import { stat } from 'node:fs/promises';
import { resolve, sep } from 'node:path';
import { homedir } from 'node:os';

// All processing lives here (the platform is just a proxy). Files live under the owner's home — single
// super user, so HOME_DIR. Paths from the app are home-relative (e.g. "Music/Artist/Album/track.mp3"),
// exactly like file-browser /raw.
const ROOT_DIR = homedir();

const CONTENT_TYPES: Record<string, string> = {
  mp3: 'audio/mpeg',
  m4a: 'audio/mp4',
  mp4: 'audio/mp4',
  aac: 'audio/aac',
  flac: 'audio/flac',
  wav: 'audio/wav',
  ogg: 'audio/ogg',
  opus: 'audio/opus',
  wma: 'audio/x-ms-wma',
};

// NO ffprobe HERE, and no `X-Audio-Duration`.
//
// This used to shell out to ffprobe on the first request for each file — measured at 50ms warm and 315ms
// cold, paid before the first byte, once per file per sidecar restart. It filled a header that nothing in
// the web read, duplicating `durationSec` which the indexer already wrote into the album's `meta.json`
// and which every client fetches anyway to build its queue.
//
// Removed rather than cached harder: the fastest work is the work not done, and a second copy of a number
// is a second thing that can disagree.

/** Resolve a home-relative path within ROOT_DIR; null if it escapes (traversal). */
function resolveWithinRoot(relPath: string): string | null {
  const clean = relPath.replace(/^\/+/, '');
  const abs = resolve(ROOT_DIR, clean);
  if (abs !== ROOT_DIR && !abs.startsWith(ROOT_DIR + sep)) return null;
  return abs;
}

/** Serve an audio file with byte-range support and an mtime+size ETag. */
export async function streamAudioFile(
  relPath: string,
  rangeHeader: string | null,
  ifNoneMatch: string | null = null,
): Promise<Response> {
  const absPath = resolveWithinRoot(relPath);
  if (!absPath) return new Response('Invalid path', { status: 400 });

  let s;
  try {
    s = await stat(absPath);
  } catch {
    return new Response('Not found', { status: 404 });
  }
  if (!s.isFile()) return new Response('Not a file', { status: 404 });

  // TEMPORARY diagnostic (2026-08-29): iOS first-play issues ~28 range requests in 2 s where Android
  // issues one. This prints each request range so we can see WHICH bytes AVPlayer asks for — small
  // sequential chunks would mean a transport problem, scattered offsets a VBR duration scan.
  console.log(
    `[stream] ${new Date().toISOString().slice(11, 23)} ${rangeHeader ?? "FULL"} · ${relPath.slice(relPath.lastIndexOf("/") + 1)}`,
  );

  const total = s.size;
  const ext = absPath.slice(absPath.lastIndexOf('.') + 1).toLowerCase();
  const contentType = CONTENT_TYPES[ext] ?? 'application/octet-stream';
  const file = Bun.file(absPath);

  // An audio file's bytes do not change; a re-encode replaces the file, which moves mtime and size. So
  // the pair identifies the content, and a client that has played this track once can seek in it without
  // fetching anything again.
  //
  // This was the ONLY route with no validator at all — cover, meta, lyrics and poster have had one all
  // along — so every seek and every replay re-read the file over the network.
  const etag = `"${s.mtimeMs.toString(36)}-${total.toString(36)}"`;

  const baseHeaders: Record<string, string> = {
    'Content-Type': contentType,
    'Accept-Ranges': 'bytes',
    ETag: etag,
    // `no-cache` means "you may keep it, but ask first" — a conditional request rather than a blind
    // refetch. `private` because a member's library is not a proxy's to hold.
    'Cache-Control': 'private, no-cache',
  };

  // Whole-file revalidation. Deliberately NOT applied to a Range request: a 304 there would answer a
  // question about part of a file with a statement about all of it, and players handle that badly.
  if (!rangeHeader && ifNoneMatch === etag) {
    return new Response(null, { status: 304, headers: baseHeaders });
  }

  if (rangeHeader) {
    const m = rangeHeader.match(/bytes=(\d*)-(\d*)/);
    if (m) {
      const start = m[1] ? parseInt(m[1], 10) : 0;
      const end = m[2] ? parseInt(m[2], 10) : total - 1;
      if (Number.isNaN(start) || start < 0 || end >= total || start > end) {
        return new Response('Invalid range', { status: 416, headers: { 'Content-Range': `bytes */${total}` } });
      }
      return new Response(file.slice(start, end + 1), {
        status: 206,
        headers: {
          ...baseHeaders,
          'Content-Range': `bytes ${start}-${end}/${total}`,
          'Content-Length': String(end - start + 1),
        },
      });
    }
  }

  return new Response(file, { status: 200, headers: { ...baseHeaders, 'Content-Length': String(total) } });
}