dynamicweb/cms/plugin_rendering.py

import contextlib
import logging
import sys
from collections import OrderedDict
from collections.abc import Generator
from functools import partial
from typing import Any

from classytags.utils import flatten_context
from django.conf import settings
from django.contrib.sites.models import Site
from django.db import models
from django.http import HttpRequest
from django.template import Context
from django.utils.functional import cached_property
from django.utils.html import format_html
from django.utils.module_loading import import_string
from django.utils.safestring import SafeText, mark_safe
from django.utils.translation import get_language, override
from django.views.debug import ExceptionReporter

from cms.cache.placeholder import get_placeholder_cache, set_placeholder_cache
from cms.exceptions import PlaceholderNotFound
from cms.models import CMSPlugin, Page, PageContent, Placeholder
from cms.plugin_pool import PluginPool
from cms.toolbar.utils import (
    get_placeholder_toolbar_js,
    get_plugin_toolbar_js,
    get_toolbar_from_request,
)
from cms.utils import get_language_from_request
from cms.utils.compat.warnings import RemovedInDjangoCMS60Warning
from cms.utils.conf import get_cms_setting
from cms.utils.permissions import has_plugin_permission
from cms.utils.placeholder import (
    get_toolbar_plugin_struct,
    rescan_placeholders_for_obj,
    restore_sekizai_context,
)
from cms.utils.plugins import get_plugin_restrictions

logger = logging.getLogger(__name__)


def _unpack_plugins(parent_plugin: CMSPlugin) -> Generator[CMSPlugin, None, None]:
    yield parent_plugin
    for plugin in parent_plugin.child_plugin_instances or []:
        yield from _unpack_plugins(plugin)


class RenderedPlaceholder:
    __slots__ = (
        "language",
        "site_id",
        "cached",
        "editable",
        "placeholder",
        "has_content",
    )

    def __init__(
        self,
        placeholder: Placeholder,
        language: str,
        site_id: int,
        cached: bool = False,
        editable: bool = False,
        has_content: bool = False,
    ):
        self.language = language
        self.site_id = site_id
        self.cached = cached
        self.editable = editable
        self.placeholder = placeholder
        self.has_content = has_content

    def __eq__(self, other):
        # The same placeholder rendered with different
        # parameters is considered the same.
        # This behavior is compatible with previous djangoCMS releases.
        return self.placeholder == other.placeholder

    def __ne__(self, other):
        return not self.__eq__(other)

    def __hash__(self):
        return hash(self.placeholder)


class BaseRenderer:
    load_structure: bool = False
    placeholder_edit_template: str = ""

    def __init__(self, request: HttpRequest):
        self.request = request
        self._cached_plugin_classes = {}
        self._placeholders_content_cache = {}
        self._placeholders_by_page_cache = {}
        self._rendered_placeholders = OrderedDict()
        self._rendered_plugins_by_placeholder = {}
        self._plugins_with_perms = None

    @cached_property
    def current_page(self) -> Page:
        return self.request.current_page

    @cached_property
    def current_site(self) -> Site:
        return Site.objects.get_current(self.request)

    @cached_property
    def toolbar(self):
        return get_toolbar_from_request(self.request)

    @cached_property
    def templates(self):
        return self.toolbar.templates

    @cached_property
    def plugin_pool(self) -> PluginPool:
        import cms.plugin_pool

        return cms.plugin_pool.plugin_pool

    @cached_property
    def request_language(self) -> str:
        return get_language_from_request(self.request)

    def get_plugins_with_perms(self) -> list[CMSPlugin]:
        if self._plugins_with_perms is None:
            registered_plugins = self.plugin_pool.registered_plugins
            can_add_plugin = partial(has_plugin_permission, user=self.request.user, permission_type="add")
            self._plugins_with_perms = [
                plugin for plugin in registered_plugins if can_add_plugin(plugin_type=plugin.value)
            ]

        return self._plugins_with_perms

    def get_placeholder_plugin_menu(self, placeholder: Placeholder, page: Page | None = None):
        plugin_menu = get_toolbar_plugin_struct(
            plugins=self.get_plugins_with_perms(),
            slot=placeholder.slot,
            obj=page,
        )
        plugin_menu_template = self.templates.placeholder_plugin_menu_template
        return plugin_menu_template.render({"plugin_menu": plugin_menu})

    def get_placeholder_toolbar_js(self, placeholder, page: models.Model | None = None):
        if page:
            import warnings

