import { mkdir, stat, writeFile } from "node:fs/promises";
import path from "node:path";
import { BROWSE_ROOT, isSegment, songDir } from "../browse";
import { writeSpec } from "../spec";

// Start a song. Moved verbatim from app/api/browse/init/route.ts, which this
// replaces; TypeScript because writeSpec is, and the CLI keeps refusing
// `--kind song` for the same reason it cannot compute the song reducer.
//
// The tree has been made by hand five times, and each time something was left
// out -- pokemon is the only one with a clips.csv, two have no vertical cut, and
// three have plan/ directories whose contents nobody can now attribute. This
// makes the shape once: the directories the scan expects, and a spec sheet with
// the song's name in it, so the very first thing the UI shows is a sheet to
// fill in rather than an empty page.
//
// It does NOT create empty cut files. A cut that does not exist must read as a
// hole in the set -- that is the whole reason the cut list is fixed rather than
// derived -- and a zero-byte wide.mp4 would read as a built one.

const README = (id: string, title: string) => `# ${title}

_New song, nothing built yet._

Fill in \`spec.json\` with what this song is made of — the background video, any
one-off sounds, the drum map, the vocal hooks, the arrangement. What is declared
there is what the browse UI will offer to do.

| file | |
|---|---|
| \`wide.mp4\` | not built |
| \`wide-short.mp4\` | not built |
| \`vertical.mp4\` | not built |
| \`vertical-short.mp4\` | not built |
`;

export class ScaffoldError extends Error {
  constructor(message: string, public status = 400) {
    super(message);
  }
}

export async function scaffoldSong({ slug, title }: { slug: string; title?: string | null }) {
  const id = (slug ?? "").trim().toLowerCase();
  if (!isSegment(id)) {
    throw new ScaffoldError("a song name is letters, digits, dots, dashes and underscores — no slashes");
  }
  const dir = songDir(id);
  // Containment check as well as the name check. songDir() joins under
  // BROWSE_ROOT, and isSegment() already rules out traversal, but a mkdir is
  // the first thing here that CREATES something and it gets both gates.
  if (dir !== path.join(BROWSE_ROOT, id)) throw new ScaffoldError("refusing to create outside the tree");
  if (await stat(dir).then(() => true, () => false)) throw new ScaffoldError(`${id} already exists`, 409);

  const finalTitle = (title ?? "").trim() || id;
  await mkdir(path.join(dir, "plan"), { recursive: true });
  await mkdir(path.join(dir, "variants"), { recursive: true });
  await writeFile(path.join(dir, "README.md"), README(id, finalTitle));
  const spec = await writeSpec(id, { version: 1, song: id, title: finalTitle });
  return { song: id, spec, href: `/browse/${id}` };
}