import shutil
import struct
import subprocess
from io import BytesIO


def _find_ffmpeg(configured: str = "ffmpeg") -> str:
    if shutil.which(configured):
        return configured
    try:
        from imageio_ffmpeg import get_ffmpeg_exe
        return get_ffmpeg_exe()
    except Exception:
        raise RuntimeError(
            "ffmpeg not found: install it on PATH, set runtime.ffmpeg_path "
            "in config.json, or `pip install imageio-ffmpeg`"
        ) from None


_SUPPORTED_FORMATS = {"mp3", "wav", "pcm", "opus", "aac", "flac"}

_CONTENT_TYPES = {
    "mp3": "audio/mpeg",
    "wav": "audio/wav",
    "pcm": "audio/pcm",
    "opus": "audio/opus",
    "aac": "audio/aac",
    "flac": "audio/flac",
}

_FFMPEG_CODECS = {
    "mp3": "libmp3lame",
    "opus": "libopus",
    "aac": "aac",
    "flac": "flac",
}


def pcm_to_wav(pcm: bytes, sample_rate: int = 24000) -> bytes:
    data_size = len(pcm)
    byte_rate = sample_rate * 2
    header = struct.pack(
        "<4sI4s4sI4sI",
        b"RIFF",
        36 + data_size,
        b"WAVE",
        b"fmt ",
        16,
        b"data",
        data_size,
    )
    fmt = struct.pack("<HHIIHH", 1, 1, sample_rate, byte_rate, 2, 16)
    return header[:20] + fmt + header[20:] + pcm


def pcm_to_raw(pcm: bytes) -> bytes:
    return pcm


def pcm_to_ffmpeg(
    pcm: bytes, fmt: str, sample_rate: int = 24000, ffmpeg_path: str = "ffmpeg"
) -> bytes:
    codec = _FFMPEG_CODECS.get(fmt)
    if codec is None:
        raise ValueError(f"Unsupported ffmpeg format: {fmt}")

    cmd = [
        ffmpeg_path, "-y",
        "-f", "s16le",
        "-ar", str(sample_rate),
        "-ac", "1",
        "-i", "pipe:0",
        "-f", _ffprobe_fmt(fmt),
        "-codec:a", codec,
        "pipe:1",
    ]

    proc = subprocess.run(
        cmd,
        input=pcm,
        stdout=subprocess.PIPE,
        stderr=subprocess.PIPE,
    )
    if proc.returncode != 0:
        raise RuntimeError(f"ffmpeg failed: {proc.stderr.decode(errors='replace')}")
    return proc.stdout


def _ffprobe_fmt(fmt: str) -> str:
    return {"mp3": "mp3", "opus": "opus", "aac": "adts", "flac": "flac"}.get(fmt, fmt)


def encode(pcm: bytes, fmt: str, sample_rate: int = 24000, ffmpeg_path: str = "ffmpeg") -> tuple[bytes, str]:
    if fmt not in _SUPPORTED_FORMATS:
        raise ValueError(f"Unsupported response_format: {fmt}")

    if fmt == "wav":
        data = pcm_to_wav(pcm, sample_rate)
    elif fmt == "pcm":
        data = pcm
    else:
        data = pcm_to_ffmpeg(pcm, fmt, sample_rate, _find_ffmpeg(ffmpeg_path))

    return data, _CONTENT_TYPES[fmt]