"""
The :mod:`views` module provides the Views you will most probably
be subclassing in your implementation.

By setting or modifying class attributes on your view, you change it's predefined behaviour.
"""

import re
from django.core.exceptions import PermissionDenied
from django.http import Http404
from django.utils.html import escape
from django.utils.safestring import mark_safe
from django.views.decorators.csrf import csrf_exempt
from django.views.generic.detail import SingleObjectMixin
from django.views.generic.list import MultipleObjectMixin

from djangorestframework.compat import View as _View, apply_markdown
from djangorestframework.response import Response
from djangorestframework.request import Request
from djangorestframework.settings import api_settings
from djangorestframework import parsers, authentication, status, exceptions, mixins


__all__ = (
    'View',
    'ModelView',
    'InstanceModelView',
    'ListModelView',
    'ListOrCreateModelView'
)


def _remove_trailing_string(content, trailing):
    """
    Strip trailing component `trailing` from `content` if it exists.
    Used when generating names from view classes.
    """
    if content.endswith(trailing) and content != trailing:
        return content[:-len(trailing)]
    return content


def _remove_leading_indent(content):
    """
    Remove leading indent from a block of text.
    Used when generating descriptions from docstrings.
    """
    whitespace_counts = [len(line) - len(line.lstrip(' '))
                         for line in content.splitlines()[1:] if line.lstrip()]

    # unindent the content if needed
    if whitespace_counts:
        whitespace_pattern = '^' + (' ' * min(whitespace_counts))
        return re.sub(re.compile(whitespace_pattern, re.MULTILINE), '', content)
    return content


def _camelcase_to_spaces(content):
    """
    Translate 'CamelCaseNames' to 'Camel Case Names'.
    Used when generating names from view classes.
    """
    camelcase_boundry = '(((?<=[a-z])[A-Z])|([A-Z](?![A-Z]|$)))'
    return re.sub(camelcase_boundry, ' \\1', content).strip()


class APIView(_View):
    """
    Handles incoming requests and maps them to REST operations.
    Performs request deserialization, response serialization, authentication and input validation.
    """

    renderers = api_settings.DEFAULT_RENDERERS
    """
    List of renderer classes the view can serialize the response with, ordered by preference.
    """

    parsers = parsers.DEFAULT_PARSERS
    """
    List of parser classes the view can parse the request with.
    """

    authentication = (authentication.SessionAuthentication,
                      authentication.BasicAuthentication)
    """
    List of all authenticating methods to attempt.
    """

    throttle_classes = ()
    """
    List of all throttles to check.
    """

    permission_classes = ()
    """
    List of all permissions that must be checked.
    """

    @classmethod
    def as_view(cls, **initkwargs):
        """
        Override the default :meth:`as_view` to store an instance of the view
        as an attribute on the callable function.  This allows us to discover
        information about the view when we do URL reverse lookups.
        """
        view = super(APIView, cls).as_view(**initkwargs)
        view.cls_instance = cls(**initkwargs)
        return view

    @property
    def allowed_methods(self):
        """
        Return the list of allowed HTTP methods, uppercased.
        """
        return [method.upper() for method in self.http_method_names
                if hasattr(self, method)]

    @property
    def default_response_headers(self):
        return {
            'Allow': ', '.join(self.allowed_methods),
            'Vary': 'Authenticate, Accept'
        }

    def get_name(self):
        """
        Return the resource or view class name for use as this view's name.
        Override to customize.
        """
        name = self.__class__.__name__
        name = _remove_trailing_string(name, 'View')
        return _camelcase_to_spaces(name)

    def get_description(self, html=False):
        """
        Return the resource or view docstring for use as this view's description.
        Override to customize.
        """
        description = self.__doc__ or ''
        description = _remove_leading_indent(description)
        if html:
            return self.markup_description(description)
        return description

    def markup_description(self, description):
        """
        Apply HTML markup to the description of this view.
        """
        if apply_markdown:
            description = apply_markdown(description)
        else:
            description = escape(description).replace('\n', '<br />')
        return mark_safe(description)

    def http_method_not_allowed(self, request, *args, **kwargs):
        """
        Called if `request.method` does not corrospond to a handler method.
        We raise an exception, which is handled by `.handle_exception()`.
        """
        raise exceptions.MethodNotAllowed(request.method)

    @property
    def _parsed_media_types(self):
        """
        Return a list of all the media types that this view can parse.
        """
        return [parser.media_type for parser in self.parsers]

    @property
    def _default_parser(self):
        """
        Return the view's default parser class.
        """
        return self.parsers[0]

    @property
    def _rendered_media_types(self):
        """
        Return an list of all the media types that this response can render.
        """
        return [renderer.media_type for renderer in self.renderers]

    @property
    def _rendered_formats(self):
        """
        Return a list of all the formats that this response can render.
        """
        return [renderer.format for renderer in self.renderers]

    @property
    def _default_renderer(self):
        """
        Return the response's default renderer class.
        """
        return self.renderers[0]

    def get_permissions(self):
        """
        Instantiates and returns the list of permissions that this view requires.
        """
        return [permission(self) for permission in self.permission_classes]

    def get_throttles(self):
        """
        Instantiates and returns the list of thottles that this view requires.
        """
        return [throttle(self) for throttle in self.throttle_classes]

    def check_permissions(self, request, obj=None):
        """
        Check user permissions and either raise an ``PermissionDenied`` or return.
        """
        for permission in self.get_permissions():
            if not permission.check_permission(request, obj):
                raise exceptions.PermissionDenied()

    def check_throttles(self, request):
        """
        Check throttles and either raise a `Throttled` exception or return.
        """
        for throttle in self.get_throttles():
            if not throttle.check_throttle(request):
                raise exceptions.Throttled(throttle.wait())

    def initial(self, request, *args, **kargs):
        """
        This method runs prior to anything else in the view.
        It should return the initial request object.

