**Project** Part 1. 회원가입 페이지 및 송금페이지

"프로젝트 초기 환경"
운영체제: MAC OS
데이터베이스: MySQL
사용 언어: HTML, CSS, Javascript

"조원 웹 페이지 역할 분담"
동욱 - 대시보드, 로그인
유진 - 메인페이지, 거래내역
정미 - 계정 관리, 대출 신청
지향 - 송금페이지, 회원가입
=> 우선 각자 로컬호스트 환경에서 구축해보기로 했음!

웹페이지 구성 - 9월 27일 금요일까지

 

데이터베이스 생성

create database bank;
use bank;

CREATE TABLE users ( /* 회원 테이블 */
    user_num INT AUTO_INCREMENT PRIMARY KEY,
    userid VARCHAR(20) NOT NULL UNIQUE,
    username VARCHAR(50) NOT NULL,
    password VARCHAR(255) NOT NULL,
    email VARCHAR(100) NOT NULL UNIQUE,
    phone_number VARCHAR(20) NOT NULL UNIQUE,
    date_of_birth CHAR(6) NOT NULL,
    account_created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
    last_login TIMESTAMP NULL
);

CREATE TABLE transaction_types ( /* 거래 유형 참조 테이블 */
    id INT AUTO_INCREMENT PRIMARY KEY,
    type VARCHAR(50) NOT NULL UNIQUE
);

CREATE TABLE accounts ( /* 계좌 테이블 */
    account_id INT AUTO_INCREMENT PRIMARY KEY,
    user_num INT NOT NULL,
    account_number VARCHAR(20) NOT NULL UNIQUE,
    balance BIGINT NOT NULL DEFAULT 0,
    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
    FOREIGN KEY (user_num) REFERENCES users(user_num)
);

CREATE TABLE transactions ( /* 거래내역 테이블 */
    transaction_id INT AUTO_INCREMENT PRIMARY KEY,
    account_id INT NOT NULL,
    transaction_type_id INT NOT NULL,
    amount BIGINT NOT NULL,
    amount_after BIGINT NOT NULL,
    receiver_account VARCHAR(20),
    transaction_date TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
    FOREIGN KEY (account_id) REFERENCES accounts(account_id),
    FOREIGN KEY (transaction_type_id) REFERENCES transaction_types(id)
);

CREATE TABLE loan_types ( /* 대출 유형 참조 테이블 */
    id INT AUTO_INCREMENT PRIMARY KEY,
    type VARCHAR(50) NOT NULL UNIQUE
);

CREATE TABLE loan_statuses ( /* 대출 상태 참조 테이블 */
    id INT AUTO_INCREMENT PRIMARY KEY,
    status VARCHAR(50) NOT NULL UNIQUE
);

CREATE TABLE loans ( /* 대출 테이블 */
    loan_id INT AUTO_INCREMENT PRIMARY KEY,
    user_num INT NOT NULL,
    loan_type_id INT NOT NULL,
    loan_amount BIGINT NOT NULL,
    interest_rate DECIMAL(5, 2) NOT NULL,
    loan_start_date DATE NOT NULL,
    loan_end_date DATE NOT NULL,
    loan_status_id INT NOT NULL,
    FOREIGN KEY (user_num) REFERENCES users(user_num),
    FOREIGN KEY (loan_type_id) REFERENCES loan_types(id),
    FOREIGN KEY (loan_status_id) REFERENCES loan_statuses(id)
);

CREATE TABLE transfer_statuses ( /* 송금 상태 참조 테이블 */
    id INT AUTO_INCREMENT PRIMARY KEY,
    status VARCHAR(50) NOT NULL UNIQUE  
    -- 상태 이름: 'Pending', 'Completed', 'Failed'
    -- name에서 변경
);

CREATE TABLE transfers ( /* 송금 테이블 */
    transfer_id INT AUTO_INCREMENT PRIMARY KEY,
    sender_account_id INT NOT NULL,
    receiver_account VARCHAR(20) NOT NULL,
    amount BIGINT NOT NULL,
    transfer_date TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
    status_id INT NOT NULL,
    FOREIGN KEY (sender_account_id) REFERENCES accounts(account_id),
    FOREIGN KEY (status_id) REFERENCES transfer_statuses(id)
);

