/*******************************************************************************
 * Copyright (c) 2000, 2017 IBM Corporation and others.
 *
 * This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License 2.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-2.0/
 *
 * SPDX-License-Identifier: EPL-2.0
 *
 * Contributors:
 *     Peter Shipton - original hashtable implementation
 *     Nick Edgar - added element comparer support
 *******************************************************************************/

package org.eclipse.jface.viewers;

import java.util.Enumeration;
import java.util.NoSuchElementException;

/**
 * CustomHashtable associates keys with values. Keys and values cannot be null.
 * The size of the Hashtable is the number of key/value pairs it contains.
 * The capacity is the number of key/value pairs the Hashtable can hold.
 * The load factor is a float value which determines how full the Hashtable
 * gets before expanding the capacity. If the load factor of the Hashtable
 * is exceeded, the capacity is doubled.
 * <p>
 * CustomHashtable allows a custom comparator and hash code provider.
 */
/* package */final class CustomHashtable {

	/**
	 * HashMapEntry is an internal class which is used to hold the entries of a Hashtable.
	 */
	private static class HashMapEntry {
		Object key, value;

		HashMapEntry next;

		HashMapEntry(Object theKey, Object theValue) {
			key = theKey;
			value = theValue;
		}
	}

	private static final class EmptyEnumerator implements Enumeration {
		@Override
		public boolean hasMoreElements() {
			return false;
		}

		@Override
		public Object nextElement() {
			throw new NoSuchElementException();
		}
	}

	private class HashEnumerator implements Enumeration {
		boolean key;

		int start;

		HashMapEntry entry;

		HashEnumerator(boolean isKey) {
			key = isKey;
			start = firstSlot;
		}

		@Override
		public boolean hasMoreElements() {
			if (entry != null) {
				return true;
			}
			while (start <= lastSlot) {
				if (elementData[start++] != null) {
					entry = elementData[start - 1];
					return true;
				}
			}
			return false;
		}

		@Override
		public Object nextElement() {
			if (hasMoreElements()) {
				Object result = key ? entry.key : entry.value;
				entry = entry.next;
				return result;
			}
			throw new NoSuchElementException();
		}
	}

	transient int elementCount;

	transient HashMapEntry[] elementData;

	private float loadFactor;

	private int threshold;

	transient int firstSlot = 0;

	transient int lastSlot = -1;

	transient private IElementComparer comparer;

	private static final EmptyEnumerator emptyEnumerator = new EmptyEnumerator();

	/**
	 * The default capacity used when not specified in the constructor.
	 */
	public static final int DEFAULT_CAPACITY = 13;

	/**
	 * Constructs a new Hashtable using the default capacity
	 * and load factor.
	 */
	public CustomHashtable() {
		this(13);
	}

	/**
	 * Constructs a new Hashtable using the specified capacity
	 * and the default load factor.
	 *
	 * @param capacity the initial capacity
	 */
	public CustomHashtable(int capacity) {
		this(capacity, null);
	}

	/**
	 * Constructs a new hash table with the default capacity and the given
	 * element comparer.
	 *
	 * @param comparer the element comparer to use to compare keys and obtain
	 *   hash codes for keys, or <code>null</code>  to use the normal
	 *   <code>equals</code> and <code>hashCode</code> methods
	 */
	public CustomHashtable(IElementComparer comparer) {
		this(DEFAULT_CAPACITY, comparer);
	}

	/**
	 * Constructs a new hash table with the given capacity and the given
	 * element comparer.
	 *
	 * @param capacity the maximum number of elements that can be added without
	 *   rehashing
	 * @param comparer the element comparer to use to compare keys and obtain
	 *   hash codes for keys, or <code>null</code>  to use the normal
	 *   <code>equals</code> and <code>hashCode</code> methods
	 */
	public CustomHashtable(int capacity, IElementComparer comparer) {
		if (capacity >= 0) {
			elementCount = 0;
			elementData = new HashMapEntry[capacity == 0 ? 1 : capacity];
			firstSlot = elementData.length;
			loadFactor = 0.75f;
			computeMaxSize();
		} else {
			throw new IllegalArgumentException();
		}
		this.comparer = comparer;
	}

	/**
	 * Constructs a new hash table with enough capacity to hold all keys in the
	 * given hash table, then adds all key/value pairs in the given hash table
	 * to the new one, using the given element comparer.
	 * @param table the original hash table to copy from
	 *
	 * @param comparer the element comparer to use to compare keys and obtain
	 *   hash codes for keys, or <code>null</code>  to use the normal
	 *   <code>equals</code> and <code>hashCode</code> methods
	 */
	public CustomHashtable(CustomHashtable table, IElementComparer comparer) {
		this(table.size() * 2, comparer);
		for (int i = table.elementData.length; --i >= 0;) {
			HashMapEntry entry = table.elementData[i];
			while (entry != null) {
				put(entry.key, entry.value);
				entry = entry.next;
			}
		}
	}

	/**
	 * Returns the element comparer used  to compare keys and to obtain
	 * hash codes for keys, or <code>null</code> if no comparer has been
	 * provided.
	 *
	 * @return the element comparer or <code>null</code>
	 *
	 * @since 3.2
	 */
	public IElementComparer getComparer() {
		return comparer;
	}

	private void computeMaxSize() {
		threshold = (int) (elementData.length * loadFactor);
	}

	/**
	 * Answers if this Hashtable contains the specified object as a key
	 * of one of the key/value pairs.
	 *
	 * @param		key	the object to look for as a key in this Hashtable
	 * @return		true if object is a key in this Hashtable, false otherwise
	 */
	public boolean containsKey(Object key) {
		return getEntry(key) != null;
	}

