/*
 * SVG Salamander
 * Copyright (c) 2004, Mark McKay
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or 
 * without modification, are permitted provided that the following
 * conditions are met:
 *
 *   - Redistributions of source code must retain the above 
 *     copyright notice, this list of conditions and the following
 *     disclaimer.
 *   - Redistributions in binary form must reproduce the above
 *     copyright notice, this list of conditions and the following
 *     disclaimer in the documentation and/or other materials 
 *     provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE. 
 * 
 * Mark McKay can be contacted at mark@kitfox.com.  Salamander and other
 * projects can be found at http://www.kitfox.com
 */

package com.kitfox.svg.xml;

import java.io.FilterInputStream;
import java.io.IOException;
import java.io.InputStream;

/**
 *
 * @author kitfox
 */
public class Base64InputStream extends FilterInputStream {
	int buf; // Cached bytes to read
	int bufSize; // Number of bytes waiting to be read from buffer
	boolean drain = false; // After set, read no more chunks

	public Base64InputStream(InputStream in) {
		super(in);
	}

	@Override
	public int read() throws IOException {
		if (drain && bufSize == 0) {
			return -1;
		}

		if (bufSize == 0) {
			// Read next chunk into 4 byte buffer
			int chunk = in.read();
			if (chunk == -1) {
				drain = true;
				return -1;
			}

			// get remaining 3 bytes
			for (int i = 0; i < 3; ++i) {
				int value = in.read();
				if (value == -1) {
					throw new IOException("Early termination of base64 stream");
				}
				chunk = (chunk << 8) | (value & 0xff);
			}

			// Check for special termination characters
			if ((chunk & 0xffff) == (((byte) '=' << 8) | (byte) '=')) {
				bufSize = 1;
				drain = true;
			} else if ((chunk & 0xff) == (byte) '=') {
				bufSize = 2;
				drain = true;
			} else {
				bufSize = 3;
			}

			// Fill buffer with decoded characters
			for (int i = 0; i < bufSize + 1; ++i) {
				buf = (buf << 6) | Base64Util.decodeByte((chunk >> 24) & 0xff);
				chunk <<= 8;
			}
		}

		// Return nth remaing bte & decrement counter
		return (buf >> (--bufSize * 8)) & 0xff;
	}
}