode);
		if (keyTable[index] == key) {
			keyTable[index] = null;
			V oldValue = valueTable[index];
			valueTable[index] = null;
			size--;
			return oldValue;
		}

		return removeStash(key);
	}

	V removeStash (K key) {
		K[] keyTable = this.keyTable;
		for (int i = capacity, n = i + stashSize; i < n; i++) {
			if (keyTable[i] == key) {
				V oldValue = valueTable[i];
				removeStashIndex(i);
				size--;
				return oldValue;
			}
		}
		return null;
	}

	void removeStashIndex (int index) {
		// If the removed location was not last, move the last tuple to the removed location.
		stashSize--;
		int lastIndex = capacity + stashSize;
		if (index < lastIndex) {
			keyTable[index] = keyTable[lastIndex];
			valueTable[index] = valueTable[lastIndex];
			valueTable[lastIndex] = null;
		} else
			valueTable[index] = null;
	}

	public void clear () {
		K[] keyTable = this.keyTable;
		V[] valueTable = this.valueTable;
		for (int i = capacity + stashSize; i-- > 0;) {
			keyTable[i] = null;
			valueTable[i] = null;
		}
		size = 0;
		stashSize = 0;
	}

	/** Returns true if the specified value is in the map. Note this traverses the entire map and compares every value, which may be
	 * an expensive operation.
	 * @param identity If true, uses == to compare the specified value with values in the map. If false, uses
	 *           {@link #equals(Object)}. */
	public boolean containsValue (Object value, boolean identity) {
		V[] valueTable = this.valueTable;
		if (value == null) {
			K[] keyTable = this.keyTable;
			for (int i = capacity + stashSize; i-- > 0;)
				if (keyTable[i] != null && valueTable[i] == null) return true;
		} else if (identity) {
			for (int i = capacity + stashSize; i-- > 0;)
				if (valueTable[i] == value) return true;
		} else {
			for (int i = capacity + stashSize; i-- > 0;)
				if (value.equals(valueTable[i])) return true;
		}
		return false;
	}

	public boolean containsKey (K key) {
		int hashCode = System.identityHashCode(key);
		int index = hashCode & mask;
		if (key != keyTable[index]) {
			index = hash2(hashCode);
			if (key != keyTable[index]) {
				index = hash3(hashCode);
				if (key != keyTable[index]) return containsKeyStash(key);
			}
		}
		return true;
	}

	private boolean containsKeyStash (K key) {
		K[] keyTable = this.keyTable;
		for (int i = capacity, n = i + stashSize; i < n; i++)
			if (keyTable[i] == key) return true;
		return false;
	}

	/** Returns the key for the specified value, or null if it is not in the map. Note this traverses the entire map and compares
	 * every value, which may be an expensive operation.
	 * @param identity If true, uses == to compare the specified value with values in the map. If false, uses
	 *           {@link #equals(Object)}. */
	public K findKey (Object value, boolean identity) {
		V[] valueTable = this.valueTable;
		if (value == null) {
			K[] keyTable = this.keyTable;
			for (int i = capacity + stashSize; i-- > 0;)
				if (keyTable[i] != null && valueTable[i] == null) return keyTable[i];
		} else if (identity) {
			for (int i = capacity + stashSize; i-- > 0;)
				if (valueTable[i] == value) return keyTable[i];
		} else {
			for (int i = capacity + stashSize; i-- > 0;)
				if (value.equals(valueTable[i])) return keyTable[i];
		}
		return null;
	}

	/** Increases the size of the backing array to acommodate the specified number of additional items. Useful before adding many
	 * items to avoid multiple backing array resizes. */
	public void ensureCapacity (int additionalCapacity) {
		int sizeNeeded = size + additionalCapacity;
		if (sizeNeeded >= threshold) resize(ObjectMap.nextPowerOfTwo((int)(sizeNeeded / loadFactor)));
	}

	private void resize (int newSize) {
		int oldEndIndex = capacity + stashSize;

		capacity = newSize;
		threshold = (int)(newSize * loadFactor);
		mask = newSize - 1;
		hashShift = 31 - Integer.numberOfTrailingZeros(newSize);
		stashCapacity = Math.max(3, (int)Math.ceil(Math.log(newSize)) * 2);
		pushIterations = Math.max(Math.min(newSize, 8), (int)Math.sqrt(newSize) / 8);

		K[] oldKeyTable = keyTable;
		V[] oldValueTable = valueTable;

		keyTable = (K[])new Object[newSize + stashCapacity];
		valueTable = (V[])new Object[newSize + stashCapacity];

		size = 0;
		stashSize = 0;
		for (int i = 0; i < oldEndIndex; i++) {
			K key = oldKeyTable[i];
			if (key != null) putResize(key, oldValueTable[i]);
		}
	}

	private int hash2 (long h) {
		h *= PRIME2;
		return (int)((h ^ h >>> hashShift) & mask);
	}

	private int hash3 (long h) {
		h *= PRIME3;
		return (int)((h ^ h >>> hashShift) & mask);
	}

	public String toString () {
		if (size == 0) return "[]";
		StringBuilder buffer = new StringBuilder(32);
		buffer.append('[');
		K[] keyTable = this.keyTable;
		V[] valueTable = this.valueTable;
		int i = keyTable.length;
		while (i-- > 0) {
			K key = keyTable[i];
			if (key == null) continue;
			buffer.append(key);
			buffer.append('=');
			buffer.append(valueTable[i]);
			break;
		}
		while (i-- > 0) {
			K key = keyTable[i];
			if (key == null) continue;
			buffer.append(", ");
			buffer.append(key);
			buffer.append('=');
			buffer.append(valueTable[i]);
		}
		buffer.append(']');
		return buffer.toString();
	}

