se-panfilov/jsvat

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

export const latvia: Country = {
  name: 'Latvia',
  codes: ['LV', 'LVA', '428'],
  calcFn: (vat: string): boolean => {
    let total = 0;

    // Differentiate between legal entities and natural bodies. For the latter we simply check that
    // the first six digits correspond to valid DDMMYY dates.
    if (/^[0-3]/.test(vat)) {
      return Boolean(/^[0-3][0-9][0-1][0-9]/.test(vat));
    } else {
      // Extract the next digit and multiply by the counter.
      for (let i = 0; i < 10; i++) {
        total += Number(vat.charAt(i)) * latvia.rules.multipliers.common[i];
      }

      // Establish check digits by getting modulus 11.
      if (total % 11 === 4 && Number(vat[0]) === 9) total = total - 45;

      if (total % 11 === 4) {
        total = 4 - (total % 11);
      } else if (total % 11 > 4) {
        total = 14 - (total % 11);
      } else if (total % 11 < 4) {
        total = 3 - (total % 11);
      }

      // Compare it with the last character of the VAT number. If it's the same, then it's valid.
      const expect = Number(vat.slice(10, 11));
      return total === expect;
    }
  },
  rules: {
    multipliers: {
      common: [9, 1, 4, 8, 3, 10, 2, 5, 7, 6]
    },
    regex: [/^(LV)(\d{11})$/]
  }
};