Explode with operator - php

Question

I have a working code to restrict & validate subdomain.
$exp = explode('.', 'blog.mydomain.my.');
print_r($exp);
if(count($exp) == 3 && $exp[1] == "mydomain" && $exp[2] == "my" || $exp[3] == "") {
echo "<br>";
echo 'subdomain valid';
} else{
echo "<br>";
echo 'not valid';
}
now it need to check if its only false and I'm not so sure about the $exp[3] != "" comparison. From example below the subdomain should be valid but it give me error.
echo "<br>";echo "<br>";
$exp2 = explode('.', 'blog.mydomain.my.');
print_r($exp2);
if(count($exp2) != 3 || $exp2[1] != "mydomain" || $exp2[2] != "my" || $exp[3] != "") {
echo "<br>";
echo 'not valid';
}
Accepted numbers of subdomain is hello.mydomain.my or hello.mydomain.my. (with trailing dot). While hello.world.mydomain.my is not accepted.
Thanks in advance

Answer 1

This should give you what you want.
if(count($exp2) < 3 || count($exp2) > 4 || $exp2[1] != "mydomain" || $exp2[2] != "my" || (count($exp2) != 4 && $exp[3] != "")) {
echo "<br>";
echo 'not valid';
}

Answer 2

I would go for a regex solution, possibly even encapsulate it in a function:
function isValidDomain($domain)
{
return preg_match('/^[\w]+\.(mydomain)\.(my)\.?$/', $domain) ? true : false;
}
var_dump(isValidDomain('www.google.com'));
var_dump(isValidDomain('test.invalid.domain'));
var_dump(isValidDomain('hello.mydomain.my'));
var_dump(isValidDomain('hello.mydomain.my.'));