middleware.py

import re

from django.conf import settings
from django.forms import Media
from django.http import StreamingHttpResponse

RENDERED_COMPONENTS_CONTEXT_KEY = "_COMPONENT_DEPENDENCIES"
CSS_DEPENDENCY_PLACEHOLDER = '<link name="CSS_PLACEHOLDER">'
JS_DEPENDENCY_PLACEHOLDER = '<script name="JS_PLACEHOLDER">'

SCRIPT_TAG_REGEX = re.compile('<script')
COMPONENT_COMMENT_REGEX = re.compile(rb'<!-- _RENDERED (?P<name>\w+?) -->')
PLACEHOLDER_REGEX = re.compile(rb'<!-- _RENDERED (?P<name>\w+?) -->'
                               rb'|<link name="CSS_PLACEHOLDER">'
                               rb'|<script name="JS_PLACEHOLDER">')


class ComponentDependencyMiddleware:
    """Middleware that inserts CSS/JS dependencies for all rendered components at points marked with template tags."""

    dependency_regex = COMPONENT_COMMENT_REGEX

    def __init__(self, get_response):
        self.get_response = get_response

    def __call__(self, request):
        response = self.get_response(request)
        if getattr(settings, "COMPONENTS", {}).get('RENDER_DEPENDENCIES', False)\
                and not isinstance(response, StreamingHttpResponse)\
                and response['Content-Type'].startswith('text/html'):
            response.content = process_response_content(response.content)
        return response


def process_response_content(content):
    from django_components.component import registry

    component_names_seen = {match.group('name') for match in COMPONENT_COMMENT_REGEX.finditer(content)}
    all_components = [registry.get(name.decode('utf-8'))('') for name in component_names_seen]
    all_media = join_media(all_components)
    js_dependencies = b''.join(media.encode('utf-8') for media in all_media.render_js())
    css_dependencies = b''.join(media.encode('utf-8') for media in all_media.render_css())
    return PLACEHOLDER_REGEX.sub(DependencyReplacer(css_dependencies, js_dependencies), content)


def add_module_attribute_to_scripts(scripts):
    return re.sub(SCRIPT_TAG_REGEX, '<script type="module"', scripts)


class DependencyReplacer:
    """Replacer for use in re.sub that replaces the first placeholder CSS and JS
    tags it encounters and removes any subsequent ones."""

    CSS_PLACEHOLDER = bytes(CSS_DEPENDENCY_PLACEHOLDER, encoding='utf-8')
    JS_PLACEHOLDER = bytes(JS_DEPENDENCY_PLACEHOLDER, encoding='utf-8')

    def __init__(self, css_string, js_string):
        self.js_string = js_string
        self.css_string = css_string

    def __call__(self, match):
        if match[0] == self.CSS_PLACEHOLDER:
            replacement, self.css_string = self.css_string, b""
        elif match[0] == self.JS_PLACEHOLDER:
            replacement, self.js_string = self.js_string, b""
        else:
            replacement = b''
        return replacement


def join_media(components):
    """Return combined media object for iterable of components."""

    return sum([component.media for component in components], Media())