"""Gap 13: BWF/INFO metadata chunks cho WAV export (EBU Tech 3285 + RIFF INFO).

sf.write chi ghi fmt/data — ham nay chen bext (602 bytes fixed + coding history)
va LIST/INFO (INAM title, IART artist, ISRC, ICMT comment) ngay truoc data chunk
roi ghi lai file. Pure stdlib (struct/datetime).
"""
import datetime
import struct

_BEXT_FIXED = 602


def _pad(text, length):
    raw = text.encode("utf-8", errors="replace")
    return (raw[:length] + b"\x00" * length)[:length]


def _chunk(fourcc, payload):
    pad = b"\x00" if len(payload) % 2 else b""
    return fourcc + struct.pack("<I", len(payload)) + payload + pad


def _info_sub(fourcc, text):
    if not text:
        return b""
    return _chunk(fourcc, _pad(text, len(text.encode("utf-8", errors="replace")) + 1))


def _bext(md, now):
    fixed = bytearray(_BEXT_FIXED)
    fixed[0:256] = _pad(md.get("description", ""), 256)
    fixed[256:288] = _pad(md.get("originator", "ScoreFXStudio"), 32)
    fixed[288:320] = _pad(md.get("originator_reference", ""), 32)
    fixed[320:330] = _pad((md.get("date") or now.strftime("%Y-%m-%d")), 10)
    fixed[330:338] = _pad((md.get("time") or now.strftime("%H:%M:%S")), 8)
    struct.pack_into("<II", fixed, 338, 0, 0)          # time reference low/high
    struct.pack_into("<H", fixed, 346, 1)              # version = 1
    fixed[348:412] = bytes(64)                         # UMID (zero)
    struct.pack_into("<hhhhh", fixed, 412, -32768, -32768, -32768, -32768, -32768)  # loudness: 0x8000 = unset
    fixed[422:602] = bytes(180)                        # reserved
    coding = md.get("coding_history", "").encode("utf-8", errors="replace")
    return bytes(fixed) + coding


def patch_bwf_metadata(path, metadata=None):
    """Chen bext + LIST/INFO vao WAV tai path (rewrite in-place, giu nguyen PCM bits).

    metadata keys: title, artist, isrc, comment, description, originator,
    originator_reference, date (YYYY-MM-DD), time (HH:MM:SS), coding_history.
    Bo qua neu file khong phai RIFF/WAVE hop le hoac metadata rong.
    """
    if not metadata:
        return
    md = {k: (v or "").strip() for k, v in metadata.items() if v}
    if not md:
        return
    with open(path, "rb") as f:
        data = f.read()
    if len(data) < 12 or data[:4] != b"RIFF" or data[8:12] != b"WAVE":
        return

    off = 12
    pre = b""
    data_chunk = None
    while off + 8 <= len(data):
        cid = data[off:off + 4]
        size = struct.unpack("<I", data[off + 4:off + 8])[0]
        body = data[off + 8:off + 8 + size]
        if cid == b"data":
            data_chunk = (cid, size, body)
            break
        pre += _chunk(cid, body)
        off += 8 + size + (size % 2)
    if data_chunk is None:
        return

    now = datetime.datetime.now()
    info_payload = b"INFO" + b"".join([
        _info_sub(b"INAM", md.get("title", "")),
        _info_sub(b"IART", md.get("artist", "")),
        _info_sub(b"ISRC", md.get("isrc", "")),
        _info_sub(b"ICMT", md.get("comment", "")),
    ])
    extra = _chunk(b"bext", _bext(md, now)) + _chunk(b"LIST", info_payload)
    new_data = data[:12] + pre + extra + _chunk(data_chunk[0], data_chunk[2])
    new_data = new_data[:4] + struct.pack("<I", len(new_data) - 8) + new_data[8:]
    with open(path, "wb") as f:
        f.write(new_data)