printmaker/src/pdf-annotations.ts

Generate PDF documents and from JavaScript objects

import { PDFArray, PDFDict, PDFName, PDFObject, PDFPage, PDFString } from 'pdf-lib';

import { Box, Pos } from './box.js';

export function createLinkAnnotation(page: PDFPage, box: Box, uri: string) {
  const annots = getOrCreate(page.node, 'Annots', () => []) as PDFArray;
  const annot = page.doc.context.obj({
    Type: 'Annot',
    Subtype: 'Link',
    Rect: [box.x, box.y, box.x + box.width, box.y + box.height],
    ...(uri.startsWith('#')
      ? { A: { Type: 'Action', S: 'GoTo', D: PDFString.of(uri.slice(1)) } }
      : { A: { Type: 'Action', S: 'URI', URI: PDFString.of(uri) } }),
    C: page.doc.context.obj([]),
    F: 0, // required for PDF/A
  });
  annots.push(page.doc.context.register(annot));
}

export function createNamedDest(page: PDFPage, name: string, pos: Pos) {
  const names = getOrCreate(page.doc.catalog, 'Names', () => ({})) as PDFDict;
  const dests = getOrCreate(names, 'Dests', () => ({})) as PDFDict;
  const destNames = getOrCreate(dests, 'Names', () => []) as PDFArray;
  for (let i = 0; i < destNames.size(); i += 2) {
    if ((destNames.get(i) as PDFString).asString() === name) {
      throw new Error(`Duplicate id ${name}`);
    }
  }
  destNames.push(PDFString.of(name));
  destNames.push(page.doc.context.obj([page.ref, 'XYZ', pos.x, pos.y, null]));
}

function getOrCreate(dict: PDFDict, name: string, creatorFn: () => any): PDFObject {
  if (!dict.has(PDFName.of(name))) {
    dict.set(PDFName.of(name), dict.context.obj(creatorFn()));
  }
  return dict.get(PDFName.of(name));
}