import { promises as fs } from "node:fs";
import os from "node:os";
import path from "node:path";
import { runFfmpeg, ffprobeDuration } from "../ffmpeg";

/**
 * Concatenate per-segment MP3 buffers into one normalized episode MP3.
 *
 * Segments are re-encoded (not stream-copied) through a single libmp3lame pass
 * with loudness normalization, which guarantees a uniform codec/bitrate and
 * avoids the header/timestamp glitches that `-c copy` concat can produce.
 */
export async function stitchMp3(
  segments: Buffer[]
): Promise<{ data: Buffer; durationSec: number | null }> {
  if (segments.length === 0) throw new Error("No audio segments to stitch");

  const dir = await fs.mkdtemp(path.join(os.tmpdir(), "podcastyes-"));
  try {
    const files: string[] = [];
    for (let i = 0; i < segments.length; i++) {
      const file = path.join(dir, `seg_${String(i).padStart(4, "0")}.mp3`);
      await fs.writeFile(file, segments[i]);
      files.push(file);
    }

    // concat demuxer list — forward slashes so it parses on Windows and Linux.
    const listPath = path.join(dir, "list.txt");
    const listBody = files
      .map((f) => `file '${f.split(path.sep).join("/").replace(/'/g, "'\\''")}'`)
      .join("\n");
    await fs.writeFile(listPath, listBody);

    const outPath = path.join(dir, "episode.mp3");
    await runFfmpeg([
      "-y",
      "-f",
      "concat",
      "-safe",
      "0",
      "-i",
      listPath,
      "-af",
      "loudnorm=I=-16:TP=-1.5:LRA=11",
      "-c:a",
      "libmp3lame",
      "-b:a",
      "128k",
      "-ar",
      "44100",
      outPath,
    ]);

    const data = await fs.readFile(outPath);
    const durationSec = await ffprobeDuration(outPath);
    return { data, durationSec };
  } finally {
    await fs.rm(dir, { recursive: true, force: true }).catch(() => {});
  }
}