"""Minimal reader for this dataset's versioned condition archives."""
import json
from pathlib import Path
import zipfile

import torch
import zstandard as zstd
from safetensors.torch import load


def load_conditions(archive, member):
    """Return saved tensors; this does not load RGB or construct external targets."""
    with zipfile.ZipFile(Path(archive)) as z:
        raw = zstd.ZstdDecompressor().decompress(z.read(member), max_output_size=1024**3)
    header = json.loads(raw[8:8 + int.from_bytes(raw[:8], "little")])
    fmt = header.get("__metadata__", {}).get("format")
    if fmt not in {"bf16_dynamic_zstd_v1", "int8_dynamic_zstd_v1", "int8_dynamic_zstd_v2"}:
        raise ValueError(f"Unsupported condition format: {fmt}")
    tensors = load(raw)
    for key in ("memory_latent", "control_latents"):
        scale = tensors.pop("_qscale_" + key, None)
        if scale is not None:
            tensors[key] = (tensors[key].float() * scale).to(torch.bfloat16)
        if tensors[key].dtype != torch.bfloat16:
            raise ValueError(f"{key} is not BF16")
    return tensors