credit-card-type/src/lib/find-best-match.ts

A library for determining credit card type

import { CreditCardType } from "../types";

function hasEnoughResultsToDetermineBestMatch(
  results: CreditCardType[],
): boolean {
  const numberOfResultsWithMaxStrengthProperty = results.filter(
    (result) => result.matchStrength,
  ).length;

  /*
   * if all possible results have a maxStrength property that means the card
   * number is sufficiently long enough to determine conclusively what the card
   * type is
   * */
  return (
    numberOfResultsWithMaxStrengthProperty > 0 &&
    numberOfResultsWithMaxStrengthProperty === results.length
  );
}

export function findBestMatch(
  results: CreditCardType[],
): CreditCardType | null {
  if (!hasEnoughResultsToDetermineBestMatch(results)) {
    return null;
  }

  return results.reduce((bestMatch, result) => {
    if (!bestMatch) {
      return result;
    }

    /*
     * If the current best match pattern is less specific than this result, set
     * the result as the new best match
     * */
    if (Number(bestMatch.matchStrength) < Number(result.matchStrength)) {
      return result;
    }

    return bestMatch;
  });
}