firebase.php

<?php

class Firebase
{
    // kirim push notif satu user
    public function send($to, $message)
    {
        $fields = array(
            'to' => $to,
            'data' => $message,
        );
        return $this->sendPushNotification($fields);
    }

    // kirim push notif di banyak user
    public function sendMultiple($registration_ids, $message)
    {
        $fields = array(
            'registration_ids'  => $registration_ids,
            'data'              => $message,
        );

        return $this->sendPushNotification($fields);
    }

    // fungsi  curl untuk request ke firebase server
    private function sendPushNotification($fields)
    {

        $url = 'https://fcm.googleapis.com/fcm/send';

        $headers = array(
            'Authorization: key=' . FIREBASE_API_KEY,
            'Content-Type: application/json'
        );
        $ch = curl_init();

        curl_setopt($ch, CURLOPT_URL, $url);

        curl_setopt($ch, CURLOPT_POST, true);
        curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);

        curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);

        curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode($fields));

        $result = curl_exec($ch);

        if ($result === FALSE) {
            die('Curl failed: ' . curl_error($ch));
        }

        curl_close($ch);

        return $result;
    }
}