import { download } from './imageOps';

// Posting the export to a social site. A page cannot reach into another
// origin's composer: the cookie is the browser's to send, never ours to read,
// and the window we open has no DOM we may touch — which is the same rule that
// keeps any other site from posting as the visitor. So there is no way to drop
// the picture into the site's own picker from here. Two things do work, and
// this takes the best one the browser offers:
//
//   sheet     on a phone the OS share sheet opens and the target app —
//             Facebook, Instagram, Reddit — comes up with the picture already
//             in its composer. Only the caption is left to type.
//   clipboard the desktop path: the picture goes on the clipboard and the site
//             opens beside it, so one paste (Ctrl+V) puts it in the composer.
//   download  no share sheet and no clipboard — an http origin is not a secure
//             context, so the API is not even there: the file is handed over the
//             old way and the site opens beside it.
//
// ponytail: the four sites are listed here rather than in a config file. Add a
// network when someone asks for one; these three paths serve any site alike.
export const SHARE_SITES = {
  facebook: 'https://www.facebook.com/',
  instagram: 'https://www.instagram.com/',
  reddit: 'https://www.reddit.com/submit',
  x: 'https://x.com/compose/post',
} as const;

export type ShareSite = keyof typeof SHARE_SITES;

export type SharePath = 'sheet' | 'clipboard' | 'download';

// The clipboard takes PNG in every engine — Chromium silently refuses a JPEG —
// so the file is drawn to a canvas once. No resample: the bytes handed in are
// already the size the visitor chose.
async function pngOf(file: File): Promise<Blob> {
  const bitmap = await createImageBitmap(file);
  const canvas = document.createElement('canvas');
  canvas.width = bitmap.width;
  canvas.height = bitmap.height;
  const ctx = canvas.getContext('2d');
  if (!ctx) throw new Error('no 2d context');
  ctx.drawImage(bitmap, 0, 0);
  bitmap.close();
  return await new Promise<Blob>((resolve, reject) =>
    canvas.toBlob((b) => (b ? resolve(b) : reject(new Error('toBlob failed'))), 'image/png')
  );
}

export async function sharePhoto(bytes: Uint8Array, filename: string, site: ShareSite): Promise<SharePath> {
  const file = new File([bytes as BlobPart], filename, { type: 'image/jpeg' });
  // A phone is the only place the picture reaches the target app on its own:
  // the sheet hands the file over and that app owns its own composer.
  if (navigator.canShare?.({ files: [file] })) {
    try {
      await navigator.share({ files: [file] });
    } catch (err) {
      // The sheet was closed: a "not now", not a failure, and nothing else opens
      // on top of the choice the visitor just made.
      if (!(err instanceof DOMException && err.name === 'AbortError')) throw err;
    }
    return 'sheet';
  }
  try {
    await navigator.clipboard.write([new ClipboardItem({ 'image/png': await pngOf(file) })]);
    window.open(SHARE_SITES[site], '_blank', 'noopener');
    return 'clipboard';
  } catch {
    window.open(SHARE_SITES[site], '_blank', 'noopener');
    download(bytes, filename);
    return 'download';
  }
}