helpers do
  def current_user
    User.find_by(id: session[:user_id])
  end
end

post '/login' do
  username = params[:username]
  password = params[:password]

  user = User.find_by(username: username)

  if user && user.password == password
    session[:user_id] = user.id
    redirect to('/')
  else
    @error_message = "Login failed."
    erb(:login)
  end
end

get '/logout' do
  session[:user_id] = nil
  "Logout successful!"
  redirect to('/')
end