            warnings.warn(
                "The 'page' argument of 'get_placeholder_toolbar_js' is deprecated and will be removed in a future "
                "release. It can be safely removed from the call.",
                RemovedInDjangoCMS60Warning,
                stacklevel=2,
            )
        plugins = self.plugin_pool.get_root_plugins(placeholder)  # original
        plugin_types = [cls.__name__ for cls in plugins]
        allowed_plugins = plugin_types + self.plugin_pool.get_system_plugins()
        placeholder_toolbar_js = get_placeholder_toolbar_js(
            placeholder=placeholder,
            allowed_plugins=allowed_plugins,
        )
        return placeholder_toolbar_js

    def get_plugin_toolbar_js(self, plugin: CMSPlugin, obj: models.Model):
        placeholder_cache = self._rendered_plugins_by_placeholder.setdefault(plugin.placeholder_id, {})
        child_classes, _ = get_plugin_restrictions(
            plugin=plugin,
            page=obj,
            restrictions_cache=placeholder_cache,  # Store non-global plugin-restriction in placeholder_cache
        )
        # Make the resolved restrictions available to the drag-item template (which renders the
        # same instances) so it can decide whether children may be added without recomputing.
        plugin.child_class_restrictions = child_classes
        content = get_plugin_toolbar_js(
            plugin,
            children=child_classes,
        )
        return content

    def get_plugin_class(self, plugin: CMSPlugin) -> type:
        plugin_type = plugin.plugin_type

        if plugin_type not in self._cached_plugin_classes:
            self._cached_plugin_classes[plugin_type] = self.plugin_pool.get_plugin(plugin_type)
        return self._cached_plugin_classes[plugin_type]

    def get_plugins_to_render(self, placeholder: Placeholder, language: str, template: str | None):
        from cms.utils.plugins import get_plugins

        plugins = get_plugins(
            request=self.request,
            placeholder=placeholder,
            template=template,
            lang=language,
        )
        return plugins

    def get_rendered_plugins_cache(self, placeholder: Placeholder):
        blank: dict[str, Any] = {
            "plugins": [],
            "plugin_parents": {},
            "plugin_children": {},
        }
        return self._rendered_plugins_by_placeholder.get(placeholder.pk, blank)

    def get_rendered_placeholders(self) -> list[Placeholder]:
        rendered = list(self._rendered_placeholders.values())
        return [r.placeholder for r in rendered]

    def get_rendered_editable_placeholders(self) -> list[Placeholder]:
        rendered = list(self._rendered_placeholders.values())
        return [r.placeholder for r in rendered if r.editable]


class ContentRenderer(BaseRenderer):
    plugin_edit_template = (
        '<template class="cms-plugin '
        'cms-plugin-start cms-plugin-{pk}{disabled}" data-cms-placeholder="{placeholder}"></template>{content}'
        '<template class="cms-plugin cms-plugin-end cms-plugin-{pk}"></template>'
    )
    placeholder_edit_template = (
        '{content} <div class="cms-placeholder cms-placeholder-{placeholder_id}"></div>{plugin_js}{placeholder_js}'
    )

    def __init__(self, request: HttpRequest):
        super().__init__(request)
        self._placeholders_are_editable = bool(self.toolbar.edit_mode_active)

    def placeholder_cache_is_enabled(self):
        if not get_cms_setting("PLACEHOLDER_CACHE"):
            return False
        if self.request.user.is_staff:
            return False
        return not self._placeholders_are_editable

    def render_placeholder(
        self,
        placeholder: Placeholder,
        context: Context,
        language: str | None = None,
        page: Page | None = None,
        editable: bool = False,
        use_cache: bool = False,
        nodelist: Any | None = None,
        width: int | None = None,
    ):
        from sekizai.helpers import Watcher

        language = language or self.request_language
        editable = editable and self._placeholders_are_editable

        if use_cache and not editable and placeholder.cache_placeholder:
            use_cache = self.placeholder_cache_is_enabled()
        else:
            use_cache = False

        if use_cache:
            cached_value = self._get_cached_placeholder_content(
                placeholder=placeholder,
                language=language,
            )
        else:
            cached_value = None

        if cached_value is not None:
            # User has opted to use the cache
            # and there is something in the cache
            restore_sekizai_context(context, cached_value["sekizai"])
            return mark_safe(cached_value["content"])

        context.push()

