Made of little things.

import { currentLevelOverlay, currentPackBuffer, fetchPackLink, installLevelOverlay, installPack, isGlb } from './assets.js';
import { assetDescriptor } from './onlineSession.js';
import { mismatch, type Descriptor } from './onlineProtocol.js';

const link = (hash: string, servers: string[] = []) => `blossom:${hash}?${new URLSearchParams(servers.map(s => ['xs', s]))}`;

export const onlineAssetIO = {
  descriptor: assetDescriptor,
  pack: currentPackBuffer,
  level: currentLevelOverlay,
  download: fetchPackLink,
  installPack,
  installLevel: installLevelOverlay,
  isGlb,
};

/** Download first, then rebuild atomically; failed or cancelled joins restore the old scene. */
export async function loadHostAssets(target: Descriptor, isActive: () => boolean, reload: () => Promise<void>, io = onlineAssetIO): Promise<Descriptor> {
  const local = await io.descriptor();
  if (!isActive()) throw new Error('Joining cancelled.');
  if (local.physics !== target.physics) throw new Error('Game versions differ. Open the same game release as the host.');
  const previousPack = io.pack(), previousLevel = io.level();
  const [pack, level] = await Promise.all([
    local.pack === target.pack ? Promise.resolve(previousPack) : io.download(link(target.pack, target.packServers)),
    target.level === null ? Promise.resolve(null)
      : local.level === target.level ? Promise.resolve(previousLevel) : io.download(link(target.level, target.levelServers)),
  ]);
  if (!isActive()) throw new Error('Joining cancelled.');
  if (!pack || io.isGlb(pack)) throw new Error('The host’s asset pack is not an .ssrcpack file.');
  if (level && !io.isGlb(level)) throw new Error('The host’s custom level is not a .glb file.');
  let installed = false;
  try {
    if (pack !== previousPack) { io.installPack(pack); installed = true; }
    io.installLevel(level);
    installed = true;
    const actual = await io.descriptor();
    const reason = mismatch(target, actual);
    if (reason) throw new Error('The downloaded game data does not match the host’s hashes.');
    if (!isActive()) throw new Error('Joining cancelled.');
    await reload();
    if (!isActive()) throw new Error('Joining cancelled.');
    return actual;
  } catch (error) {
    // A separate asset switch owns its own scene; do not overwrite it on cancellation.
    if (installed && io.pack() === pack && (io.level() === level || io.level() === null)) {
      if (previousPack) io.installPack(previousPack);
      io.installLevel(previousLevel);
      await reload();
    }
    throw error;
  }
}