text: import hashlib
  import re
  import logging
  from datetime import datetime
  from django.conf import settings
  # Avoid shadowing the login() view below.
  from django.views.decorators.csrf import csrf_protect
  from django.core.cache import cache
  from django.core.urlresolvers import reverse
  from django.contrib import messages
  from django.shortcuts import render_to_response
  from django.contrib.sites.models import Site, RequestSite
  from django.http import HttpResponseRedirect, Http404
  from django.template import RequestContext
  from django.utils.http import urlquote, base36_to_int
  from django.utils.translation import ugettext as _
  from django.views.decorators.cache import never_cache
  
  from seahub.auth import REDIRECT_FIELD_NAME, get_backends
  from seahub.auth import login as auth_login
  from seahub.auth.decorators import login_required
  from seahub.auth.forms import AuthenticationForm, CaptchaAuthenticationForm
  from seahub.auth.forms import PasswordResetForm, SetPasswordForm, PasswordChangeForm
  from seahub.auth.tokens import default_token_generator
  from seahub.base.accounts import User
  from seahub.utils import is_ldap_user
  from seahub.utils.ip import get_remote_ip
  from seahub.settings import USER_PASSWORD_MIN_LENGTH, \
      USER_STRONG_PASSWORD_REQUIRED, USER_PASSWORD_STRENGTH_LEVEL
  
  # Get an instance of a logger
  logger = logging.getLogger(__name__)
  
  LOGIN_ATTEMPT_PREFIX = 'UserLoginAttempt_'
  
  def log_user_in(request, user, redirect_to):
      # Light security check -- make sure redirect_to isn't garbage.
      if not redirect_to or ' ' in redirect_to:
          redirect_to = settings.LOGIN_REDIRECT_URL
  
      # Heavier security check -- redirects to http://example.com should
      # not be allowed, but things like /view/?param=http://example.com
      # should be allowed. This regex checks if there is a '//' *before* a
      # question mark.
      elif '//' in redirect_to and re.match(r'[^\?]*//', redirect_to):
          redirect_to = settings.LOGIN_REDIRECT_URL
  
      # Okay, security checks complete. Log the user in.
      auth_login(request, user)
  
      if request.session.test_cookie_worked():
          request.session.delete_test_cookie()
  
      _clear_login_failed_attempts(request)
  
      return HttpResponseRedirect(redirect_to)
  
  def _get_login_failed_attempts(username=None, ip=None):
      """Get login failed attempts base on username and ip.
      If both username and ip are provided, return the max value.
  
      Arguments:
      - `username`:
      - `ip`:
      """
      if username is None and ip is None:
          return 0
  
      username_attempts = ip_attempts = 0
  
      if username:
          username_attempts = cache.get(LOGIN_ATTEMPT_PREFIX + username, 0)
  
      if ip:
          ip_attempts = cache.get(LOGIN_ATTEMPT_PREFIX + ip, 0)
  
      return max(username_attempts, ip_attempts)
  
  def _incr_login_faied_attempts(username=None, ip=None):
      """Increase login failed attempts by 1 for both username and ip.
  
      Arguments:
      - `username`:
      - `ip`:
  
      Returns new value of failed attempts.
      """
      timeout = settings.LOGIN_ATTEMPT_TIMEOUT
      username_attempts = 0
      ip_attempts = 0
  
      if username:
          try:
              username_attempts = cache.incr(LOGIN_ATTEMPT_PREFIX + username)
          except ValueError:
              cache.set(LOGIN_ATTEMPT_PREFIX + username, 0, timeout)
  
      if ip:
          try:
              ip_attempts = cache.incr(LOGIN_ATTEMPT_PREFIX + ip)
          except ValueError:
              cache.set(LOGIN_ATTEMPT_PREFIX + ip, 0, timeout)
  
      return max(username_attempts, ip_attempts)
  
  def _clear_login_failed_attempts(request):
      """Clear login failed attempts records.
  
