se-panfilov/jsvat

import { Country, Rules } from '../jsvat';

export const lithuania: Country = {
  name: 'Lithuania',
  codes: ['LT', 'LTU', '440'],
  calcFn: (vat: string): boolean => {
    return _check9DigitVat(vat, lithuania.rules) || _check12DigitVat(vat, lithuania.rules);
  },
  rules: {
    multipliers: {
      short: [3, 4, 5, 6, 7, 8, 9, 1],
      med: [1, 2, 3, 4, 5, 6, 7, 8, 9, 1, 2],
      alt: [3, 4, 5, 6, 7, 8, 9, 1, 2, 3, 4]
    },
    check: /^\d{10}1/,
    regex: [/^(LT)(\d{9}|\d{12})$/]
  }
};

function _extractDigit(vat: string, multiplierList: ReadonlyArray<number>, key: number): number {
  return Number(vat.charAt(key)) * multiplierList[key];
}

function _doubleCheckCalculation(vat: string, total: number, rules: Rules): number {
  let result = total;
  if (result % 11 === 10) {
    result = 0;
    for (let i = 0; i < 8; i++) {
      result += _extractDigit(vat, rules.multipliers.short, i);
    }
  }

  return result;
}

function extractDigit(vat: string, total: number): number {
  let result = total;
  for (let i = 0; i < 8; i++) {
    result += Number(vat.charAt(i)) * (i + 1);
  }
  return result;
}

function checkDigit(total: number): number {
  let result = total % 11;
  if (result === 10) {
    result = 0;
  }

  return result;
}

function _check9DigitVat(vat: string, rules: Rules): boolean {
  // 9 character VAT numbers are for legal persons
  let total = 0;
  if (vat.length === 9) {
    // 8th character must be one
    if (!/^\d{7}1/.test(vat)) return false;

    // Extract the next digit and multiply by the counter+1.
    total = extractDigit(vat, total);

    // Can have a double check digit calculation!
    total = _doubleCheckCalculation(vat, total, rules);

    // Establish check digit.
    total = checkDigit(total);

    // Compare it with the last character of the VAT number. If it's the same, then it's valid.
    const expect = Number(vat.slice(8, 9));
    return total === expect;
  }
  return false;
}

function extractDigit12(vat: string, total: number, rules: Rules): number {
  let result = total;
  for (let k = 0; k < 11; k++) {
    result += _extractDigit(vat, rules.multipliers.med, k);
  }

  return result;
}

function _doubleCheckCalculation12(vat: string, total: number, rules: Rules): number {
  let result = total;
  if (total % 11 === 10) {
    result = 0;
    for (let l = 0; l < 11; l++) {
      result += _extractDigit(vat, rules.multipliers.alt, l);
    }
  }

  return result;
}

function _check12DigitVat(vat: string, rules: Rules): boolean {
  let total = 0;
  // 12 character VAT numbers are for temporarily registered taxpayers
  if (vat.length === 12) {
    if (!rules.check) return false;
    // 11th character must be one
    if (!rules.check.test(vat)) return false;

    // Extract the next digit and multiply by the counter+1.
    total = extractDigit12(vat, total, rules);

    // Can have a double check digit calculation!
    total = _doubleCheckCalculation12(vat, total, rules);

    // Establish check digit.
    total = checkDigit(total);

    // Compare it with the last character of the VAT number. If it's the same, then it's valid.
    const expect = Number(vat.slice(11, 12));
    return total === expect;
  }

  return false;
}