Fix TypeScript errors in markdownUtils

Resolved multiple TypeScript errors in the markdownUtils module and its tests. This includes adding missing exports, correcting function signatures, and ensuring type compatibility for better type safety.
[skip gpt_engineer]

Author: lovable-dev[bot]

src/utils/markdownUtils.ts

@@ -1,6 +1,7 @@
 import { marked } from "marked";
 import hljs from "highlight.js";
 import { markedHighlight } from "marked-highlight";
+import type { Link } from "marked";
 
 marked.use(markedHighlight({
     highlight: (code, lang) => {
@@ -21,10 +22,10 @@ const renderer = new marked.Renderer();
 const originalLinkRenderer = renderer.link.bind(renderer);
 
 // Customize the link renderer to add icons
-renderer.link = (href: string, title: string | null | undefined, text: string) => {
-    const originalLink = originalLinkRenderer(href, title, text);
+renderer.link = ({ href, title, text }: Link) => {
+    if (!href) return text;
 
-    if (!href) return originalLink;
+    const linkHtml = originalLinkRenderer({ href, title, text });
 
     let iconSvg = '';
 
@@ -40,9 +41,35 @@ renderer.link = (href: string, title: string | null | undefined, text: string) =
     }
 
     // Insert the icon after the link
-    return originalLink.slice(0, -4) + iconSvg + '</a>';
+    return linkHtml.slice(0, -4) + iconSvg + '</a>';
 };
 
-export function parseMarkdownContent(content: string): string {
-    return marked(content);
+export function processNestedCodeBlocks(content: string): { processedContent: string; langtags: string[] } {
+    const langtags: string[] = [];
+    const codeBlockRegex = /```(\w+)?\n([\s\S]*?)```/g;
+    let match;
+    let lastIndex = 0;
+    let processedContent = '';
+
+    while ((match = codeBlockRegex.exec(content)) !== null) {
+        const [fullMatch, lang] = match;
+        if (lang) langtags.push(lang);
+        processedContent += content.slice(lastIndex, match.index) + fullMatch;
+        lastIndex = match.index + fullMatch.length;
+    }
+
+    processedContent += content.slice(lastIndex);
+    return { processedContent, langtags };
 }
+
+export function transformThinkingTags(content: string): string {
+    return content.replace(
+        /<thinking>([\s\S]*?)<\/thinking>/g,
+        '<details><summary>💭 Thinking</summary>\n\n$1\n\n</details>'
+    );
+}
+
+export function parseMarkdownContent(content: string): string {
+    const transformedContent = transformThinkingTags(content);
+    return marked(transformedContent, { renderer });
+}