mtg_image_proxy.js

addEventListener("fetch", (event) => {
  event.respondWith(
    handleRequest(event).catch(
      (err) => new Response(err.stack, { status: 500 })
    )
  );
});

/**
 * Many more examples available at:
 *   https://developers.cloudflare.com/workers/examples
 */
async function handleRequest(event) {
  const { request } = event;
  const { pathname } = new URL(request.url);

  if (pathname.startsWith("/cardimage")) {
    let cardname = pathname.split("/")[2];
    let card_meta = await getCardMeta(cardname);
    if (card_meta == null) {
      return new Response("404 not found", {status: 404});
    }
    let cardset = card_meta.set;
    let cardnum = card_meta.collector_number;
    if (card_meta.image_uris == undefined) {
      return Response.redirect("https://api.scryfall.com/cards/named?format=image&exact=" + cardname, 302)
    }
    let fallbackimage = card_meta.image_uris.png || card_meta.image_uris.normal;
    let zhimage = await getZhCardImage(cardset, cardnum);
    if (zhimage != null) {
      return Response.redirect(zhimage, 302);
    }
    return Response.redirect(fallbackimage, 302)
  }

  return new Response("err", { status: 500 })
}

async function getCardMeta(cardname) {
  let meta_resp = await fetch("https://api.scryfall.com/cards/named?exact=" + cardname);
  if (meta_resp.status != 200) {
    return null;
  }
  return await meta_resp.json();
}

async function getZhCardImage(cardset, cardnum) {
  let apiurl = "https://api.scryfall.com/cards/"
      + cardset + "/"
      + new String(cardnum) + "/zhs";
  let resp = await fetch(apiurl);
  let body = await resp.json();
  if (resp.status != 200) {
    return null;
  }
  if (body.image_status == "placeholder") {
    return null;
  }
  return body.image_uris && body.image_uris.png || body.image_uris.normal;
}