/**
 * Phone identity.
 *
 * Phone is the primary identity on this platform, which makes its *string form*
 * load-bearing: `users.phone` carries a UNIQUE constraint, bans are enforced per
 * account, and duplicate detection matches on it. If "+34600111222" and
 * "0034 600 111 222" can both be stored, then one handset holds two distinct
 * "unique" accounts — which defeats the constraint, lets a banned user return,
 * and hides the duplicate from `findPossibleDuplicates`.
 *
 * So there is exactly one accepted stored form: E.164, no spaces, no separators.
 * Normalise on the way in, reject anything that cannot be normalised.
 */

/** E.164: a leading +, a nonzero leading digit, and 8–15 digits total. */
const E164 = /^\+[1-9]\d{7,14}$/;

export function isE164(value: string): boolean {
  return E164.test(value);
}

/**
 * Coerce common user input into E.164, or return null if it cannot be done
 * unambiguously.
 *
 * Handles the shapes people actually type: spaces, hyphens, parentheses and dots
 * as separators, and a `00` international prefix instead of `+`. It deliberately
 * does NOT guess a country code for a bare national number — "600111222" is
 * meaningless without knowing the country, and silently assuming one would
 * attach a real person's account to the wrong number.
 */
export function toE164(input: string | null | undefined): string | null {
  if (!input) return null;

  // Strip everything a human might use as a separator.
  let s = input.trim().replace(/[\s().-]/g, '');
  if (s.length === 0) return null;

  // "0034..." is the same as "+34..."
  if (s.startsWith('00')) s = `+${s.slice(2)}`;

  // A bare national number is ambiguous — refuse rather than guess a country.
  if (!s.startsWith('+')) return null;

  if (!/^\+\d+$/.test(s)) return null;
  return isE164(s) ? s : null;
}

/**
 * Last four digits, for display ("••• ••• 222"). Never render a full number
 * belonging to someone other than the viewer.
 */
export function phoneLast4(e164: string): string {
  return e164.slice(-4);
}