// IS ANYTHING WRITING INTO THIS CHANNEL'S MEDIA RIGHT NOW?
//
// One question, one answer, three callers: the per-channel Storage panel's
// actions, the bulk move from /channels, and the channel page that greys the
// buttons out with a reason. They each used to ask the job registry and only
// the job registry — and the registry is HALF the truth.
//
// THE OMNIMIRROR INCIDENT (2026-09-13) is the half that was missing. The
// auto-queue lanes run their units IN-PROCESS: "the auto-queue runner's
// per-video units are IN-PROCESS and make no job record" (operationBatch.ts's
// header says so, and that is deliberate — 119,600 job records would evict the
// registry). So a digest unit was writing a sidecar into `data/` while the
// relocate job's rsync was already past that directory; nothing in the registry
// named the channel, the move was allowed, and the copy's verify refused at the
// last step with 131 GB on the far side.
//
// `getAutoRunnerStatus(kind).inFlight[]` is the in-process half: one entry per
// reserved unit, each carrying the `channelSlug` it belongs to. Asking every
// lane is four map reads — no disk, no await — so this is cheap enough to call
// on a render.
//
// SERVER-SIDE ONLY. It reaches into the controller (which imports execa,
// transitively), so nothing reachable from a `"use client"` file may import it;
// `next build` is what proves that.

import {
  channelWriters,
  describeChannelWriter,
} from "yt-dlp-transcript-common/controller/channelWriters";
import { channelMediaWriters } from "yt-dlp-transcript-common/controller/relocateChannelMedia";

// A sentence naming what is holding the channel, or null when nothing is. The
// caller supplies the verb (`"moving its media"`) so the same reason reads as
// an instruction in every panel it appears in.
//
// THE COUNTS, THEN THE FIRST WRITER BY NAME (release 16 slice RM): "Finish or
// cancel 1 running/queued job(s) for this channel before moving its media.
// Now: a transcription of v50t5yt is running (Transcribe all, job 01M…)." The
// list is common/controller/channelWriters.ts's — the one the move's preview
// and its job's first step ask — with queued jobs counted here, because this is
// the courtesy before anything is enqueued. A lane's download unit is also a
// registry job; it is counted once, as the unit.
//
// `mediaOnly` (release 17): a MOVE of the media tier is held only by the
// channel's media writers — a digest may run during it (`channelMediaWriters`,
// the same list the move's preview and its first step ask). A rename or a
// delete moves or removes the whole channel and asks every writer.
export function channelMediaBusyReason(
  slug: string,
  what?: string,
  opts: { mediaOnly?: boolean } = {},
): string | null {
  const writers = opts.mediaOnly
    ? channelMediaWriters(slug, { includeQueued: true })
    : channelWriters(slug, { includeQueued: true });
  if (writers.length === 0) return null;
  const jobs = writers.filter((w) => w.source === "job").length;
  const units = writers.length - jobs;

  const parts: string[] = [];
  if (jobs > 0) parts.push(`${jobs} running/queued job(s)`);
  if (units > 0) parts.push(`${units} auto-queue unit(s) in flight`);
  const subject = `${parts.join(" and ")} for this channel`;
  const now = `Now: ${describeChannelWriter(writers[0])}.`;
  return what
    ? `Finish or cancel ${subject} before ${what}. ${now}`
    : `${subject}. ${now}`;
}