# SPDX-License-Identifier: Apache-2.0
# SPDX-FileCopyrightText: Copyright contributors to the vLLM project

from collections.abc import Callable, Iterable
from enum import Enum
from typing import Literal, cast, get_args, overload

import torch
from torch.nn.parameter import UninitializedParameter

import vllm.envs as envs
from vllm._aiter_ops import rocm_aiter_ops
from vllm.config import VllmConfig, get_current_vllm_config
from vllm.config.parallel import ExpertPlacementStrategy
from vllm.distributed import (
    get_dp_group,
    get_pcp_group,
    get_tensor_model_parallel_world_size,
)
from vllm.distributed.eplb.eplb_state import EplbLayerState, EplbState
from vllm.logger import init_logger
from vllm.model_executor.custom_op import CustomOp
from vllm.model_executor.layers.fused_moe.activation import MoEActivation
from vllm.model_executor.layers.fused_moe.config import (
    FusedMoEConfig,
    FusedMoEParallelConfig,
    FusedMoEQuantConfig,
    RoutingMethodType,
)
from vllm.model_executor.layers.fused_moe.fused_moe_method_base import (
    FusedMoEMethodBase,
)
from vllm.model_executor.layers.fused_moe.fused_moe_modular_method import (
    FusedMoEModularMethod,
)
from vllm.model_executor.layers.fused_moe.rocm_aiter_fused_moe import (
    init_aiter_topK_meta_data,
)
from vllm.model_executor.layers.fused_moe.router.router_factory import (
    create_fused_moe_router,
)
from vllm.model_executor.layers.fused_moe.runner.default_moe_runner import (
    DefaultMoERunner,
)
from vllm.model_executor.layers.fused_moe.unquantized_fused_moe_method import (
    UnquantizedFusedMoEMethod,
)
from vllm.model_executor.layers.fused_moe.utils import (
    disable_inplace,
)
from vllm.model_executor.layers.quantization.base_config import (
    QuantizationConfig,
)
from vllm.platforms import current_platform
from vllm.utils.math_utils import round_up

logger = init_logger(__name__)


class FusedMoeWeightScaleSupported(Enum):
    TENSOR = "tensor"
    CHANNEL = "channel"
    GROUP = "group"
    BLOCK = "block"


def determine_expert_map(
    ep_size: int,
    ep_rank: int,
    global_num_experts: int,
    expert_placement_strategy: ExpertPlacementStrategy = "linear",
    num_fused_shared_experts: int = 0,
    return_expert_mask: bool = False,
) -> tuple[int, torch.Tensor | None, torch.Tensor | None]:
    """
    Calculates how many experts should be assigned to each rank for EP and
    creates a mapping from global to local expert index. Experts are
    distributed evenly across ranks. Any remaining are assigned to the
    last rank.

    Args:
        ep_size: The size of the expert parallel group
        ep_rank: The rank of the current process in the expert parallel
            group
        global_num_experts: The total number of experts in the model.
        expert_placement_strategy: The expert placement strategy.

    Returns:
        tuple[int, Optional[torch.Tensor]]: A tuple containing:
            - local_num_experts (int): The number of experts assigned
                to the current rank.
            - expert_map (Optional[torch.Tensor]): A tensor of shape
                (global_num_experts,) mapping from global to local index.
                Contains -1 for experts not assigned to the current rank.
                Returns None if ep_size is 1.
            - expert_mask (Optional[torch.Tensor]): A tensor of shape
                (global_num_experts + num_fused_shared_experts + 1,)
                containing 1 for experts assigned to the current rank
                and 0 for sentinel.
                Returns None if ep_size is 1.
                Used only when AITER MOE is enabled.
    """
    assert ep_size > 0
    if ep_size == 1:
        return (global_num_experts, None, None)

    # Distribute experts as evenly as possible to each rank.
    base_experts = global_num_experts // ep_size
    remainder = global_num_experts % ep_size
    local_num_experts = base_experts + 1 if ep_rank < remainder else base_experts

