php random string generator with custom choise

Im trying to make a "special" string generator, with a custom selection for wich characters you want.
shortly in the code when you call this function:

generateRandomString(length, [special characters], [numbers], [lower characters], [upper characters]);

for example:
generateRandomString(5, true, true, true, true);

the code should be max 5 characters, with letters, numbers and special charaters… like: fE3%!

but is give me 5 random string for each bool active so if it 4 i have back 20 characters instead of 5

this is the code
what im doing wrong?

function generateRandomString($length, $special, $numbers, $upper, $lower)
{
    //$characters = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
    $characters["special"] = "!%";
    $characters["numbers"] = "01";
    $characters["upper"] = "ABC";
    $characters["lower"] = "abc";
    $randomString = '';
 
    for ($i = 0; $i < $length; $i++)
    {
        if($special)
        {
            $randomString .= $characters["special"][rand(0, strlen($characters["special"]) - 1)];
        }
        if($numbers)
        {
            $randomString .= $characters["numbers"][rand(0, strlen($characters["numbers"]) - 1)];
        }
        if($upper)
        {
            $randomString .= $characters["upper"][rand(0, strlen($characters["upper"]) - 1)];
        }
        if($lower)
        {
            $randomString .= $characters["lower"][rand(0, strlen($characters["lower"]) - 1)];
        }
    }
 
    return $randomString;
}

>Solution :

You should first build valid characters range based on given parameters, and only then build random string.

Added validator to ensure that at least one character from each required group exists in random string.

function generateRandomString($length, $special, $numbers, $upper, $lower)
{
    //$characters = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
    $characters["special"] = "!%";
    $characters["numbers"] = implode('', range(0, 9));
    $characters["upper"] = implode('', range('A', 'Z'));
    $characters["lower"] = implode('', range('a', 'z'));

    $charactersSet = '';
    $validators = [];
    $randomString = '';

    if ($special) {
        $charactersSet .= $characters["special"];
        $validators[] = '/[' . preg_quote($characters["special"]) . ']/';
    }

    if ($numbers) {
        $charactersSet .= $characters["numbers"];
        $validators[] = '/\d/';
    }
    
    if ($upper) {
        $charactersSet .= $characters["upper"];
        $validators[] = '/[A-Z]/';
    }

    if ($lower) {
        $charactersSet .= $characters["lower"];
        $validators[] = '/[a-z]/';
    }

    for ($i = 0; $i < $length; $i++) {
        $randomString .= $charactersSet[rand(0, strlen($charactersSet) - 1)];
    }

    foreach ($validators as $pattern) {
        if (preg_match($pattern, $randomString) === 0) {
            $randomString = generateRandomString($length, $special, $numbers, $upper, $lower);

            break;
        }
    }

    return $randomString;
}