        You may need to override this if you want to do things like set
        `request.upload_handlers` before the authentication and dispatch
        handling is run.
        """
        return Request(request, parsers=self.parsers, authentication=self.authentication)

    def final(self, request, response, *args, **kargs):
        """
        This method runs after everything else in the view.
        It should return the final response object.
        """
        if isinstance(response, Response):
            response.view = self
            response.request = request
            response.renderers = self.renderers

        for key, value in self.headers.items():
            response[key] = value

        return response

    def handle_exception(self, exc):
        """
        Handle any exception that occurs, by returning an appropriate response,
        or re-raising the error.
        """
        if isinstance(exc, exceptions.Throttled):
            self.headers['X-Throttle-Wait-Seconds'] = '%d' % exc.wait

        if isinstance(exc, exceptions.APIException):
            return Response({'detail': exc.detail}, status=exc.status_code)
        elif isinstance(exc, Http404):
            return Response({'detail': 'Not found'},
                            status=status.HTTP_404_NOT_FOUND)
        elif isinstance(exc, PermissionDenied):
            return Response({'detail': 'Permission denied'},
                            status=status.HTTP_403_FORBIDDEN)
        raise

    # Note: session based authentication is explicitly CSRF validated,
    # all other authentication is CSRF exempt.
    @csrf_exempt
    def dispatch(self, request, *args, **kwargs):
        self.args = args
        self.kwargs = kwargs
        self.headers = self.default_response_headers

        try:
            self.request = self.initial(request, *args, **kwargs)

            # Check that the request is allowed
            self.check_permissions(request)
            self.check_throttles(request)

            # Get the appropriate handler method
            if request.method.lower() in self.http_method_names:
                handler = getattr(self, request.method.lower(), self.http_method_not_allowed)
            else:
                handler = self.http_method_not_allowed

            response = handler(request, *args, **kwargs)

        except Exception as exc:
            response = self.handle_exception(exc)

        self.response = self.final(request, response, *args, **kwargs)
        return self.response


# Abstract view classes that do not provide any method handlers,
# but which provide required behaviour for concrete views to build on.

class BaseView(APIView):
    """
    Base class for all generic views.
    """
    serializer_class = None

    def get_serializer(self, data=None, files=None, instance=None):
        # TODO: add support for files
        context = {
            'request': self.request,
            'format': self.kwargs.get('format', None)
        }
        return self.serializer_class(data, instance=instance, context=context)


class MultipleObjectBaseView(MultipleObjectMixin, BaseView):
    """
    Base class for generic views onto a queryset.
    """
    pass


class SingleObjectBaseView(SingleObjectMixin, BaseView):
    """
    Base class for generic views onto a model instance.
    """

    def get_object(self):
        """
        Override default to add support for object-level permissions.
        """
        super(self, SingleObjectBaseView).get_object()
        self.check_permissions(self.request, self.object)


# Concrete view classes that provide method handlers
# by composing the mixin classes with a base view.

class ListAPIView(mixins.ListModelMixin,
                  mixins.MetadataMixin,
                  MultipleObjectBaseView):
    """
    Concrete view for listing a queryset.
    """
    def get(self, request, *args, **kwargs):
        return self.list(request, *args, **kwargs)

    def options(self, request, *args, **kwargs):
        return self.metadata(request, *args, **kwargs)


class RootAPIView(mixins.ListModelMixin,
                  mixins.CreateModelMixin,
                  mixins.MetadataMixin,
                  MultipleObjectBaseView):
    """
    Concrete view for listing a queryset or creating a model instance.
    """
    def get(self, request, *args, **kwargs):
        return self.list(request, *args, **kwargs)

    def post(self, request, *args, **kwargs):
        return self.create(request, *args, **kwargs)

    def options(self, request, *args, **kwargs):
        return self.metadata(request, *args, **kwargs)


class DetailAPIView(mixins.RetrieveModelMixin,
                    mixins.MetadataMixin,
                    SingleObjectBaseView):
    """
    Concrete view for retrieving a model instance.
    """
    def get(self, request, *args, **kwargs):
        return self.retrieve(request, *args, **kwargs)

    def options(self, request, *args, **kwargs):
        return self.metadata(request, *args, **kwargs)


class InstanceAPIView(mixins.RetrieveModelMixin,
                      mixins.UpdateModelMixin,
                      mixins.DestroyModelMixin,
                      mixins.MetadataMixin,
                      SingleObjectBaseView):
    """
    Concrete view for retrieving, updating or deleting a model instance.
    """
    def get(self, request, *args, **kwargs):
        return self.retrieve(request, *args, **kwargs)

    def put(self, request, *args, **kwargs):
        return self.update(request, *args, **kwargs)

    def delete(self, request, *args, **kwargs):
        return self.destroy(request, *args, **kwargs)

    def options(self, request, *args, **kwargs):
        return self.metadata(request, *args, **kwargs)