import path from "node:path";
import { rename, rm } from "node:fs/promises";
import { execa } from "execa";
import type { Paths } from "../lib/paths";
import type { AudioFormat } from "../lib/channelConfig";
import { tierMediaFile } from "../lib/mediaTier-server";

const CODEC_ARGS: Record<AudioFormat, string[]> = {
  m4a: ["-c:a", "aac"],
  mp3: ["-c:a", "libmp3lame"],
  opus: ["-c:a", "libopus"],
};

export type TranscodeAudioOptions = {
  paths: Paths;
  videoDir: string;
  sourceFilename: string;
  targetFormat: AudioFormat;
  onLog: (s: string) => void;
  signal: AbortSignal;
};

export async function transcodeAudio(opts: TranscodeAudioOptions): Promise<void> {
  const src = path.join(opts.videoDir, opts.sourceFilename);
  const out = path.join(opts.videoDir, `audio.${opts.targetFormat}`);
  if (src === out) {
    throw new Error("Source and target are the same file");
  }
  // Keep the target extension last so ffmpeg can infer the output format.
  const tmp = path.join(
    opts.videoDir,
    `audio.tmp-${process.pid}.${opts.targetFormat}`,
  );
  const args = [
    "-y",
    "-i",
    src,
    "-vn",
    ...CODEC_ARGS[opts.targetFormat],
    tmp,
  ];
  opts.onLog(`$ ${opts.paths.ffmpegBin} ${args.join(" ")}\n`);
  const child = execa(opts.paths.ffmpegBin, args, {
    cancelSignal: opts.signal,
    all: true,
    buffer: false,
    reject: false,
  });
  child.all?.on("data", (c: Buffer) => opts.onLog(c.toString("utf8")));
  const result = await child;
  if (result.exitCode !== 0) {
    await rm(tmp, { force: true });
    if (opts.signal.aborted) return;
    throw new Error(`ffmpeg exited with code ${result.exitCode}`);
  }
  await rename(tmp, out);
  opts.onLog(`Wrote ${out}\n`);
  // THE MEDIA TIER'S HOOK (release 17). The rename above put a real file over
  // the name — over a tiered LINK, when the channel had one — so the fresh
  // file moves into channels/<slug>/media (over the stale copy there) and the
  // link is made again. Every finalising transcode is this function: the app
  // extraction, the audio-checked download, the video page's Transcode. Never
  // throws; on a classic channel it leaves the file where it is.
  await tierMediaFile(opts.videoDir, path.basename(out), { onLog: opts.onLog });
}