// services/voicePin/generatePin.js
// Crypto-random PIN generation with configurable length and passcode rules.

import { randomInt } from 'node:crypto';

const DEFAULT_MIN = 6;
const DEFAULT_MAX = 6;

function digitPin(length) {
  let pin = '';
  for (let i = 0; i < length; i += 1) {
    pin += String(randomInt(0, 10));
  }
  return pin;
}

function hasSequentialDigits(pin, maxRun = 3) {
  for (let i = 0; i <= pin.length - maxRun; i += 1) {
    const slice = pin.slice(i, i + maxRun);
    const asc = slice.split('').every((d, idx) => idx === 0 || Number(d) === Number(slice[idx - 1]) + 1);
    const desc = slice.split('').every((d, idx) => idx === 0 || Number(d) === Number(slice[idx - 1]) - 1);
    if (asc || desc) return true;
  }
  return false;
}

function isAllSameDigit(pin) {
  return /^(\d)\1+$/.test(pin);
}

function violatesRules(pin, rules = {}) {
  const length = pin.length;
  const minLength = rules.minLength ?? rules.length?.min ?? DEFAULT_MIN;
  const maxLength = rules.maxLength ?? rules.length?.max ?? DEFAULT_MAX;
  if (length < minLength || length > maxLength) return true;

  if (rules.disallowSequential === true && hasSequentialDigits(pin)) return true;
  if (rules.disallowRepeating === true && isAllSameDigit(pin)) return true;
  if (rules.disallowSameAsExtension === true && rules.extension && pin === String(rules.extension)) {
    return true;
  }

  return false;
}

/**
 * Generate a numeric PIN that satisfies the provided rules.
 *
 * @param {object} [opts]
 * @param {number} [opts.minLength]
 * @param {number} [opts.maxLength]
 * @param {object} [opts.rules] full passcodeRules object from Webex
 * @param {number} [opts.maxAttempts]
 * @returns {string}
 */
export function generatePin(opts = {}) {
  const rules = opts.rules || {};
  const minLength = opts.minLength ?? rules.length?.min ?? DEFAULT_MIN;
  const maxLength = opts.maxLength ?? rules.length?.max ?? minLength;
  const targetLength = Math.max(minLength, Math.min(maxLength, opts.length ?? minLength));
  const maxAttempts = opts.maxAttempts ?? 50;

  const mergedRules = {
    ...rules,
    minLength,
    maxLength,
    extension: opts.extension ?? rules.extension,
  };

  for (let attempt = 0; attempt < maxAttempts; attempt += 1) {
    const pin = digitPin(targetLength);
    if (!violatesRules(pin, mergedRules)) return pin;
  }

  throw new Error(`Could not generate a compliant PIN after ${maxAttempts} attempts`);
}