feat: footnotes (#2384)

* feat: footnotes

* feat: proper DOCX support

packages/editor-ext/src/lib/markdown/utils/footnotes.marked.ts

@@ -0,0 +1,110 @@
+import { Token, marked } from 'marked';
+import { generateNodeId } from '../../utils';
+
+interface FootnoteRefToken {
+  type: 'footnoteRef';
+  label: string;
+  raw: string;
+}
+
+interface FootnoteDefToken {
+  type: 'footnoteDef';
+  label: string;
+  text: string;
+  raw: string;
+}
+
+// Parse-scoped state: markdownToHtml resets before the top-level parse and
+// appends the collected list after it. Nested marked.parse calls (callout,
+// footnote definitions) share this state, so hooks cannot be used here.
+let footnoteRefs: { label: string; id: string; number: number }[] = [];
+let footnoteDefs = new Map<string, string>();
+
+export function resetFootnotes() {
+  footnoteRefs = [];
+  footnoteDefs = new Map();
+}
+
+export function renderFootnotesList(): string {
+  if (!footnoteRefs.length) return '';
+  const items = footnoteRefs.map(({ label, id, number }) => {
+    const body = footnoteDefs.get(label) || '<p></p>';
+    return `<li id="fn:${number}" data-id="${id}">${body}</li>`;
+  });
+  return `<ol class="footnotes">\n${items.join('\n')}\n</ol>\n`;
+}
+
+export const footnoteRefExtension = {
+  name: 'footnoteRef',
+  level: 'inline',
+  start(src: string) {
+    return src.indexOf('[^');
+  },
+  tokenizer(src: string): FootnoteRefToken | undefined {
+    const match = /^\[\^([^\]\s]+)\]/.exec(src);
+    if (match) {
+      return {
+        type: 'footnoteRef',
+        raw: match[0],
+        label: match[1].toLowerCase(),
+      };
+    }
+  },
+  renderer(token: Token) {
+    const refToken = token as FootnoteRefToken;
+    const number = footnoteRefs.length + 1;
+    const id = generateNodeId();
+    footnoteRefs.push({ label: refToken.label, id, number });
+    return `<sup id="fnref:${number}"><a class="footnote-ref" data-id="${id}" data-reference-number="${number}" href="#fn:${number}">${number}</a></sup>`;
+  },
+};
+
+export const footnoteDefExtension = {
+  name: 'footnoteDef',
+  level: 'block',
+  start(src: string) {
+    return src.match(/^\[\^[^\]\s]+\]:/m)?.index ?? -1;
+  },
+  tokenizer(src: string): FootnoteDefToken | undefined {
+    const firstLine = /^\[\^([^\]\s]+)\]:[ \t]*/.exec(src);
+    if (!firstLine) return undefined;
+
+    const lines = src.split('\n');
+    const contentLines = [lines[0].slice(firstLine[0].length)];
+    let consumed = 1;
+    while (consumed < lines.length) {
+      const line = lines[consumed];
+      if (/^[ \t]{2,}\S/.test(line)) {
+        contentLines.push(line.replace(/^[ \t]{1,4}/, ''));
+        consumed += 1;
+      } else if (
+        /^[ \t]*$/.test(line) &&
+        consumed + 1 < lines.length &&
+        /^[ \t]{2,}\S/.test(lines[consumed + 1])
+      ) {
+        contentLines.push('');
+        consumed += 1;
+      } else {
+        break;
+      }
+    }
+
+    const raw =
+      lines.slice(0, consumed).join('\n') +
+      (consumed < lines.length ? '\n' : '');
+    return {
+      type: 'footnoteDef',
+      raw,
+      label: firstLine[1].toLowerCase(),
+      text: contentLines.join('\n').trim(),
+    };
+  },
+  renderer(token: Token) {
+    const defToken = token as FootnoteDefToken;
+    const body = defToken.text
+      ? marked.parse(defToken.text).toString()
+      : '<p></p>';
+    footnoteDefs.set(defToken.label, body);
+    return '';
+  },
+};

packages/editor-ext/src/lib/markdown/utils/marked.utils.ts

@@ -2,6 +2,12 @@ import { marked } from "marked";
 import { calloutExtension } from "./callout.marked";
 import { mathBlockExtension } from "./math-block.marked";
 import { mathInlineExtension } from "./math-inline.marked";
+import {
+  footnoteDefExtension,
+  footnoteRefExtension,
+  renderFootnotesList,
+  resetFootnotes,
+} from "./footnotes.marked";
 
 marked.use({
   renderer: {
@@ -34,7 +40,13 @@ marked.use({
 });
 
 marked.use({
-  extensions: [calloutExtension, mathBlockExtension, mathInlineExtension],
+  extensions: [
+    calloutExtension,
+    mathBlockExtension,
+    mathInlineExtension,
+    footnoteDefExtension,
+    footnoteRefExtension,
+  ],
 });
 
 marked.setOptions({ breaks: true });
@@ -48,5 +60,7 @@ export function markdownToHtml(
     .replace(YAML_FONT_MATTER_REGEX, "")
     .trimStart();
 
-  return marked.parse(markdown).toString();
+  resetFootnotes();
+  const html = marked.parse(markdown).toString();
+  return html + renderFootnotesList();
 }

packages/editor-ext/src/lib/markdown/utils/turndown.utils.ts

@@ -34,6 +34,8 @@ export function htmlToMarkdown(html: string): string {
     iframeEmbed,
     image,
     video,
+    footnoteRef,
+    footnotesList,
   ]);
   return turndownService.turndown(html).replaceAll('<br>', ' ');
 }
@@ -203,6 +205,56 @@ function image(turndownService: _TurndownService) {
   });
 }
 
+function getFootnoteAnchor(node: HTMLElement): HTMLElement | null {
+  const child = node.firstElementChild as HTMLElement | null;
+  return child?.nodeName === 'A' && child.classList.contains('footnote-ref')
+    ? child
+    : null;
+}
+
+function footnoteRef(turndownService: _TurndownService) {
+  turndownService.addRule('footnoteRef', {
+    filter: function (node: HTMLInputElement) {
+      return node.nodeName === 'SUP' && !!getFootnoteAnchor(node);
+    },
+    replacement: function (_content: string, node: HTMLInputElement) {
+      const anchor = getFootnoteAnchor(node);
+      const number =
+        anchor.getAttribute('data-reference-number') || anchor.textContent;
+      return `[^${number}]`;
+    },
+  });
+}
+
+function footnotesList(turndownService: _TurndownService) {
+  turndownService.addRule('footnotesList', {
+    filter: function (node: HTMLInputElement) {
+      return node.nodeName === 'OL' && node.classList.contains('footnotes');
+    },
+    replacement: function (_content: string, node: HTMLInputElement) {
+      const items = Array.from(node.children).filter(
+        (child) => child.nodeName === 'LI',
+      );
+      const definitions = items.map((li, index) => {
+        const number =
+          (li.getAttribute('id') || '').replace('fn:', '') ||
+          String(index + 1);
+        const markdown = turndownService
+          .turndown((li as HTMLElement).innerHTML)
+          .trim();
+        // continuation lines need a 4-space indent to stay in the footnote
+        const [first, ...rest] = markdown.split('\n');
+        const body = [
+          first,
+          ...rest.map((line: string) => (line.trim() ? `    ${line}` : line)),
+        ].join('\n');
+        return `[^${number}]: ${body}`;
+      });
+      return `\n\n${definitions.join('\n')}\n\n`;
+    },
+  });
+}
+
 function video(turndownService: _TurndownService) {
   turndownService.addRule('video', {
     filter: function (node: HTMLInputElement) {