/**
 * Resolves the dump whose media a route under `/api/dumps/:dumpId/` serves:
 * its file (`routes/files.ts`), its thumbnail (`routes/thumbnails.ts`) or its
 * waveform (`routes/waveforms.ts`). Media elements and `<img>`s can't send an
 * Authorization header, so these routes take the viewer's media token from
 * the query string, and are cached by the file's version.
 *
 * @module
 */

import type { Context } from "@oak/oak";
import { APIException } from "./api-exception.ts";
import { authenticateMedia } from "./auth.ts";
import { type Dump, dumpFileVersion } from "../../shared/dump.ts";
import { UUID_RE } from "../../shared/validation.ts";
import { getDump } from "../services/dump-service.ts";

/**
 * Returns dump `dumpId` as the viewer of `ctx`'s `?token=` may see it, and the
 * Cache-Control its media get: kept for good under a URL naming the file's
 * current version (`?v=`, as `dumpFileVersion` gives), revalidated under any
 * other, and never in a shared cache for a private dump. It also keeps the
 * token out of the Referer of whatever the response links to.
 *
 * @throws {APIException} 400 when `dumpId` isn't an id, which names files on
 * disk, and 404 when the viewer can't see the dump.
 */
export async function resolveMediaDump(
  ctx: Context,
  dumpId: string,
): Promise<{ dump: Dump; cacheControl: string }> {
  if (!UUID_RE.test(dumpId)) throw new APIException(400, "Invalid dump ID");
  const token = ctx.request.url.searchParams.get("token");
  const viewerId = token ? await authenticateMedia(token) : null;
  const dump = getDump(dumpId, viewerId ?? undefined);
  ctx.response.headers.set("Referrer-Policy", "no-referrer");
  const scope = dump.isPrivate ? "private" : "public";
  const current = ctx.request.url.searchParams.get("v") ===
    dumpFileVersion(dump);
  return {
    dump,
    cacheControl: current
      ? `${scope}, max-age=31536000, immutable`
      : `${scope}, no-cache`,
  };
}