        width = width or placeholder.default_width
        template = page.get_template() if page and hasattr(page, "get_template") else None

        if width:
            context["width"] = width

        # Add extra context as defined in settings, but do not overwrite existing context variables,
        # since settings are general and database/template are specific
        # TODO this should actually happen as a plugin context processor, but these currently overwrite
        # existing context -- maybe change this order?
        for key, value in placeholder.get_extra_context(template).items():
            if key not in context:
                context[key] = value

        if use_cache:
            watcher = Watcher(context)

        plugin_content = self.render_plugins(
            placeholder,
            language=language,
            context=context,
            editable=editable,
            template=template,
        )
        try:
            placeholder_content = "".join(plugin_content)
        except Exception as e:
            context["exc_info"] = sys.exc_info()
            placeholder_content = self.render_exception("rendering placeholder", context, placeholder, editable)
            if not get_cms_setting("CATCH_PLUGIN_500_EXCEPTION"):
                if not self.toolbar.edit_mode_active and not self.toolbar.preview_mode_active:
                    raise e from None

        if not placeholder_content and nodelist:
            # should be nodelist from a template
            placeholder_content = nodelist.render(context)

        if use_cache:
            content = {
                "content": placeholder_content,
                "sekizai": watcher.get_changes(),
            }
            set_placeholder_cache(
                placeholder,
                lang=language,
                site_id=self.current_site.pk,
                content=content,
                request=self.request,
            )

        rendered_placeholder = RenderedPlaceholder(
            placeholder=placeholder,
            language=language,
            site_id=self.current_site.pk,
            cached=use_cache,
            editable=editable,
            has_content=bool(placeholder_content),
        )

        if placeholder.pk not in self._rendered_placeholders:
            # First time this placeholder is rendered
            if not self.toolbar._cache_disabled:
                # The toolbar middleware needs to know if the response
                # is to be cached.
                # Set the _cache_disabled flag to the value of cache_placeholder
                # only if the flag is False (meaning cache is enabled).
                self.toolbar._cache_disabled = not use_cache
            self._rendered_placeholders[placeholder.pk] = rendered_placeholder

        if editable:
            request = context.get("request", None)
            with override(request.toolbar.toolbar_language) if request else contextlib.nullcontext():
                data = self.get_editable_placeholder_context(placeholder, page=page)
            data["content"] = placeholder_content
            placeholder_content = self.placeholder_edit_template.format(**data)

        context.pop()
        return mark_safe(placeholder_content)

    def get_editable_placeholder_context(self, placeholder: Placeholder, page: Page | None = None) -> dict:
        obj = page or placeholder.source
        placeholder_cache = self.get_rendered_plugins_cache(placeholder)
        placeholder_toolbar_js = self.get_placeholder_toolbar_js(placeholder)
        plugin_toolbar_js_bits = (
            self.get_plugin_toolbar_js(plugin, obj=obj) for plugin in placeholder_cache["plugins"]
        )
        context = {
            "plugin_js": "".join(plugin_toolbar_js_bits),
            "placeholder_js": placeholder_toolbar_js,
            "placeholder_id": placeholder.pk,
        }
        return context

    def render_obj_placeholder(
        self,
        slot: str,
        context: Context,
        inherit: bool,
        nodelist=None,
        editable: bool = True,
    ):
        # Get current object from toolbar
        current_obj = self.toolbar.get_object()
        # Check if page, if so delegate to render_page_placeholder
        if self.current_page and (isinstance(current_obj, (PageContent, type(None)))):
            return self.render_page_placeholder(
                slot,
                context,
                inherit,
                nodelist=nodelist,
                editable=editable,
            )
        # Not page, therefore we will use toolbar object as
        # the current object and render the placeholder
        if current_obj is None:
            raise PlaceholderNotFound(f"No object found for placeholder '{slot}'")
        placeholder = rescan_placeholders_for_obj(current_obj).get(slot)
        content = self.render_placeholder(
            placeholder,
            context=context,
            page=current_obj,
            editable=editable,
            use_cache=True,
            nodelist=None,
        )
        return content

    def render_page_placeholder(
        self,
        slot: str,
        context: Context,
        inherit: bool,
        page: Page | None = None,
        nodelist=None,
        editable: bool = True,
    ):
        if not self.current_page:
            # This method should only be used when rendering a cms page.
            return ""

        current_page = page or self.current_page
        language = get_language()
        placeholder_cache = self._placeholders_by_page_cache

