⚗️ Support render-document hook

To enable experimentation with custom rendering logic, this commit adds
support for an undocumented `onRenderDocument` hook in the document
definition.

Author: ralfstx

src/read-document.test.ts

@@ -113,6 +113,13 @@ describe('readDocumentDefinition', () => {
     ]);
   });
 
+  it(`includes onRenderDocument hook`, () => {
+    const onRenderDocument = () => {};
+    const def = readDocumentDefinition({ ...input, onRenderDocument });
+
+    expect(def.onRenderDocument).toBe(onRenderDocument);
+  });
+
   (['header', 'footer'] as const).forEach((name) => {
     it(`supports dynamic ${name}`, () => {
       const defaultStyle = { fontSize: 23 };

src/read-document.ts

@@ -1,3 +1,5 @@
+import type { PDFDocument } from 'pdf-lib';
+
 import type { BoxEdges, Size } from './box.ts';
 import { parseEdges } from './box.ts';
 import type { FontDef } from './fonts.ts';
@@ -31,6 +33,7 @@ export type DocumentDefinition = {
     creationDate?: Date;
     modificationDate?: Date;
   }[];
+  onRenderDocument?: (pdfDoc: PDFDocument) => void;
 };
 
 export type Metadata = {
@@ -61,6 +64,7 @@ export function readDocumentDefinition(input: unknown): DocumentDefinition {
     dev: optional(types.object({ guides: optional(types.boolean()) })),
     customData: optional(readCustomData),
     embeddedFiles: optional(types.array(readEmbeddedFiles)),
+    onRenderDocument: optional(),
   });
   const tBlock = (block: unknown) => readBlock(block, def1.defaultStyle);
   const def2 = readObject(input, {

src/render/render-document.test.ts

@@ -68,4 +68,20 @@ describe('renderDocument', () => {
     expect(lookup('XXFoo').getContentsString()).toBe('Foo');
     expect(lookup('XXBar').getContents()).toEqual(Uint8Array.of(1, 2, 3));
   });
+
+  it('calls custom render hook', async () => {
+    const def = {
+      content: [],
+      onRenderDocument: (pdfDoc: PDFDocument) => {
+        pdfDoc.setTitle('Test Title');
+      },
+    };
+
+    const pdfData = await renderDocument(def, []);
+
+    const pdfDoc = await PDFDocument.load(pdfData, { updateMetadata: false });
+    const infoDict = pdfDoc.context.lookup(pdfDoc.context.trailerInfo.Info) as PDFDict;
+    const getInfo = (name: string) => infoDict.get(PDFName.of(name));
+    expect(getInfo('Title')).toEqual(PDFHexString.fromText('Test Title'));
+  });
 });

src/render/render-document.ts

@@ -22,6 +22,7 @@ export async function renderDocument(def: DocumentDefinition, pages: Page[]): Pr
     });
   }
 
+  def.onRenderDocument?.(pdfDoc);
   const idInfo = {
     creator: 'pdfmkr',
     time: new Date().toISOString(),