Convert images to WebP

<?php

declare(strict_types=1);

function convert_images(string $directory): void {
    $directory = realpath($directory);

    if ($dh = opendir($directory)) {
        /* process all the files in the specified directory */
        while (($file = readdir($dh)) !== false) {
            if (
                in_array($file, ['.', '..'])
                || is_dir("$directory/$file")
                || is_link("$directory/$file")
            ) {
                /* exclude directories and symbolic links */
                continue;
            }

            if (
                ($image_type = exif_imagetype("$directory/$file")) === false
                || ! in_array($image_type, [IMAGETYPE_GIF, IMAGETYPE_JPEG, IMAGETYPE_PNG])
                || ($image_extension = image_type_to_extension($image_type, false)) === false
            ) {
                /* only process certain image types */
                continue;
            }

            /* create an image based on the image file format */
            $image_create = 'imagecreatefrom' . $image_extension;
            if (($image = $image_create("$directory/$file")) === false) {
                echo 'failed to create image from ', $file, PHP_EOL;
                continue;
            }

            /* format the WebP filename */
            $webp = "$directory/" . pathinfo($file, PATHINFO_FILENAME)
                    . image_type_to_extension(IMAGETYPE_WEBP);

            /* delete the WebP file if it already exists */
            if (file_exists($webp)) {
                if (unlink($webp) === false) {
                    echo 'failed to delete ', $webp, PHP_EOL;
                    continue;
                }
            }

            /* generate the WebP image */
            $quality = 10;  // see documentation for imagewebp
            if (imagewebp($image, $webp, $quality) === false) {
                echo 'failed to convert ', $file, PHP_EOL;
            }
        }

        closedir($dh);
    }
}