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package org.xbib.net.security.util;

import java.io.IOException;
import java.math.BigInteger;

/**
 * An ASN.1 TLV. The object is not parsed. It can only handle integers and strings.
 */
public class Asn1Object {

    protected final int type;
    protected final int length;
    protected final byte[] value;
    protected final int tag;

    /**
     * Construct a ASN.1 TLV. The TLV could be either a
     * constructed or primitive entity.
     * The first byte in DER encoding is made of following fields,
     *      * -------------------------------------------------
     * |Bit 8|Bit 7|Bit 6|Bit 5|Bit 4|Bit 3|Bit 2|Bit 1|
     * -------------------------------------------------
     * |  Class    | CF  |     +      Type             |
     * -------------------------------------------------
     * 
     * 
     * Class: Universal, Application, Context or Private
     * 
CF: Constructed flag. If 1, the field is constructed.
     * 
Type: This is actually called tag in ASN.1. It
     * indicates data type (Integer, String) or a construct
     * (sequence, choice, set).
     * 
     *
     * @param tag    Tag or Identifier
     * @param length Length of the field
     * @param value  Encoded octet string for the field.
     */
    public Asn1Object(int tag, int length, byte[] value) {
        this.tag = tag;
        this.type = tag & 0x1F;
        this.length = length;
        this.value = value;
    }

    public int getType() {
        return type;
    }

    public int getLength() {
        return length;
    }

    public byte[] getValue() {
        return value;
    }

    public boolean isConstructed() {
        return (tag & DerParser.CONSTRUCTED) == DerParser.CONSTRUCTED;
    }

    public DerParser getParser() throws IOException {
        if (!isConstructed()) {
            throw new IOException("Invalid DER: can't parse primitive entity"); //$NON-NLS-1$
        }
        return new DerParser(value);
    }

    public BigInteger getInteger() throws IOException {
        if (type != DerParser.INTEGER) {
            throw new IOException("Invalid DER: object is not integer"); //$NON-NLS-1$
        }
        return new BigInteger(value);
    }

    public String getString() throws IOException {
        String encoding;
        switch (type) {
            case DerParser.NUMERIC_STRING:
            case DerParser.PRINTABLE_STRING:
            case DerParser.VIDEOTEX_STRING:
            case DerParser.IA5_STRING:
            case DerParser.GRAPHIC_STRING:
            case DerParser.ISO646_STRING:
            case DerParser.GENERAL_STRING:
                encoding = "ISO-8859-1"; //$NON-NLS-1$
                break;
            case DerParser.BMP_STRING:
                encoding = "UTF-16BE"; //$NON-NLS-1$
                break;
            case DerParser.UTF8_STRING:
                encoding = "UTF-8"; //$NON-NLS-1$
                break;
            case DerParser.UNIVERSAL_STRING:
                throw new IOException("Invalid DER: can't handle UCS-4 string"); //$NON-NLS-1$
            default:
                throw new IOException("Invalid DER: object is not a string"); //$NON-NLS-1$
        }
        return new String(value, encoding);
    }
}