/**
 * Serves an audio file dump's waveform, a sub-resource of its dump, for the
 * player to seek on. The frontend builds the URL with `dumpWaveformUrl`.
 * lib/ffmpeg.ts makes it from the upload on first request and keeps it, so a
 * listener downloads a few hundred bytes of peaks rather than the file a
 * second time to decode it.
 *
 * - `GET /api/dumps/:dumpId/waveform?v=&token=` — public; a private dump's
 *   waveform needs its poster's media `token`. Answers a `DumpWaveform`; 404
 *   when the dump isn't an audio file or its audio can't be read.
 *
 * @module
 */

import { Router } from "@oak/oak";
import { APIException } from "../lib/api-exception.ts";
import { DUMPS_DIR } from "../config.ts";
import { resolveMediaDump } from "../lib/dump-media.ts";
import {
  audioWaveform,
  ensureGenerated,
  generatedPaths,
} from "../lib/ffmpeg.ts";
import { serveFile } from "../lib/serve-file.ts";

/**
 * Mounted by `api/main.ts` behind the error, Open Graph and CORS middleware.
 * An `APIException` thrown by a handler becomes the JSON error response there.
 */
const router: Router = new Router({ prefix: "/api/dumps" });

router.get("/:dumpId/waveform", async (ctx) => {
  const { dump, cacheControl } = await resolveMediaDump(ctx, ctx.params.dumpId);
  if (dump.kind !== "file" || !dump.fileMime?.startsWith("audio/")) {
    throw new APIException(404, "No waveform for this dump");
  }

  const outPath = generatedPaths(dump.id).waveform;
  const srcPath = `${DUMPS_DIR}/${dump.id}`;
  if (
    !await ensureGenerated(outPath, () => audioWaveform(srcPath, outPath)) ||
    !await serveFile(ctx, outPath, { mime: "application/json", cacheControl })
  ) {
    throw new APIException(404, "Could not generate waveform");
  }
});

export default router;