public static string CheckEmailValidity(ref string input)
{
if (input == null)
{
return("No email found as input");
}
input = input.ToLower();
if (input.Length < 10)
{
return("Too short");
}
for (int i = 0; i < input.Length; i++)
{
if (input[i] == ' ')
{
return("Email contains white space");
}
if (!((input[i] >= 'a' && input[i] <= 'z') || input[i] == '_' || input[i] == '.' || input[i] == '@' || (input[i] >= '0' && input[i] <= '9')))
{
return("Contains invalid characters");
}
}
int itr = 0;
while (itr < input.Length && input[itr] != '@')
{
itr++;
}
if (itr >= input.Length)
{
return("Incomplete");
}
itr++;
int domainPrefix = 0;
while (itr < input.Length && ((input[itr] >= 'a' && input[itr] <= 'z') || input[itr] == '_' || (input[itr] >= '0' && input[itr] <= '9')))
{
domainPrefix++;
itr++;
}
if (domainPrefix < 2)
{
return("Incomplete email domain");
}
if (itr >= input.Length)
{
return("Incomplete");
}
if (input[itr] != '.')
{
return("Domain contains invalid characters");
}
itr++;
char last = '.';
while (itr < input.Length)
{
if (!((input[itr] >= 'a' && input[itr] <= 'z') || (input[itr] >= '0' && input[itr] <= '9') || input[itr] == '.' || input[itr] == '_'))
{
return("Domain contains invalid characters");
}
if (last == input[itr] && last == '.')
{
return("Domain contains invalid characters");
}
last = input[itr];
itr++;
}
if (!((input[input.Length - 1] >= 'a' && input[input.Length - 1] <= 'z') || (input[input.Length - 1] >= '0' && input[input.Length - 1] <= '9') || input[input.Length - 1] == '_'))
{
return("Domain contains invalid characters");
}
if (input.Length > 45)
{
return("Too long");
}
bool?existsOnDatabase = ServerRequest.EmailAlreadyExists(input);
if (existsOnDatabase == true)
{
return("Email already belongs to a user");
}
else if (existsOnDatabase == null)
{
return("Availability checking failed");
}
return(null);
}