text: from urllib import parse
  
  from django.conf import settings
  from django.db import ProgrammingError
  from django.http import Http404, HttpResponseRedirect
  from django.urls import reverse
  
  from .views import server_error
  
  
  class LoginRequiredMiddleware(object):
      """
      If LOGIN_REQUIRED is True, redirect all non-authenticated users to the login page.
      """
      def __init__(self, get_response):
          self.get_response = get_response
  
      def __call__(self, request):
          if settings.LOGIN_REQUIRED and not request.user.is_authenticated:
              # Redirect unauthenticated requests to the login page. API requests are exempt from redirection as the API
              # performs its own authentication. Also metrics can be read without login.
              api_path = reverse('api-root')
              if not request.path_info.startswith((api_path, '/metrics')) and request.path_info != settings.LOGIN_URL:
                  return HttpResponseRedirect(
                      '{}?next={}'.format(
                          settings.LOGIN_URL,
                          parse.quote(request.get_full_path_info())
                      )
                  )
          return self.get_response(request)
  
  
  class APIVersionMiddleware(object):
      """
      If the request is for an API endpoint, include the API version as a response header.
      """
      def __init__(self, get_response):
          self.get_response = get_response
  
      def __call__(self, request):
          api_path = reverse('api-root')
          response = self.get_response(request)
          if request.path_info.startswith(api_path):
              response['API-Version'] = settings.REST_FRAMEWORK_VERSION
          return response
  
  
  class ExceptionHandlingMiddleware(object):
      """
      Intercept certain exceptions which are likely indicative of installation issues and provide helpful instructions
      to the user.
      """
      def __init__(self, get_response):
          self.get_response = get_response
  
      def __call__(self, request):
          return self.get_response(request)
  
      def process_exception(self, request, exception):
  
          # Don't catch exceptions when in debug mode
          if settings.DEBUG:
              return
  
          # Ignore Http404s (defer to Django's built-in 404 handling)
          if isinstance(exception, Http404):
              return
  
          # Determine the type of exception. If it's a common issue, return a custom error page with instructions.
          custom_template = None
          if isinstance(exception, ProgrammingError):
              custom_template = 'exceptions/programming_error.html'
          elif isinstance(exception, ImportError):
              custom_template = 'exceptions/import_error.html'
          elif isinstance(exception, PermissionError):
              custom_template = 'exceptions/permission_error.html'
  
          # Return a custom error message, or fall back to Django's default 500 error handling
          if custom_template:
              return server_error(request, template_name=custom_template)
  