/**
 * License Agreement.
 *
 * Rich Faces - Natural Ajax for Java Server Faces (JSF)
 *
 * Copyright (C) 2007 Exadel, Inc.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License version 2.1 as published by the Free Software Foundation.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301  USA
 */

package org.ajax4jsf.io;

import java.io.UnsupportedEncodingException;

/**
 * A single link in chain of char arrays. 
 * @author glory
 */
public class CharBuffer {
	private CharBuffer prev;
	private CharBuffer next;
	
	/**
	 * Stored characters
	 */
	private char[] chars;
	
	/**
	 * Length of char array.
	 */
	private int cacheSize;
	private static int MIN_CACHE_SIZE = 64;
	/**
	 * number of characters stored in the array.
	 */
	private int usedSize;
	
	/**
	 * Creates instance of CharBuffer with char array of required length.
	 * @param cacheSize length of char array
	 */	
	public CharBuffer(int cacheSize) {
		if (cacheSize<MIN_CACHE_SIZE) {
			this.cacheSize = MIN_CACHE_SIZE;
		} else {
			this.cacheSize = cacheSize;
		}
		chars = new char[this.cacheSize];
		usedSize = 0;
	}
	
	/**
	 * Creates instance of CharBuffer already filled by chars.
	 * @param bytes
	 */
	public CharBuffer(char[] chars) {
		this.chars = chars;
		usedSize = chars.length;
		if (usedSize<MIN_CACHE_SIZE) {
			this.cacheSize = MIN_CACHE_SIZE;
		} else {
			this.cacheSize = usedSize;
		}
	}
	
	/**
	 * Appends character to array chars if there are unfilled positions in it.
	 * Otherwise creates next link in the chain, and appends the character to it.
	 * @param c
	 * @return instance of CharBuffer to which character was appended.
	 */	
	public CharBuffer append(char c) {
		if(next != null) {
			return next.append(c);
		}
		if(usedSize < cacheSize) {
			chars[usedSize] = c;
			usedSize++;
			return this;
		} else {
			next = new CharBuffer(cacheSize * 2);
			next.prev = this;
			return next.append(c);
		}
	}
	
	/**
	 * Appends segment of a char array to array if there are unfilled positions in it.
	 * Otherwise creates next link in the chain, and appends data to it.
	 * @param c
	 * @return instance of CharBuffer to which char array was appended.
	 */	
	public CharBuffer append(char[] cs, int off, int len) {
		if(next != null) {
			return next.append(cs, off, len);
		}
		if(len + usedSize <= cacheSize) {
			System.arraycopy(cs, off, chars, usedSize, len);
			usedSize += len;
			return this;
		}
		int av = cacheSize - usedSize;
		if(av > 0) {
			System.arraycopy(cs, off, chars, usedSize, av);
			usedSize += av;
			off += av;
			len -= av;
		}
		next = new CharBuffer(cacheSize * 2);
		next.prev = this;
		return next.append(cs, off, len);
	}

	/**
	 * Returns stored char array.
	 * @return stored char array
	 */	
	public char[] getChars() {
		return chars;
	}

	/**
	 * Returns character at index. No check is fulfilled to provide high speed.
	 * @param index
	 * @return
	 */
	public char getCharAt(int index) {
		return chars[index];
	}
	
	/**
	 * Returns actual number of characters stored in this link.
	 * @return
	 */	
	public int getUsedSize() {
		return usedSize;
	}
	
	/**
	 * Returns capacity of this link.
	 * @return
	 */	
	public int getCacheSize() {
		return cacheSize;
	}
	
	/**
	 * Returns total number of characters stored in this link and all its predecessors. 
	 * @return
	 */	
	public int getTotalSize() {
		return (prev == null) ? usedSize : prev.getTotalSize() + usedSize;
	}
	
	/**
	 * Returns the previous link in the chain.
	 * @return
	 */	
	public CharBuffer getPrevious() {
		return prev;
	}
	
	/**
	 * Returns the next link in the chain.
	 * @return
	 */	
	public CharBuffer getNext() {
		return next;
	}
	
	/**
	 * Sets the next link in the chain.
	 * @param b
	 */	
	public void setNext(CharBuffer b) {
		next = b;
		if(b != null) b.prev = this;
	}

	/**
	 * Transforms this instance to instance of ByteBuffer (a link of chain of byte arrays).
	 * @param encoding
	 * @return link of chain of byte arrays
	 * @throws UnsupportedEncodingException
	 */
	public ByteBuffer toByteBuffer(String encoding) throws UnsupportedEncodingException {
		byte[] bs = new String(chars, 0, usedSize).getBytes(encoding);
		return new ByteBuffer(bs);
	}

	/**
	 * Transforms this instance to instance of ByteBuffer (a link of chain of byte arrays).
	 * @return link of chain of byte arrays
	 */
	public ByteBuffer toByteBuffer() {
		byte[] bs = new String(chars, 0, usedSize).getBytes();
		return new ByteBuffer(bs);
	}

	/**
	 * Resets this char buffer to empty state
	 * @since 3.3.0
	 */
	public void reset() {
		usedSize = 0;
		next = null;
		prev = null;
	}
}
