# app/services/export.py — Stitch committed spine audio files via ffmpeg
#
# Uses ffmpeg concat demuxer (list-form args, no shell injection).
# WAV output: copy codec. MP3 output: libmp3lame 320k.
from __future__ import annotations

import asyncio
import logging
import os
import shutil
import tempfile
from pathlib import Path
from typing import Literal

logger = logging.getLogger(__name__)

ExportFormat = Literal["wav", "mp3"]


async def stitch(
    audio_paths: list[str],
    output_path: str,
    fmt: ExportFormat = "wav",
) -> str:
    """
    Concatenate audio_paths in order and write to output_path.

    Returns output_path on success. Raises RuntimeError on ffmpeg failure.
    Requires ffmpeg on PATH.
    """
    if not audio_paths:
        raise ValueError("No audio paths to stitch.")

    Path(output_path).parent.mkdir(parents=True, exist_ok=True)

    # Single file: just copy, no concatenation needed
    if len(audio_paths) == 1:
        shutil.copy2(audio_paths[0], output_path)
        return output_path

    # Write ffmpeg concat file list to a tempfile
    with tempfile.NamedTemporaryFile(
        mode="w", suffix=".txt", delete=False
    ) as flist:
        for p in audio_paths:
            # ffmpeg concat list format requires one "file '/abs/path'" per line
            flist.write(f"file '{p}'\n")
        flist_path = flist.name

    try:
        codec_args: list[str] = (
            ["-c:a", "copy"] if fmt == "wav"
            else ["-c:a", "libmp3lame", "-b:a", "320k"]
        )
        # create_subprocess_exec uses a list of args — no shell interpolation
        proc = await asyncio.create_subprocess_exec(
            "ffmpeg", "-y",
            "-f", "concat",
            "-safe", "0",
            "-i", flist_path,
            *codec_args,
            output_path,
            stdout=asyncio.subprocess.PIPE,
            stderr=asyncio.subprocess.PIPE,
        )
        _, stderr = await proc.communicate()
        if proc.returncode != 0:
            raise RuntimeError(
                f"ffmpeg concat failed (exit {proc.returncode}): {stderr.decode()}"
            )
    finally:
        os.unlink(flist_path)

    logger.info("Stitched %d files -> %s", len(audio_paths), output_path)
    return output_path


def make_export_path(data_dir: str, chain_id: str, fmt: ExportFormat) -> str:
    """Standard export output path."""
    return str(Path(data_dir) / "chains" / chain_id / f"export.{fmt}")