"""Converte um WAV PCM 8 ou 16 bits (mono ou estereo) em WAV estereo de 16 bits, para o wav2ogg (Builds/pygame-music).

Uso: python3 -I wav2stereo.py entrada.wav saida.wav
Mono vira estereo com o mesmo sinal nos dois canais (o Vorbis codifica isso quase de graca)."""
import struct
import sys


def main(src: str, dst: str) -> None:
    data = open(src, "rb").read()
    if data[:4] != b"RIFF" or data[8:12] != b"WAVE":
        raise SystemExit(f"{src}: nao e WAV")
    pos, fmt, pcm = 12, None, None
    while pos + 8 <= len(data):
        tag, size = data[pos:pos + 4], struct.unpack("<I", data[pos + 4:pos + 8])[0]
        body = data[pos + 8:pos + 8 + size]
        if tag == b"fmt ":
            fmt = struct.unpack("<HHIIHH", body[:16])
        elif tag == b"data":
            pcm = body
        pos += 8 + size + (size & 1)
    if fmt is None or pcm is None:
        raise SystemExit(f"{src}: sem fmt/data")
    encoding, channels, rate, _, _, bits = fmt
    if encoding != 1 or bits not in (8, 16) or channels not in (1, 2):
        raise SystemExit(f"{src}: so PCM 8/16 bits mono/estereo (encoding={encoding} canais={channels} bits={bits})")
    if bits == 8:
        # 8 bits e sem sinal: vira 16 bits com sinal.
        pcm = b"".join(struct.pack("<h", (b - 128) << 8) for b in pcm)
    if channels == 1:
        pcm = pcm[: len(pcm) // 2 * 2]
        out = bytearray(len(pcm) * 2)
        for i in range(0, len(pcm), 2):
            out[i * 2:i * 2 + 2] = pcm[i:i + 2]
            out[i * 2 + 2:i * 2 + 4] = pcm[i:i + 2]
        pcm = bytes(out)
    header = b"RIFF" + struct.pack("<I", 36 + len(pcm)) + b"WAVE"
    header += b"fmt " + struct.pack("<IHHIIHH", 16, 1, 2, rate, rate * 4, 4, 16)
    header += b"data" + struct.pack("<I", len(pcm))
    open(dst, "wb").write(header + pcm)


if __name__ == "__main__":
    if len(sys.argv) != 3:
        raise SystemExit(__doc__)
    main(sys.argv[1], sys.argv[2])