from __future__ import annotations

import importlib.util
import sys
from pathlib import Path
from types import ModuleType


def load_encoder(model_name: str) -> ModuleType:
    """Import the chat encoder that ships inside the checkpoint directory."""
    from examples._config import resolve_model_path

    path = Path(resolve_model_path(model_name)) / "encoding" / "encoding.py"
    if not path.is_file():
        raise SystemExit(f"checkpoint has no encoding/encoding.py: {path}")
    mod_name = "ckpt_encoding"
    if mod_name in sys.modules:
        return sys.modules[mod_name]
    spec = importlib.util.spec_from_file_location(mod_name, path)
    module = importlib.util.module_from_spec(spec)
    sys.modules[mod_name] = module
    spec.loader.exec_module(module)
    return module