PHP Reference Code Generator with Custom Base. Increment 0-9 A-Z alphanumeric

ReferenceCodeGenerator.php

<?PHP
class ReferenceCodeGenerator {

    private readonly int $base;

    public function __construct(
      private readonly int $codeLength = 6,
      private readonly string $characters = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ',
    ) {
        $this->base = strlen($this->characters);
    }

    /**
     * Increment the given reference code.
     *
     * @param string $currentCode The current reference code to be incremented.
     * @return string The incremented reference code.
     * @throws InvalidArgumentException If the current code is not valid.
     */
    public function increment(string $currentCode): string
    {
        $this->validateCode($currentCode);

        $currentInt = $this->convertToInteger($currentCode);
        $currentInt++;
        return $this->convertToCustomBase($currentInt);
    }

    /**
     * Validate the reference code.
     *
     * @param string $code The code to be validated.
     * @throws InvalidArgumentException If the code is not valid.
     */
    private function validateCode(string $code): void
    {
        if (strlen($code) !== $this->codeLength) {
            throw new InvalidArgumentException('Invalid code length.');
        }

        if (!preg_match('/^[0-9A-Z]+$/', $code)) {
            throw new InvalidArgumentException('Code contains invalid characters.');
        }
    }

    /**
     * Convert a custom base code to an integer.
     *
     * @param string $code The code to be converted.
     * @return int The converted integer.
     */
    private function convertToInteger(string $code): int
    {
        $length = strlen($code);
        $currentInt = 0;
        for ($i = 0; $i < $length; $i++) {
            $currentInt = $currentInt * $this->base + strpos($this->characters, $code[$i]);
        }
        return $currentInt;
    }

    /**
     * Convert an integer to a custom base code.
     *
     * @param int $int The integer to be converted.
     * @return string The converted custom base code.
     */
    private function convertToCustomBase(int $int): string
    {
        $newCode = '';
        while ($int > 0) {
            $newCode = $this->characters[$int % $this->base] . $newCode;
            $int = intdiv($int, $this->base);
        }
        return str_pad($newCode, $this->codeLength, '0', STR_PAD_LEFT);
    }
}

Usage

<?PHP

try {
    $generator = new ReferenceCodeGenerator();
    $currentCode = '000009';
    $newCode = $generator->increment($currentCode);
    echo $newCode; // Outputs: 00000A
} catch (InvalidArgumentException $e) {
    echo 'Error: ' . $e->getMessage();
}