import { flattenPages, type CanvasLike, type FlattenResult, type PdfDocLike } from "../pdf/flatten";

/** Lets the browser paint and handle input; falls back to a timer when rAF is paused (hidden window). */
export const yieldToBrowser = (): Promise<void> =>
  new Promise<void>((resolve) => {
    let done = false;
    const finish = () => {
      if (!done) {
        done = true;
        resolve();
      }
    };
    setTimeout(finish, 50);
    requestAnimationFrame(() => setTimeout(finish, 0));
  });

/** JPEG bytes of a canvas via the browser's encoder. */
export function encodeCanvasJpeg(canvas: CanvasLike, quality: number): Promise<Uint8Array> {
  return new Promise((resolve, reject) => {
    (canvas as unknown as HTMLCanvasElement).toBlob(
      (blob) => {
        if (!blob) return reject(new Error("the browser could not encode the page image (out of memory?)"));
        blob.arrayBuffer().then((buf) => resolve(new Uint8Array(buf)), reject);
      },
      "image/jpeg",
      quality,
    );
  });
}

export interface BrowserFlattenOptions {
  signal?: AbortSignal;
  onProgress?: (page: number, pages: number) => void;
}

/** Flattens PDF bytes at 300 DPI with pdf.js and a DOM canvas; opens and closes the document itself. */
export async function flattenInBrowser(bytes: Uint8Array, opts: BrowserFlattenOptions = {}): Promise<FlattenResult> {
  const { openPdf, closePdf } = await import("./pdfjs");
  const doc = await openPdf(bytes);
  try {
    return await flattenPages({
      pdf: doc as unknown as PdfDocLike,
      createCanvas: (width, height) => {
        const canvas = document.createElement("canvas");
        canvas.width = width;
        canvas.height = height;
        return canvas as unknown as CanvasLike;
      },
      encodeJpeg: encodeCanvasJpeg,
      yieldToUi: yieldToBrowser,
      signal: opts.signal,
      onProgress: opts.onProgress,
    });
  } finally {
    await closePdf(doc).catch(() => {});
  }
}