        if current_page.pk not in placeholder_cache:
            # Instead of loading plugins for this one placeholder
            # try and load them for all placeholders on the page.
            self._preload_placeholders_for_page(current_page, language=language)

        try:
            placeholder = placeholder_cache[current_page.pk][slot]
        except KeyError:
            content = ""
            placeholder = None
        else:
            content = self.render_placeholder(
                placeholder,
                context=context,
                language=language,
                page=placeholder.source,
                editable=editable,
                use_cache=True,
                nodelist=None,
            )
        should_inherit = (
            inherit
            and not content
            and current_page.parent
            # The placeholder cache is primed when the first placeholder
            # is loaded. If the current page's parent is not in there,
            # it means its cache was never primed as it wasn't necessary.
            and current_page.parent.pk in placeholder_cache
            # don't display inherited plugins in edit mode, so that the user doesn't
            # mistakenly edit/delete them. This is a fix for issue #1303. See the discussion
            # there for possible enhancements
            and not self.toolbar.edit_mode_active
        )

        if should_inherit:
            # nodelist is set to None to avoid rendering the nodes inside
            # a {% placeholder or %} block tag.
            content = self.render_page_placeholder(
                slot,
                context,
                inherit=True,
                page=current_page.parent,
                nodelist=None,
                editable=False,
            )

        if placeholder and (editable and self._placeholders_are_editable):
            # In edit mode, the contents of the placeholder are mixed with our
            # internal toolbar markup, so the content variable will always be True.
            # Use the rendered placeholder has_content flag instead.
            has_content = self._rendered_placeholders[placeholder.pk].has_content
        else:
            # User is not in edit mode or the placeholder doesn't exist.
            # Either way, we can trust the content variable.
            has_content = bool(content)

        if not has_content and nodelist:
            return content + nodelist.render(context)
        return content

    def render_plugin(
        self,
        instance: CMSPlugin,
        context: Context,
        placeholder: Placeholder | None = None,
        editable: bool = False,
    ):
        context["_last_plugin"] = instance  # Used if an exception is rendered
        if placeholder is None:
            placeholder = instance.placeholder

        instance, plugin = instance.get_plugin_instance()

        if not instance or not plugin.render_plugin:
            return ""

        # we'd better pass a flat dict to template.render
        # as plugin.render can return pretty much any kind of context / dictionary
        # we'd better flatten it and force to a Context object
        # flattening the context means that template must be an engine-specific template object
        # which is guaranteed by get_cached_template if the template returned by
        # plugin._get_render_template is either a string or an engine-specific template object
        context = PluginContext(context, instance, placeholder)
        context = plugin.render(context, instance, placeholder.slot)
        context = flatten_context(context)
        template_name = plugin._get_render_template(context, instance, placeholder)
        template = self.templates.get_cached_template(template_name)
        content = template.render(context)

        for path in get_cms_setting("PLUGIN_PROCESSORS"):
            processor = import_string(path)
            content = processor(instance, placeholder, content, context)

        if editable:
            is_slot = getattr(plugin, "is_slot", False)
            content = self.plugin_edit_template.format(
                pk=instance.pk,
                placeholder=instance.placeholder_id,
                content=content,
                position=instance.position,
                disabled=' cms-slot' if is_slot else '',
            )
            placeholder_cache = self._rendered_plugins_by_placeholder.setdefault(placeholder.pk, {})
            placeholder_cache.setdefault("plugins", []).append(instance)
        return mark_safe(content)

    def render_exception(self, action: str, context: Context, placeholder: Placeholder, editable: bool) -> str:
        exc, value, traceback = context["exc_info"]
        placeholder_source_obj = placeholder.source.__class__._meta.verbose_name
        message = (
            f'{exc.__name__}: {value} when {action} "{placeholder}" on '
            f'{placeholder_source_obj} object "{placeholder.source}"'
        )
        if "_last_plugin" in context:
            instance = context["_last_plugin"]
            try:
                description = f"{instance._meta.verbose_name} {instance.get_short_description()}"
            except Exception:
                description = f"{instance._meta.verbose_name}"
            message += f', plugin #{instance.pk} "{description}"'
        logger.error(message, exc_info=(exc, value, traceback))

