src/shared/utils/maskEmail.ts

/**
 * maskEmail — Privacy display utility for email addresses.
 *
 * Masks both username and domain portions of an email address.
 * - Username: keep the first `visibleChars`, mask the rest
 * - Domain: mask everything except the final `visibleChars`
 *
 * @example
 *   maskEmail("diego.souza@outlook.com.br")  // "die********@***********.br"
 *   maskEmail("user@gmail.com")              // "use*@******.com"
 *   maskEmail("a@b.com")                     // "a@b.com"  (too short to mask)
 */
export function maskEmail(email: string | null | undefined, visibleChars = 3): string {
  if (!email) return "";
  if (!email.includes("@")) return email;

  const atIndex = email.lastIndexOf("@");
  const username = email.slice(0, atIndex);
  const domain = email.slice(atIndex + 1);

  // If username is too short to mask meaningfully, return as-is
  if (username.length <= visibleChars) return email;

  const maskedUser = username.slice(0, visibleChars) + "*".repeat(username.length - visibleChars);
  if (domain.length <= visibleChars) {
    return `${maskedUser}@${domain}`;
  }

  const maskedDomain =
    "*".repeat(domain.length - visibleChars) + domain.slice(domain.length - visibleChars);

  return `${maskedUser}@${maskedDomain}`;
}

/**
 * Masks the value only when it looks like an email address.
 * Useful for fields like `name` that may be normalized to the raw email.
 */
export function maskEmailLikeValue(value: string | null | undefined, visibleChars = 3): string {
  if (!value) return "";
  const trimmed = value.trim();
  if (!trimmed) return "";
  return trimmed.includes("@") ? maskEmail(trimmed, visibleChars) : trimmed;
}

/**
 * Returns the first non-empty display value, masking it if it contains an email.
 */
export function pickMaskedDisplayValue(
  values: Array<string | null | undefined>,
  fallback = ""
): string {
  for (const value of values) {
    const masked = maskEmailLikeValue(value);
    if (masked) return masked;
  }
  return fallback;
}

/**
 * Visibility-aware variant of pickMaskedDisplayValue.
 * When `showFull` is true, returns the raw (unmasked) value.
 * When `showFull` is false, returns the masked value (default behavior).
 */
export function pickDisplayValue(
  values: Array<string | null | undefined>,
  showFull: boolean,
  fallback = ""
): string {
  if (showFull) {
    for (const value of values) {
      if (value?.trim()) return value.trim();
    }
    return fallback;
  }
  return pickMaskedDisplayValue(values, fallback);
}