FRB's De S'er

function.php

/**
 * We were auditing ~1000 iPads, and found that if you use a Barcode Scanner to 
 * get the Serial number of a product, it tended to prefix the serial number 
 * with "S". This was annoying as we were then trying to programatically 
 * match Serial Numbers against a 3rd party API which didn't have the
 * S prefixed!. 
 *
 * This gets rid of the S. We found that all our iPad serial numbers
 * started with either "DM" or "F9", but you can change that by
 * setting your own $startingChars.
 */
if (! function_exists('deSSerialNumberFromFirstThreeCharacters')) {
    function deSSerialNumberFromFirstThreeCharacters(string $input, array $startingChars=null): string
    {
        // Firstly, all Serial Numbers should be upper case anyway.
        // This catches any that have slipped through the net.
        $input = strtoupper($input);

        // If the user hasn't defined their own starting characters, we have our defaults here.
        if (is_null($startingChars)) {
            $startingChars = [
                "SDM",
                "SF9"
            ];
        }

        // Get the first three characters of our $input (serial number)
        $substr = substr($input, 0, 3);

        // Does the serial number start with one of our $startingChars?
        if (in_array($substr, $startingChars)) {
            // If so, then trim the (any amount) S off the left hand side of the string.
            return ltrim($input, 'S');
        }

        // If the serial number doesn't start with one of our startingChars, then just return string unchanged.
        return $input;
    }
}