Cache expensive Typst operations for quick iterations during development

lib/cache.ts

@@ -0,0 +1,32 @@
+import {hash} from "./hash.ts";
+
+const cacheKeys = new Map<string, string>();
+
+/**
+ * Check if the content of a file has changed since the last time it was checked.
+ * Stores the hash of the content in a cache to compare it later.
+ *
+ * @param path the path to the file
+ * @param content the content of the file
+ * @returns an object with the cache key and a boolean indicating if the content has changed since the last time it was checked
+ *
+ * @example
+ * ```ts
+ * const {cacheKey, shouldRecompile} = checkForChanges(
+ *   "file.txt",
+ *   "Hello, world!"
+ * );
+ *
+ * if (shouldRecompile) {
+ *   // Recompile the file
+ *   // ...
+*  }
+ * console.log("The cache key is", cacheKey);
+ * ```
+ */
+export function checkForChanges(path: string, content: string) {
+  const cacheKey = hash(content)
+  const shouldRecompile = cacheKeys.get(path) !== cacheKey;
+  cacheKeys.set(path, cacheKey);
+  return {cacheKey, shouldRecompile};
+}

lib/hash.ts

@@ -0,0 +1,12 @@
+/**
+ * Hash a string
+ * @param s
+ */
+export function hash(s: string) {
+  let hash = 0;
+  for (let i = 0; i < s.length; i++) {
+    hash = ((hash << 5) - hash) + s.charCodeAt(i);
+    hash |= 0;
+  }
+  return hash.toString(16);
+}

lib/metadata.ts

@@ -15,13 +15,25 @@ export const MetadataSchema = z.object({
 
 export type Metadata = z.infer<typeof MetadataSchema>;
 
-export async function readMetadata(filePath: string): Promise<Metadata> {
-  return {
-    title: await readMetadataField(filePath, "title"),
-    abbreviation: await readMetadataField(filePath, "abbreviation"),
-    resolution: await readMetadataField(filePath, "resolution"),
-    inEffect: await readMetadataField(filePath, "in-effect"),
-  };
+const metadataCache = new Map<string, Metadata>();
+
+/**
+ * Reads metadata from a file using the typst CLI.
+ * The metadata is cached to avoid reading the same file multiple times, which is slow.
+ * @param filePath The path to the file to read metadata from
+ * @param cacheKey A key to use for caching the metadata.
+ * This should be a hash of the file content.
+ */
+export async function readMetadata(filePath: string, cacheKey: string): Promise<Metadata> {
+  if (!metadataCache.has(cacheKey)) {
+    metadataCache.set(cacheKey, {
+      title: await readMetadataField(filePath, "title"),
+      abbreviation: await readMetadataField(filePath, "abbreviation"),
+      resolution: await readMetadataField(filePath, "resolution"),
+      inEffect: await readMetadataField(filePath, "in-effect"),
+    });
+  }
+  return metadataCache.get(cacheKey)!;
 }
 
 export async function readMetadataField(

lib/typst-delegis.ts

@@ -1,13 +1,17 @@
-import { Page } from "lume/core/file.ts";
+import {Page} from "lume/core/file.ts";
 import Site from "lume/core/site.ts";
-import { Metadata, readMetadata } from "./metadata.ts";
-import { compileTypst } from "./compile.ts";
+import {Metadata, readMetadata} from "./metadata.ts";
+import {compileTypst} from "./compile.ts";
+import {checkForChanges} from "./cache.ts";
 
 export const typstDelegis = () => (site: Site) => {
   site.preprocess([".typ"], async (filteredPages, allPages) => {
     const urls: Record<string, Metadata> = {};
     for (const page of filteredPages) {
-      const metadata = await readMetadata(site.src(page.sourcePath));
+      const {cacheKey, shouldRecompile} = checkForChanges(page.sourcePath, page.data.content?.toString() ?? "");
+
+      const metadata = await readMetadata(site.src(page.sourcePath), cacheKey);
+
       urls[site.url(page.data.url)] = metadata;
 
       allPages.push(Page.create({
@@ -22,22 +26,25 @@ export const typstDelegis = () => (site: Site) => {
       page.data = {
         ...page.data,
         layout: "vo.tsx",
-        content: site.url(page.data.url + "rendered.pdf"),
+        // cache key included to make the SSG detect changes in the resulting content and reload the page
+        content: site.url(page.data.url + "rendered.pdf#" + cacheKey),
         title: metadata.abbreviation + " - " + metadata.title + ` (WüSpace VOS)`,
       };
 
-      await Deno.mkdir(
-        site.dest(page.outputPath, ".."),
-        { recursive: true },
-      );
-
-      await compileTypst(
-        site.src(page.sourcePath),
-        site.dest(page.outputPath.replace("index.html", "rendered.pdf")),
-      );
+      if (shouldRecompile) {
+        await Deno.mkdir(
+          site.dest(page.outputPath, ".."),
+          { recursive: true },
+        );
+        await compileTypst(
+          site.src(page.sourcePath),
+          site.dest(page.outputPath.replace("index.html", "rendered.pdf")),
+        );
+      }
     }
 
     allPages.map((page) => page.data = { ...page.data, vos: urls });
   });
   site.loadPages([".typ"]);
 };
+