"""The :mod:`authenticators` modules provides for pluggable authentication behaviour.

Authentication behaviour is provided by adding the mixin class :class:`AuthenticatorMixin` to a :class:`.Resource` or Django :class:`View` class.

The set of authenticators which are use is then specified by setting the :attr:`authenticators` attribute on the class, and listing a set of authenticator classes.
"""
from django.contrib.auth import authenticate
from django.middleware.csrf import CsrfViewMiddleware
from djangorestframework.utils import as_tuple
import base64


class BaseAuthenticator(object):
    """All authenticators should extend BaseAuthenticator."""

    def __init__(self, mixin):
        """Initialise the authenticator with the mixin instance as state,
        in case the authenticator needs to access any metadata on the mixin object."""
        self.mixin = mixin

    def authenticate(self, request):
        """Authenticate the request and return the authentication context or None.

        An authentication context might be something as simple as a User object, or it might
        be some more complicated token, for example authentication tokens which are signed
        against a particular set of permissions for a given user, over a given timeframe.

        The default permission checking on Resource will use the allowed_methods attribute
        for permissions if the authentication context is not None, and use anon_allowed_methods otherwise.

        The authentication context is available to the method calls eg Resource.get(request)
        by accessing self.auth in order to allow them to apply any more fine grained permission
        checking at the point the response is being generated.
        
        This function must be overridden to be implemented."""
        return None


class BasicAuthenticator(BaseAuthenticator):
    """Use HTTP Basic authentication"""
    def authenticate(self, request):
        from django.utils.encoding import smart_unicode, DjangoUnicodeDecodeError
        
        if 'HTTP_AUTHORIZATION' in request.META:
            auth = request.META['HTTP_AUTHORIZATION'].split()
            if len(auth) == 2 and auth[0].lower() == "basic":
                try:
                    auth_parts = base64.b64decode(auth[1]).partition(':')
                except TypeError:
                    return None
                
                try:
                    uname, passwd = smart_unicode(auth_parts[0]), smart_unicode(auth_parts[2])
                except DjangoUnicodeDecodeError:
                    return None
                    
                user = authenticate(username=uname, password=passwd)
                if user is not None and user.is_active:
                    return user
        return None
                

class UserLoggedInAuthenticator(BaseAuthenticator):
    """Use Djagno's built-in request session for authentication."""
    def authenticate(self, request):
        if getattr(request, 'user', None) and request.user.is_active:
            # Temporarily request.POST with .RAW_CONTENT, so that we use our more generic request parsing
            request._post = self.mixin.RAW_CONTENT
            resp = CsrfViewMiddleware().process_view(request, None, (), {})
            del(request._post)
            if resp is None:  # csrf passed
                return request.user
        return None