CREATE TABLE login_history ( /* 로그인 기록 테이블 */
    login_id INT AUTO_INCREMENT PRIMARY KEY,
    user_num INT NOT NULL,
    login_time TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
    ip_address VARCHAR(45),
    device_info VARCHAR(255),
    FOREIGN KEY (user_num) REFERENCES users(user_num)
);

 

 

생성된 데이터베이스 다이어그램

 

 

회원가입, 송금 페이지 파일 연결도

 

DB연결

dbconn.php

0.00MB

<?php
if (session_status() == PHP_SESSION_NONE) {
    session_start();
}

$current_file = basename($_SERVER['PHP_SELF']);

//a페이지나 b페이지가 아닐 경우 로그인 페이지로 다시 이동
/*if (($current_file != '#' && $current_file != '#') && !isset($_SESSION['userid'])) {
    echo "<script>alert('로그인이 필요합니다');</script>";

    echo "<script>location.href='#';</script>"; //로그인 후 이동할 페이지
    exit;
}*/
?>

<?php
$serverName = "localhost";
$database = "bank";

$uid = "root";
$pwd = "wlgid0420@";

try {
    $conn = new PDO("mysql:host=$serverName;dbname=$database", $uid, $pwd);

    $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
} catch (PDOException $e) {
    die("Error connecting to mysql");
}
?>

 

 

회원가입

register.php

0.00MB

 

<?php
include 'dbconn.php';

//회원가입 처리
if ($_SERVER["REQUEST_METHOD"] == "POST") {
    $userid = $_POST['userid'];
    $username = $_POST['username'];
    $password = $_POST['password'];
    $email = $_POST['email'];
    $phone_number = $_POST['phone1'] . '-' . $_POST['phone2'] . '-' . $_POST['phone3'];
    $birth = $_POST['birth'];

    try {
        $sql = "INSERT INTO users(userid, username, password, email, phone_number, date_of_birth) VALUES('$userid', '$username', '$password', '$email', '$phone_number', '$birth')";

        //쿼리 실행
        $conn->exec($sql);

        echo "회원가입이 완료되었습니다."; //성공 메시지 출력
        header('Location: login.php'); //로그인 페이지 이동
    } catch (PDOException $e) {
        //쿼리 실행 실패 시 오류 메시지 출력
        die("회원가입 중 오류가 발생했습니다: " . $e->getMessage());
    }
}
?>
<html>

<head>
    <script src="javascript/register.js"></script>
    <link rel="stylesheet" href="css/register.css">
</head>

<body>
    <!--회원가입 폼-->
    <form id="signForm" method="POST">
        <div> <!--아이디 입력-->
            <label>사용자 ID:</label>
            <input type="text" name="userid" maxlength="20" id="userid" placeholder="아이디를 입력해주세요." required>
            <button type="button" onclick="checkUserID()">중복체크</button>
            <div id="idError" class="error"></div> <!--입력 값 확인 메시지 출력-->
            <span id="useridFeedback"></span> <!--중복체크 메시지 출력-->
        </div>
        <div> <!--이름 입력-->
            <label>사용자 이름:</label>
            <input type="text" name="username" maxlength="10" id="username" placeholder="이름을 입력해주세요." required>
            <div id="nameError" class="error"></div> <!--입력 값 확인 메시지 출력-->
        </div>
        <div> <!--비밀번호 입력-->
            <label>비밀번호:</label>
            <input type="password" name="password" maxlength="20" id="password" placeholder="영문, 숫자, 특수문자 포함 8자리 이상 입력"
                required>
            <div id="passError" class="error"></div> <!--입력 값 확인 메시지 출력-->
        </div>
        <div> <!--이메일 입력-->
            <label>이메일:</label>
            <input type="text" name="email" maxlength="20" id="email" placeholder="이메일을 입력해주세요." required>
            <div id="emailError" class="error"></div> <!--입력 값 확인 메시지 출력-->
        </div>
        <div> <!--핸드폰 번호 입력-->
            <label>핸드폰 번호:</label>
            <div id="phoneNum">
                <input type="text" name="phone1" size="3" id="phone1" maxlength="3" oninput="nextPhone1()" required> -
                <input type="text" name="phone2" size="6" id="phone2" maxlength="4" oninput="nextPhone2()" required> -
                <input type="text" name="phone3" size="6" id="phone3" maxlength="4" required>
            </div>
            <div id="phoneError" class="error"></div> <!--입력 값 확인 메시지 출력-->
        </div>
        <div> <!--생년월일 입력-->
            <label>생년월일:</label>
            <input type="text" name="birth" id="birth" maxlength="6" placeholder="주민번호 앞 6자리 입력" required>
            <div id="birthError" class="error"></div> <!--입력 값 확인 메시지 출력-->
        </div>
        <button type="button" id="signUp" onclick="signupCheck()">회원가입</button>
    </form>
</body>

