def METHOD_NAME():
    print("INFO: Reading config file: " + config_file)
    with open(config_file, "r") as f:
        cfg = json.load(f)
    expand_cfg_layers(cfg)
    cfg = cfg["layers"]  # ignore the rest
    # Map gds layers & datatype to KLayout indices
    # These are arrays for the different mask numbers
    for layer, vals in cfg.items():
        layer = vals["layer"]
        for key in ("opc", "non-opc"):
            if key not in vals:
                continue
            data = vals[key]
            if isinstance(data["datatype"], int):
                data["datatype"] = [data["datatype"]]  # convert to array
            data["klayout"] = [
                main_layout.find_layer(layer, datatype) for datatype in data["datatype"]
            ]
    return cfg