	/** Returns an iterator for the entries in the map. Remove is supported. Note that the same iterator instance is returned each
	 * time this method is called. Use the {@link Entries} constructor for nested or multithreaded iteration. */
	public Entries<K, V> entries () {
		if (entries == null)
			entries = new Entries(this);
		else
			entries.reset();
		return entries;
	}

	/** Returns an iterator for the values in the map. Remove is supported. Note that the same iterator instance is returned each
	 * time this method is called. Use the {@link Entries} constructor for nested or multithreaded iteration. */
	public Values<V> values () {
		if (values == null)
			values = new Values(this);
		else
			values.reset();
		return values;
	}

	/** Returns an iterator for the keys in the map. Remove is supported. Note that the same iterator instance is returned each time
	 * this method is called. Use the {@link Entries} constructor for nested or multithreaded iteration. */
	public Keys<K> keys () {
		if (keys == null)
			keys = new Keys(this);
		else
			keys.reset();
		return keys;
	}

	static public class Entry<K, V> {
		public K key;
		public V value;

		public String toString () {
			return key + "=" + value;
		}
	}

	static private class MapIterator<K, V> {
		public boolean hasNext;

		final IdentityMap<K, V> map;
		int nextIndex, currentIndex;

		public MapIterator (IdentityMap<K, V> map) {
			this.map = map;
			reset();
		}

		public void reset () {
			currentIndex = -1;
			nextIndex = -1;
			findNextIndex();
		}

		void findNextIndex () {
			hasNext = false;
			K[] keyTable = map.keyTable;
			for (int n = map.capacity + map.stashSize; ++nextIndex < n;) {
				if (keyTable[nextIndex] != null) {
					hasNext = true;
					break;
				}
			}
		}

		public void remove () {
			if (currentIndex < 0) throw new IllegalStateException("next must be called before remove.");
			if (currentIndex >= map.capacity) {
				map.removeStashIndex(currentIndex);
			} else {
				map.keyTable[currentIndex] = null;
				map.valueTable[currentIndex] = null;
			}
			currentIndex = -1;
			map.size--;
		}
	}

	static public class Entries<K, V> extends MapIterator<K, V> implements Iterable<Entry<K, V>>, Iterator<Entry<K, V>> {
		private Entry<K, V> entry = new Entry();

		public Entries (IdentityMap<K, V> map) {
			super(map);
		}

		/** Note the same entry instance is returned each time this method is called. */
		public Entry<K, V> next () {
			if (!hasNext) throw new NoSuchElementException();
			K[] keyTable = map.keyTable;
			entry.key = keyTable[nextIndex];
			entry.value = map.valueTable[nextIndex];
			currentIndex = nextIndex;
			findNextIndex();
			return entry;
		}

		public boolean hasNext () {
			return hasNext;
		}

		public Iterator<Entry<K, V>> iterator () {
			return this;
		}
	}

	static public class Values<V> extends MapIterator<Object, V> implements Iterable<V>, Iterator<V> {
		public Values (IdentityMap<?, V> map) {
			super((IdentityMap<Object, V>)map);
		}

		public boolean hasNext () {
			return hasNext;
		}

		public V next () {
			V value = map.valueTable[nextIndex];
			currentIndex = nextIndex;
			findNextIndex();
			return value;
		}

		public Iterator<V> iterator () {
			return this;
		}

		/** Returns a new array containing the remaining values. */
		public ArrayList<V> toArray () {
			ArrayList array = new ArrayList(map.size);
			while (hasNext)
				array.add(next());
			return array;
		}

		/** Returns a new array containing the remaining values. */
		public void toArray (ArrayList<V> array) {
			while (hasNext)
				array.add(next());
		}
	}

	static public class Keys<K> extends MapIterator<K, Object> implements Iterable<K>, Iterator<K> {
		public Keys (IdentityMap<K, ?> map) {
			super((IdentityMap<K, Object>)map);
		}

		public boolean hasNext () {
			return hasNext;
		}

		public K next () {
			K key = map.keyTable[nextIndex];
			currentIndex = nextIndex;
			findNextIndex();
			return key;
		}

		public Iterator<K> iterator () {
			return this;
		}

		/** Returns a new array containing the remaining keys. */
		public ArrayList<K> toArray () {
			ArrayList array = new ArrayList(map.size);
			while (hasNext)
				array.add(next());
			return array;
		}
	}
}