from module_business.domain.enums import PalletFlowState


class InvalidPalletTransition(ValueError):
    """托盘状态迁移不符合业务规则。"""


class PalletStateMachine:
    _ALLOWED_TRANSITIONS = frozenset(
        {
            (PalletFlowState.UNSTOCKED, PalletFlowState.EMPTY_IN_WAREHOUSE),
            (
                PalletFlowState.EMPTY_IN_WAREHOUSE,
                PalletFlowState.FILLED_IN_WAREHOUSE,
            ),
            (PalletFlowState.FILLED_IN_WAREHOUSE, PalletFlowState.AT_SITE_UNUSED),
            (PalletFlowState.AT_SITE_UNUSED, PalletFlowState.AT_SITE_PARTIAL),
            (PalletFlowState.AT_SITE_UNUSED, PalletFlowState.AT_SITE_EMPTY),
            (PalletFlowState.AT_SITE_UNUSED, PalletFlowState.RETURNING),
            (PalletFlowState.AT_SITE_PARTIAL, PalletFlowState.AT_SITE_PARTIAL),
            (PalletFlowState.AT_SITE_PARTIAL, PalletFlowState.AT_SITE_EMPTY),
            (PalletFlowState.AT_SITE_PARTIAL, PalletFlowState.RETURNING),
            (PalletFlowState.AT_SITE_EMPTY, PalletFlowState.RETURNING),
            (PalletFlowState.RETURNING, PalletFlowState.FILLED_IN_WAREHOUSE),
            (PalletFlowState.RETURNING, PalletFlowState.EMPTY_IN_WAREHOUSE),
        }
    )

    @classmethod
    def ensure_transition(
        cls,
        current: PalletFlowState,
        target: PalletFlowState,
    ) -> None:
        if (current, target) not in cls._ALLOWED_TRANSITIONS:
            raise InvalidPalletTransition(
                f'不允许的托盘状态迁移：{current.value} -> {target.value}'
            )