isValid static method

Implementation

static bool isValid(String value) {
  if (value.isEmpty) return false;

  // At most one '::' is allowed in any IPv6 address.
  final dcCount = '::'.allMatches(value).length;
  if (dcCount > 1) return false;

  final hasDoubleColon = dcCount == 1;

  // Detect an IPv4-mapped tail (e.g. ::ffff:1.2.3.4).
  // The IPv4 portion appears after the last ':' when the string contains a
  // dotted-quad pattern.
  final lastColon = value.lastIndexOf(':');
  if (lastColon >= 0) {
    final tail = value.substring(lastColon + 1);
    if (tail.contains('.')) {
      // The tail looks like an IPv4 address — validate as IPv4-mapped.
      return _validateIpv4Mapped(value, tail, hasDoubleColon);
    }
  }

  // Pure hex form (no IPv4 tail).
  if (hasDoubleColon) {
    return _validateCompressed(value);
  } else {
    return _validateFull(value);
  }
}