text: from __future__ import unicode_literals
  
  import os
  import sys
  import threading
  from contextlib import contextmanager
  
  from django.contrib.sites.models import Site
  
  from mezzanine.conf import settings
  from mezzanine.core.request import current_request
  from mezzanine.utils.deprecation import get_middleware_setting
  
  
  SITE_PERMISSION_MIDDLEWARE = \
      "mezzanine.core.middleware.SitePermissionMiddleware"
  
  
  def current_site_id():
      """
      Responsible for determining the current ``Site`` instance to use
      when retrieving data for any ``SiteRelated`` models. If we're inside an
      override_current_site_id context manager, return the overriding site ID.
      Otherwise, try to determine the site using the following methods in order:
  
        - ``site_id`` in session. Used in the admin so that admin users
          can switch sites and stay on the same domain for the admin.
        - The id of the Site object corresponding to the hostname in the current
          request. This result is cached.
        - ``MEZZANINE_SITE_ID`` environment variable, so management
          commands or anything else outside of a request can specify a
          site.
        - ``SITE_ID`` setting.
  
      If a current request exists and the current site is not overridden, the
      site ID is stored on the request object to speed up subsequent calls.
      """
  
      if hasattr(override_current_site_id.thread_local, "site_id"):
          return override_current_site_id.thread_local.site_id
  
      from mezzanine.utils.cache import cache_installed, cache_get, cache_set
      request = current_request()
      site_id = getattr(request, "site_id", None)
      if request and not site_id:
          site_id = request.session.get("site_id", None)
          if not site_id:
              domain = request.get_host().lower()
              if cache_installed():
                  # Don't use Mezzanine's cache_key_prefix here, since it
                  # uses this very function we're in right now to create a
                  # per-site cache key.
                  bits = (settings.CACHE_MIDDLEWARE_KEY_PREFIX, domain)
                  cache_key = "%s.site_id.%s" % bits
                  site_id = cache_get(cache_key)
              if not site_id:
                  try:
                      site = Site.objects.get(domain__iexact=domain)
                  except Site.DoesNotExist:
                      pass
                  else:
                      site_id = site.id
                      if cache_installed():
                          cache_set(cache_key, site_id)
      if not site_id:
          site_id = os.environ.get("MEZZANINE_SITE_ID", settings.SITE_ID)
      if request and site_id and not getattr(settings, "TESTING", False):
          request.site_id = site_id
      return site_id
  
  
  @contextmanager
  def override_current_site_id(site_id):
      """
      Context manager that overrides the current site id for code executed
      within it. Used to access SiteRelated objects outside the current site.
      """
      override_current_site_id.thread_local.site_id = site_id
      yield
      del override_current_site_id.thread_local.site_id
  override_current_site_id.thread_local = threading.local()
  
  
  def has_site_permission(user):
      """
      Checks if a staff user has staff-level access for the current site.
      The actual permission lookup occurs in ``SitePermissionMiddleware``
      which then marks the request with the ``has_site_permission`` flag,
      so that we only query the db once per request, so this function
      serves as the entry point for everything else to check access. We
      also fall back to an ``is_staff`` check if the middleware is not
      installed, to ease migration.
      """
      if SITE_PERMISSION_MIDDLEWARE not in get_middleware_setting():
          return user.is_staff and user.is_active
      return getattr(user, "has_site_permission", False)
  
  
  def host_theme_path():
      """
      Returns the directory of the theme associated with the given host.
      """
  
      # Set domain to None, which we'll then query for in the first
      # iteration of HOST_THEMES. We use the current site_id rather
      # than a request object here, as it may differ for admin users.
      domain = None
  
      for (host, theme) in settings.HOST_THEMES:
          if domain is None:
              domain = Site.objects.get(id=current_site_id()).domain
          if host.lower() == domain.lower():
              try:
                  __import__(theme)
                  module = sys.modules[theme]
              except ImportError:
                  pass
              else:
                  return os.path.dirname(os.path.abspath(module.__file__))
      return ""
  