Skrypt sprawdzający poprawność "numerów referencyjnych" z systemu KSeF, obsługuje zarówno numery faktur jak i numery sesji. Bonusową funkcją jest możliwość dopisania sumy kontrolnej dla dowolnego numeru bez niej :)

ksef.js

class KsefIdUtils {
  static INVOICE_PATTERN =
    /^([1-9]((\d[1-9])|([1-9]\d))\d{7}|M\d{9}|[A-Z]{3}\d{7})-(20[2-9][0-9]|2[1-9][0-9]{2}|[3-9][0-9]{3})(0[1-9]|1[0-2])(0[1-9]|[1-2][0-9]|3[0-1])-([0-9A-F]{6})-?([0-9A-F]{6})-([0-9A-F]{2})$/;

  static SESSION_PATTERN =
    /^(20[2-9][0-9]|2[1-9][0-9]{2}|[3-9][0-9]{3})(0[1-9]|1[0-2])(0[1-9]|[1-2][0-9]|3[0-1])-([0-9A-Z]{2})-([0-9A-F]{10})-([0-9A-F]{10})-([0-9A-F]{2})$/;

  static isValid(id) {
    if (
      !id ||
      (!this.INVOICE_PATTERN.test(id) && !this.SESSION_PATTERN.test(id))
    ) {
      return false;
    }

    const parts = id.split("-");
    const partCount = parts.length;

    if (partCount !== 5 && partCount !== 4) {
      return false;
    }

    if (partCount === 4 && parts[0].length !== 10) {
      return false;
    }

    const checksumPart = parts[partCount - 1];
    const calculatedChecksum = this.calculateChecksum(parts);

    return calculatedChecksum === checksumPart.toUpperCase();
  }

  static calculateChecksum(parts) {
    const hasher = new KsefHash();

    hasher.addDigitString(parts[0]);
    hasher.addDigitString(parts[1]);

    if (parts.length === 4) {
      hasher.addHexString(parts[2].substring(0, 6));
      hasher.addHexString(parts[2].substring(6));
    } else {
      hasher.addHexString(parts[2]);
      hasher.addHexString(parts[3]);
    }

    let checksumValue = (hasher.value % 256)
      .toString(16)
      .toUpperCase()
      .padStart(2, "0");
    return checksumValue;
  }

  static expand(idWithoutHash) {
    return (
      idWithoutHash +
      "-" +
      this.calculateChecksum((idWithoutHash + "-00").split("-"))
    );
  }
}

class KsefHash {
  constructor() {
    this.value = 1;
  }

  addDigitString(digitStr) {
    for (let i = 0; i < digitStr.length; i++) {
      this.value = 3 * this.value + (digitStr.charCodeAt(i) - 48);
    }
  }

  addHexString(hexStr) {
    for (let i = 0; i < hexStr.length; i += 2) {
      this.value = 3 * this.value + parseInt(hexStr.substring(i, i + 2), 16);
    }
  }
}