"""Unzip service — extract files from ZIP archive (no DB, no parse)."""
import zipfile, io, base64, os

MAX_FILES = 500
MAX_UNCOMPRESSED = 500 * 1024 * 1024  # 500 MB total
MAX_RATIO = 100  # max compression ratio (uncompressed/compressed)


def _sanitize_zip_name(name: str) -> str | None:
    """Decode cp437→utf8, strip path traversal, return safe name or None."""
    # Decode cp437 filenames (common in ZIPs from Windows)
    try:
        name = name.encode("cp437").decode("utf-8", errors="replace")
    except (UnicodeDecodeError, UnicodeEncodeError):
        pass
    # Strip directory prefixes and path traversal
    name = os.path.basename(name)
    if not name or name.endswith("/") or ".." in name or "/" in name or "\\" in name:
        return None
    return name


def handle_unzip(rfile, content_length):
    """Parse ZIP upload, return list of extracted files as base64."""
    body = rfile.read(content_length)

    # Find file data in raw multipart
    idx = body.find(b"\r\n\r\n")
    if idx < 0:
        return {"ok": False, "error": "invalid multipart"}

    raw = body[idx + 4:]
    zip_start = raw.find(b"PK\x03\x04")
    if zip_start < 0:
        return {"ok": False, "error": "not a ZIP file"}

    zip_data = raw[zip_start:]

    files = []
    total_uncompressed = 0
    with zipfile.ZipFile(io.BytesIO(zip_data)) as zf:
        namelist = zf.namelist()
        if len(namelist) > MAX_FILES:
            return {"ok": False, "error": f"too many files in ZIP (max {MAX_FILES})"}

        for info in zf.infolist():
            if info.is_dir():
                continue

            # ZIP bomb: compression ratio check
            if info.compress_size > 0:
                ratio = info.file_size / info.compress_size
                if ratio > MAX_RATIO:
                    return {"ok": False, "error": f"suspicious compression ratio ({ratio:.0f}:1) — possible ZIP bomb"}

            name = _sanitize_zip_name(info.filename)
            if not name:
                continue  # skip unsafe names

            data = zf.read(info)
            total_uncompressed += len(data)
            if total_uncompressed > MAX_UNCOMPRESSED:
                return {"ok": False, "error": f"uncompressed size exceeds {MAX_UNCOMPRESSED // 1024 // 1024}MB"}

            ext = name.rsplit(".", 1)[-1].lower() if "." in name else ""
            files.append({
                "filename": name,
                "data_b64": base64.b64encode(data).decode(),
                "ext": ext,
                "size": len(data),
            })

    return {"ok": True, "files": files}