/**
 * Runs the DjVu module for johnmcm.com's /djvu-to-pdf and /open-file/djvu.
 * The page sends the book once; each request after that reads from it.
 *
 * Messages in:  { id, type: 'open', file: File }
 *               { id, type: 'render', page, dpi }
 *               { id, type: 'text', page, dpi }        (the page's words and where they are)
 *               { id, type: 'texts' }                  (every page's text, for search)
 *               { id, type: 'pdf', start, end, quality, dpi, g4 }
 * Messages out: { id, ... } answers, { id, progress: { done, total } } while
 *               a PDF is made, or { id, error }.
 *
 * Written for johnmcm.com (2026); part of the module published at /source/djvu/.
 */

import init, { WasmDocument, export_pdf, outline_json } from './djvu.js';

let ready = null;
let bytes = null;
let doc = null;

/** Each page's size in points and its own resolution. */
function pageInfo() {
  const pages = [];
  for (let i = 0; i < doc.page_count(); i++) {
    const p = doc.page(i);
    try {
      pages.push({ width: p.width_at(72), height: p.height_at(72), dpi: p.dpi() });
    } finally {
      p.free();
    }
  }
  return pages;
}

function withPage(index, fn) {
  const p = doc.page(index);
  try {
    return fn(p);
  } finally {
    p.free();
  }
}

self.onmessage = async (e) => {
  const msg = e.data;
  try {
    ready ??= init({ module_or_path: new URL('./djvu_bg.wasm', import.meta.url) }).catch((err) => {
      ready = null;
      throw new Error('load: ' + err);
    });
    await ready;
    if (msg.type === 'open') {
      bytes = new Uint8Array(await msg.file.arrayBuffer());
      doc?.free();
      // Cleared first: if the new file fails to parse, later requests say no
      // book is open rather than touching the freed one ("null pointer").
      doc = null;
      doc = WasmDocument.from_bytes(bytes);
      let outline = [];
      try {
        outline = JSON.parse(outline_json(bytes));
      } catch {
        // A damaged outline loses the bookmarks, not the book.
      }
      self.postMessage({ id: msg.id, pages: pageInfo(), outline });
      return;
    }
    if (!doc) throw new Error('No book was opened.');
    if (msg.type === 'render') {
      const out = withPage(msg.page, (p) => ({ width: p.width_at(msg.dpi), height: p.height_at(msg.dpi), rgba: p.render(msg.dpi) }));
      self.postMessage({ id: msg.id, ...out }, [out.rgba.buffer]);
    } else if (msg.type === 'text') {
      const out = withPage(msg.page, (p) => ({ text: p.text() ?? '', zones: JSON.parse(p.text_zones_json(msg.dpi) ?? '[]') }));
      self.postMessage({ id: msg.id, ...out });
    } else if (msg.type === 'texts') {
      const texts = [];
      for (let i = 0; i < doc.page_count(); i++) {
        try {
          texts.push(withPage(i, (p) => p.text() ?? ''));
        } catch {
          texts.push('');
        }
      }
      self.postMessage({ id: msg.id, texts });
    } else if (msg.type === 'pdf') {
      const pdf = export_pdf(bytes, msg.start, msg.end, msg.quality, msg.dpi, msg.g4, (done, total) =>
        self.postMessage({ id: msg.id, progress: { done, total } }),
      );
      self.postMessage({ id: msg.id, pdf }, [pdf.buffer]);
    }
  } catch (err) {
    self.postMessage({ id: msg.id, error: String(err?.message || err) });
  }
};