import uaparser from "ua-parser-js";

export function roundTo2(num) {
  return Math.round((num + Number.EPSILON) * 100) / 100;
}

export function escapeRegExp(str) {
  return str.replace(/[.*+?^${}()|[\]\\]/g, "\\$&");
}

export function stdDev(array) {
  const n = array.length;
  const mean = array.reduce((a, b) => a + b) / n;
  return Math.sqrt(
    array.map((x) => Math.pow(x - mean, 2)).reduce((a, b) => a + b) / n
  );
}

export function mean(array) {
  try {
    return (
      array.reduce((previous, current) => (current += previous)) / array.length
    );
  } catch (e) {
    return 0;
  }
}

export function kogasa(cov) {
  return (
    100 * (1 - Math.tanh(cov + Math.pow(cov, 3) / 3 + Math.pow(cov, 5) / 5))
  );
}

export function identity(value) {
  return Object.prototype.toString
    .call(value)
    .replace(/^\[object\s+([a-z]+)\]$/i, "$1")
    .toLowerCase();
}

export function base64UrlEncode(string) {
  return Buffer.from(string).toString("base64url");
}

export function base64UrlDecode(string) {
  return Buffer.from(string, "base64url").toString();
}

export function buildAgentLog(req) {
  const agent = uaparser(req.headers["user-agent"]);

  const agentLog = {
    ip:
      req.headers["cf-connecting-ip"] ||
      req.headers["x-forwarded-for"] ||
      req.ip ||
      "255.255.255.255",
    agent: `${agent.os.name} ${agent.os.version} ${agent.browser.name} ${agent.browser.version}`,
  };

  const {
    device: { vendor, model, type },
  } = agent;
  if (vendor) {
    agentLog.device = `${vendor} ${model} ${type}`;
  }

  return agentLog;
}