src/services/audioConversionService.js

import { promises as fs } from "node:fs";
import os from "node:os";
import path from "node:path";
import { spawn } from "node:child_process";
import ffmpegPath from "ffmpeg-static";
import { HttpError } from "../utils/httpError.js";

function runFfmpeg(inputPath, outputPath, outputArgs) {
  return new Promise((resolve, reject) => {
    const child = spawn(ffmpegPath, [
      "-y",
      "-i",
      inputPath,
      "-vn",
      ...outputArgs,
      outputPath
    ]);

    let stderr = "";

    child.stderr.on("data", (chunk) => {
      stderr += chunk.toString();
    });

    child.on("error", (error) => {
      reject(new HttpError(400, "Failed to convert audio to mp3.", error.message));
    });
    child.on("close", (code) => {
      if (code === 0) {
        resolve();
        return;
      }

      reject(new HttpError(400, "Failed to convert audio to mp3.", stderr.trim() || undefined));
    });
  });
}

export function createAudioConversionService({ fetchImpl = fetch, maxAudioDownloadMb = 25 } = {}) {
  const maxBytes = maxAudioDownloadMb * 1024 * 1024;

  return {
    async downloadAndConvertToMp3Base64(url) {
      const parsedUrl = new URL(url);
      if (!["http:", "https:"].includes(parsedUrl.protocol)) {
        throw new HttpError(400, "Audio URL must use http or https.");
      }

      const response = await fetchImpl(url);
      if (!response.ok) {
        throw new HttpError(400, `Failed to download audio URL: ${response.status} ${response.statusText}`);
      }

      const audioBuffer = Buffer.from(await response.arrayBuffer());
      if (audioBuffer.length > maxBytes) {
        throw new HttpError(413, `Audio URL exceeded ${maxAudioDownloadMb}MB download limit.`);
      }

      const inputFormat = inferAudioFormatFromUrl(url) || inferAudioFormatFromMimeType(response.headers.get("content-type")) || "unknown";
      return transcodeAudioBuffer(audioBuffer, inputFormat);
    },

    async normalizeBase64Audio({ data, format }) {
      const audioBuffer = Buffer.from(data, "base64");
      if (audioBuffer.length === 0) {
        throw new HttpError(400, "Audio input must include base64 data.");
      }

      if (audioBuffer.length > maxBytes) {
        throw new HttpError(413, `Audio input exceeded ${maxAudioDownloadMb}MB upload limit.`);
      }

      if (!["mp3", "wav", "m4a"].includes(format)) {
        throw new HttpError(400, "Audio input format must be mp3, wav, or m4a.");
      }

      try {
        return await transcodeAudioBuffer(audioBuffer, format);
      } catch (error) {
        if (error instanceof HttpError) {
          throw error;
        }

        throw new HttpError(400, `Failed to normalize audio input as ${format}.`, error.message);
      }
    }
  };

  async function transcodeAudioBuffer(audioBuffer, inputFormat) {
    const tempDir = await fs.mkdtemp(path.join(os.tmpdir(), "oapix-audio-"));
    const normalizedInputFormat = normalizeInputFormat(inputFormat);
    const inputPath = path.join(tempDir, `input-media.${normalizedInputFormat === "unknown" ? "bin" : normalizedInputFormat}`);
    const outputPath = path.join(tempDir, "output.mp3");

    try {
      console.log(`audio conversion started: format=${normalizedInputFormat}, target=mp3`);
      await fs.writeFile(inputPath, audioBuffer);
      await runFfmpeg(inputPath, outputPath, ffmpegOutputArgs());
      const convertedBuffer = await fs.readFile(outputPath);
      console.log(`audio conversion successful: format=${normalizedInputFormat}->mp3`);

      return {
        data: convertedBuffer.toString("base64"),
        format: "mp3"
      };
    } catch (error) {
      const detail = error instanceof Error ? error.message : String(error);
      console.error(`audio conversion failed: format=${normalizedInputFormat}, target=mp3, error=${detail}`);
      throw error;
    } finally {
      await fs.rm(tempDir, { force: true, recursive: true });
    }
  }
}

function ffmpegOutputArgs() {
  return ["-acodec", "libmp3lame", "-q:a", "4"];
}

function inferAudioFormatFromUrl(url) {
  try {
    const pathname = new URL(url).pathname.toLowerCase();

    if (pathname.endsWith(".m4a")) {
      return "m4a";
    }

    if (pathname.endsWith(".wav")) {
      return "wav";
    }

    if (pathname.endsWith(".mp3")) {
      return "mp3";
    }
  } catch (_error) {
    return "unknown";
  }

  return "unknown";
}

function inferAudioFormatFromMimeType(mimeType) {
  const value = String(mimeType || "").split(";")[0].trim().toLowerCase();

  if (value === "audio/mp4" || value === "audio/x-m4a") {
    return "m4a";
  }

  if (value === "audio/wav" || value === "audio/x-wav") {
    return "wav";
  }

  if (value === "audio/mpeg" || value === "audio/mp3") {
    return "mp3";
  }

  return "unknown";
}

function normalizeInputFormat(format) {
  return ["m4a", "wav", "mp3"].includes(format) ? format : "unknown";
}