// Copyright 2003, FreeHEP.
package org.freehep.util.io;

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

/**
 * The Base64InputStream decodes binary data according to RFC 2045.
 * 
 * IMPORTANT: inherits from InputStream rather than FilterInputStream so that
 * the correct read(byte[], int, int) method is used.
 * 
 * @author Mark Donszelmann
 * @version $Id: Base64InputStream.java 8584 2006-08-10 23:06:37Z duns $
 */
public class Base64InputStream extends InputStream {

    private int b[] = new int[3];

    private int bIndex;

    private int bLength;

    private boolean endReached;

    private int lineNo;

    private InputStream in;

    private static final int ILLEGAL = -1;

    // private static final int WHITESPACE = -2;
    private static final int LINEFEED = -3;

    private static final int CARRIAGERETURN = -4;

    private static final int EQUALS = -5;

    private static final byte base64toInt[] = { -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -2, -3, -1, -1, -4,
            -1,
            -1, // Tab, LineFeed, CarriageReturn
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -2,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1,
            63, // Space, Plus, Slash
            52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -5, -1,
            -1, // 0 - 9, =
            -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13,
            14, // A-Z
            15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1, -1,
            26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, // a-z
            41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1 };

    /**
     * Creates a Base64 input stream for given input
     * 
     * @param input to be read from
     */
    public Base64InputStream(InputStream input) {
        super();
        in = input;
        endReached = false;
        bIndex = 0;
        bLength = 0;
        lineNo = 1;
    }

    public int read() throws IOException {

        if (bIndex >= bLength) {
            if (endReached)
                return -1;
            bLength = readTuple();
            if (bLength <= 0)
                return -1;
            bIndex = 0;
        }
        int a = b[bIndex];
        bIndex++;

        return a;
    }

    /**
     * @return current line number
     */
    public int getLineNo() {
        return lineNo;
    }

    private int readTuple() throws IOException, EncodingException {
        byte c[] = new byte[4];
        int cIndex = 0;
        int encoding = 0;
        int prevEncoding = 0;
        int i = 0;

        if (endReached)
            return 0;

        while (i < c.length) {
            int ch = in.read();
            if (ch < 0) {
                endReached = true;
                if (cIndex == 0) {
                    // still a proper end.
                    return 0;
                } else {
                    throw new EncodingException(
                            "Improperly padded Base64 Input.");
                }
            }

            prevEncoding = encoding;
            encoding = base64toInt[ch & 0x7f];
            switch (encoding) {
            case ILLEGAL:
                if (ch < 0)
                    throw new EncodingException(
                            "Illegal character in Base64 encoding '" + ch
                                    + "'.");
            case EQUALS:
                // ignore, but keep reading padding
                i++;
                break;
            case CARRIAGERETURN:
                lineNo++;
                break;
            case LINEFEED:
                if (prevEncoding != CARRIAGERETURN) {
                    lineNo++;
                }
                break;
            default:
                c[cIndex] = (byte) (encoding & 0xFF);
                cIndex++;
                i++;
                break;
            }
        }

        int data;
        switch (cIndex) {
        case 2:
            data = (c[0] << 18) | (c[1] << 12);

            b[0] = data >>> 16;
            return 1;

        case 3:
            data = (c[0] << 18) | (c[1] << 12) | (c[2] << 6);

            b[0] = data >>> 16;
            b[1] = data >>> 8;
            return 2;

        case 4:
            data = (c[0] << 18) | (c[1] << 12) | (c[2] << 6) | (c[3]);

            b[0] = data >>> 16;
            b[1] = data >>> 8;
            b[2] = data;
            return 3;

        default:
            throw new EncodingException("Base64InputStream: internal error.");
        }
    }
}