<?php 
include_once('config.php');

$params = $_GET; 
$hmac = (isset($_GET['hmac']) ? $_GET['hmac'] : ''); 

$params = array_diff_key($params, array('hmac' => '')); 
ksort($params); 

$computed_hmac = hash_hmac('sha256', http_build_query($params), SHARED_SECRET);


if(!isset($_GET['shop']))
{
    echo SHOP_REQUIRED;
    exit;
}

if(strpos($_GET['shop'],SHOPIFY_DOMAIN) == FALSE)
{
    echo ACCESS_DENIED;
    exit;
}

if(isset($_GET['state']) && $_GET['state'] != NONCE)
{
    echo ACCESS_DENIED;
    exit;
}

if (!hash_equals($hmac, $computed_hmac))
{
    echo ACCESS_DENIED;
    exit;
}

if(isset($_GET['client_id']) && $_GET['client_id'] != API_KEY)
{
    echo ACCESS_DENIED;
    exit;
}

if(isset($_GET['client_secret']) && $_GET['client_secret'] != SHARED_SECRET)
{
    echo ACCESS_DENIED;
    exit;
}

if(isset($_GET['code']) && $_GET['code'] == '')
{
    echo ACCESS_DENIED;
    exit;
}