function vietnameseToEnglishName(name) {
  if (!name) return "";

  // 1. Normalize Unicode + remove accents
  let noAccent = name.normalize("NFD")
    .replace(/[\u0300-\u036f]/g, "") // remove diacritic marks
    .replace(/đ/g, "d").replace(/Đ/g, "D");

  // 2. Trim + remove multiple spaces
  noAccent = noAccent.trim().replace(/\s+/g, " ");

  // 3. Capitalize each word
  let englishName = noAccent
    .split(" ")
    .map(w => w.charAt(0).toUpperCase() + w.slice(1).toLowerCase())
    .join(" ");

  return englishName;
}


let currentStudentData = null;

// Show error modal
function showError(message) {
    const errorModal = document.createElement('div');
    errorModal.className = 'modal fade';
    errorModal.innerHTML = `
        <div class="modal-dialog">
            <div class="modal-content">
                <div class="modal-header bg-danger text-white">
                    <h5 class="modal-title">
                        <i class="fas fa-exclamation-triangle me-2"></i>Lỗi
                    </h5>
                    <button type="button" class="btn-close btn-close-white" data-bs-dismiss="modal"></button>
                </div>
                <div class="modal-body">
                    <p class="mb-0">${message}</p>
                </div>
                <div class="modal-footer">
                    <button type="button" class="btn btn-secondary" data-bs-dismiss="modal">Đóng</button>
                </div>
            </div>
        </div>
    `;
    document.body.appendChild(errorModal);
    const modal = new bootstrap.Modal(errorModal);
    modal.show();
    
    // Remove modal from DOM after it's hidden
    errorModal.addEventListener('hidden.bs.modal', () => {
        document.body.removeChild(errorModal);
    });
}

// Show success modal  
function showSuccess(message) {
    const successModal = document.createElement('div');
    successModal.className = 'modal fade';
    successModal.innerHTML = `
        <div class="modal-dialog">
            <div class="modal-content">
                <div class="modal-header bg-success text-white">
                    <h5 class="modal-title">
                        <i class="fas fa-check-circle me-2"></i>Thành công
                    </h5>
                    <button type="button" class="btn-close btn-close-white" data-bs-dismiss="modal"></button>
                </div>
                <div class="modal-body">
                    <p class="mb-0">${message}</p>
                </div>
                <div class="modal-footer">
                    <button type="button" class="btn btn-success" data-bs-dismiss="modal">Đóng</button>
                </div>
            </div>
        </div>
    `;
    document.body.appendChild(successModal);
    const modal = new bootstrap.Modal(successModal);
    modal.show();
    
    // Remove modal from DOM after it's hidden
    successModal.addEventListener('hidden.bs.modal', () => {
        document.body.removeChild(successModal);
    });
}

// Load student info by SBD
document.getElementById('loadInfoBtn').addEventListener('click', async function() {
    const sbd = document.getElementById('cccd').value.trim();
    
    if (!sbd) {
        showError('Vui lòng nhập số báo danh');
        return;
    }

    const loadBtn = this;
    
    
    // Show loading state
    loadBtn.disabled = true;
    
    loadBtn.innerHTML = '<span class="spinner-border spinner-border-sm me-2"></span>Đang tải...';
    const spinner = loadBtn.querySelector('.loading-spinner');
    if(spinner)
        spinner.style.display = 'inline-block';

    try {
        const response = await fetch('/api/candidate/' + sbd);
        const data = await response.json();

        if (response.ok && data.success) {
            currentStudentData = data.candidate;
            fillFormData(data.candidate);
            document.getElementById('studentInfo').style.display = 'block';
            
            // Scroll to form
            document.getElementById('studentInfo').scrollIntoView({ behavior: 'smooth' });
        } else {
            showError(data.message || 'Không tìm thấy thông tin sinh viên với số báo danh này');
            document.getElementById('studentInfo').style.display = 'none';
        }
    } catch (error) {
        showError('Có lỗi xảy ra khi tải thông tin');
        console.error(error);
    } finally {
        // Reset button state
        loadBtn.disabled = false;
        if(spinner)
            spinner.style.display = 'none';
        loadBtn.innerHTML = 'Tải thông tin';
    }
});

function fillFormData(candidate) {
    // Fill display fields (with _display suffix to avoid form submission)
    document.getElementById('hoten_display').value = candidate.hoten;
    document.getElementById('gioitinh_display').value = candidate.gioitinh;
    
