Revert "remove all caching logic from mdx"

This reverts commit 2c2dcc9.

Author: BYK

src/mdx.ts

@@ -1,10 +1,22 @@
+import {BinaryLike, createHash} from 'crypto';
+
 import {cache} from 'react';
 import matter from 'gray-matter';
 import {s} from 'hastscript';
 import yaml from 'js-yaml';
 import {bundleMDX} from 'mdx-bundler';
+import {createReadStream, createWriteStream, mkdirSync} from 'node:fs';
 import {access, opendir, readFile} from 'node:fs/promises';
 import path from 'node:path';
+// @ts-expect-error ts(2305) -- For some reason "compose" is not recognized in the types
+import {compose, Readable} from 'node:stream';
+import {json} from 'node:stream/consumers';
+import {pipeline} from 'node:stream/promises';
+import {
+  constants as zlibConstants,
+  createBrotliCompress,
+  createBrotliDecompress,
+} from 'node:zlib';
 import rehypeAutolinkHeadings from 'rehype-autolink-headings';
 import rehypePresetMinify from 'rehype-preset-minify';
 import rehypePrismDiff from 'rehype-prism-diff';
@@ -41,6 +53,33 @@ type SlugFile = {
 };
 
 const root = process.cwd();
+const CACHE_COMPRESS_LEVEL = 4;
+const CACHE_DIR = path.join(root, '.next', 'cache', 'mdx-bundler');
+mkdirSync(CACHE_DIR, {recursive: true});
+
+const md5 = (data: BinaryLike) => createHash('md5').update(data).digest('hex');
+
+async function readCacheFile<T>(file: string): Promise<T> {
+  const reader = createReadStream(file);
+  const decompressor = createBrotliDecompress();
+
+  return (await json(compose(reader, decompressor))) as T;
+}
+
+async function writeCacheFile(file: string, data: string) {
+  await pipeline(
+    Readable.from(data),
+    createBrotliCompress({
+      chunkSize: 32 * 1024,
+      params: {
+        [zlibConstants.BROTLI_PARAM_MODE]: zlibConstants.BROTLI_MODE_TEXT,
+        [zlibConstants.BROTLI_PARAM_QUALITY]: CACHE_COMPRESS_LEVEL,
+        [zlibConstants.BROTLI_PARAM_SIZE_HINT]: data.length,
+      },
+    }),
+    createWriteStream(file)
+  );
+}
 
 function formatSlug(slug: string) {
   return slug.replace(/\.(mdx|md)/, '');
@@ -436,6 +475,24 @@ export async function getFileBySlug(slug: string): Promise<SlugFile> {
     );
   }
 
+  let cacheKey: string | null = null;
+  let cacheFile: string | null = null;
+  if (process.env.CI === '1') {
+    cacheKey = md5(source);
+    cacheFile = path.join(CACHE_DIR, cacheKey);
+
+    try {
+      const cached = await readCacheFile<SlugFile>(cacheFile);
+      return cached;
+    } catch (err) {
+      if (err.code !== 'ENOENT' && err.code !== 'ABORT_ERR') {
+        // If cache is corrupted, ignore and proceed
+        // eslint-disable-next-line no-console
+        console.warn(`Failed to read MDX cache: ${cacheFile}`, err);
+      }
+    }
+  }
+
   process.env.ESBUILD_BINARY_PATH = path.join(
     root,
     'node_modules',
@@ -561,6 +618,13 @@ export async function getFileBySlug(slug: string): Promise<SlugFile> {
     },
   };
 
+  if (cacheFile) {
+    writeCacheFile(cacheFile, JSON.stringify(resultObj)).catch(e => {
+      // eslint-disable-next-line no-console
+      console.warn(`Failed to write MDX cache: ${cacheFile}`, e);
+    });
+  }
+
   return resultObj;
 }