/*******************************************************************************
 *
 * Copyright (c) 2004-2010 Oracle Corporation.
 *
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *
 *
 *******************************************************************************/ 

package hudson.util;

import org.apache.commons.codec.binary.Base64;

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

/**
 * Filter InputStream that decodes base64 without doing any buffering.
 *
 * <p> This is slower implementation, but it won't consume unnecessary bytes
 * from the underlying {@link InputStream}, allowing the reader to switch
 * between the unencoded bytes and base64 bytes.
 *
 * @author Kohsuke Kawaguchi
 * @since 1.349
 */
public class UnbufferedBase64InputStream extends FilterInputStream {

    private byte[] encoded = new byte[4];
    private byte[] decoded;
    private int pos;
    private final DataInputStream din;

    public UnbufferedBase64InputStream(InputStream in) {
        super(in);
        din = new DataInputStream(in);
        // initial placement to force the decoding in the next read()
        pos = 4;
        decoded = encoded;
    }

    @Override
    public int read() throws IOException {
        if (decoded.length == 0) {
            return -1; // EOF
        }
        if (pos == decoded.length) {
            din.readFully(encoded);
            decoded = Base64.decodeBase64(encoded);
            if (decoded.length == 0) {
                return -1; // EOF
            }
            pos = 0;
        }

        return (decoded[pos++]) & 0xFF;
    }

    @Override
    public int read(byte[] b, int off, int len) throws IOException {
        int i;
        for (i = 0; i < len; i++) {
            int ch = read();
            if (ch < 0) {
                break;
            }
            b[off + i] = (byte) ch;
        }
        return i == 0 ? -1 : i;
    }

    @Override
    public long skip(long n) throws IOException {
        long r = 0;
        while (n > 0) {
            int ch = read();
            if (ch < 0) {
                break;
            }
            n--;
            r++;
        }
        return r;
    }
}