/**
 * Vietnamese phone number helpers.
 *
 * Regex covers the current VN numbering plan:
 *   0[35789]x xxxxxxx — Viettel, Mobifone, Vinaphone, Gmobile, Indochina
 *
 * See: https://en.wikipedia.org/wiki/Telephone_numbers_in_Vietnam
 */

/** Matches a VN mobile number, with optional +84 or leading 0. */
export const VN_PHONE_REGEX =
  /^(0|\+84)(3[2-9]|5[2689]|7[06-9]|8[1-9]|9[0-9])\d{7}$/;

/**
 * Normalise a VN phone number to the E.164-ish form used by Zalo / APIs:
 * strip leading 0 and prepend the country code (84).
 *
 * "0987654321" → "84987654321"
 * "+84987654321" → "84987654321"
 * "84987654321" → "84987654321"  (already normalised — idempotent)
 */
export function normalizePhone(phone: string): string {
  const cleaned = phone.trim();
  if (cleaned.startsWith('+84')) return `84${cleaned.slice(3)}`;
  if (cleaned.startsWith('84')) return cleaned;
  if (cleaned.startsWith('0')) return `84${cleaned.slice(1)}`;
  return cleaned;
}

/**
 * Format a raw VN phone number for display.
 * Handles 10-digit numbers (0xx xxxx xxxx).
 *
 * "0987654321" → "0987 654 321"
 * Passthrough for anything that doesn't match.
 */
export function formatPhone(phone: string): string {
  const cleaned = phone.trim().replace(/\s+/g, '');

  // 10-digit local format: 0xxx yyy zzz
  const tenDigit = cleaned.match(/^(0\d{3})(\d{3})(\d{3})$/);
  if (tenDigit) return `${tenDigit[1]} ${tenDigit[2]} ${tenDigit[3]}`;

  // +84 prefix → treat as 10-digit local after swapping prefix
  const e164 = cleaned.match(/^\+84(\d{9})$/);
  if (e164) return formatPhone(`0${e164[1]}`);

  return phone;
}

/**
 * Returns the https://zalo.me deep-link URL for a given phone number.
 *
 * Zalo expects the number without a leading zero, prefixed with 84.
 * "0987654321" → "https://zalo.me/84987654321"
 */
export function zaloHref(phone: string): string {
  return `https://zalo.me/${normalizePhone(phone)}`;
}