package model.asn1;

import model.asn1.exceptions.ParseException;
import model.asn1.parsing.BytesReader;

/**
 * Represents the ASN.1 NULL type. It always has zero length. With the default assigned tag, it always encodes
 * into 0x05 0x00.
 */
public class Null extends ASN1Object {
    /**
     * The X.680 universal class tag assignment.
     */
    public static final Tag TAG = new Tag(TagClass.UNIVERSAL, false, 0x5);

    /**
     * EFFECTS: Initiate the NULL with the given tag and an optional context-specific tag number for explicit
     * encoding. For more information, consult {@link ASN1Object}. NULL does not take any other arguments.
     * REQUIRES: Consult {@link ASN1Object}.
     */
    public Null(Tag tag, Tag parentTag) {
        super(tag, parentTag);
    }

    /**
     * EFFECTS: Parse input bytes. For more information on tags parsing, consult {@link ASN1Object}.
     *   Throws {@link ParseException} if the input data is invalid:
     *     - The length is not 0
     *     - Other cases as denoted in {@link ASN1Object}
     */
    public Null(BytesReader encoded, boolean hasParentTag) throws ParseException {
        super(encoded, hasParentTag);
        if (getLength() != 0) {
            throw new ParseException("NULL must have zero length!");
        }
    }

    /**
     * EFFECTS: Always produce an empty array.
     */
    @Override
    public Byte[] encodeValueDER() {
        return new Byte[0];
    }
}