tools (common/template): expose theme settings to the template:

- `css`: additional sheets rendered after the regular css files (can be used for a dark
  theme)
- `html_data_theme`: copied to the <html> data-theme attribute
- `themes_items`: theme selector entries (theme, label, icon)
- fix missing parenthesis in `is_file`

libervia/backend/tools/common/template.py

@@ -26,7 +26,7 @@ import os.path
 from pathlib import Path
 import re
 import time
-from typing import List, Optional, Tuple, Union
+from typing import List, NotRequired, Optional, Tuple, TypedDict, Union
 from xml.sax.saxutils import quoteattr
 
 from babel import support
@@ -374,6 +374,12 @@ class Environment(jinja2.Environment):
         return super(Environment, self).get_template(name, parent, globals)
 
 
+class ThemeItem(TypedDict):
+    theme: str
+    label: str
+    icon: NotRequired[str]
+
+
 class Renderer:
 
     def __init__(self, host, front_url_filter=None, trusted=False, private=False):
@@ -440,7 +446,7 @@ class Renderer:
                     "settings": {},
                 }
                 theme_settings = p / "settings.json"
-                if theme_settings.is_file:
+                if theme_settings.is_file():
                     try:
                         with theme_settings.open() as f:
                             settings = json.load(f)
@@ -656,6 +662,26 @@ class Renderer:
         except KeyError:
             raise exceptions.NotFound(f"no theme found for {site_name}")
 
+    def _get_themes_items(self, site: str) -> list[ThemeItem] | None:
+        """Build the theme selector items from the site themes.
+
+        Get items for every theme with a "label" in its settings.
+        @param site: site name ("" for the default site)
+        @return: the items, sorted by label, None if empty
+        """
+        themes = self.sites_themes.get(site, {})
+        items: list[ThemeItem] = []
+        for name, data in themes.items():
+            settings = data["settings"]
+            if "label" not in settings:
+                continue
+            item = ThemeItem(theme=name, label=settings["label"])
+            if "icon" in settings:
+                item["icon"] = settings["icon"]
+            items.append(item)
+        items.sort(key=lambda item: item["label"])
+        return items or None
+
     def get_static_path(
         self, template_data: TemplateData, filename: str, settings: Optional[dict] = None
     ) -> Optional[TemplateData]:
@@ -1180,6 +1206,38 @@ class Renderer:
                 if css_contents:
                     kwargs["css_content" + suffix] = "\n".join(css_contents)
 
+        # extra css sheets from theme settings are rendered after the regular css files in
+        # base.html so they can override them
+        css_links = []
+        html_data_theme = None
+        themes_items = None
+        # template_data.site is None for absolute template paths
+        if template_data.site is not None:
+            theme_settings = self.sites_themes[template_data.site][template_data.theme][
+                "settings"
+            ]
+            html_data_theme = theme_settings.get("html_data_theme")
+            themes_items = self._get_themes_items(template_data.site)
+            for entry in theme_settings.get("css", []):
+                css_path = self.get_static_path(
+                    template_data, entry["file"], theme_settings
+                )
+                if css_path is None:
+                    log.warning(
+                        _("theme css file {file!r} not found, skipping").format(
+                            file=entry["file"]
+                        )
+                    )
+                    continue
+                link = {
+                    "rel": "stylesheet",
+                    "type": "text/css",
+                    "href": self.get_front_url(css_path),
+                }
+                if entry.get("media"):
+                    link["media"] = entry["media"]
+                css_links.append(link)
+
         scripts_handler = ScriptsHandler(self, template_data)
         self.set_locale(locale)
 
@@ -1190,6 +1248,9 @@ class Renderer:
             media_path=media_path,
             css_files=css_files,
             css_files_noscript=css_files_noscript,
+            css_links=css_links,
+            html_data_theme=html_data_theme,
+            themes_items=themes_items,
             locale=self._locale,
             locales=self.locales,
             gidx=Indexer(),