</html>

 

Javascript

register.js

0.00MB

⬇️ 아래 코드 보기

function nextPhone1() {
  const phone1 = document.getElementById("phone1").value;
  if (phone1.length === 3) {
    document.getElementById("phone2").focus();
  }
}
function nextPhone2() {
  const phone2 = document.getElementById("phone2").value;
  if (phone2.length === 4) {
    document.getElementById("phone3").focus();
  }
}

let isIdChecked = false;
//ID중복체크
function checkUserID() {
  const userid = document.getElementById("userid").value;
  const feedback = document.getElementById("useridFeedback");

  if (userid.trim() === "") {
    feedback.textContent = "아이디를 입력해주세요.";
    return;
  }
  fetch("../api/check_userid.php", {
    method: "POST",
    headers: {
      "Content-Type": "application/json",
    },
    body: JSON.stringify({ userid: userid }),
  })
    .then((response) => response.json())
    .then((data) => {
      if (data.exists) {
        feedback.textContent = "이미 사용 중인 아이디입니다.";
        feedback.style.color = "red";
        isIdChecked = false;
      } else {
        feedback.textContent = "사용 가능한 아이디입니다.";
        feedback.style.color = "green";
        isIdChecked = true;
      }
    })
    .catch((error) => {
      console.error("Error:", error);
    });
}

//회원가입 버튼 클릭 시 입력값 검증
function signupCheck() {
  let id = document.getElementById("userid").value;
  let name = document.getElementById("username").value;
  let password = document.getElementById("password").value;
  let email = document.getElementById("email").value;
  let birth = document.getElementById("birth").value;
  // let phone1 = document.getElementById("phone1").value;
  let check = true;

  //아이디확인
  if (id.trim() === "") {
    document.getElementById("idError").innerHTML = "아이디를 입력해주세요.";
    check = false;
  } else if (id.includes(" ")) {
    document.getElementById("idError").innerHTML =
      "아이디를 다시 입력해주세요.";
    check = false;
  } else {
    document.getElementById("idError").innerHTML = "";
  }
  if (!isIdChecked) {
    document.getElementById("idError").innerHTML =
      "아이디 중복체크를 해주세요.";
    check = false;
  } else {
    document.getElementById("idError").innerHTML = "";
  }

  //이름확인
  if (name.includes(" ")) {
    document.getElementById("nameError").innerHTML =
      "공백이 포함되어 있습니다. 공백을 제거해주세요.";
    check = false;
  } else if (name === "") {
    document.getElementById("nameError").innerHTML =
      "이름이 올바르지 않습니다. 다시 입력해주세요.";
    check = false;
  } else {
    document.getElementById("nameError").innerHTML = "";
  }

  //비밀번호확인
  let hasLetter = /[a-zA-Z]/.test(password); //영문 확인(T/F 반환)
  let hasNumber = /[0-9]/.test(password); //숫자 확인(T/F 반환)
  let hasSpecial = /[!@#$%^&*(),.?":{}|<>]/.test(password); //특수문자 확인(T/F 반환)
  if (!hasLetter) {
    document.getElementById("passError").innerHTML =
      "비밀번호에 영문을 포함해주세요.";
    check = false;
  } else if (!hasNumber) {
    document.getElementById("passError").innerHTML =
      "비밀번호에 숫자를 포함해주세요.";
    check = false;
  } else if (!hasSpecial) {
    document.getElementById("passError").innerHTML =
      "비밀번호에 특수문자를 포함해주세요.";
    check = false;
  } else if (password.length < 8) {
    document.getElementById("passError").innerHTML =
      "비밀번호를 8자리 이상 입력해주세요.";
    check = false;
  } else {
    document.getElementById("passError").innerHTML = "";
  }

