1 files changed, 152 insertions, 0 deletions
diff --git a/packages/blog-markdown-headings/lektor_blog_markdown_headings.py b/packages/blog-markdown-headings/lektor_blog_markdown_headings.py
new file mode 100644
index 0000000..5293676
--- /dev/null
+++ b/packages/blog-markdown-headings/lektor_blog_markdown_headings.py
@@ -0,0 +1,152 @@
+import uuid
+from collections import namedtuple
+from html.parser import HTMLParser
+
+import mistune
+from lektor.pluginsystem import Plugin
+from lektor.utils import slugify
+from markupsafe import Markup, escape
+
+TocEntry = namedtuple("TocEntry", ["anchor", "title", "children"])
+
+
+def get_int_config(config, key, default, minimum=None, maximum=None):
+    value = config.get(key, str(default))
+
+    try:
+        value = int(value)
+    except (TypeError, ValueError):
+        value = default
+
+    if minimum is not None:
+        value = max(value, minimum)
+
+    if maximum is not None:
+        value = min(value, maximum)
+
+    return value
+
+
+class BlogMarkdownHeadingsPlugin(Plugin):
+    name = "Blog Markdown Headings"
+    description = (
+        "Adds Markdown heading anchors, TOC metadata, and configurable heading offsets."
+    )
+
+    def on_markdown_config(self, config, **extra):
+        plugin_config = self.get_config()
+
+        anchor_type = plugin_config.get("anchors.type", "slug")
+
+        heading_offset = get_int_config(
+            plugin_config,
+            "headings.offset",
+            default=2,
+            minimum=-5,
+            maximum=5,
+        )
+
+        max_heading_level = get_int_config(
+            plugin_config,
+            "headings.max_level",
+            default=6,
+            minimum=1,
+            maximum=6,
+        )
+
+        min_heading_level = get_int_config(
+            plugin_config,
+            "headings.min_level",
+            default=1,
+            minimum=1,
+            maximum=6,
+        )
+
+        def adjusted_level(level):
+            return min(
+                max(level + heading_offset, min_heading_level),
+                max_heading_level,
+            )
+
+        config.renderer_mixins.append(
+            renderer_mixin_factory(
+                anchor_type=anchor_type,
+                adjusted_level=adjusted_level,
+            )
+        )
+
+    def on_markdown_meta_init(self, meta, **extra):
+        meta["toc"] = []
+
+    def on_markdown_meta_postprocess(self, meta, **extra):
+        prev_level = None
+        toc = []
+        stack = [toc]
+
+        for level, anchor, title in meta["toc"]:
+            if prev_level is None:
+                prev_level = level
+            elif prev_level == level - 1:
+                stack.append(stack[-1][-1].children)
+                prev_level = level
+            elif prev_level > level:
+                while prev_level > level:
+                    if len(stack) > 1:
+                        stack.pop()
+                    prev_level -= 1
+
+            stack[-1].append(TocEntry(anchor, title, []))
+
+        meta["toc"] = toc
+
+
+def renderer_mixin_factory(anchor_type, adjusted_level):
+    def render_heading(text, original_level, meta, raw=None):
+        level = adjusted_level(original_level)
+
+        if anchor_type == "random":
+            anchor = uuid.uuid4().hex[:6]
+        else:
+            if raw is None:
+                raw = escape(_strip_tags(text))
+            anchor = slugify(raw)
+
+        meta["toc"].append((level, anchor, Markup(text)))
+
+        return '<h%d id="%s">%s</h%d>' % (level, anchor, text, level)
+
+    class RendererMixinMistune0(object):
+        def header(self, text, level, raw):
+            return render_heading(text, level, self.meta, raw)
+
+    class RendererMixinMistune2(object):
+        def heading(self, text, level):
+            meta = self.lektor.meta
+            return render_heading(text, level, meta)
+
+    if mistune.__version__.startswith("0."):
+        return RendererMixinMistune0
+
+    if mistune.__version__.startswith("2."):
+        return RendererMixinMistune2
+
+    raise RuntimeError("Unsupported mistune version: %s" % mistune.__version__)
+
+
+def _strip_tags(inline_html):
+    parser = _StripTagsParser()
+    parser.feed(inline_html)
+    return parser.close()
+
+
+class _StripTagsParser(HTMLParser):
+    def reset(self):
+        super().reset()
+        self._data = []
+
+    def handle_data(self, data):
+        self._data.append(data)
+
+    def close(self):
+        super().close()
+        return "".join(self._data)