from django.http import HttpResponse
from django.utils import six

from .loader import get_template, select_template


class ContentNotRenderedError(Exception):
    pass


class SimpleTemplateResponse(HttpResponse):
    rendering_attrs = ['template_name', 'context_data', '_post_render_callbacks']

    def __init__(self, template, context=None, content_type=None, status=None,
                 charset=None, using=None):
        # It would seem obvious to call these next two members 'template' and
        # 'context', but those names are reserved as part of the test Client
        # API. To avoid the name collision, we use different names.
        self.template_name = template
        self.context_data = context

        self.using = using

        self._post_render_callbacks = []

        # _request stores the current request object in subclasses that know
        # about requests, like TemplateResponse. It's defined in the base class
        # to minimize code duplication.
        # It's called self._request because self.request gets overwritten by
        # django.test.client.Client. Unlike template_name and context_data,
        # _request should not be considered part of the public API.
        self._request = None

        # content argument doesn't make sense here because it will be replaced
        # with rendered template so we always pass empty string in order to
        # prevent errors and provide shorter signature.
        super(SimpleTemplateResponse, self).__init__('', content_type, status, charset)

        # _is_rendered tracks whether the template and context has been baked
        # into a final response.
        # Super __init__ doesn't know any better than to set self.content to
        # the empty string we just gave it, which wrongly sets _is_rendered
        # True, so we initialize it to False after the call to super __init__.
        self._is_rendered = False

    def __getstate__(self):
        """Pickling support function.

        Ensures that the object can't be pickled before it has been
        rendered, and that the pickled state only includes rendered
        data, not the data used to construct the response.
        """
        obj_dict = self.__dict__.copy()
        if not self._is_rendered:
            raise ContentNotRenderedError('The response content must be '
                                          'rendered before it can be pickled.')
        for attr in self.rendering_attrs:
            if attr in obj_dict:
                del obj_dict[attr]

        return obj_dict

    def resolve_template(self, template):
        "Accepts a template object, path-to-template or list of paths"
        if isinstance(template, (list, tuple)):
            return select_template(template, using=self.using)
        elif isinstance(template, six.string_types):
            return get_template(template, using=self.using)
        else:
            return template

    def resolve_context(self, context):
        return context

    @property
    def rendered_content(self):
        """Returns the freshly rendered content for the template and context
        described by the TemplateResponse.

        This *does not* set the final content of the response. To set the
        response content, you must either call render(), or set the
        content explicitly using the value of this property.
        """
        template = self.resolve_template(self.template_name)
        context = self.resolve_context(self.context_data)
        content = template.render(context, self._request)
        return content

    def add_post_render_callback(self, callback):
        """Adds a new post-rendering callback.

        If the response has already been rendered,
        invoke the callback immediately.
        """
        if self._is_rendered:
            callback(self)
        else:
            self._post_render_callbacks.append(callback)

    def render(self):
        """Renders (thereby finalizing) the content of the response.

        If the content has already been rendered, this is a no-op.

        Returns the baked response instance.
        """
        retval = self
        if not self._is_rendered:
            self.content = self.rendered_content
            for post_callback in self._post_render_callbacks:
                newretval = post_callback(retval)
                if newretval is not None:
                    retval = newretval
        return retval

    @property
    def is_rendered(self):
        return self._is_rendered

    def __iter__(self):
        if not self._is_rendered:
            raise ContentNotRenderedError(
                'The response content must be rendered before it can be iterated over.'
            )
        return super(SimpleTemplateResponse, self).__iter__()

    @property
    def content(self):
        if not self._is_rendered:
            raise ContentNotRenderedError(
                'The response content must be rendered before it can be accessed.'
            )
        return super(SimpleTemplateResponse, self).content

    @content.setter
    def content(self, value):
        """Sets the content for the response
        """
        HttpResponse.content.fset(self, value)
        self._is_rendered = True


class TemplateResponse(SimpleTemplateResponse):
    rendering_attrs = SimpleTemplateResponse.rendering_attrs + ['_request']

    def __init__(self, request, template, context=None, content_type=None,
                 status=None, charset=None, using=None):
        super(TemplateResponse, self).__init__(
            template, context, content_type, status, charset, using)
        self._request = request