	/**
	 * Answers an Enumeration on the values of this Hashtable. The
	 * results of the Enumeration may be affected if the contents
	 * of this Hashtable are modified.
	 *
	 * @return		an Enumeration of the values of this Hashtable
	 */
	public Enumeration elements() {
		if (elementCount == 0) {
			return emptyEnumerator;
		}
		return new HashEnumerator(false);
	}

	/**
	 * Answers the value associated with the specified key in
	 * this Hashtable.
	 *
	 * @param		key	the key of the value returned
	 * @return		the value associated with the specified key, null if the specified key
	 *				does not exist
	 */
	public Object get(Object key) {
		int index = (hashCode(key) & 0x7FFFFFFF) % elementData.length;
		HashMapEntry entry = elementData[index];
		while (entry != null) {
			if (keyEquals(key, entry.key)) {
				return entry.value;
			}
			entry = entry.next;
		}
		return null;
	}

	private HashMapEntry getEntry(Object key) {
		int index = (hashCode(key) & 0x7FFFFFFF) % elementData.length;
		HashMapEntry entry = elementData[index];
		while (entry != null) {
			if (keyEquals(key, entry.key)) {
				return entry;
			}
			entry = entry.next;
		}
		return null;
	}

	/**
	 * Answers the hash code for the given key.
	 */
	private int hashCode(Object key) {
		if (comparer == null) {
			return key.hashCode();
		}
		return comparer.hashCode(key);
	}

	/**
	 * Compares two keys for equality.
	 */
	private boolean keyEquals(Object a, Object b) {
		if (comparer == null) {
			return a.equals(b);
		}
		return comparer.equals(a, b);
	}

	/**
	 * Answers an Enumeration on the keys of this Hashtable. The
	 * results of the Enumeration may be affected if the contents
	 * of this Hashtable are modified.
	 *
	 * @return		an Enumeration of the keys of this Hashtable
	 */
	public Enumeration keys() {
		if (elementCount == 0) {
			return emptyEnumerator;
		}
		return new HashEnumerator(true);
	}

	/**
	 * Associate the specified value with the specified key in this Hashtable.
	 * If the key already exists, the old value is replaced. The key and value
	 * cannot be null.
	 *
	 * @param		key	the key to add
	 * @param		value	the value to add
	 * @return		the old value associated with the specified key, null if the key did
	 *				not exist
	 */
	public Object put(Object key, Object value) {
		if (key != null && value != null) {
			int index = (hashCode(key) & 0x7FFFFFFF) % elementData.length;
			HashMapEntry entry = elementData[index];
			while (entry != null && !keyEquals(key, entry.key)) {
				entry = entry.next;
			}
			if (entry == null) {
				if (++elementCount > threshold) {
					rehash();
					index = (hashCode(key) & 0x7FFFFFFF) % elementData.length;
				}
				if (index < firstSlot) {
					firstSlot = index;
				}
				if (index > lastSlot) {
					lastSlot = index;
				}
				entry = new HashMapEntry(key, value);
				entry.next = elementData[index];
				elementData[index] = entry;
				return null;
			}
			Object result = entry.value;
			entry.key = key; // important to avoid hanging onto keys that are equal but "old" -- see bug 30607
			entry.value = value;
			return result;
		}
		throw new NullPointerException();
	}

	/**
	 * Increases the capacity of this Hashtable. This method is sent when
	 * the size of this Hashtable exceeds the load factor.
	 */
	private void rehash() {
		int length = elementData.length << 1;
		if (length == 0) {
			length = 1;
		}
		firstSlot = length;
		lastSlot = -1;
		HashMapEntry[] newData = new HashMapEntry[length];
		for (int i = elementData.length; --i >= 0;) {
			HashMapEntry entry = elementData[i];
			while (entry != null) {
				int index = (hashCode(entry.key) & 0x7FFFFFFF) % length;
				if (index < firstSlot) {
					firstSlot = index;
				}
				if (index > lastSlot) {
					lastSlot = index;
				}
				HashMapEntry next = entry.next;
				entry.next = newData[index];
				newData[index] = entry;
				entry = next;
			}
		}
		elementData = newData;
		computeMaxSize();
	}

	/**
	 * Remove the key/value pair with the specified key from this Hashtable.
	 *
	 * @param		key	the key to remove
	 * @return		the value associated with the specified key, null if the specified key
	 *				did not exist
	 */
	public Object remove(Object key) {
		HashMapEntry last = null;
		int index = (hashCode(key) & 0x7FFFFFFF) % elementData.length;
		HashMapEntry entry = elementData[index];
		while (entry != null && !keyEquals(key, entry.key)) {
			last = entry;
			entry = entry.next;
		}
		if (entry != null) {
			if (last == null) {
				elementData[index] = entry.next;
			} else {
				last.next = entry.next;
			}
			elementCount--;
			return entry.value;
		}
		return null;
	}

	/**
	 * Answers the number of key/value pairs in this Hashtable.
	 *
	 * @return		the number of key/value pairs in this Hashtable
	 */
	public int size() {
		return elementCount;
	}

	@Override
	public String toString() {
		if (size() == 0) {
			return "{}"; //$NON-NLS-1$
		}

		StringBuilder buffer = new StringBuilder();
		buffer.append('{');
		for (int i = elementData.length; --i >= 0;) {
			HashMapEntry entry = elementData[i];
			while (entry != null) {
				buffer.append(entry.key);
				buffer.append('=');
				buffer.append(entry.value);
				buffer.append(", "); //$NON-NLS-1$
				entry = entry.next;
			}
		}
		// Remove the last ", "
		if (elementCount > 0) {
			buffer.setLength(buffer.length() - 2);
		}
		buffer.append('}');
		return buffer.toString();
	}
}
