Scheduled web page changes watcher and notifier

watch.php

<?php

class Watch
{
    public function __construct(
        private readonly string $logFilePath,
        private readonly string $cacheFilePath,
    ) {
    }
    
    public function watch(string $url, string $attribute, string $value): void {
        // call remote URL
        $ch = curl_init($url);
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
        curl_setopt($ch, CURLOPT_FOLLOWLOCATION, true);
        $response = curl_exec($ch);
        $httpCode = curl_getinfo($ch, CURLINFO_HTTP_CODE);
        $contentLength = curl_getinfo($ch, CURLINFO_SIZE_DOWNLOAD);
        curl_close($ch);

        $this->log("URL: $url ; HTTP code: $httpCode ; Content size: $contentLength Bytes");

        if (200 !== $httpCode) {
            return;
        }

        // load DOM and search element
        $dom = new DOMDocument();
        @$dom->loadHTML($response);

        if ('id' === $attribute) {
            $element = $dom->getElementById($value);
        } else {
            $xpath = new DOMXPath($dom);
            $elements = $xpath->query("//*[@$attribute='$value']");

            if ($elements->length) {
                $element = $elements->item(0);
            }
        }

        if (empty($element)) {
            $this->log("Error: no element found with attribute $attribute=$value");
            
            return;
        }

        $elementContent = $dom->saveHTML($element);

        if (!strlen(trim((string) $elementContent))) {
            $this->log("Error: no content found in element with attribute $attribute=$value.");
            
            return;
        }

        // generate and compare hashs
        $newHash = hash('sha256', $elementContent);
        $hashFile = $this->cacheFilePath;
        $hashs = file_exists($hashFile) ? (array)json_decode((string)file_get_contents($hashFile), true) : [];
        $hashKey = md5($url);
        $storedHash = $hashs[$hashKey] ?? '';

        if (hash_equals($storedHash, $newHash)) {
            $this->log("Hashs are equals");
        } else {
            $this->log("Hashs are different");

            // save new hash
            $hashs[$hashKey] = $newHash;
            file_put_contents($hashFile, json_encode($hashs));

            // send notification email
            if (
                !$this->sendEmail(
                    EMAIL,
                    null,
                    EMAIL,
                    null,
                    'Watch - Found a change',
                    "A change was found on page $url"
                )
            ) {
                $this->log("Error: email not sent");
            }
        }
    }
    
    private function log(string $message): void
    {
        file_put_contents(
            $this->logFilePath, 
            sprintf('%s %s%s', date('Y-m-d H:i:s'), $message, PHP_EOL),
            FILE_APPEND
        );
    }

    private function sendEmail(
        string $senderEmail,
        ?string $senderName,
        string $recipientEmail,
        ?string $recipientName,
        string $subject,
        string $body
    ): bool {
        $recipient = $recipientEmail;

        if ($recipientName) {
            $recipient = "$recipientName <$recipientEmail>";
        }

        $subject = '=?utf-8?b?' . base64_encode($subject) . '?=';

        $sender = $senderEmail;

        if ($senderName) {
            $sender = '=?utf-8?b?' . base64_encode($senderName) . "?= <$senderEmail>";
        }

        $headers = [
            'MIME-Version'  => '1.0',
            'Content-Type'  => 'text/plain;charset=utf-8',
            'From'          => $sender,
            'Reply-To'      => $sender,
            'X-Mailer'      => 'PHP/' . phpversion()
        ];

        return mail($recipient, $subject, $body, $headers);
    }
}

const EMAIL = '...';

$rootDirPath = dirname(__DIR__);
$watchDirPath = $rootDirPath . '/watch';

$watch = new Watch($watchDirPath . '/watch.log', $watchDirPath . '/cache.json');

$watch->watch('...', 'id', '...');