calculateRank.js

/**
 * Calculates the probability of x taking on x or a value less than x in a normal distribution
 * with mean and standard deviation.
 *
 * @see https://stackoverflow.com/a/5263759/10629172
 *
 * @param {string} mean The mean of the normal distribution.
 * @param {number} sigma The standard deviation of the normal distribution.
 * @param {number} to The value to calculate the probability for.
 * @returns {number} Probability.
 */
const normalcdf = (mean, sigma, to) => {
  var z = (to - mean) / Math.sqrt(2 * sigma * sigma);
  var t = 1 / (1 + 0.3275911 * Math.abs(z));
  var a1 = 0.254829592;
  var a2 = -0.284496736;
  var a3 = 1.421413741;
  var a4 = -1.453152027;
  var a5 = 1.061405429;
  var erf =
    1 - ((((a5 * t + a4) * t + a3) * t + a2) * t + a1) * t * Math.exp(-z * z);
  var sign = 1;
  if (z < 0) {
    sign = -1;
  }
  return (1 / 2) * (1 + sign * erf);
};

/**
 * Calculates the users rank.
 *
 * @param {object} params Parameters on which the user's rank depends.
 * @param {number} params.totalRepos Total number of repos.
 * @param {number} params.totalCommits Total number of commits.
 * @param {number} params.contributions The number of contributions.
 * @param {number} params.followers The number of followers.
 * @param {number} params.prs The number of pull requests.
 * @param {number} params.issues The number of issues.
 * @param {number} params.stargazers The number of stars.
 * @returns {{level: string, score: number}}} The users rank.
 */
const calculateRank = ({
  totalRepos,
  totalCommits,
  contributions,
  followers,
  prs,
  issues,
  stargazers,
}) => {
  const COMMITS_OFFSET = 1.65;
  const CONTRIBS_OFFSET = 1.65;
  const ISSUES_OFFSET = 1;
  const STARS_OFFSET = 0.75;
  const PRS_OFFSET = 0.5;
  const FOLLOWERS_OFFSET = 0.45;
  const REPO_OFFSET = 1;

  const ALL_OFFSETS =
    CONTRIBS_OFFSET +
    ISSUES_OFFSET +
    STARS_OFFSET +
    PRS_OFFSET +
    FOLLOWERS_OFFSET +
    REPO_OFFSET;

  const RANK_S_VALUE = 1;
  const RANK_DOUBLE_A_VALUE = 25;
  const RANK_A2_VALUE = 45;
  const RANK_A3_VALUE = 60;
  const RANK_B_VALUE = 100;

  const TOTAL_VALUES =
    RANK_S_VALUE +
    RANK_DOUBLE_A_VALUE +
    RANK_A2_VALUE +
    RANK_A3_VALUE +
    RANK_B_VALUE;

  // prettier-ignore
  const score = (
    totalCommits * COMMITS_OFFSET +
    contributions * CONTRIBS_OFFSET +
    issues * ISSUES_OFFSET +
    stargazers * STARS_OFFSET +
    prs * PRS_OFFSET +
    followers * FOLLOWERS_OFFSET +
    totalRepos * REPO_OFFSET
  ) / 100;

  const normalizedScore = normalcdf(score, TOTAL_VALUES, ALL_OFFSETS) * 100;

  const level = (() => {
    if (normalizedScore < RANK_S_VALUE) return "S+";
    if (normalizedScore < RANK_DOUBLE_A_VALUE) return "S";
    if (normalizedScore < RANK_A2_VALUE) return "A++";
    if (normalizedScore < RANK_A3_VALUE) return "A+";
    return "B+";
  })();

  return { level, score: normalizedScore };
};

export { calculateRank };
export default calculateRank;