feat(export): convert single-line display math to multi-line

main.js

@@ -50,6 +50,49 @@ function upsertFrontmatter(content, frontmatterLines, keys) {
   return ["---", ...frontmatterLines, "---", "", content].join("\n");
 }
 
+function splitFrontmatter(content) {
+  const frontmatterRegex = /^---\s*\n([\s\S]*?)\n---\s*\n?/;
+  const match = content.match(frontmatterRegex);
+  if (!match) {
+    return { frontmatter: "", body: content };
+  }
+  return { frontmatter: match[0], body: content.slice(match[0].length) };
+}
+
+function convertSingleLineDisplayMath(content) {
+  const { frontmatter, body } = splitFrontmatter(content);
+  const newline = content.includes("\r\n") ? "\r\n" : "\n";
+  const lines = body.split(/\r?\n/);
+  let inFence = false;
+  let fenceMarker = "";
+  let fenceLength = 0;
+  const converted = lines.flatMap((line) => {
+    const fenceMatch = line.match(/^\s*([`~]{3,})/);
+    if (fenceMatch) {
+      if (!inFence) {
+        inFence = true;
+        fenceMarker = fenceMatch[1][0];
+        fenceLength = fenceMatch[1].length;
+      } else if (fenceMatch[1][0] === fenceMarker && fenceMatch[1].length >= fenceLength) {
+        inFence = false;
+        fenceMarker = "";
+        fenceLength = 0;
+      }
+      return [line];
+    }
+
+    if (inFence) return [line];
+
+    const match = line.match(/^(\s*)\$\$(.+?)\$\$\s*$/);
+    if (!match) return [line];
+    const indent = match[1] || "";
+    const inner = match[2].trim();
+    return [indent + "$$", indent + inner, indent + "$$"];
+  });
+
+  return frontmatter + converted.join(newline);
+}
+
 class AstroPostExporter extends Plugin {
   async onload() {
     await this.loadSettings();
@@ -152,7 +195,8 @@ class AstroPostExporter extends Plugin {
     for (const file of files) {
       try {
         const content = await this.app.vault.read(file);
-        const output = this.applyFrontmatter(file, content);
+        const transformed = convertSingleLineDisplayMath(content);
+        const output = this.applyFrontmatter(file, transformed);
         const destinationPath = this.getDestinationPath(file, exportDir);
         await fs.promises.mkdir(path.dirname(destinationPath), { recursive: true });
         await fs.promises.writeFile(destinationPath, output, "utf8");