  //이메일확인
  if (email.includes("@")) {
    let emailID = email.split("@")[0];
    let emailServer = email.split("@")[1];
    if (emailID === "" || emailServer === "") {
      document.getElementById("emailError").innerHTML =
        "이메일을 알맞은 형식으로 입력해주세요.";
      check = false;
    } else if (!emailServer.includes(".")) {
      document.getElementById("emailError").innerHTML =
        "이메일을 알맞은 형식으로 입력해주세요.";
      check = false;
    } else {
      document.getElementById("emailError").innerHTML = "";
    }
  } else {
    document.getElementById("emailError").innerHTML =
      "이메일을 다시 입력해주세요.";
    check = false;
  }

  //생년월일확인
  let birthNumber = /[0-9]/.test(birth);
  if (!birthNumber) {
    document.getElementById("birthError").innerHTML =
      "주민번호 앞 6자리를 숫자로 입력해주세요.";
    check = false;
  } else {
    document.getElementById("birthError").innerHTML = "";
  }

  //모든 값 true일 경우
  if (check) {
    document.getElementById("idError").innerHTML = "";
    document.getElementById("nameError").innerHTML = "";
    document.getElementById("passError").innerHTML = "";
    document.getElementById("emailError").innerHTML = "";
    document.getElementById("birthError").innerHTML = "";
    document.getElementById("signForm").submit();

    setTimeout(function () {
      alert("가입이 완료되었습니다.");
    }, 0);
  }
}

 

php(api 역할)

check_userid.php

0.00MB

⬇️ 아래 코드 보기

<?php
include "../dbconn.php";

// Get the username from the request
$data = json_decode(file_get_contents('php://input'), true);
$userid = $data['userid'];

// Check if the username exists
$sql = "SELECT * FROM users WHERE userid='$userid'";
$stmt = $conn->prepare($sql);
$stmt->execute();

$response = array();
$response['exists'] = ($stmt->rowCount() > 0);

echo json_encode($response);

$conn = null;
exit();
?>

 

송금 페이지

transfer.php

0.00MB

<?php
session_start();
if (!isset($_SESSION["userid"]) || !isset($_SESSION["username"])) {
    echo "로그인이 필요합니다.";
}
?>

<!DOCTYPE html>
<html>

<head>
    <script src="javascript/transfer.js"></script>
</head>

<body>
    <form method="POST">
        <div>
            <?php echo $_SESSION["username"]; ?>님
            <a href="#"> <!--로그아웃 페이지-->
                <button>로그아웃</button>
            </a>
        </div>
        <div> <!--출금계좌선택-->
            <label>출금계좌번호</label>
            <select id="out_account" name="out_account">
                <option value="">선택하세요</option>
                <?php
                include "dbconn.php";

                $select_user_num = $_SESSION['user_num'];
                if ($select_user_num) {
                    $query = "SELECT * FROM accounts WHERE user_num = $select_user_num";
                    $stmt = $conn->prepare($query);
                    $stmt->execute();

                    if ($stmt->rowCount() > 0) {
                        while ($row = $stmt->fetch(PDO::FETCH_ASSOC)) {
                            ?>
                            <option value="<?= $row['account_number'] ?>"><?= $row['account_number'] ?></option>
                            <?php
                        }
                    } else {
                        echo "<option value=''>계좌가 없습니다.</option>";
                    }

                } else {
                    echo "<option value=''>user_num이 전달되지 않았습니다.</option>";
                } ?>
            </select>
            <div>
                <button type="button" onclick="myAccount()">출금가능금액 조회</button>
                <div id="balance">잔액: 0원</div>
            </div>
        </div>
        <!-- <div> 
            <label>입금기관</label>
            <input type="text" id="select_bank" name="select_bank" readonly>
            <button type="button" onclick="popupBank()">기관선택</button>
        </div> -->
        <div> <!--입금계좌번호 입력-->
            <label>입금계좌번호</label>
            <input type="text" id="in_account" name="in_account" required>
        </div>
        <div> <!--이체금액 입력-->
            <label>이체금액</label>
            <input type="number" id="transfer_amount" name="transfer_amount" required>
        </div>
        <button type="submit" onclick="transferSubmit()">이체하기</button>
    </form>
</body>

