2 files changed, 130 insertions, 0 deletions
diff --git a/mdit_py_plugins/anchors/__init__.py b/mdit_py_plugins/anchors/__init__.py
new file mode 100644
index 0000000..d9c4f05
--- /dev/null
+++ b/mdit_py_plugins/anchors/__init__.py
@@ -0,0 +1 @@
+from .index import anchors_plugin  # noqa F401
diff --git a/mdit_py_plugins/anchors/index.py b/mdit_py_plugins/anchors/index.py
new file mode 100644
index 0000000..abbd48a
--- /dev/null
+++ b/mdit_py_plugins/anchors/index.py
@@ -0,0 +1,129 @@
+import re
+from typing import Callable, List, Optional, Set
+
+from markdown_it import MarkdownIt
+from markdown_it.rules_core import StateCore
+from markdown_it.token import Token
+
+
+def anchors_plugin(
+    md: MarkdownIt,
+    min_level: int = 1,
+    max_level: int = 2,
+    slug_func: Optional[Callable[[str], str]] = None,
+    permalink: bool = False,
+    permalinkSymbol: str = "¶",
+    permalinkBefore: bool = False,
+    permalinkSpace: bool = True,
+):
+    """Plugin for adding header anchors, based on
+    `markdown-it-anchor <https://github.com/valeriangalliat/markdown-it-anchor>`__
+
+    .. code-block:: md
+
+        # Title String
+
+    renders as:
+
+    .. code-block:: html
+
+        <h1 id="title-string">Title String <a class="header-anchor" href="#title-string">¶</a></h1>
+
+    :param min_level: minimum header level to apply anchors
+    :param max_level: maximum header level to apply anchors
+    :param slug_func: function to convert title text to id slug.
+    :param permalink: Add a permalink next to the title
+    :param permalinkSymbol: the symbol to show
+    :param permalinkBefore: Add the permalink before the title, otherwise after
+    :param permalinkSpace: Add a space between the permalink and the title
+
+    Note, the default slug function aims to mimic the GitHub Markdown format, see:
+
+    - https://github.com/jch/html-pipeline/blob/master/lib/html/pipeline/toc_filter.rb
+    - https://gist.github.com/asabaylus/3071099
+
+    """
+    selected_levels = list(range(min_level, max_level + 1))
+    md.core.ruler.push(
+        "anchor",
+        _make_anchors_func(
+            selected_levels,
+            slug_func or slugify,
+            permalink,
+            permalinkSymbol,
+            permalinkBefore,
+            permalinkSpace,
+        ),
+    )
+
+
+def _make_anchors_func(
+    selected_levels: List[int],
+    slug_func: Callable[[str], str],
+    permalink: bool,
+    permalinkSymbol: str,
+    permalinkBefore: bool,
+    permalinkSpace: bool,
+):
+    def _anchor_func(state: StateCore):
+        slugs: Set[str] = set()
+        for (idx, token) in enumerate(state.tokens):
+            if token.type != "heading_open":
+                continue
+            level = int(token.tag[1])
+            if level not in selected_levels:
+                continue
+            inline_token = state.tokens[idx + 1]
+            assert inline_token.children is not None
+            title = "".join(
+                child.content
+                for child in inline_token.children
+                if child.type in ["text", "code_inline"]
+            )
+            slug = unique_slug(slug_func(title), slugs)
+            token.attrSet("id", slug)
+
+            if permalink:
+                link_open = Token(
+                    "link_open",
+                    "a",
+                    1,
+                )
+                link_open.attrSet("class", "header-anchor")
+                link_open.attrSet("href", f"#{slug}")
+                link_tokens = [
+                    link_open,
+                    Token("html_block", "", 0, content=permalinkSymbol),
+                    Token("link_close", "a", -1),
+                ]
+                if permalinkBefore:
+                    inline_token.children = (
+                        link_tokens
+                        + (
+                            [Token("text", "", 0, content=" ")]
+                            if permalinkSpace
+                            else []
+                        )
+                        + inline_token.children
+                    )
+                else:
+                    inline_token.children.extend(
+                        ([Token("text", "", 0, content=" ")] if permalinkSpace else [])
+                        + link_tokens
+                    )
+
+    return _anchor_func
+
+
+def slugify(title: str):
+    return re.sub(r"[^\w\u4e00-\u9fff\- ]", "", title.strip().lower().replace(" ", "-"))
+
+
+def unique_slug(slug: str, slugs: set):
+    uniq = slug
+    i = 1
+    while uniq in slugs:
+        uniq = f"{slug}-{i}"
+        i += 1
+    slugs.add(uniq)
+    return uniq