vat/es.c

/*
 * SPDX-FileCopyrightText: 2023 jordi fita mas <jfita@peritasoft.com>
 *
 * SPDX-License-Identifier: PostgreSQL
 */
#include "es.h"
#include <stdbool.h>
#include <ctype.h>
#include <postgres.h>
#include <utils/palloc.h>

static char
compute_dni_check_digit(const char *start, const char *end)
{
	unsigned long int n = 0;
	const char *p = start;
	for(; p != end; p++) {
		n = n * 10 + *p - 48;
	}
	return "TRWAGMYFPDXBNJZSQVHLCKE"[n % 23];
}

static bool
valid_short_dni(const char *dni) {
	return dni[8] == compute_dni_check_digit(dni + 1, dni + 8);
}

static bool
valid_dni(const char *dni) {
	return dni[8] == compute_dni_check_digit(dni, dni + 8);
}

static bool
valid_nie(char *nie) {
	bool valid = false;
	nie[0] -= 'X' - 48;
	valid = nie[8] == compute_dni_check_digit(nie, nie + 8);
	nie[0] += 'X' - 48;	
	return valid;
}

static bool
valid_cif(const char *cif) {
	int odds = 0;
	int evens = 0;
	int n = 0;
	int checksum;

	for (n = 1; n < 8; n++) {
		if (n % 2 == 0) {
			evens += cif[n] - 48;
		} else {
			int d = cif[n] * 2;
			int a = d / 10;
			int b = d % 10;
			odds += a + b;
		}
	}
	checksum = 10 - (odds + evens) % 10;
	return cif[8] == checksum + 48 || cif[8] == "JABCDEFGHI"[checksum];
}

char *
check_es_vat(const char *str, size_t len) {
	const char *p = str;
	const char *end = p + len;
	char buf[10] = { 0 };
	int n = 0;

	if (len < 9 ) {
		return NULL;
	}

	for (; p != end && n < 10; p++) {
		char c = *p;
		if (c == ' ' || c == '-') continue;
		if (n > 0 && n < 8) {
			if (!isdigit(c)) {
				return NULL;
			}
			buf[n] = c;
		} else {
			buf[n] = toupper(c);
		}
		n++;
	}
	if (n == 10) {
		return NULL;
	}
	buf[9] = 0;

	switch (buf[0]) {
		case 'K':
		case 'L':
		case 'M':
			if (!valid_short_dni(buf)) {
				return NULL;
			}
			break;
		case '0':
		case '1':
		case '2':
		case '3':
		case '4':
		case '5':
		case '6':
		case '7':
		case '8':
		case '9':
			if (!valid_dni(buf)) {
				return NULL;
			}
			break;
		case 'X':
		case 'Y':
		case 'Z':
			if (!valid_nie(buf)) {
				return NULL;
			}
			break;
		case 'A':
		case 'B':
		case 'C':
		case 'D':
		case 'E':
		case 'F':
		case 'G':
		case 'H':
		case 'J':
		case 'N':
		case 'P':
		case 'Q':
		case 'R':
		case 'S':
		case 'U':
		case 'V':
		case 'W':
			if (!valid_cif(buf)) {
				return NULL;
			}
			break;
		default:
			return NULL;
	}

	return pstrdup(buf);
}