feat(preview-comment): add symmetry preview (#3823)

docs/.vitepress/api/gh-icon/symmetry/[...data].get.ts

@@ -0,0 +1,55 @@
+import { eventHandler, setResponseHeader, defaultContentType } from 'h3';
+import { renderToString } from 'react-dom/server';
+import { createElement } from 'react';
+import Diff from '../../../lib/SvgPreview/Diff.tsx';
+
+export default eventHandler((event) => {
+  const { params } = event.context;
+
+  const pathData = params.data.split('/');
+  const data = pathData.at(-1).slice(0, -4);
+  const [operation] = pathData;
+
+  const newSrc = Buffer.from(data, 'base64')
+    .toString('utf8')
+    .replaceAll('\n', '')
+    .replace(/<svg[^>]*>|<\/svg>/g, '');
+
+  const width = parseInt(
+    (newSrc.includes('<svg ') ? newSrc.match(/width="(\d+)"/)?.[1] : null) ?? '24',
+  );
+  const height = parseInt(
+    (newSrc.includes('<svg ') ? newSrc.match(/height="(\d+)"/)?.[1] : null) ?? '24',
+  );
+
+  const children = [];
+
+  let oldSrc = '';
+  if (operation.startsWith('rotate-')) {
+    const degrees = parseInt(operation.replace('rotate-', ''));
+    if (isNaN(degrees)) return '';
+    oldSrc = `<g transform="rotate(${degrees} ${width / 2} ${height / 2})">${newSrc}</g>`;
+  } else if (operation === 'flip-horizontal') {
+    oldSrc = `<g transform="scale(1, -1) translate(0, -${height})">${newSrc}</g>`;
+  } else if (operation === 'flip-vertical') {
+    oldSrc = `<g transform="scale(-1, 1) translate(-${width}, 0)">${newSrc}</g>`;
+  } else if (operation === 'flip-backslash') {
+    oldSrc = `<g transform="rotate(90, ${width / 2}, ${height / 2}) scale(1, -1) translate(0, -${height})">${newSrc}</g>`;
+  } else if (operation === 'flip-slash') {
+    oldSrc = `<g transform="rotate(90, ${width / 2}, ${height / 2}) scale(-1, 1) translate(-${width}, 0)">${newSrc}</g>`;
+  } else {
+    return '';
+  }
+
+  const svg = Buffer.from(
+    // We can't use jsx here, is not supported here by nitro.
+    renderToString(
+      createElement(Diff, { oldSrc, newSrc, showGrid: true, height, width }, children),
+    ),
+  ).toString('utf8');
+
+  defaultContentType(event, 'image/svg+xml');
+  setResponseHeader(event, 'Cache-Control', 'public,max-age=31536000');
+
+  return svg;
+});