        if editable:
            if settings.DEBUG:
                reporter = ExceptionReporter(context["request"], exc, value, traceback)
                html = reporter.get_traceback_html()
            else:
                html = ""
            heading = format_html('<h2 class="cms-rendering-exception-title">{}</h2>', message)
            if "_last_plugin" in context:
                # Make error message editable by double-click to open the editor for the plugin causing the exception
                is_slot = getattr(instance, "is_slot", False)
                heading = self.plugin_edit_template.format(
                    pk=instance.pk,
                    placeholder=instance.placeholder_id,
                    content=heading,
                    position=instance.position,
                    disabled=' cms-slot' if is_slot else '',
                )
                placeholder_cache = self._rendered_plugins_by_placeholder.setdefault(placeholder.pk, {})
                placeholder_cache.setdefault("plugins", []).append(instance)

            return f'<div class="cms-rendering-exception">{heading}{html}</div>'
        return ""

    def render_plugins(
        self,
        placeholder: Placeholder,
        language: str,
        context,
        editable: bool = False,
        template: str | None = None,
    ) -> Generator[SafeText | str, None, None]:
        plugins = self.get_plugins_to_render(
            placeholder=placeholder,
            template=template,
            language=language,
        )

        for plugin in plugins:
            plugin._placeholder_cache = placeholder
            yield self.render_plugin(plugin, context, placeholder, editable)

    def _get_cached_placeholder_content(self, placeholder, language):
        """
        Returns a dictionary mapping placeholder content and sekizai data.
        Returns None if no cache is present.
        """
        # Placeholders can be rendered multiple times under different sites
        # it's important to have a per-site "cache".
        site_id = self.current_site.pk
        site_cache = self._placeholders_content_cache.setdefault(site_id, {})
        # Placeholders can be rendered multiple times under different languages
        # it's important to have a per-language "cache".
        language_cache = site_cache.setdefault(language, {})

        if placeholder.pk not in language_cache:
            cached_value = get_placeholder_cache(
                placeholder,
                lang=language,
                site_id=site_id,
                request=self.request,
            )

            if cached_value is not None:
                # None means nothing in the cache
                # Anything else is a valid value
                language_cache[placeholder.pk] = cached_value
        return language_cache.get(placeholder.pk)

    def _get_content_object(self, page, slots=None):
        toolbar_obj = self.toolbar.get_object()
        if isinstance(toolbar_obj, PageContent) and toolbar_obj.page == page:
            # Current object belongs to the page itself
            return Placeholder.objects.get_for_obj(toolbar_obj)
        elif slots:
            # If looking for inherited placeholders, slots is specified
            if self.toolbar.preview_mode_active or self.toolbar.edit_mode_active:
                page_content = (
                    page.pagecontent_set(manager="admin_manager")
                    .current_content(language=self.request_language)
                    .first()
                )
            else:
                page_content = page.pagecontent_set.filter(language=self.request_language).first()
            return Placeholder.objects.get_for_obj(page_content) if page_content else Placeholder.objects.none()
        elif page_content := page.get_content_obj(self.request_language, fallback=False):
            PageContent.page.field.set_cached_value(page_content, page)
            # Creates any placeholders missing on the page
            return page_content.rescan_placeholders().values()
        else:
            return Placeholder.objects.none()

    def _preload_placeholders_for_page(self, page, language=None, slots=None, inherit=False):
        """
        Populates the internal plugin cache of each placeholder
        in the given page if the placeholder has not been
        previously cached.
        """
        from cms.utils.plugins import assign_plugins

        placeholders = self._get_content_object(page, slots=slots)
        language = language or self.request_language

        if inherit:
            # When the inherit flag is True,
            # assume all placeholders found are inherited and thus prefetch them.
            slots_w_inheritance = [pl.slot for pl in placeholders]
        elif not self.toolbar.edit_mode_active:
            # Scan through the page template to find all placeholders
            # that have inheritance turned on.
            slots_w_inheritance = [pl.slot for pl in page.get_declared_placeholders() if pl.inherit]
        else:
            # Inheritance is turned off on edit-mode
            slots_w_inheritance = []

        if self.placeholder_cache_is_enabled():
            _cached_content = self._get_cached_placeholder_content
            # Only prefetch plugins if the placeholder
            # has not been cached.
            placeholders_to_fetch = [
                placeholder
                for placeholder in placeholders
                if _cached_content(placeholder, language) is None
            ]
        else:
            # cache is disabled, prefetch plugins for all
            # placeholders in the page.
            placeholders_to_fetch = placeholders

        if placeholders_to_fetch:
            assign_plugins(
                request=self.request,
                placeholders=placeholders_to_fetch,
                template=page.get_template(),
                lang=language,
            )

