/**
 * The public half of an account: the profile record every ATProto account
 * keeps, and the picture in it.
 *
 * Read straight from the account's own PDS, like everything else this site
 * only reads (pds.ts). Not from an appview: it only knows accounts it has
 * indexed, and its CDN sends no `Access-Control-Allow-Origin` at all — which
 * the camo editor cannot live with, because it draws the avatar into a canvas
 * and reads the pixels back out. A blob from the PDS does send the header, and
 * it is the account's own copy of the picture.
 */

import { blobUrl, resolvePds } from "./pds";

/**
 * The two fields naming an account that this module needs.
 *
 * A `Session` is one of these and so is identity.ts's `Actor`: the signed-in
 * account and a player whose page is being read want the same name and the
 * same letter, and neither of them wants the rest of a session.
 */
export interface Named {
  readonly did: string;
  readonly handle: string | null;
}

/**
 * What to call an account on screen.
 *
 * A null handle means the handle in the DID document did not resolve back to
 * this DID, so it is not a name we are willing to put in front of anyone. The
 * DID is not friendly, but it is the account, and it is always true.
 */
export function accountName(session: Named): string {
  return session.handle ? `@${session.handle}` : session.did;
}

/** The one letter an account stands behind until its picture has loaded. */
export function monogram(session: Named): string {
  const source = session.handle ?? session.did.replace(/^did:[a-z]+:/, "");
  const letter = [...source].find((character) => /[a-z0-9]/i.test(character));
  return (letter ?? "?").toUpperCase();
}

/** The collection and rkey a profile is always at. */
const COLLECTION = "app.bsky.actor.profile";
const RKEY = "self";

/**
 * The avatar's CID, or null where the account has no picture.
 *
 * A modern blob carries `ref.$link`; ones written before the blob format
 * settled carry a bare `cid`. Both are still sitting in live repositories, so
 * both are read. Everything here comes off the network, so nothing is assumed
 * about its shape.
 */
export function avatarCid(value: unknown): string | null {
  if (typeof value !== "object" || value === null) return null;
  const avatar = (value as { avatar?: unknown }).avatar;
  if (typeof avatar !== "object" || avatar === null) return null;
  const ref = (avatar as { ref?: { $link?: unknown } }).ref;
  const cid = ref?.$link ?? (avatar as { cid?: unknown }).cid;
  return typeof cid === "string" && cid !== "" ? cid : null;
}

/**
 * Where to find an account's avatar, or null where there is no picture.
 *
 * The original upload, at whatever size it was uploaded — a PDS keeps no
 * resized copy, so this is a full-size image behind a 1.75rem masthead icon.
 * It is content-addressed and cached by the browser, so that costs the first
 * page load of a session and nothing after it.
 */
export async function avatarUrl(did: string): Promise<string | null> {
  const pds = await resolvePds(did);
  const url = new URL(`${pds}/xrpc/com.atproto.repo.getRecord`);
  url.searchParams.set("repo", did);
  url.searchParams.set("collection", COLLECTION);
  url.searchParams.set("rkey", RKEY);

  const response = await fetch(url);
  // An account that has never written a profile is answered with
  // RecordNotFound, which is a 400. That is an ordinary account, not a fault.
  if (response.status === 400) return null;
  if (!response.ok)
    throw new Error("Your account's profile could not be read.");

  const { value } = (await response.json()) as { value?: unknown };
  const cid = avatarCid(value);
  return cid ? blobUrl(pds, did, cid) : null;
}