import { getDocument, GlobalWorkerOptions, type PDFDocumentProxy, type PDFPageProxy, type RenderTask } from "pdfjs-dist";
import { installStreamAsyncIterator } from "./streamPolyfill";

GlobalWorkerOptions.workerSrc = new URL("pdfjs-dist/build/pdf.worker.min.mjs", import.meta.url).toString();
installStreamAsyncIterator();

export type { PDFDocumentProxy, PDFPageProxy };

/**
 * Opens PDF bytes. The bytes are copied because pdf.js transfers the buffer to its worker, which
 * would detach the caller's array. Glyphs are drawn as paths (`disableFontFace`) so the preview looks
 * the same on WebKitGTK and WebView2. (pdf.js 6 dropped `isEvalSupported`; it no longer evaluates font code.)
 */
export function openPdf(bytes: Uint8Array): Promise<PDFDocumentProxy> {
  return getDocument({ data: bytes.slice(), disableFontFace: true }).promise;
}

/** Releases the document and its worker resources. */
export function closePdf(doc: PDFDocumentProxy): Promise<void> {
  return doc.loadingTask.destroy();
}

const tasks = new WeakMap<object, RenderTask>();

/** Cancels whatever render is running for `slot` (a canvas, or any object the caller keys on). */
export function cancelPageRender(slot: object): void {
  tasks.get(slot)?.cancel();
  tasks.delete(slot);
}

/**
 * Draws `page` into `canvas` at `scale` device pixels per PDF point, sizing the backing store to
 * match. Starting a render for a slot cancels its previous one; a cancelled render rejects with
 * pdf.js's RenderingCancelledException (see isRenderCancelled).
 */
export async function renderPageToCanvas(page: PDFPageProxy, canvas: HTMLCanvasElement, scale: number, slot: object = canvas): Promise<void> {
  cancelPageRender(slot);
  const viewport = page.getViewport({ scale });
  canvas.width = Math.ceil(viewport.width);
  canvas.height = Math.ceil(viewport.height);
  const task = page.render({ canvas, viewport });
  tasks.set(slot, task);
  try {
    await task.promise;
  } finally {
    if (tasks.get(slot) === task) tasks.delete(slot);
  }
}

export const isRenderCancelled = (err: unknown): boolean => (err as { name?: string } | null)?.name === "RenderingCancelledException";