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// 生成待签名字符串：字典序排序，剔除 sign、sign_type 与空值
function lj_build_sign_str(array $params) {
    ksort($params);
    $pairs = array();
    foreach ($params as $k => $v) {
        if ($k === 'sign' || $k === 'sign_type' || $v === '' || $v === null || is_array($v)) continue;
        $pairs[] = $k . '=' . $v;
    }
    return implode('&', $pairs);
}

// 用商户私钥生成 RSA2 签名（返回 Base64）
function lj_sign(array $params, $merchantPrivateKey) {
    openssl_sign(lj_build_sign_str($params), $sign, $merchantPrivateKey, OPENSSL_ALGO_SHA256);
    return base64_encode($sign);
}

// 用平台公钥验证返回或通知签名
function lj_verify(array $params, $signBase64, $platformPublicKey) {
    return openssl_verify(
        lj_build_sign_str($params),
        base64_decode($signBase64),
        $platformPublicKey,
        OPENSSL_ALGO_SHA256
    ) === 1;
}

{
  "code": 0,
  "trade_no": "2026101314300012345",
  "pay_type": "qrcode",
  "pay_info": "weixin://wxpay/bizpayurl?pr=04IPMKM",
  "timestamp": "1781206072",
  "sign_type": "RSA",
  "sign": "K8d9xQM7...Base64..."
}

$params = array(
    'pid'          => '10001',
    'type'         => 'wxpay',
    'method'       => 'web',
    'device'       => 'pc',
    'out_trade_no' => '202610130001',
    'notify_url'   => 'https://www.example.com/notify.php',
    'return_url'   => 'https://www.example.com/return.php',
    'name'         => 'VIP会员',
    'money'        => '1.00',
    'clientip'     => $_SERVER['REMOTE_ADDR'],
    'timestamp'    => (string)time(),
    'sign_type'    => 'RSA',
);
$params['sign'] = lj_sign($params, $merchantPrivateKey);

$ch = curl_init('https://ljepay.com/api.php?s=pay/create');
curl_setopt_array($ch, array(
    CURLOPT_POST           => true,
    CURLOPT_POSTFIELDS     => http_build_query($params),
    CURLOPT_RETURNTRANSFER => true,
    CURLOPT_TIMEOUT        => 15,
));
$response = json_decode(curl_exec($ch), true);
if ($response['code'] === 0) {
    // 按 $response['pay_type'] 处理 $response['pay_info']
}

<form action="https://ljepay.com/submit.php" method="post">
  <input type="hidden" name="pid" value="10001">
  <input type="hidden" name="type" value="alipay">
  <input type="hidden" name="out_trade_no" value="202610130001">
  <input type="hidden" name="notify_url" value="https://www.example.com/notify.php">
  <input type="hidden" name="return_url" value="https://www.example.com/return.php">
  <input type="hidden" name="name" value="VIP会员">
  <input type="hidden" name="money" value="1.00">
  <input type="hidden" name="sign_type" value="RSA">
  <input type="hidden" name="sign" value="<?php echo lj_sign($params, $merchantPrivateKey); ?>">
  <button type="submit">立即支付</button>
</form>

// notify.php —— 平台以 GET 方式通知
$params = $_GET;
$sign = isset($params['sign']) ? $params['sign'] : '';

// 使用平台公钥验签
if (!lj_verify($params, $sign, $platformPublicKey)) {
    exit('fail');
}
if ($params['trade_status'] !== 'TRADE_SUCCESS') {
    exit('success'); // 非成功状态无需发货，同样应答 success
}

// 校验订单存在且金额一致
$order = $db->findOrder($params['out_trade_no']);
if (!$order || bccomp($order['money'], $params['money'], 2) !== 0) {
    exit('fail');
}

// 幂等发货
if ($order['status'] !== 1) {
    $db->deliverOrder($order);
}
echo 'success';