import sharp from "sharp";
import { BlobRef } from "@atproto/api";
import { fetchAtprotoBlob } from "app/api/atproto_images/route";

// Flattened onto an opaque background because link-card consumers (notably the
// Bluesky composer, which re-encodes og:image through a canvas as JPEG)
// composite transparent pixels onto black, turning dark line art on a
// transparent cover into a solid black card.
export function coverImageCardPipeline(
  bytes: ArrayBuffer | Buffer,
  size: { width: number; height: number },
) {
  return sharp(bytes)
    .resize({ ...size, fit: "cover" })
    .flatten({ background: "#ffffff" });
}

// Fetch a document's cover image from its author's PDS. Returns null when
// there's no cover image or the fetch fails.
export async function fetchCoverImageBytes(
  coverImage: BlobRef | undefined,
  authorDid: string | undefined,
): Promise<ArrayBuffer | null> {
  if (!coverImage || !authorDid) return null;

  let cid =
    (coverImage.ref as unknown as { $link: string })["$link"] ||
    coverImage.ref.toString();

  let coverImageResponse = await fetchAtprotoBlob(authorDid, cid);
  if (!coverImageResponse) return null;
  return await (await coverImageResponse.blob()).arrayBuffer();
}

// Fetch a document's cover image from its author's PDS, resize it to a Bluesky
// external-card thumbnail (1200x630 webp), and upload it via `uploadThumb`.
// The blob is uploaded to whichever repo `uploadThumb` targets, which is the
// post author's — not necessarily the cover image's author, since a viewer
// cross-posting someone else's post uploads the thumb to their own repo.
//
// Returns null when there's no cover image or any step fails so callers degrade
// to a card without a thumbnail rather than failing the post.
export async function uploadCoverImageThumb<T>(
  coverImage: BlobRef | undefined,
  authorDid: string | undefined,
  uploadThumb: (bytes: Buffer) => Promise<T>,
): Promise<T | null> {
  let bytes = await fetchCoverImageBytes(coverImage, authorDid);
  if (!bytes) return null;

  try {
    let resizedImage = await coverImageCardPipeline(bytes, {
      width: 1200,
      height: 630,
    })
      .webp({ quality: 85 })
      .toBuffer();
    return await uploadThumb(resizedImage);
  } catch (e) {
    console.error("Failed to process bsky card thumbnail:", e);
    return null;
  }
}