const Department = require('../models/department');
const Degree = require('../models/degree');

// GET /admin/department
exports.index = async (req, res) => {
  try {
    const departments = await Department.find();
    res.render('admin/department/index', {
      departments,
      user: req.session.user,
      layout: 'layouts/admin',
      title: 'Quản lý Khoa/Bộ môn'
    });
  } catch (err) {
    console.error('departmentController.index error:', err);
    req.flash('error', 'Đã xảy ra lỗi khi tải danh sách khoa/bộ môn');
    res.redirect('/admin/dashboard');
  }
};

// POST /admin/department/create
exports.create = async (req, res) => {
  try {
    const { name } = req.body;
    const slug = name.toLowerCase().trim().replace(/\s+/g, '-').replace(/[^a-z0-9-]/g, '');

    const existing = await Department.findOne({ slug });
    if (existing) {
      req.flash('error', 'Department already exists');
      return res.redirect('back');
    }

    await Department.create({ name, slug });
    req.flash('success', 'Department created');
    res.redirect('/admin/department');
  } catch (err) {
    console.error('departmentController.create error:', err);
    req.flash('error', 'Đã xảy ra lỗi khi tạo khoa/bộ môn');
    res.redirect('back');
  }
};

// POST /admin/department/:id/edit
exports.update = async (req, res) => {
  try {
    const { id } = req.params;
    const { name } = req.body;
    const slug = name.toLowerCase().trim().replace(/\s+/g, '-').replace(/[^a-z0-9-]/g, '');

    await Department.findByIdAndUpdate(id, { name, slug });
    req.flash('success', 'Department updated');
    res.redirect('/admin/department');
  } catch (err) {
    console.error('departmentController.update error:', err);
    req.flash('error', 'Đã xảy ra lỗi khi cập nhật khoa/bộ môn');
    res.redirect('back');
  }
};

// POST /admin/department/:id/delete
exports.destroy = async (req, res) => {
  try {
    const { id } = req.params;
    const count = await Degree.countDocuments({ department: id });

    if (count > 0) {
      req.flash('error', 'Cannot delete: Department is referenced by existing degrees');
      return res.redirect('back');
    }

    await Department.findByIdAndDelete(id);
    req.flash('success', 'Department deleted');
    res.redirect('/admin/department');
  } catch (err) {
    console.error('departmentController.destroy error:', err);
    req.flash('error', 'Đã xảy ra lỗi khi xóa khoa/bộ môn');
    res.redirect('back');
  }
};