feat(md-print): add timestamp footer option

src/components/md-print/PrintPreview.tsx

@@ -28,6 +28,11 @@ import {
 } from "./paginate";
 import { exportPrintPDF } from "./print-export";
 
+function formatTimestamp(date: Date): string {
+  const pad = (n: number) => String(n).padStart(2, "0");
+  return `${date.getFullYear()}-${pad(date.getMonth() + 1)}-${pad(date.getDate())} ${pad(date.getHours())}:${pad(date.getMinutes())}`;
+}
+
 export interface PrintPreviewProps {
   src: string;
   section?: string;
@@ -69,6 +74,23 @@ export function PrintPreview(props: PrintPreviewProps) {
     articlePath: props.articlePath,
   });
 
+  const applyFooter = (pageList: HTMLElement[], timestamp: string) => {
+    pageList.forEach((page, index) => {
+      const footer = page.querySelector(".md-print-footer");
+      if (!footer) return;
+      const pageLabel = props.config.pageNumbers
+        ? `${index + 1} / ${pageList.length}`
+        : "";
+      footer.textContent = [pageLabel, timestamp].filter(Boolean).join(" · ");
+      // Left A5 gets the left corner, right A5 gets the right corner.
+      footer.classList.add(
+        index % 2 === 0
+          ? "md-print-footer--left"
+          : "md-print-footer--right",
+      );
+    });
+  };
+
   const runPagination = async () => {
     const md = content();
     const source = sourceEl();
@@ -88,18 +110,10 @@ export function PrintPreview(props: PrintPreviewProps) {
       await waitForStableSize(source, 300, 4000);
 
       const result = paginate(source, options(), mount);
-      result.pages.forEach((page, index) => {
-        const footer = page.querySelector(".md-print-footer");
-        if (footer) {
-          footer.textContent = `${index + 1} / ${result.pages.length}`;
-          // Left A5 gets the left corner, right A5 gets the right corner.
-          footer.classList.add(
-            index % 2 === 0
-              ? "md-print-footer--left"
-              : "md-print-footer--right",
-          );
-        }
-      });
+      applyFooter(
+        result.pages,
+        props.config.timestamp ? formatTimestamp(new Date()) : "",
+      );
       setPages(result.pages);
       setWarnings(result.warnings);
     } catch (e) {
@@ -164,6 +178,10 @@ export function PrintPreview(props: PrintPreviewProps) {
 
   const handleExport = async () => {
     try {
+      // Refresh the timestamp so the exported file records the export time.
+      if (props.config.timestamp) {
+        applyFooter(pages(), formatTimestamp(new Date()));
+      }
       await exportPrintPDF(pages(), props.config, title(), props.articlePath);
     } catch (e) {
       setError(e instanceof Error ? e.message : String(e));