import path from "node:path";
import { labelFor, resolveInRoots } from "./paths";
import { probeMedia } from "./media";
import { projectRef } from "./projects";

// ---------------------------------------------------------------------------
// A deep link into /mix.
//
// Resolved SERVER-SIDE, in the page, which is why this feature needs no
// useSearchParams and no Suspense boundary -- app/mix/page.tsx is a server
// component that simply did not read searchParams before.
//
// REFUSE, NEVER CLAMP. A body outside the roots produces a bench with no preset
// and a visible reason. Silently opening a DIFFERENT file than the link named is
// the one outcome worse than an error, and lib/mix.ts already takes this line
// for the same reason.
// ---------------------------------------------------------------------------

export type MixPreset = {
  body: string;
  label: string;
  start: number;
  end: number;
  duration: number;
  hasAudio: boolean;
  /** Where the link came from, for the back-crumb. Never used to resolve media. */
  from: string | null;
  fromHref: string | null;
  clip: string | null;
  /** The file's own span, so "there is more material here" is visible. */
  fileFrom: number;
  fileTo: number;
};

export type MixRefusal = { reason: string };

export async function resolvePreset(params: {
  body?: string;
  start?: string;
  end?: string;
  from?: string;
  clip?: string;
}): Promise<MixPreset | MixRefusal | null> {
  if (!params.body) return null;

  const abs = resolveInRoots(params.body);
  if (!abs) return { reason: `that file is not inside any known root: ${params.body}` };

  let info;
  try {
    info = await probeMedia(abs);
  } catch (e) {
    return { reason: `could not read it: ${e instanceof Error ? e.message : String(e)}` };
  }
  // A body with no audio fails at render time anyway (lib/mix.ts throws), so
  // say it now rather than after the numbers have been set.
  if (!info.hasAudio) return { reason: `${labelFor(abs)} has no audio track` };

  const num = (v: string | undefined) => {
    const n = Number(v);
    return Number.isFinite(n) && n >= 0 ? n : 0;
  };

  // `from` and `clip` are PROVENANCE, for the crumb and the header line. They
  // are deliberately not used to resolve the media -- that would be a second,
  // divergent resolver for the thing this one already did.
  const project = params.from ? await projectRef(params.from) : null;

  // The file's own span, when its name carries one. A raw clip is
  // <video>_<from>-<to>.mp4, so the bench can say "this file runs 0–31.4s"
  // rather than leaving the material outside the window looking unreachable.
  const m = /_(\d+(?:\.\d+)?)-(\d+(?:\.\d+)?)\.mp4$/.exec(path.basename(abs));
  const fileFrom = m ? Number(m[1]) : 0;

  return {
    body: abs,
    label: labelFor(abs),
    start: num(params.start),
    end: num(params.end),
    duration: info.duration,
    hasAudio: info.hasAudio,
    from: project?.id ?? null,
    fromHref: project ? `/browse/${project.id}` : null,
    clip: params.clip ?? null,
    fileFrom,
    fileTo: fileFrom + info.duration,
  };
}

export const isRefusal = (v: MixPreset | MixRefusal | null): v is MixRefusal =>
  !!v && "reason" in v;