package ch.ethz.ssh2.crypto;

import java.io.IOException;

import java.math.BigInteger;

/**
 * SimpleDERReader.
 *
 * @author Christian Plattner, plattner@trilead.com
 * @version $Id: SimpleDERReader.java,v 1.1 2007/10/15 12:49:56 cplattne Exp $
 */
public class SimpleDERReader {
    private static final int CONSTRUCTED = 0x20;

    byte[] buffer;
    int pos;
    int count;

    public SimpleDERReader(byte[] b) {
        resetInput(b);
    }

    public SimpleDERReader(byte[] b, int off, int len) {
        resetInput(b, off, len);
    }

    public void resetInput(byte[] b) {
        resetInput(b, 0, b.length);
    }

    public void resetInput(byte[] b, int off, int len) {
        buffer = b;
        pos = off;
        count = len;
    }

    private byte readByte() throws IOException {
        if (count <= 0)
            throw new IOException("DER byte array: out of data");

        count--;
        return buffer[pos++];
    }

    private byte[] readBytes(int len) throws IOException {
        if (len > count)
            throw new IOException("DER byte array: out of data");

        byte[] b = new byte[len];
        System.arraycopy(buffer, pos, b, 0, len);
        pos += len;
        count -= len;
        return b;
    }

    public int available() {
        return count;
    }

    private int readLength() throws IOException {
        int len = readByte() & 0xff;

        if ((len & 0x80) == 0)
            return len;

        int remain = len & 0x7F;

        if (remain == 0)
            return -1;

        len = 0;

        while (remain > 0) {
            len = len << 8;
            len = len | (readByte() & 0xff);
            remain--;
        }

        return len;
    }

    public int ignoreNextObject() throws IOException {
        int type = readByte() & 0xff;
        int len = readLength();

        if ((len < 0) || len > available())
            throw new IOException("Illegal len in DER object (" + len  + ")");

        readBytes(len);
        return type;
    }

    public BigInteger readInt() throws IOException {
        int type = readByte() & 0xff;

        if (type != 0x02)
            throw new IOException("Expected DER Integer, but found type " + type);

        int len = readLength();

        if ((len < 0) || len > available())
            throw new IOException("Illegal len in DER object (" + len  + ")");

        byte[] b = readBytes(len);
        BigInteger bi = new BigInteger(b);
        return bi;
    }

    public int readConstructedType() throws IOException {
        int type = readByte() & 0xff;

        if ((type & CONSTRUCTED) != CONSTRUCTED)
            throw new IOException("Expected constructed type, but was " + type);

        return type & 0x1f;
    }

    public SimpleDERReader readConstructed() throws IOException {
        int len = readLength();

        if ((len < 0) || len > available())
            throw new IOException("Illegal len in DER object (" + len  + ")");

        SimpleDERReader cr = new SimpleDERReader(buffer, pos, len);
        pos += len;
        count -= len;
        return cr;
    }

    public byte[] readSequenceAsByteArray() throws IOException {
        int type = readByte() & 0xff;

        if (type != 0x30)
            throw new IOException("Expected DER Sequence, but found type " + type);

        int len = readLength();

        if ((len < 0) || len > available())
            throw new IOException("Illegal len in DER object (" + len  + ")");

        byte[] b = readBytes(len);
        return b;
    }

    public String readOid() throws IOException {
        int type = readByte() & 0xff;

        if (type != 0x06)
            throw new IOException("Expected DER OID, but found type " + type);

        int len = readLength();

        if ((len < 1) || len > available())
            throw new IOException("Illegal len in DER object (" + len  + ")");

        byte[] b = readBytes(len);
        long value = 0;
        StringBuilder sb = new StringBuilder(64);

        switch (b[0] / 40) {
            case 0:
                sb.append('0');
                break;

            case 1:
                sb.append('1');
                b[0] -= 40;
                break;

            default:
                sb.append('2');
                b[0] -= 80;
                break;
        }

        for (int i = 0; i < len; i++) {
            value = (value << 7) + (b[i] & 0x7F);

            if ((b[i] & 0x80) == 0) {
                sb.append('.');
                sb.append(value);
                value = 0;
            }
        }

        return sb.toString();
    }

    public byte[] readOctetString() throws IOException {
        int type = readByte() & 0xff;

        if (type != 0x04 && type != 0x03)
            throw new IOException("Expected DER Octetstring, but found type " + type);

        int len = readLength();

        if ((len < 0) || len > available())
            throw new IOException("Illegal len in DER object (" + len  + ")");

        byte[] b = readBytes(len);
        return b;
    }

}