"""
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.urlresolvers import set_script_prefix, get_script_prefix
from django.http import HttpResponse
from django.utils.html import escape
from django.utils.safestring import mark_safe
from django.views.decorators.csrf import csrf_exempt

from djangorestframework.compat import View as DjangoView, apply_markdown
from djangorestframework.response import Response, ImmediateResponse
from djangorestframework.mixins import *
from djangorestframework.utils import allowed_methods
from djangorestframework import resources, renderers, parsers, authentication, permissions, status


__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/resource 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/resource classes.
    """
    camelcase_boundry = '(((?<=[a-z])[A-Z])|([A-Z](?![A-Z]|$)))'
    return re.sub(camelcase_boundry, ' \\1', content).strip()


_resource_classes = (
    None,
    resources.Resource,
    resources.FormResource,
    resources.ModelResource
)


class View(ResourceMixin, RequestMixin, ResponseMixin, AuthMixin, DjangoView):
    """
    Handles incoming requests and maps them to REST operations.
    Performs request deserialization, response serialization, authentication and input validation.
    """

    resource = None
    """
    The resource to use when validating requests and filtering responses,
    or `None` to use default behaviour.
    """

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

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

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

    permissions = (permissions.FullAnonAccess,)
    """
    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(View, 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 allowed_methods(self)

    def get_name(self):
        """
        Return the resource or view class name for use as this view's name.
        Override to customize.
        """
        # If this view has a resource that's been overridden, then use that resource for the name
        if getattr(self, 'resource', None) not in _resource_classes:
            name = self.resource.__name__
            name = _remove_trailing_string(name, 'Resource')
            name += getattr(self, '_suffix', '')

        # If it's a view class with no resource then grok the name from the class name
        else:
            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 = None

        # If this view has a resource that's been overridden,
        # then try to use the resource's docstring
        if getattr(self, 'resource', None) not in _resource_classes:
            description = self.resource.__doc__

        # Otherwise use the view docstring
        if not description:
            description = self.__doc__ or ''

        description = _remove_leading_indent(description)

        if html:
            return self.markup_description(description)
        return description

    def markup_description(self, description):
        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):
        """
        Return an HTTP 405 error if an operation is called which does not have a handler method.
        """
        raise ImmediateResponse(
                {'detail': 'Method \'%s\' not allowed on this resource.' % request.method},
            status=status.HTTP_405_METHOD_NOT_ALLOWED)

    def initial(self, request, *args, **kargs):
        """
        Returns an `HttpRequest`. This method is a hook for any code that needs to run
        prior to anything else.
        Required if you want to do things like set `request.upload_handlers` before
        the authentication and dispatch handling is run.
        """
        # Calls to 'reverse' will not be fully qualified unless we set the
        # scheme/host/port here.
        self.orig_prefix = get_script_prefix()
        if not (self.orig_prefix.startswith('http:') or self.orig_prefix.startswith('https:')):
            prefix = '%s://%s' % (request.is_secure() and 'https' or 'http', request.get_host())
            set_script_prefix(prefix + self.orig_prefix)
        return request

    def final(self, request, response, *args, **kargs):
        """
        Returns an `HttpResponse`. This method is a hook for any code that needs to run
        after everything else in the view.
        """
        # Restore script_prefix.
        set_script_prefix(self.orig_prefix)

        # Always add these headers.
        response['Allow'] = ', '.join(allowed_methods(self))
        # sample to allow caching using Vary http header
        response['Vary'] = 'Authenticate, Accept'

        return response

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

        try:
            # Get a custom request, built form the original request instance
            self.request = request = self.create_request(request)

            # `initial` is the opportunity to temper with the request, 
            # even completely replace it.
            self.request = request = self.initial(request, *args, **kwargs)

            # Authenticate and check request has the relevant permissions
            self._check_permissions()

            # 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
 
            # TODO: should we enforce HttpResponse, like Django does ?
            response = handler(request, *args, **kwargs)

            # Prepare response for the response cycle.
            self.response = response = self.prepare_response(response)

            # Pre-serialize filtering (eg filter complex objects into natively serializable types)
            # TODO: ugly hack to handle both HttpResponse and Response. 
            if hasattr(response, 'raw_content'):
                response.raw_content = self.filter_response(response.raw_content)
            else:
                response.content = self.filter_response(response.content)

        except ImmediateResponse, response:
            # Prepare response for the response cycle.
            self.response = response = self.prepare_response(response)

        # `final` is the last opportunity to temper with the response, or even
        # completely replace it.
        return self.final(request, response, *args, **kwargs)

    def options(self, request, *args, **kwargs):
        content = {
            'name': self.get_name(),
            'description': self.get_description(),
            'renders': self._rendered_media_types,
            'parses': self._parsed_media_types,
        }
        form = self.get_bound_form()
        if form is not None:
            field_name_types = {}
            for name, field in form.fields.iteritems():
                field_name_types[name] = field.__class__.__name__
            content['fields'] = field_name_types
        raise ImmediateResponse(content, status=status.HTTP_200_OK)


class ModelView(View):
    """
    A RESTful view that maps to a model in the database.
    """
    resource = resources.ModelResource


class InstanceModelView(InstanceMixin, ReadModelMixin, UpdateModelMixin, DeleteModelMixin, ModelView):
    """
    A view which provides default operations for read/update/delete against a model instance.
    """
    _suffix = 'Instance'


class ListModelView(ListModelMixin, ModelView):
    """
    A view which provides default operations for list, against a model in the database.
    """
    _suffix = 'List'


class ListOrCreateModelView(ListModelMixin, CreateModelMixin, ModelView):
    """
    A view which provides default operations for list and create, against a model in the database.
    """
    _suffix = 'List'