feat(export/markdown): basic support for admonitions

src/services/export/markdown.spec.ts

@@ -103,4 +103,94 @@ describe("Markdown export", () => {
         expect(markdownExportService.toMarkdown(html)).toBe(html);
     });
 
+    it("exports admonitions properly", () => {
+        const html = trimIndentation`\
+            <p>
+                Before
+            </p>
+            <aside class="admonition note">
+                <p>
+                    This is a note.
+                </p>
+            </aside>
+            <aside class="admonition tip">
+                <p>
+                    This is a tip.
+                </p>
+            </aside>
+            <aside class="admonition important">
+                <p>
+                    This is a very important information.
+                </p>
+                <figure class="table">
+                    <table>
+                        <tbody>
+                            <tr>
+                                <td>
+                                    1
+                                </td>
+                                <td>
+                                    2
+                                </td>
+                            </tr>
+                            <tr>
+                                <td>
+                                    3
+                                </td>
+                                <td>
+                                    4
+                                </td>
+                            </tr>
+                        </tbody>
+                    </table>
+                </figure>
+            </aside>
+            <aside class="admonition caution">
+                <p>
+                    This is a caution.
+                </p>
+            </aside>
+            <aside class="admonition warning">
+                <h2>
+                    Title goes here
+                </h2>
+                <p>
+                    This is a warning.
+                </p>
+            </aside>
+            <p>
+                After
+            </p>
+        `;
+
+        const space = " ";  // editor config trimming space.
+        const expected = trimIndentation`\
+            Before
+
+            > [!NOTE]
+            > This is a note.
+
+            > [!TIP]
+            > This is a tip.
+
+            > [!IMPORTANT]
+            > This is a very important information.
+            >${space}
+            > |     |     |
+            > | --- | --- |
+            > | 1   | 2   |
+            > | 3   | 4   |
+
+            > [!CAUTION]
+            > This is a caution.
+
+            > [!WARNING]
+            > ## Title goes here
+            >${space}
+            > This is a warning.
+
+            After`;
+        expect(markdownExportService.toMarkdown(html)).toBe(expected);
+    });
+
 });

src/services/export/markdown.ts

@@ -31,6 +31,7 @@ function toMarkdown(content: string) {
         // Filter is heavily based on: https://github.com/mixmark-io/turndown/issues/274#issuecomment-458730974
         instance.addRule("fencedCodeBlock", fencedCodeBlockFilter);
         instance.addRule("img", buildImageFilter());
+        instance.addRule("admonition", buildAdmonitionFilter());
         instance.use(turndownPluginGfm.gfm);
         instance.keep([ "kbd" ]);
     }
@@ -100,6 +101,57 @@ function buildImageFilter() {
     return imageFilter;
 }
 
+function buildAdmonitionFilter() {
+    const admonitionTypeMappings: Record<string, string> = {
+        note: "NOTE",
+        tip: "TIP",
+        important: "IMPORTANT",
+        caution: "CAUTION",
+        warning: "WARNING"
+    };
+
+    const defaultAdmonitionType = admonitionTypeMappings.note;
+
+    function parseAdmonitionType(_node: Node) {
+        if (!("getAttribute" in _node)) {
+            return defaultAdmonitionType;
+        }
+
+        const node = _node as Element;
+        const classList = node.getAttribute("class")?.split(" ") ?? [];
+
+        for (const className of classList) {
+            if (className === "admonition") {
+                continue;
+            }
+
+            const mappedType = admonitionTypeMappings[className];
+            if (mappedType) {
+                return mappedType;
+            }
+        }
+
+        return defaultAdmonitionType;
+    }
+
+    const admonitionFilter: TurndownService.Rule = {
+        filter(node, options) {
+            return node.nodeName === "ASIDE" && node.classList.contains("admonition");
+        },
+        replacement(content, node) {
+            // Parse the admonition type.
+            const admonitionType = parseAdmonitionType(node);
+
+            content = content.replace(/^\n+|\n+$/g, '');
+            content = content.replace(/^/gm, '> ');
+            content = `> [!${admonitionType}]\n` + content;
+
+            return "\n\n" + content + "\n\n";
+        }
+    }
+    return admonitionFilter;
+}
+
 export default {
     toMarkdown
 };