        # Inherit only placeholders that have no plugins
        # or are not cached.
        placeholders_to_inherit = [
            pl.slot
            for pl in placeholders
            if not getattr(pl, "_plugins_cache", None) and pl.slot in slots_w_inheritance
        ]

        if page.parent and placeholders_to_inherit:
            self._preload_placeholders_for_page(
                page=page.parent,
                language=language,
                slots=placeholders_to_inherit,
                inherit=True,
            )

        # Internal cache mapping placeholder slots
        # to placeholder instances.
        page_placeholder_cache = {}

        for placeholder in placeholders:
            # Save a query when the placeholder toolbar is rendered.
            placeholder.page = page
            page_placeholder_cache[placeholder.slot] = placeholder

        self._placeholders_by_page_cache[page.pk] = page_placeholder_cache


class StructureRenderer(BaseRenderer):
    load_structure = True
    placeholder_edit_template = """
        <template data-cms id="cms-plugin-child-classes-{placeholder_id}" type="text/cms-template">
            {plugin_menu_js}
        </template>
        {plugin_js}{placeholder_js}
        """

    def get_plugins_to_render(self, *args, **kwargs):
        plugins = super().get_plugins_to_render(*args, **kwargs)

        for plugin in plugins:
            yield from _unpack_plugins(plugin)

    def render_placeholder(self, placeholder, language, obj=None):
        rendered_plugins = self.render_plugins(placeholder, language=language, obj=obj)
        plugin_js_output = "".join(rendered_plugins)

        placeholder_toolbar_js = self.get_placeholder_toolbar_js(placeholder)
        rendered_placeholder = RenderedPlaceholder(
            placeholder=placeholder,
            language=language,
            site_id=self.current_site.pk,
            cached=False,
            editable=True,
        )

        if placeholder.pk not in self._rendered_placeholders:
            self._rendered_placeholders[placeholder.pk] = rendered_placeholder

        placeholder_structure_js = self.placeholder_edit_template.format(
            placeholder_id=placeholder.pk,
            plugin_js=plugin_js_output,
            plugin_menu_js=self.get_placeholder_plugin_menu(placeholder, page=obj),
            placeholder_js=placeholder_toolbar_js,
        )
        return mark_safe(placeholder_structure_js)

    def render_page_placeholder(self, page, placeholder, language=None):
        return self.render_placeholder(placeholder, language=language, obj=page)

    def render_plugin(self, instance, obj=None):
        placeholder_cache = self._rendered_plugins_by_placeholder.setdefault(instance.placeholder_id, {})
        placeholder_cache.setdefault("plugins", []).append(instance)
        return self.get_plugin_toolbar_js(instance, obj=obj)

    def render_plugins(self, placeholder, language, obj=None):
        template = obj.get_template() if obj and hasattr(obj, "get_template") else None
        plugins = self.get_plugins_to_render(placeholder, language, template)

        for plugin in plugins:
            plugin._placeholder_cache = placeholder
            yield self.render_plugin(plugin, obj=obj)


class LegacyRenderer(ContentRenderer):
    load_structure = True
    placeholder_edit_template = """
        {content}
        <div class="cms-placeholder cms-placeholder-{placeholder_id}"></div>
        <template data-cms id="cms-plugin-child-classes-{placeholder_id}" type="text/cms-template">
            {plugin_menu_js}
        </template>
        {plugin_js}{placeholder_js}
        """

    def get_editable_placeholder_context(self, placeholder, page=None):
        context = super().get_editable_placeholder_context(placeholder, page)
        context["plugin_menu_js"] = self.get_placeholder_plugin_menu(placeholder, page=page)
        return context


class PluginContext(Context):
    """
    This subclass of template.Context automatically populates itself using
    the processors defined in CMS_PLUGIN_CONTEXT_PROCESSORS.
    Additional processors can be specified as a list of callables
    using the "processors" keyword argument.
    """

    def __init__(self, dict_, instance, placeholder, processors=None, current_app=None):
        dict_ = flatten_context(dict_)
        super().__init__(dict_)

        if not processors:
            processors = []

        for path in get_cms_setting("PLUGIN_CONTEXT_PROCESSORS"):
            processor = import_string(path)
            self.update(processor(instance, placeholder, self))
        for processor in processors:
            self.update(processor(instance, placeholder, self))