Only render dependencies that are used of a specific page (#52)

Co-authored-by: rbeard0330 <@dul2k3BKW6m>

django_components/middleware.py

@@ -0,0 +1,74 @@
+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())