/// <summary>
/// Returns the Country based on an international dialing code.
/// </summary>
public static Country? GetCountry(ReadOnlySpan<char> phoneNumber) {
if (phoneNumber.Length==0) return null;
var isFirstDigit = true;
DigitInfo? digitInfo = null;
Country? country = null;
foreach (var digitChar in phoneNumber) {
var digitIndex = digitChar - '0';
if (isFirstDigit) {
isFirstDigit = false;
digitInfo = ByPhone[digitIndex];
} else {
if (digitInfo!.Digits is null) return country;
digitInfo = digitInfo.Digits[digitIndex];
}
if (digitInfo is null) return country;
country = digitInfo.Country??country;
}
return country;
}