Log image links to error log file

fp-scan-images-batch-v4.php

<?php
/**
 * Log scanned image links to debug.log.
 *
 * Make sure to enable WP_DEBUG_LOG from wp-config.php to use this command.
 */ 
function process_image_batch_new($batch_size = 500, $reset = false)
{
    $upload_dir = wp_get_upload_dir();
    $batch      = [];
    $log_file   = trailingslashit(WP_CONTENT_DIR) . 'debug.log';

    if (!file_exists($log_file)) {
        file_put_contents($log_file, "");
    }

    // Get all lines from log file.
    $lines = preg_grep('/\[FP-SCAN\]/', file($log_file, FILE_IGNORE_NEW_LINES | FILE_SKIP_EMPTY_LINES) ?: []);

    // Get already logged images
    $logged = [];
    foreach ($lines as $line) {
        if (strpos($line, '[FP-SCAN]') !== false) {
            $url = preg_replace('/^.*\[FP-SCAN\]\s*/', '', $line);
            $logged[] = trim($url);
        }
    }

    if(!is_array($logged)) {
        $logged = [];
    }

    if($reset && empty($logged)) {
        error_log("============= FP Image List - Start =============");
    }

    // Make a lookup for O(1) checks
    $lookup = array_flip($logged);

    $iterator = new RecursiveIteratorIterator(
        new RecursiveDirectoryIterator($upload_dir['basedir'], FilesystemIterator::SKIP_DOTS)
    );

    foreach($iterator as $file){
        if($file->isFile() && in_array(strtolower($file->getExtension()), ['jpg', 'jpeg', 'png'], true)){
            $link = str_replace($upload_dir['basedir'], $upload_dir['baseurl'], $file->getPathname());

            // Skip already logged images
            if (isset($lookup[$link])) {
                continue;
            }

            $batch[] = '[FP-SCAN] ' . $link;

            if (count($batch) >= $batch_size) {
                break;
            }
        }
    }

    if(!empty($batch)){
        $log_content = implode(PHP_EOL, $batch).PHP_EOL;
        error_log($log_content);
    }
}