PHPで開発した中古品リサイクルサイトが複数の決済方法に対応

CREATE TABLE users (
  id INT PRIMARY KEY AUTO_INCREMENT,
  name VARCHAR(50) NOT NULL,
  email VARCHAR(100) NOT NULL,
  password VARCHAR(100) NOT NULL
);

CREATE TABLE items (
  id INT PRIMARY KEY AUTO_INCREMENT,
  name VARCHAR(100) NOT NULL,
  description TEXT,
  price DECIMAL(10, 2) NOT NULL,
  user_id INT,
  FOREIGN KEY (user_id) REFERENCES users(id)
);

<form action="register.php" method="POST">
  <input type="text" name="name" placeholder="姓名" required>
  <input type="email" name="email" placeholder="邮箱" required>
  <input type="password" name="password" placeholder="密码" required>
  <button type="submit">注册</button>
</form>

<form action="login.php" method="POST">
  <input type="email" name="email" placeholder="邮箱" required>
  <input type="password" name="password" placeholder="密码" required>
  <button type="submit">登录</button>
</form>

<?php
  // 查询数据库中的商品信息
  $items = DB::table('items')->get();

  foreach ($items as $item) {
    echo $item->name . ' - ￥' . $item->price;
    echo '<a href="buy_item.php?id=' . $item->id . '">购买</a>';
    echo '<br>';
  }
?>

<form action="create_item.php" method="POST">
  <input type="text" name="name" placeholder="商品名称" required>
  <textarea name="description" placeholder="商品描述" required></textarea>
  <input type="number" name="price" placeholder="商品价格" required>
  <select name="payment_method">
    <option value="alipay">支付宝</option>
    <option value="wechatpay">微信支付</option>
    <option value="bank">银行转账</option>
  </select>
  <button type="submit">发布商品</button>
</form>

<?php
  $itemId = $_GET['id'];
  $item = DB::table('items')->where('id', $itemId)->first();
?>

商品名称：<?php echo $item->name; ?><br>
商品价格：￥<?php echo $item->price; ?><br>
选择支付方式：<br>
<form action="pay.php" method="POST">
  <input type="hidden" name="item_id" value="<?php echo $itemId; ?>">
  <select name="payment_method">
    <option value="alipay">支付宝</option>
    <option value="wechatpay">微信支付</option>
    <option value="bank">银行转账</option>
  </select>
  <button type="submit">立即支付</button>
</form>

<?php
  $itemId = $_POST['item_id'];
  $paymentMethod = $_POST['payment_method'];

  // 根据选择的支付方式进行支付处理

  echo '支付成功！';
?>