import os


BACKEND_ENV_VAR = "BLE_RETICULUM_SESSION_BACKEND"
DEFAULT_BACKEND = "auto"
VALID_BACKENDS = {"auto", "cpp", "python"}


def _requested_backend():
    value = os.environ.get(BACKEND_ENV_VAR, DEFAULT_BACKEND).strip().lower()
    if value not in VALID_BACKENDS:
        raise ValueError(
            f"Invalid {BACKEND_ENV_VAR}={value!r}; expected 'auto', 'cpp', or 'python'"
        )
    return value


def _load_cpp_backend():
    try:
        from ble_protocol_core_cpp import (
            BLEPeerSessionManager,
            ConnectionId,
            ConnectionSnapshot,
            InputDecision,
            LocalRole,
            SessionActionType,
        )
    except ImportError as e:
        raise ImportError(
            "C++ BLE session backend is not available. Build or install "
            "ble_protocol_core_cpp, or set BLE_RETICULUM_SESSION_BACKEND=python."
        ) from e

    return (
        "cpp",
        BLEPeerSessionManager,
        ConnectionId,
        ConnectionSnapshot,
        InputDecision,
        LocalRole,
        SessionActionType,
    )


def _load_python_backend():
    return ("python", None, None, None, None, None, None)


REQUESTED_BACKEND = _requested_backend()

if REQUESTED_BACKEND == "python":
    (
        BACKEND,
        BLEPeerSessionManager,
        ConnectionId,
        ConnectionSnapshot,
        InputDecision,
        LocalRole,
        SessionActionType,
    ) = _load_python_backend()
elif REQUESTED_BACKEND == "cpp":
    (
        BACKEND,
        BLEPeerSessionManager,
        ConnectionId,
        ConnectionSnapshot,
        InputDecision,
        LocalRole,
        SessionActionType,
    ) = _load_cpp_backend()
else:
    try:
        (
            BACKEND,
            BLEPeerSessionManager,
            ConnectionId,
            ConnectionSnapshot,
            InputDecision,
            LocalRole,
            SessionActionType,
        ) = _load_cpp_backend()
    except ImportError:
        (
            BACKEND,
            BLEPeerSessionManager,
            ConnectionId,
            ConnectionSnapshot,
            InputDecision,
            LocalRole,
            SessionActionType,
        ) = _load_python_backend()


__all__ = [
    "BACKEND",
    "BACKEND_ENV_VAR",
    "REQUESTED_BACKEND",
    "BLEPeerSessionManager",
    "ConnectionId",
    "ConnectionSnapshot",
    "InputDecision",
    "LocalRole",
    "SessionActionType",
]