From 6a69e9b208e8a0ad6677960725f0f06f0e133056 Mon Sep 17 00:00:00 2001
From: Elian Doran <contact@eliandoran.me>
Date: Sat, 5 Apr 2025 02:31:52 +0300
Subject: [PATCH] feat(markdown): use different approach for reference links

---
 src/services/export/markdown.spec.ts | 10 ++++--
 src/services/export/markdown.ts      | 50 +++++++++++++++++++++++++---
 src/services/import/markdown.spec.ts |  8 ++++-
 src/services/import/markdown.ts      | 11 ------
 4 files changed, 60 insertions(+), 19 deletions(-)

diff --git a/src/services/export/markdown.spec.ts b/src/services/export/markdown.spec.ts
index 5f14314fd..7de3dfab2 100644
--- a/src/services/export/markdown.spec.ts
+++ b/src/services/export/markdown.spec.ts
@@ -238,9 +238,15 @@ describe("Markdown export", () => {
         expect(markdownExportService.toMarkdown(html)).toBe(expected);
     });
 
-    it("exports reference links as normal links", () => {
+    it("exports normal links verbatim", () => {
+        const html = /*html*/`<p><a href="https://www.google.com">Google</a></p>`;
+        const expected = `[Google](https://www.google.com)`;
+        expect(markdownExportService.toMarkdown(html)).toBe(expected);
+    });
+
+    it("exports reference links verbatim", () => {
         const html = /*html*/`<p><a class="reference-link" href="../../Canvas.html">Canvas</a></p>`;
-        const expected = `[Canvas](../../Canvas.html)`;
+        const expected = `<a class="reference-link" href="../../Canvas.html">Canvas</a>`;
         expect(markdownExportService.toMarkdown(html)).toBe(expected);
     });
 
diff --git a/src/services/export/markdown.ts b/src/services/export/markdown.ts
index 03ac1b744..c148b9e2e 100644
--- a/src/services/export/markdown.ts
+++ b/src/services/export/markdown.ts
@@ -1,7 +1,8 @@
 "use strict";
 
-import TurndownService from "turndown";
+import TurndownService, { type Rule } from "turndown";
 import { gfm } from "../../../packages/turndown-plugin-gfm/src/gfm.js";
+import type { DOMElement } from "react";
 
 let instance: TurndownService | null = null;
 
@@ -43,6 +44,7 @@ function toMarkdown(content: string) {
         instance.addRule("fencedCodeBlock", fencedCodeBlockFilter);
         instance.addRule("img", buildImageFilter());
         instance.addRule("admonition", buildAdmonitionFilter());
+        instance.addRule("inlineLink", buildInlineLinkFilter());
         instance.use(gfm);
         instance.keep([ "kbd" ]);
     }
@@ -93,10 +95,6 @@ function buildImageFilter() {
         return title.replace(/"/g, '\\"')
     }
 
-    function cleanAttribute (attribute: string) {
-        return attribute ? attribute.replace(/(\n+\s*)+/g, '\n') : ''
-    }
-
     const imageFilter: TurndownService.Rule = {
         filter: "img",
         replacement(content, node) {
@@ -153,6 +151,48 @@ function buildAdmonitionFilter() {
     return admonitionFilter;
 }
 
+/**
+ * Variation of the original ruleset: https://github.com/mixmark-io/turndown/blob/master/src/commonmark-rules.js.
+ *
+ * Detects if the URL is a Trilium reference link and returns it verbatim if that's the case.
+ *
+ * @returns
+ */
+function buildInlineLinkFilter(): Rule {
+    return {
+        filter: function (node, options) {
+            return (
+            options.linkStyle === 'inlined' &&
+            node.nodeName === 'A' &&
+            !!node.getAttribute('href')
+            )
+        },
+
+        replacement: function (content, _node) {
+            const node = _node as HTMLElement;
+
+            // Return reference links verbatim.
+            if (node.classList.contains("reference-link")) {
+                return node.outerHTML;
+            }
+
+            // Otherwise treat as normal.
+            // TODO: Call super() somehow instead of duplicating the implementation.
+            var href = node.getAttribute('href')
+            if (href) href = href.replace(/([()])/g, '\\$1')
+            var title = cleanAttribute(node.getAttribute('title'))
+            if (title) title = ' "' + title.replace(/"/g, '\\"') + '"'
+            return '[' + content + '](' + href + title + ')'
+        }
+    }
+}
+
+// Taken from upstream since it's not exposed.
+// https://github.com/mixmark-io/turndown/blob/master/src/commonmark-rules.js
+function cleanAttribute(attribute: string | null | undefined) {
+    return attribute ? attribute.replace(/(\n+\s*)+/g, '\n') : ''
+}
+
 export default {
     toMarkdown
 };
diff --git a/src/services/import/markdown.spec.ts b/src/services/import/markdown.spec.ts
index 9ef6233e5..061e22f21 100644
--- a/src/services/import/markdown.spec.ts
+++ b/src/services/import/markdown.spec.ts
@@ -151,8 +151,14 @@ second line 2</code></pre><ul><li>Hello</li><li>world</li></ul><ol><li>Hello</li
         expect(markdownService.renderToHtml(input, "Title")).toStrictEqual(expected);
     });
 
-    it("imports back to reference links", () => {
+    it("does not touch relative links", () => {
         const input = `[Canvas](../../Canvas.html)`;
+        const expected = /*html*/`<p><a href="../../Canvas.html">Canvas</a></p>`;
+        expect(markdownService.renderToHtml(input, "Title")).toStrictEqual(expected);
+    });
+
+    it("imports back to reference links", () => {
+        const input = `<a class="reference-link" href="../../Canvas.html">Canvas</a>`;
         const expected = /*html*/`<p><a class="reference-link" href="../../Canvas.html">Canvas</a></p>`;
         expect(markdownService.renderToHtml(input, "Title")).toStrictEqual(expected);
     });
diff --git a/src/services/import/markdown.ts b/src/services/import/markdown.ts
index 3dcd2784c..57bf58dd6 100644
--- a/src/services/import/markdown.ts
+++ b/src/services/import/markdown.ts
@@ -64,17 +64,6 @@ class CustomMarkdownRenderer extends Renderer {
         return `<blockquote>${body}</blockquote>`;
     }
 
-    link(data: Tokens.Link): string {
-        let html = super.link(data);
-
-        // Rewrite local/relative links back to reference links.
-        if (data.href.indexOf("://") === -1) {
-            html = html.replace(/^<a /, `<a class="reference-link" `);
-        }
-
-        return html;
-    }
-
 }
 
 const renderer = new CustomMarkdownRenderer({ async: false });