    // Format date for display
    const date = new Date(candidate.ngaysinh);
    const formattedDate = date.toLocaleDateString('vi-VN');
    document.getElementById('ngaysinh_display').value = formattedDate;
    
    document.getElementById('dantoc_display').value = candidate.dantoc;
    document.getElementById('cccd_display').value = candidate.cccd;
    document.getElementById('dienthoai_display').value = candidate.dienthoai;
    document.getElementById('email_display').value = candidate.email;
    
    // Convert enum values to display text
    // const phuongthucText = candidate.phuongthuc === 'hocba' ? 'Học bạ' : 'Điểm xét tuyển THPT';
    const nganhText = candidate.nganh;// === 'luathoc' ? 'Luật học' : 'Luật kinh tế';
    
    // document.getElementById('phuongthuc_display').value = phuongthucText;
    document.getElementById('nganh_display').value = nganhText;

    // Show current image status
    const imageStatusDiv = document.getElementById('imageStatus');
    if (candidate.filename) {
        imageStatusDiv.innerHTML = `
            <span class="badge bg-success me-2">Đã có ảnh</span>
            <a href="/uploads/${candidate.filename}" target="_blank" class="btn btn-sm btn-outline-primary">
                <i class="fas fa-eye me-1"></i>Xem ảnh hiện tại
            </a>
        `;
    } else {
        imageStatusDiv.innerHTML = '<span class="badge bg-warning text-dark">Chưa có ảnh</span>';
    }

    var options = {
        text: makeVietQRContent({bankId: "970405", accountId: "4000337338339", amount: "9400000", description: "K49_" + vietnameseToEnglishName(candidate.hoten) + "_" + candidate.cccd}),
        width: 200,
        height: 200,
        colorDark : "#000000",
        colorLight : "#ffffff",
        dotScale: 1,
        logo:"https://hul.edu.vn/bundles/web/assets/images/logo.png", // Relative address, relative to `easy.easy.qrcode.min.js`
        logoWidth:36, // widht. default is automatic width
        logoHeight:36, // height. default is automatic height
        logoBackgroundColor:'#fffff', // Logo backgroud color, Invalid when `logBgTransparent` is true; default is '#ffffff'
        logoBackgroundTransparent:false, // Whether use transparent image, default is false
    };
    document.getElementById("qr_vietqr").innerHTML = "";
    document.getElementById("noidungchuyenkhoan").innerHTML = "K49_" + vietnameseToEnglishName(candidate.hoten) + "_" + candidate.cccd;
    var qrcode = new QRCode(document.getElementById("qr_vietqr"), options);
}

// Load completed registrations
function loadStudents() {
    fetch('/api/students')
        .then(response => response.json())
        .then(data => {
            const container = document.getElementById('studentsList');
            if (data.length === 0) {
                container.innerHTML = '<p class="text-center text-muted">Chưa có sinh viên nào đăng ký</p>';
                return;
            }

            let html = '<div class="table-responsive"><table class="table table-striped table-hover">';
            html += '<thead class="table-dark"><tr>';
            html += '<th>SBD</th><th>Họ tên</th><th>Giới tính</th><th>Ngày sinh</th>';
            html += '<th>Email</th><th>Ngành</th><th>Ảnh</th><th>Ngày đăng ký</th></tr></thead><tbody>';

            data.forEach(student => {
                html += '<tr>';
                html += '<td><strong>' + student.sbd + '</strong></td>';
                html += '<td>' + student.hoten + '</td>';
                html += '<td>' + student.gioitinh + '</td>';
                html += '<td>' + new Date(student.ngaysinh).toLocaleDateString('vi-VN') + '</td>';
                html += '<td>' + student.email + '</td>';
                html += '<td>' + (student.nganh === 'luathoc' ? 'Luật học' : 'Luật kinh tế') + '</td>';
                html += '<td>';
                if (student.filename) {
                    html += '<span class="badge bg-success">Có</span>';
                    html += '<br><a href="/uploads/' + student.filename + '" target="_blank" class="btn btn-sm btn-outline-primary mt-1">Xem ảnh</a>';
                } else {
                    html += '<span class="badge bg-warning text-dark">Chưa có</span>';
                }
                html += '</td>';
                html += '<td>' + new Date(student.created_at).toLocaleDateString('vi-VN') + '</td>';
                html += '</tr>';
            });

