"""Light noise reduction via ffmpeg's afftdn filter.

Use cases:
- Recordings with hiss (cheap mic preamp, RF interference)
- Recordings with AC hum (50/60Hz line noise — there's a separate `hum` filter
  for that, not implemented here)
- Tapes digitized with analog tape hiss

The `afftdn` filter is ffmpeg's built-in adaptive FFT denoiser. It's
lightweight (CPU-friendly) and good for gentle hiss removal without
artifacting speech. For heavy noise, consider a real denoiser like
RNNoise or DeepFilterNet — out of scope for sermon-clean.
"""

from __future__ import annotations

import subprocess
from dataclasses import dataclass
from pathlib import Path


@dataclass
class DenoiseResult:
    output_path: Path
    noise_floor_db: float
    noise_reduction_db: float

    def to_dict(self) -> dict:
        return {
            "output_path": str(self.output_path),
            "noise_floor_db": self.noise_floor_db,
            "noise_reduction_db": self.noise_reduction_db,
        }


def denoise(
    src: Path,
    out: Path,
    *,
    noise_reduction_db: float = 12.0,
    noise_floor_db: float = -50.0,
) -> DenoiseResult:
    """Apply FFT-based noise reduction.

    Args:
        src: input audio file
        out: output audio file
        noise_reduction_db: how much to attenuate the noise component (dB).
            Higher = more aggressive. 12dB is a reasonable default; 20dB
            starts to artifact speech.
        noise_floor_db: expected level of the noise floor below which everything
            is considered noise. -50dB is conservative. If your recording has
            louder noise (e.g. AC hum at -35dB), set this higher.

    Returns:
        DenoiseResult with the measured parameters.
    """
    src = Path(src)
    out = Path(out)

    proc = subprocess.run([
        "ffmpeg", "-y", "-v", "error",
        "-i", str(src),
        "-af", f"afftdn=nr={noise_reduction_db}:nf={noise_floor_db}",
        "-ar", "48000",  # output 48kHz to match normalize convention
        str(out),
    ], capture_output=True, text=True)

    if proc.returncode != 0:
        raise RuntimeError(f"denoise failed: {proc.stderr}")

    return DenoiseResult(
        output_path=out,
        noise_floor_db=noise_floor_db,
        noise_reduction_db=noise_reduction_db,
    )