improve djot plugin

_djot.ts

@@ -1,4 +1,25 @@
 import djot from "@djot/djot";
+import Site from "lume/core/site.ts";
+import { merge } from "lume/core/utils/object.ts";
+
+// Djot does not export these types
+type Filter = object;
+type HTMLRenderOptions = object;
+
+export interface Options {
+  /** The list of file extensions this plugin applies to */
+  extensions?: string[];
+
+  filters?: Filter[];
+
+  /** Options passed to djot library */
+  renderOptions?: HTMLRenderOptions;
+}
+
+// Default options
+export const defaults: Options = {
+  extensions: [".dj", ".djot"],
+};
 
 function extractTitle(ast: djot.Doc): string {
   const firstSection = ast.children.find((c) => c.tag == "section");
@@ -10,35 +31,80 @@ function extractTitle(ast: djot.Doc): string {
   return title ?? "No title";
 }
 
-export function djotRender(content: string): string {
-  return djot.renderHTML(djot.parse(content));
-}
-
 export async function djotLoader(path: string | URL) {
   const content = await Deno.readTextFile(path);
-
   const ast = djot.parse(content);
-
-  djot.applyFilter(ast, () => {
-    return {
-      link: (el) => {
-        if (el.destination) {
-          el.destination = el.destination.replace(
-            /(\.dj)(#[^.\s]+)?$/,
-            (_match: string, _ext: string, section: string) => {
-              return section ? section : "";
-            },
-          );
-        }
-      },
-    };
-  });
-  
   const title = extractTitle(ast);
-  const html = djot.renderHTML(ast);
 
   return {
     title,
-    content: html,
+    content,
+  };
+}
+
+const stripMarkupSourceLinks: Filter = () => {
+  return {
+    link: (el: djot.Link) => {
+      if (el.destination) {
+        el.destination = el.destination.replace(
+          /(.(?:dj|md))(#[^.\s]+)?$/,
+          (_match: string, _ext: string, section: string) => {
+            return section ?? "";
+          },
+        );
+      }
+    },
+  };
+};
+
+const defaultFilters = [
+  stripMarkupSourceLinks,
+];
+
+export class DjotEngine implements Lume.Engine {
+  filters: Filter[];
+  renderOptions?: HTMLRenderOptions;
+
+  constructor(filters: Filter[] = [], renderOptions?: HTMLRenderOptions) {
+    this.filters = [...defaultFilters, ...filters];
+    this.renderOptions = renderOptions;
+  }
+
+  render(
+    content: string | djot.Doc,
+    _data?: Record<string, unknown>,
+    _filename?: string,
+  ): string {
+    if (typeof content === "string") {
+      content = djot.parse(content);
+    }
+
+    this.filters.forEach((filter, _index, _array) => {
+      djot.applyFilter(content, filter);
+    });
+
+    return djot.renderHTML(
+      content,
+      this.renderOptions,
+    );
+  }
+
+  addHelper() {}
+
+  deleteCache() {}
+}
+
+export default function (userOptions?: Options) {
+  const options = merge(defaults, userOptions);
+
+  return function (site: Site) {
+    const engine = new DjotEngine(options.filters, options.renderOptions);
+
+    site.loadPages(options.extensions, {
+      loader: djotLoader,
+      engine,
+    });
+
+    site.filter("djot", (content) => engine.render(content as string));
   };
 }