      Arguments:
      - `request`:
      """
      username = request.user.username
      ip = get_remote_ip(request)
      cache.delete(LOGIN_ATTEMPT_PREFIX + username)
      cache.delete(LOGIN_ATTEMPT_PREFIX + ip)
  
  @csrf_protect
  @never_cache
  def login(request, template_name='registration/login.html',
            redirect_if_logged_in=None,
            redirect_field_name=REDIRECT_FIELD_NAME,
            authentication_form=AuthenticationForm):
      """Displays the login form and handles the login action."""
  
      if request.user.is_authenticated() and redirect_if_logged_in:
          return HttpResponseRedirect(reverse(redirect_if_logged_in))
  
      redirect_to = request.REQUEST.get(redirect_field_name, '')
      ip = get_remote_ip(request)
  
      if request.method == "POST":
          if request.REQUEST.get('captcha_0', '') != '':
              # have captcha
              form = CaptchaAuthenticationForm(data=request.POST)
              if form.is_valid():
                  # captcha & passwod is valid, log user in
                  remember_me = True if request.REQUEST.get(
                      'remember_me', '') == 'on' else False
                  request.session['remember_me'] = remember_me
                  return log_user_in(request, form.get_user(), redirect_to)
              else:
                  # show page with captcha and increase failed login attempts
                  _incr_login_faied_attempts(ip=ip)
          else:
              form = authentication_form(data=request.POST)
              if form.is_valid():
                  # password is valid, log user in
                  remember_me = True if request.REQUEST.get(
                      'remember_me', '') == 'on' else False
                  request.session['remember_me'] = remember_me
                  return log_user_in(request, form.get_user(), redirect_to)
              else:
                  username = urlquote(request.REQUEST.get('username', '').strip())
                  failed_attempt = _incr_login_faied_attempts(username=username,
                                                              ip=ip)
  
                  if failed_attempt >= settings.LOGIN_ATTEMPT_LIMIT:
                      logger.warn('Login attempt limit reached, username: %s, ip: %s, attemps: %d' %
                                  (username, ip, failed_attempt))
                      form = CaptchaAuthenticationForm()
                  else:
                      form = authentication_form(data=request.POST)
      else:
          ### GET
          failed_attempt = _get_login_failed_attempts(ip=ip)
          if failed_attempt >= settings.LOGIN_ATTEMPT_LIMIT:
              logger.warn('Login attempt limit reached, ip: %s, attempts: %d' %
                          (ip, failed_attempt))
              form = CaptchaAuthenticationForm(request)
          else:
              form = authentication_form(request)
  
      request.session.set_test_cookie()
  
      if Site._meta.installed:
          current_site = Site.objects.get_current()
      else:
          current_site = RequestSite(request)
  
      enable_signup = getattr(settings, 'ENABLE_SIGNUP', False)
      multi_tenancy = getattr(settings, 'MULTI_TENANCY', False)
      if enable_signup:
          if multi_tenancy:
              org_account_only = getattr(settings, 'FORCE_ORG_REGISTER', False)
              if org_account_only:
                  signup_url = reverse('org_register')
              else:
                  signup_url = reverse('choose_register')
          else:
              signup_url = reverse('registration_register')
      else:
          signup_url = ''
  
      return render_to_response(template_name, {
              'form': form,
              redirect_field_name: redirect_to,
              'site': current_site,
              'site_name': current_site.name,
              'remember_days': settings.LOGIN_REMEMBER_DAYS,
              'signup_url': signup_url,
              }, context_instance=RequestContext(request))
  
  def login_simple_check(request):
      """A simple check for login called by thirdpart systems(OA, etc).
  
      Token generation: MD5(secret_key + foo@foo.com + 2014-1-1).hexdigest()
      Token length: 32 hexadecimal digits.
      """
      username = request.REQUEST.get('user', '')
      random_key = request.REQUEST.get('token', '')
  
      if not username or not random_key:
          raise Http404
  
      today = datetime.now().strftime('%Y-%m-%d')
      expect = hashlib.md5(settings.SECRET_KEY+username+today).hexdigest()
      if expect == random_key:
          try:
              user = User.objects.get(email=username)
          except User.DoesNotExist:
              raise Http404
  
          for backend in get_backends():
              user.backend = "%s.%s" % (backend.__module__, backend.__class__.__name__)
  
          auth_login(request, user)
  
          return HttpResponseRedirect(settings.SITE_ROOT)
      else:
          raise Http404
  
  
  def logout(request, next_page=None, template_name='registration/logged_out.html', redirect_field_name=REDIRECT_FIELD_NAME):
      "Logs out the user and displays 'You are logged out' message."
      from seahub.auth import logout
      logout(request)
      if next_page is None:
          redirect_to = request.REQUEST.get(redirect_field_name, '')
          if redirect_to:
              return HttpResponseRedirect(redirect_to)
          else:
              return render_to_response(template_name, {
                  'title': _('Logged out')
              }, context_instance=RequestContext(request))
      else:
          # Redirect to this page until the session has been cleared.
          return HttpResponseRedirect(next_page or request.path)
  
  def logout_then_login(request, login_url=None):
      "Logs out the user if he is logged in. Then redirects to the log-in page."
      if not login_url:
          login_url = settings.LOGIN_URL
      return logout(request, login_url)
  
  def redirect_to_login(next, login_url=None, redirect_field_name=REDIRECT_FIELD_NAME):
      "Redirects the user to the login page, passing the given 'next' page"
      if not login_url:
          login_url = settings.LOGIN_URL
      return HttpResponseRedirect('%s?%s=%s' % (login_url, urlquote(redirect_field_name), urlquote(next)))
  
