@marketto/codice-fiscale-utils/src/classes/check-digitizer.class.ts

TS & JS utilities to handle Italian Codice Fiscale

import { CRC_OFFSET, LASTNAME_OFFSET } from "../const/cf-offsets.const";
import { PARTIAL_CF } from "../const/matcher.const";
import CRC from "../enums/crc.enum";
import generatorWrapper from "../functions/generator-wrapper.function";
import type IGeneratorWrapper from "../interfaces/generator-wrapper.interface";
import type CodiceFiscaleCRC from "../types/codice-fiscale-crc.type";
class CheckDigitizer {
	/**
	 * Evaluate given partial CF to produce last check digit character
	 * @param codiceFiscale Partial or complete Fiscal Code to evaluate to produce last character
	 * @returns 16th CF char
	 */
	public static checkDigit(codiceFiscale: string): CodiceFiscaleCRC | null {
		if (
			typeof codiceFiscale === "string" &&
			new RegExp(PARTIAL_CF).test(codiceFiscale)
		) {
			const partialCF = codiceFiscale.substr(LASTNAME_OFFSET, CRC_OFFSET);
			let partialCfValue = 0;
			for (const charValue of this.evaluateChar(partialCF)) {
				partialCfValue += charValue as number;
			}
			return String.fromCharCode(
				(partialCfValue % this.CRC_MOD) + this.CHAR_OFFSET
			) as CodiceFiscaleCRC;
		}
		return null;
	}

	public static evaluateChar(
		partialCF: string = ""
	): IGeneratorWrapper<number, 0, void> {
		return generatorWrapper(this.evaluateCharGenerator(partialCF));
	}

	private static CHAR_OFFSET: number = 65;
	private static CRC_MOD: number = 26;

	/**
	 * Partial FiscalCode Evaluator
	 * @param Partial Fiscal Code to evaluate
	 * @yields character value odd/even
	 */
	private static *evaluateCharGenerator(partialCF: string = ""): Generator {
		if (typeof partialCF === "string" && partialCF.length) {
			for (let index = 0; index < partialCF.length; index++) {
				let char: string = partialCF[index].toUpperCase();
				const isNumber: boolean = /^\d$/u.test(char);
				if (isNumber) {
					// Numbers have always (odd/even) the same values of corresponding letters (0-9 => A-J)
					char = String.fromCharCode(parseInt(char, 10) + this.CHAR_OFFSET);
				}
				// Odd/Even are shifted/swapped
				// array starts from 0, "Agenzia delle Entrate" documentation counts the string from 1
				const isOdd: boolean = !(index % 2); // Odd according to documentation
				if (isOdd) {
					// Odd positions
					yield parseInt(CRC[char as any], 10);
				} else {
					// Even positions
					yield char.charCodeAt(0) - this.CHAR_OFFSET;
				}
			}
		}
		return 0;
	}
}

export default CheckDigitizer;