1 files changed, 153 insertions, 0 deletions
diff --git a/src/mistune/plugins/footnotes.py b/src/mistune/plugins/footnotes.py
new file mode 100644
index 0000000..2e10704
--- /dev/null
+++ b/src/mistune/plugins/footnotes.py
@@ -0,0 +1,153 @@
+import re
+from ..core import BlockState
+from ..util import unikey
+from ..helpers import LINK_LABEL
+
+__all__ = ['footnotes']
+
+_PARAGRAPH_SPLIT = re.compile(r'\n{2,}')
+# https://michelf.ca/projects/php-markdown/extra/#footnotes
+REF_FOOTNOTE = (
+  r'^(?P<footnote_lead> {0,3})'
+  r'\[\^(?P<footnote_key>' + LINK_LABEL + r')]:[ \t]'
+  r'(?P<footnote_text>[^\n]*(?:\n+|$)'
+  r'(?:(?P=footnote_lead) {1,3}(?! )[^\n]*\n+)*'
+  r')'
+)
+
+INLINE_FOOTNOTE = r'\[\^(?P<footnote_key>' + LINK_LABEL + r')\]'
+
+
+def parse_inline_footnote(inline, m: re.Match, state):
+    key = unikey(m.group('footnote_key'))
+    ref = state.env.get('ref_footnotes')
+    if ref and key in ref:
+        notes = state.env.get('footnotes')
+        if not notes:
+            notes = []
+        if key not in notes:
+            notes.append(key)
+            state.env['footnotes'] = notes
+        state.append_token({
+          'type': 'footnote_ref',
+          'raw': key,
+          'attrs': {'index': notes.index(key) + 1}
+        })
+    else:
+        state.append_token({'type': 'text', 'raw': m.group(0)})
+    return m.end()
+
+
+def parse_ref_footnote(block, m: re.Match, state: BlockState):
+    ref = state.env.get('ref_footnotes')
+    if not ref:
+        ref = {}
+
+    key = unikey(m.group('footnote_key'))
+    if key not in ref:
+        ref[key] = m.group('footnote_text')
+        state.env['ref_footnotes'] = ref
+    return m.end()
+
+
+def parse_footnote_item(block, key: str, index: int, state: BlockState):
+    ref = state.env.get('ref_footnotes')
+    text = ref[key]
+
+    lines = text.splitlines()
+    second_line = None
+    for second_line in lines[1:]:
+        if second_line:
+            break
+
+    if second_line:
+      spaces = len(second_line) - len(second_line.lstrip())
+      pattern = re.compile(r'^ {' + str(spaces) + r',}', flags=re.M)
+      text = pattern.sub('', text).strip()
+      items = _PARAGRAPH_SPLIT.split(text)
+      children = [{'type': 'paragraph', 'text': s} for s in items]
+    else:
+      text = text.strip()
+      children = [{'type': 'paragraph', 'text': text}]
+    return {
+        'type': 'footnote_item',
+        'children': children,
+        'attrs': {'key': key, 'index': index}
+    }
+
+
+def md_footnotes_hook(md, result: str, state: BlockState):
+    notes = state.env.get('footnotes')
+    if not notes:
+        return result
+
+    children = [
+        parse_footnote_item(md.block, k, i + 1, state)
+        for i, k in enumerate(notes)
+    ]
+    state = BlockState()
+    state.tokens = [{'type': 'footnotes', 'children': children}]
+    output = md.render_state(state)
+    return result + output
+
+
+def render_footnote_ref(renderer, key: str, index: int):
+    i = str(index)
+    html = '<sup class="footnote-ref" id="fnref-' + i + '">'
+    return html + '<a href="#fn-' + i + '">' + i + '</a></sup>'
+
+
+def render_footnotes(renderer, text: str):
+    return '<section class="footnotes">\n<ol>\n' + text + '</ol>\n</section>\n'
+
+
+def render_footnote_item(renderer, text: str, key: str, index: int):
+    i = str(index)
+    back = '<a href="#fnref-' + i + '" class="footnote">&#8617;</a>'
+    text = text.rstrip()[:-4] + back + '</p>'
+    return '<li id="fn-' + i + '">' + text + '</li>\n'
+
+
+def footnotes(md):
+    """A mistune plugin to support footnotes, spec defined at
+    https://michelf.ca/projects/php-markdown/extra/#footnotes
+
+    Here is an example:
+
+    .. code-block:: text
+
+        That's some text with a footnote.[^1]
+
+        [^1]: And that's the footnote.
+
+    It will be converted into HTML:
+
+    .. code-block:: html
+
+        <p>That's some text with a footnote.<sup class="footnote-ref" id="fnref-1"><a href="#fn-1">1</a></sup></p>
+        <section class="footnotes">
+        <ol>
+        <li id="fn-1"><p>And that's the footnote.<a href="#fnref-1" class="footnote">&#8617;</a></p></li>
+        </ol>
+        </section>
+
+    :param md: Markdown instance
+    """
+    md.inline.register(
+        'footnote',
+        INLINE_FOOTNOTE,
+        parse_inline_footnote,
+        before='link',
+    )
+    md.block.register(
+        'ref_footnote',
+        REF_FOOTNOTE,
+        parse_ref_footnote,
+        before='ref_link',
+    )
+    md.after_render_hooks.append(md_footnotes_hook)
+
+    if md.renderer and md.renderer.NAME == 'html':
+        md.renderer.register('footnote_ref', render_footnote_ref)
+        md.renderer.register('footnote_item', render_footnote_item)
+        md.renderer.register('footnotes', render_footnotes)