            html += '</tbody></table></div>';
            container.innerHTML = html;
        })
        .catch(error => {
            console.error('Error loading students:', error);
            showError('Có lỗi xảy ra khi tải danh sách sinh viên');
        });
}

// Form submission
document.getElementById('studentForm').addEventListener('submit', function(e) {
    e.preventDefault();

    if (!currentStudentData) {
        showError('Vui lòng tải thông tin sinh viên trước');
        return;
    }

    // File upload is optional - can update without changing image
    const fileInput = document.getElementById('filename');
    if (!fileInput.files || !fileInput.files[0]) {
        showError('Vui lòng chọn ảnh để tải lên');
        return;
    }

    // Submit form
    const formData = new FormData(this);
    
    fetch('/submit', {
        method: 'POST',
        body: formData
    })
    .then(response => {
        if (response.redirected) {
            // Successful submission - redirect occurred
            showSuccess('Cập nhật ảnh thành công!');
            // loadStudents(); // Refresh the student list
            
            // Reload the student info to show updated image status
            setTimeout(() => {
                document.getElementById('loadInfoBtn').click();
            }, 1000);
        } else if (response.ok) {
            return response.json();
        } else {
            return response.json().then(data => {
                throw new Error(data.message || 'Có lỗi xảy ra');
            });
        }
    })
    .then(data => {
        if (data && !data.success) {
            showError(data.message || 'Có lỗi xảy ra khi cập nhật ảnh');
        }
    })
    .catch(error => {
        console.error('Error:', error);
        showError(error.message || 'Có lỗi xảy ra khi cập nhật ảnh. Vui lòng thử lại.');
    });
});

// Allow loading info when pressing Enter in SBD field
document.getElementById('cccd').addEventListener('keypress', function(e) {
    if (e.key === 'Enter') {
        e.preventDefault();
        document.getElementById('loadInfoBtn').click();
    }
});

// Load students on page load
// loadStudents();

// Check URL parameters for success message
const urlParams = new URLSearchParams(window.location.search);
if (urlParams.get('success') === '1') {
    showSuccess('Cập nhật ảnh thành công!');
    // Clean URL
    window.history.replaceState({}, document.title, window.location.pathname);
}


/////////////////////////////////////
function crc16(str) {
  let crc = 0xffff;

  for (let i = 0; i < str.length; i++) {
    crc ^= str.charCodeAt(i) << 8;

    for (let j = 0; j < 8; j++) {
      if (crc & 0x8000) {
        crc = (crc << 1) ^ 0x1021;
      } else {
        crc = crc << 1;
      }
    }
  }

  crc = crc & 0xffff;
  return crc.toString(16).padStart(4, "0").toUpperCase();
}

const pad2zero = (num) => num.toString().padStart(2, "0");

function makeVietQRContent(input) {
  let v =
    "000201010212" +
    "38" +
    pad2zero(input.bankId.length + input.accountId.length + 38) +
    "0010A000000727" +
    "01" +
    pad2zero(input.bankId.length + input.accountId.length + 8) +
    "00" +
    pad2zero(input.bankId.length) +
    input.bankId +
    "01" +
    pad2zero(input.accountId.length) +
    input.accountId;

  v += "0208QRIBFTTA";
  v += "5303704";

  if (input.amount) {
    const amountStr = input.amount.toString();
    v += "54" + pad2zero(amountStr.length) + amountStr;
  }
  v += "5802VN";

  if (input.description) {
    v +=
      "62" +
      pad2zero(input.description.length + 4) +
      "08" +
      pad2zero(input.description.length) +
      input.description;
  }

  v += "6304";
  v += crc16(v);

  return v;
}