refactor highlighting to use module level singletons

remove the repeated instantiation of TextLexer and HtmlFormatter in
favor of a singleton

omicron/ssg/content.py

@@ -15,6 +15,7 @@ from pygments import highlight as pygments_highlight
 from pygments.formatters import HtmlFormatter
 from pygments.lexers import get_lexer_by_name
 from pygments.lexers.special import TextLexer
+from pygments.util import ClassNotFound
 
 log = logging.getLogger(__name__)
 
@@ -26,12 +27,21 @@ class ContentError(RuntimeError):
     pass
 
 
-def _highlight_code(code: str, lang: str, attrs: str) -> str:
+text_lexer = TextLexer()
+html_formatter = HtmlFormatter()
+
+
+def highlight_style() -> str:
+    style = html_formatter.get_style_defs(".highlight")  # type: ignore[no-untyped-call]
+    return cast(str, style)
+
+
+def highlight(code: str, lang: str, attrs: str) -> str:
     try:
-        lexer = get_lexer_by_name(lang) if lang else TextLexer()
-    except Exception:
-        lexer = TextLexer()
-    return pygments_highlight(code, lexer, HtmlFormatter())
+        lexer = get_lexer_by_name(lang) if lang else text_lexer
+    except ClassNotFound:
+        lexer = text_lexer
+    return pygments_highlight(code, lexer, html_formatter)
 
 
 def read_frontmatter(path: Path) -> dict[str, Any]:
@@ -127,7 +137,7 @@ class Article(Content):
 
     def render(self, site: Site) -> None:
         md = MarkdownIt()
-        md.options["highlight"] = _highlight_code
+        md.options["highlight"] = highlight
         self.content = Markup(md.render(self.read_body()))
 
         template = site.jinja_env.get_template("article.html")

omicron/ssg/site.py

@@ -6,6 +6,7 @@ from omicron.ssg.content import (
     create_content,
     CONTENT_EXTENSIONS,
     ContentError,
+    highlight_style,
 )
 from pathlib import Path
 import yaml
@@ -90,7 +91,7 @@ class Site:
         self.discover()
         self.output_path.mkdir(parents=True, exist_ok=True)
         (self.output_path / "pygments.css").write_text(
-            HtmlFormatter().get_style_defs(".highlight"), encoding="utf-8"
+            highlight_style(), encoding="utf-8"
         )
         for content in self.content:
             content.render(self)