  # 4 views for password reset:
  # - password_reset sends the mail
  # - password_reset_done shows a success message for the above
  # - password_reset_confirm checks the link the user clicked and
  #   prompts for a new password
  # - password_reset_complete shows a success message for the above
  
  @csrf_protect
  def password_reset(request, is_admin_site=False, template_name='registration/password_reset_form.html',
          email_template_name='registration/password_reset_email.html',
          password_reset_form=PasswordResetForm, token_generator=default_token_generator,
          post_reset_redirect=None):
      if post_reset_redirect is None:
          post_reset_redirect = reverse('auth_password_reset_done')
      if request.method == "POST":
          form = password_reset_form(request.POST)
          if form.is_valid():
              opts = {}
              opts['use_https'] = request.is_secure()
              opts['token_generator'] = token_generator
              if is_admin_site:
                  opts['domain_override'] = request.META['HTTP_HOST']
              else:
                  opts['email_template_name'] = email_template_name
                  if not Site._meta.installed:
                      opts['domain_override'] = RequestSite(request).domain
              try:
                  form.save(**opts)
              except Exception, e:
                  logger.error(str(e))
                  messages.error(request, _(u'Failed to send email, please contact administrator.'))
                  return render_to_response(template_name, {
                          'form': form,
                          }, context_instance=RequestContext(request))
              else:
                  return HttpResponseRedirect(post_reset_redirect)
      else:
          form = password_reset_form()
      return render_to_response(template_name, {
          'form': form,
      }, context_instance=RequestContext(request))
  
  def password_reset_done(request, template_name='registration/password_reset_done.html'):
      return render_to_response(template_name, context_instance=RequestContext(request))
  
  # Doesn't need csrf_protect since no-one can guess the URL
  def password_reset_confirm(request, uidb36=None, token=None, template_name='registration/password_reset_confirm.html',
                             token_generator=default_token_generator, set_password_form=SetPasswordForm,
                             post_reset_redirect=None):
      """
      View that checks the hash in a password reset link and presents a
      form for entering a new password.
      """
      assert uidb36 is not None and token is not None # checked by URLconf
      if post_reset_redirect is None:
          post_reset_redirect = reverse('auth_password_reset_complete')
      try:
          uid_int = base36_to_int(uidb36)
          user = User.objects.get(id=uid_int)
      except (ValueError, User.DoesNotExist):
          user = None
  
      context_instance = RequestContext(request)
  
      if token_generator.check_token(user, token):
          context_instance['validlink'] = True
          if request.method == 'POST':
              form = set_password_form(user, request.POST)
              if form.is_valid():
                  form.save()
                  return HttpResponseRedirect(post_reset_redirect)
          else:
              form = set_password_form(None)
      else:
          context_instance['validlink'] = False
          form = None
      context_instance['form'] = form
      return render_to_response(template_name, context_instance=context_instance)
  
  def password_reset_complete(request, template_name='registration/password_reset_complete.html'):
      return render_to_response(template_name, context_instance=RequestContext(request,
                                                                               {'login_url': settings.LOGIN_URL}))
  
  @csrf_protect
  @login_required
  def password_change(request, template_name='registration/password_change_form.html',
                      post_change_redirect=None, password_change_form=PasswordChangeForm):
      if post_change_redirect is None:
          post_change_redirect = reverse('auth_password_change_done')
  
      if is_ldap_user(request.user):
          messages.error(request, _("Can not update password, please contact LDAP admin."))
  
      if request.method == "POST":
          form = password_change_form(user=request.user, data=request.POST)
          if form.is_valid():
              form.save()
              return HttpResponseRedirect(post_change_redirect)
      else:
          form = password_change_form(user=request.user)
  
      return render_to_response(template_name, {
          'form': form,
          'min_len': USER_PASSWORD_MIN_LENGTH,
          'strong_pwd_required': USER_STRONG_PASSWORD_REQUIRED,
          'level': USER_PASSWORD_STRENGTH_LEVEL,
      }, context_instance=RequestContext(request))
  
  def password_change_done(request, template_name='registration/password_change_done.html'):
      return render_to_response(template_name, context_instance=RequestContext(request))
  