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<!DOCTYPE html>
<html>
    <head>
        <title>Discord REST API</title>
        <meta charset="UTF-8" />
    </head>

    <body>
<?php
    use Elliptic\EdDSA;

    class Interaction
    {
        public static function verifyKey($rawBody, $signature, $timestamp, $client_public_key)
        {
            $ec = new EdDSA('ed25519');
            $key = $ec->keyFromPublic($client_public_key, 'hex');

            $message = array_merge(unpack('C*', $timestamp), unpack('C*', $rawBody));
            return $key->verify($message, $signature) == TRUE;
        }
    }

    abstract class InteractionResponseFlags
    {
        const EPHEMERAL = 1 << 6;
    }

    abstract class InteractionResponseType
    {
        const PONG = 1;
        const ACKNOWLEDGE = 2;
        const CHANNEL_MESSAGE = 3;
        const CHANNEL_MESSAGE_WITH_SOURCE = 4;
        const ACKNOWLEDGE_WITH_SOURCE = 5;
    }

    abstract class InteractionType
    {
        const PING = 1;
        const APPLICATION_COMMAND = 2;
    }


    if(isset($_POST["type"]))
    {
        if($_POST["type"] === 1)
        {
            $CLIENT_PUBLIC_KEY = getenv('CLIENT_PUBLIC_KEY');

            $signature = $_SERVER['HTTP_X_SIGNATURE_ED25519'];
            $timestamp = $_SERVER['HTTP_X_SIGNATURE_TIMESTAMP'];
            $postData = file_get_contents('php://input');

            if(Interaction::verifyKey($postData, $signature, $timestamp, $CLIENT_PUBLIC_KEY))
            {
                echo json_encode(array(
                'type' => InteractionResponseType::PONG
                ));
            }
            else
            {
                http_response_code(401);
                echo "Not verified";
            }

            http_response_code(200);
            echo json_encode(array("type" => 1));
        }
    }
?>
    </body>

</html>