Subversion Repositories SmartDukaan

	/** Characters of a GSTIN, in the order the checksum weights them. */

	private static final String GSTIN_ALPHABET = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";

	/**

	 * 2-digit state code, 10-char PAN (5 letters, 4 digits, 1 letter), entity number,

	 * the literal Z, then the checksum character.

	 */

	private static final java.util.regex.Pattern GSTIN_PATTERN =

			java.util.regex.Pattern.compile("^[0-9]{2}[A-Z]{5}[0-9]{4}[A-Z][1-9A-Z]Z[0-9A-Z]$");

	/** State codes issued by GSTN: 01-38, plus 97 (other territory) and 99 (centre). */

	private static final java.util.regex.Pattern GSTIN_STATE_CODE =

			java.util.regex.Pattern.compile("^(0[1-9]|[12][0-9]|3[0-8]|97|99)$");

	/**

	 * Whether a GSTIN is well formed: shape, a real state code, and the mod-36 checksum in the

	 * 15th character. A blank is still allowed - the field is optional for stores that have no

	 * registration - so callers that need one present must check for that themselves.

	 * <p>

	 * It used to accept any 15-character string, which let a pincode ({@code 110095}, rejected

	 * only for being 6 characters) and outright junk ({@code Hdjiekwbdbsjskz}) reach

	 * fofo_store.gst_number, where billing reads it. NIC then rejects the invoice and the goods

	 * cannot ship. The checksum is worth having on top of the shape: of 1,570 well-formed

	 * partner GSTINs on record exactly one fails it, so it costs nothing and catches the

	 * transposed or O-for-0 typo that the pattern alone cannot see.

	 */

		String gstin = normalizeGstNumber(gstNumber);

		if(!GSTIN_PATTERN.matcher(gstin).matches()) {

		}

		if(!GSTIN_STATE_CODE.matcher(gstin.substring(0, 2)).matches()) {

			return false;

		}

		return gstin.charAt(14) == gstinChecksum(gstin);

	}

	/** Trimmed and upper-cased, so the same registration is never stored two ways. */

	public static String normalizeGstNumber(String gstNumber) {

		return gstNumber == null ? null : gstNumber.trim().toUpperCase();

	}

	/**

	 * GSTN's mod-36 check character over the first 14 characters: each is weighted 1, 2, 1, 2 ...

	 * and the two digits of each product are added separately before the total is complemented.

	 */

	private static char gstinChecksum(String gstin) {

		int total = 0;

		for(int i = 0; i < 14; i++) {

			int product = GSTIN_ALPHABET.indexOf(gstin.charAt(i)) * (i % 2 == 0 ? 1 : 2);

			total += product / 36 + product % 36;

		}

		return GSTIN_ALPHABET.charAt((36 - total % 36) % 36);