"""Create peak-normalized listening copies of PCM16 or float32 capture WAVs.

Usage: py tools/audio_preview.py out/audio/single-450-baseline
Original files retain calibration; preview levels must not be compared by source.
"""
import argparse
import math
from pathlib import Path
import struct
import wave


def preview(path, destination):
    data = path.read_bytes()
    if data[:4] != b"RIFF" or data[8:12] != b"WAVE":
        raise ValueError(f"Not a WAV: {path}")
    offset = 12
    fmt = payload = None
    while offset + 8 <= len(data):
        tag, size = struct.unpack_from("<4sI", data, offset)
        chunk = data[offset + 8:offset + 8 + size]
        if tag == b"fmt ":
            fmt = struct.unpack_from("<HHIIHH", chunk)
        elif tag == b"data":
            payload = chunk
        offset += 8 + size + size % 2
    if fmt is None or payload is None:
        raise ValueError(f"Missing WAV chunks: {path}")
    encoding, channels, rate, _, _, bits = fmt
    if (encoding, bits) == (3, 32):
        values = [x[0] for x in struct.iter_unpack("<f", payload)]
    elif (encoding, bits) == (1, 16):
        values = [x[0] / 32768 for x in struct.iter_unpack("<h", payload)]
    else:
        raise ValueError(f"Unsupported WAV format: {path}")
    if not all(math.isfinite(x) for x in values):
        raise ValueError(f"Nonfinite audio: {path}")
    peak = max(map(abs, values), default=0)
    if peak == 0:
        print(f"{path.name}: silent; no preview")
        return
    gain = 0.8 / peak
    destination.mkdir(parents=True, exist_ok=True)
    target = destination / (path.stem + "-preview.wav")
    with wave.open(str(target), "wb") as out:
        out.setparams((channels, 2, rate, 0, "NONE", "not compressed"))
        out.writeframes(b"".join(struct.pack("<h", round(x * gain * 32767)) for x in values))
    print(f"{target.name}: gain {20 * math.log10(gain):+.1f} dB")


if __name__ == "__main__":
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument("prefix", type=Path)
    args = parser.parse_args()
    paths = sorted(args.prefix.parent.glob(args.prefix.name + "-*.wav"))
    if not paths:
        parser.error("no matching capture WAVs")
    for path in paths:
        preview(path, args.prefix.parent / "previews")