/**
 * WhatsApp Cloud API: `to` is digits with country code, no + prefix.
 * Strips spaces, letters, and punctuation; only digits are kept.
 * Indian mobiles: 10-digit values get country code 91 (12 digits). A leading 0
 * (e.g. 09823488138) is removed before applying the 10-digit rule.
 * @param {string} raw
 * @returns {string} digits only, or empty if unusable
 */
function normalizeWhatsAppTo(raw) {
  let digits = String(raw || '').replace(/\D/g, '');
  if (!digits) return '';

  if (digits.length === 11 && digits.startsWith('0')) {
    digits = digits.slice(1);
  }

  if (digits.length === 10) {
    digits = `91${digits}`;
  }

  if (digits.length < 8 || digits.length > 15) return '';
  return digits;
}

/**
 * Last 10 digits of a phone for duplicate registration matching.
 * Strips all non-digits, then takes the trailing 10 (so +91 / leading 0 are ignored).
 * @param {string} raw
 * @returns {string} up to 10 digits, or empty string
 */
function phoneLast10Digits(raw) {
  const digits = String(raw || '').replace(/\D/g, '');
  if (!digits) return '';
  if (digits.length <= 10) return digits;
  return digits.slice(-10);
}

/**
 * All last-10 digit keys from a stored phone field that may contain two numbers,
 * separators, +91, spaces, or a leading 0.
 * @param {string} raw
 * @returns {string[]}
 */
function extractPhoneLast10Keys(raw) {
  const text = String(raw || '');
  if (!text.trim()) return [];
  const parts = text.split(/\s*(?:\/|,|&|;|\||\band\b)\s*/i);
  const keys = new Set();
  const consider = (chunk) => {
    const digits = String(chunk || '').replace(/\D/g, '');
    if (!digits) return;
    if (digits.length >= 10) {
      keys.add(digits.slice(-10));
      return;
    }
    if (digits.length >= 8) keys.add(digits);
  };
  if (parts.length > 1) {
    parts.forEach(consider);
  }
  const runs = text.match(/\d[\d\s.+()-]{7,}/g) || [];
  runs.forEach(consider);
  consider(text);
  return [...keys];
}

module.exports = { normalizeWhatsAppTo, phoneLast10Digits, extractPhoneLast10Keys };