import { NextResponse } from "next/server";
import { getPaths } from "yt-dlp-transcript-common/lib/paths";
import {
  computePulse,
  type PulsePayload,
} from "yt-dlp-transcript-common/views/pulse";
import { observeInputs } from "../../lib/liveInputs";
import { cleanableTotalBytes } from "../../cleanup/lib/loadCleanup";

// The change token the global AutoRefresh polls instead of blindly re-rendering
// the whole page tree every 5 seconds. The token itself is
// `common/views/pulse.ts`; `observeInputs()` is the observer's reads.
//
// ⚠️ THIS VIEW OBSERVES; IT MUST NEVER CONSTRUCT. That is now a property of
// the two functions it calls rather than a rule this file remembers — see the
// header of either one for the ~16 flaky specs that bought it, and
// `VIEW_CONTRACT.pulse` for the same promise stated where the dispatcher can
// be read against it. `views.test.ts` re-checks it as text.
//
// Everything on the idle path is either in-memory or a stat(). NO readdir, no
// corpus contact, no large JSON parse — asserted by e2e/pulse.spec.ts, because
// the entire point of this endpoint is that it is cheap enough to poll forever.
//
// It is the only view handler that reads the request: `?rev=` is the client's
// last token, and the fast path below is what makes an idle editor nearly free.
// The rewrite from `/api/pulse` is server-internal, so that query string
// arrives here unchanged.
export async function pulseView(request: Request): Promise<Response> {
  const known = new URL(request.url).searchParams.get("rev");
  const { rev, activeJobs, runningJobs, busy } = computePulse(observeInputs());

  // Idle fast path. The client already has this rev, so nothing it displays can
  // have changed — skip the only part of this endpoint that touches disk.
  if (known && known === rev) {
    return NextResponse.json({
      rev,
      changed: false,
      activeJobs,
      runningJobs,
      cleanableBytes: -1, // not recomputed; the client keeps its last value
      busy,
    } satisfies PulsePayload);
  }

  // Something moved: it's worth the ~40 ms to refresh the badge value too.
  // (Before the corpus walk was removed this number cost ~4.4 s, which is
  // precisely why it must never be on the idle path.)
  const cleanableBytes = await cleanableTotalBytes(getPaths());
  return NextResponse.json({
    rev,
    changed: true,
    activeJobs,
    runningJobs,
    cleanableBytes,
    busy,
  } satisfies PulsePayload);
}