Luhn mod N algorithm

example.ts

const rawToken = "v83dtres";
const checksum = Luhn.generate(rawToken);
const testToken = `${rawToken}${checksum}`;
const isValid = Luhn.validate(testToken);

luhn.ts

// Luhn mod N algorithm: https://en.wikipedia.org/wiki/Luhn_mod_N_algorithm

export class Luhn {
  public static dictionary =
    "0123456789AaBbCcDdEeFfGgHhIiJjKkLlMmNnOoPpQqRrSsTtUuVvWwXxYyZz";

  public static generate(input: string) {
    const n = Luhn.dictionary.length;

    const sum = input
      .split("")
      .filter(Luhn.filterValid)
      .reverse()
      .reduce(Luhn.reduce(2), 0);

    let remainder = sum % n;
    let checkCodePoint = (n - remainder) % n;
    return Luhn.dict2char(checkCodePoint);
  }

  public static validate(input: string) {
    const sum = input
      .split("")
      .filter(Luhn.filterValid)
      .reverse()
      .reduce(Luhn.reduce(1), 0);

    return !(sum % Luhn.dictionary.length);
  }

  private static char2dict = (character: string) =>
    Luhn.dictionary.indexOf(character);
  private static dict2char = (codePoint: number) =>
    Luhn.dictionary.charAt(codePoint);
  private static filterValid = (str: string) =>
    str.indexOf(Luhn.dictionary) === -1;
  private static reduce =
    (factor: number = 1) =>
    (sum: number, current: string) => {
      let codePoint = Luhn.char2dict(current);
      let addend = factor * codePoint;

      factor = factor == 2 ? 1 : 2;

      addend =
        Math.floor(addend / Luhn.dictionary.length) +
        (addend % Luhn.dictionary.length);
      return (sum += addend);
    };
}