</html>

 

Javascript

transfer.js

0.00MB

⬇️ 아래 코드 보기

function setValueFromPopup(value) {
  document.getElementById("select_bank").value = value;
}

// function popupBank() {
//   window.open("popup.html", "popupWindow", "width=300, height=200");
// }

let currentBalance;
//잔액 조회 함수
function myAccount() {
  const user_num = document.getElementById("out_account").value;
  fetch(`../api/check_account.php?user_num=${user_num}`, {
    method: "GET",
  })
    .then((response) => response.json())
    // .then((response) => {
    //   console.log("res", response);
    // })
    .then((data) => {
      if (data.balance !== undefined) {
        currentBalance = parseFloat(data.balance);
        document.getElementById(
          "balance"
        ).innerHTML = `잔액: ${currentBalance}원`;
        console.log("잔액: " + currentBalance);
        console.log(data.balance);
      } else {
        document.getElementById("balance").innerHTML =
          "잔액 정보를 가져올 수 없습니다.";
        console.log("잔액 정보 오류");
      }
    })
    .catch((error) => {
      console.error("Error: ", error);
      document.getElementById("balance").innerHTML =
        "잔액 정보를 가져오는 중 오류가 발생하였습니다.";
    });
}

//이체 실행 함수
function transferSubmit() {
  const account_number_out = document.getElementById("out_account").value; //출금 계좌
  const account_number_in = document.getElementById("in_account").value; //입금 계좌
  const transferAmount = parseFloat(
    document.getElementById("transfer_amount").value
  );
  console.log("출금 계좌: ", account_number_out);
  console.log("입금 계좌: ", account_number_in);
  console.log("이체 금액: ", transferAmount);
  //서버로 이체 요청
  fetch(`../api/transfer_account.php`, {
    method: "POST",
    headers: {
      "Content-Type": "application/json",
    },
    body: JSON.stringify({
      account_number_out: account_number_out,
      account_number_in: account_number_in,
      transfer_amount: transferAmount,
    }),
  })
    .then((response) => response.json())
    // .then((response) => {
    //   console.log("res", response);
    // })
    .then((data) => {
      console.log("서버응답:", data);
      if (data.success) {
        alert("이체가 완료되었습니다.");
        myAccount(account_number_out);
      } else {
        alert("이체에 실패했습니다." + data.message);
      }
    })
    .catch((error) => {
      console.log("오류: ", error);
    });

  return false;
}

 

php(api 역할1) - 입출금

transfer_account.php

0.01MB

⬇️ 아래 코드 보기

<?php
include "../dbconn.php";

$data = json_decode(file_get_contents("php://input"), true);
$account_number_out = $data['account_number_out'] ?? null; //출금 계좌
$account_number_in = $data['account_number_in'] ?? null; //입금 계좌
$transfer_amount = $data['transfer_amount'] ?? null; //이체 금액

if ($_SERVER["REQUEST_METHOD"] === "POST") {
    if ($account_number_out === null || $account_number_in === null) {
        echo json_encode(['success' => false, 'message' => '필수 데이터가 누락되었습니다.']);
        exit;
    }
    try {
        //트랜잭션 시작
        $conn->beginTransaction();

        //1) 출금
        $sql = "SELECT * FROM accounts WHERE account_number = :account_number_out";
        $stmt = $conn->prepare($sql);
        $stmt->bindParam(":account_number_out", $account_number_out);
        $stmt->execute();
        $result = $stmt->fetch(PDO::FETCH_ASSOC);
        if ($result) {
            $current_balance = $result['balance'];
            $sender_account_id = $result['account_id'];
            if ($current_balance >= $transfer_amount) {
                //출금 계좌 잔액에서 이체 금액 차감
                $new_balance = $current_balance - $transfer_amount;

                //출금 계좌 업데이트
                $update_sql = "UPDATE accounts SET balance = :new_balance WHERE account_number = :account_number_out";
                $stmt = $conn->prepare($update_sql);
                $stmt->bindParam(":new_balance", $new_balance);
                $stmt->bindParam(":account_number_out", $account_number_out);
                $stmt->execute();

                //2) 입금
                $sql_in = "SELECT * FROM accounts WHERE account_number = :account_number_in";
                $stmt_in = $conn->prepare($sql_in);
                $stmt_in->bindParam(":account_number_in", $account_number_in);
                $stmt_in->execute();
                $result_in = $stmt_in->fetch(PDO::FETCH_ASSOC);
                if ($result_in) {
                    //입금 계좌 잔액에서 이체 금액 더함
                    $new_balance_in = $result_in['balance'] + $transfer_amount;
                    $receiver_account_id = $result_in['account_id'];

                    //입금 계좌 업데이트
                    $update_sql_in = "UPDATE accounts SET balance = :new_balance_in WHERE account_number = :account_number_in";
                    $stmt = $conn->prepare($update_sql_in);
                    $stmt->bindParam(":new_balance_in", $new_balance_in);
                    $stmt->bindParam(":account_number_in", $account_number_in);
                    $stmt->execute();

                    //(출금)송금 테이블에 데이터 삽입
                    $transfer_sql = "INSERT INTO transfers(sender_account_id, receiver_account, amount, transfer_date, status_id)
                    VALUES(:sender_account_id, :receiver_account, :transfer_amount, NOW(), 2)";
                    $stmt_transfer = $conn->prepare($transfer_sql);
                    $stmt_transfer->bindParam(":sender_account_id", $sender_account_id);
                    $stmt_transfer->bindParam(":receiver_account", $account_number_in);
                    $stmt_transfer->bindParam(":transfer_amount", $transfer_amount);
                    $stmt_transfer->execute();

                    //(출금)거래내역 테이블에 데이터 삽입
                    $history_out = "INSERT INTO transactions(account_id, transaction_type_id, amount, amount_after, receiver_account, transaction_date)
                    VALUES(:sender_account_id, 2, :transfer_amount, :new_balance, :account_number_in, NOW())";
                    $stmt_history_out = $conn->prepare($history_out);
                    $stmt_history_out->bindParam(":sender_account_id", $sender_account_id);
                    $stmt_history_out->bindParam(":transfer_amount", $transfer_amount);
                    $stmt_history_out->bindParam(":new_balance", $new_balance);
                    $stmt_history_out->bindParam(":account_number_in", $account_number_in);
                    $stmt_history_out->execute();

                    //(입금)거래내역 테이블에 데이터 삽입
                    $history_in = "INSERT INTO transactions(account_id, transaction_type_id, amount, amount_after, receiver_account, transaction_date)
                    VALUES(:receiver_account_id, 1, :transfer_amount, :new_balance, :account_number_in, NOW())";
                    $stmt_history_in = $conn->prepare($history_in);
                    $stmt_history_in->bindParam(":receiver_account_id", $receiver_account_id);
                    $stmt_history_in->bindParam(":transfer_amount", $transfer_amount);
                    $stmt_history_in->bindParam(":new_balance", $new_balance_in);
                    $stmt_history_in->bindParam(":account_number_in", $account_number_in);
                    $stmt_history_in->execute();
                } else {
                    throw new Exception("입금 계좌를 찾을 수 없습니다.");
                }
            } else {
                throw new Exception("잔액이 부족합니다.");
            }
        } else {
            error_log("출금 계좌를 찾을 수 없습니다. : " . $account_number_out);
            throw new Exception("출금 계좌를 찾을 수 없습니다.");
        }
        $conn->commit();
        echo json_encode(['success' => true]);
    } catch (Exception $e) {
        $conn->rollBack();
        error_log('오류 발생: ' . $e->getMessage());
        echo json_encode(['success' => false, 'message' => $e->getMessage()]);
    }
}

$conn = null;
exit();
?>

 

php(api 역할2) - 잔액확인

check_account.php

0.00MB

⬇️ 아래 코드 보기

<?php
session_start();
include "../dbconn.php";
$user_num = $_SESSION['user_num'];
try {
    $sql = "SELECT balance FROM accounts WHERE user_num = '$user_num'";
    $stmt = $conn->prepare($sql);
    $stmt->execute();
    $result = $stmt->fetch(PDO::FETCH_ASSOC);

    if ($result) {
        echo json_encode(['balance' => $result['balance']]);
    } else {
        echo json_encode(['balance' => 0]);
    }
} catch (PDOException $e) {
    echo json_encode(['error' => $e->getMessage()]);
}

$conn = null;
exit();
?>