    # Create a tensor of size num_experts filled with -1
    expert_map = torch.full((global_num_experts,), -1, dtype=torch.int32)
    # Create an expert map for the local experts
    if expert_placement_strategy == "linear":
        start_idx = ep_rank * base_experts + min(ep_rank, remainder)
        expert_map[start_idx : start_idx + local_num_experts] = torch.arange(
            0, local_num_experts, dtype=torch.int32
        )
    elif expert_placement_strategy == "round_robin":
        local_log_experts = torch.arange(
            ep_rank, global_num_experts, ep_size, dtype=torch.int32
        )

        expert_map[local_log_experts] = torch.arange(
            0, local_num_experts, dtype=torch.int32
        )
    else:
        raise ValueError(
            "Unsupported expert placement strategy "
            f"'{expert_placement_strategy}', expected one of "
            f"{get_args(ExpertPlacementStrategy)}"
        )

    expert_mask = None
    if return_expert_mask:
        expert_mask = torch.ones(
            (global_num_experts + num_fused_shared_experts + 1,), dtype=torch.int32
        )
        expert_mask[-1] = 0
        expert_mask[:global_num_experts] = expert_map > -1
        expert_map = torch.cat(
            (
                expert_map,
                torch.tensor(
                    [local_num_experts + i for i in range(num_fused_shared_experts)],
                    dtype=torch.int32,
                ),
            ),
            dim=0,
        )

    return (local_num_experts, expert_map, expert_mask)


def determine_expert_placement_strategy(
    expert_placement_strategy: ExpertPlacementStrategy,
    moe_parallel_config: FusedMoEParallelConfig,
    num_expert_group: int | None,
    num_redundant_experts: int,
    enable_eplb: bool,
) -> ExpertPlacementStrategy:
    if expert_placement_strategy == "round_robin":
        round_robin_supported = (
            (num_expert_group is not None and num_expert_group > 1)
            and num_redundant_experts == 0
            and not enable_eplb
        )

        if not round_robin_supported:
            logger.warning(
                "Round-robin expert placement is only supported for "
                "models with multiple expert groups and no redundant "
                "experts. Falling back to linear expert placement."
            )
            return "linear"
        if (
            moe_parallel_config.use_all2all_kernels
            and not moe_parallel_config.use_deepep_ll_kernels
            and not moe_parallel_config.use_nixl_ep_kernels
        ):
            logger.warning(
                "Round-robin expert placement currently only supports "
                "the DeepEP low-latency or NIXL EP backend, but '%s' was configured. "
                "Falling back to linear expert placement.",
                moe_parallel_config.all2all_backend,
            )
            return "linear"

    return expert_placement_strategy


def get_compressed_expert_map(expert_map: torch.Tensor) -> str:
    """
    Compresses the expert map by removing any -1 entries.

    Args:
        expert_map (torch.Tensor): A tensor of shape (global_num_experts,)
            mapping from global to local index. Contains -1 for experts not
            assigned to the current rank.

    Returns:
        str: A string mapping from local to global index.
            Using str to support hashing for logging once only.
    """
    global_indices = torch.where(expert_map != -1)[0]
    local_indices = expert_map[global_indices]
    return ", ".join(
        f"{local_index.item()}->{global_index.item()}"
        for local_index, global_index in zip(local_indices, global_indices)
    )


# TODO(rob): move this down to the kernel.
def maybe_roundup_hidden_size(
    hidden_size: int,
    act_dtype: torch.dtype,
    moe_parallel_config: FusedMoEParallelConfig,
    is_lora_enabled: bool,
    model_type: str | None,
    is_mxfp4_quant: bool,
) -> int:
    """
    Given layer hidden size and MoE configurations, round up hidden_size
    if necessary.

    Args:
        hidden_size: Layer hidden-size
        act_dtype: Data type of the layer activations.
        moe_parallel_config: Fused MoE parallelization strategy configuration.
        is_lora_enabled: True if the engine is enabled with LoRA. This
            is used in the case of mxfp4 quantization in selecting the
            MxFP4Backend.
        model_type: for checking if gpt-oss
        is_mxfp4_quant: whether the layer is quantized with mxfp4

    Return:
        Rounded up hidden_size if rounding up is required based on the configs.
        Original hidden size otherwise.
    """
    from vllm.model_executor.layers.fused_moe.all2all_utils import (
        maybe_roundup_layer_hidden_size,
    )

    hidden_size = maybe_roundup_layer_hidden_size(
        hidden_size, act_dtype, moe_parallel_config
    )

    # we are padding globally so EP buffer allocation works
    if model_type == "gpt_oss" and is_mxfp4_quant:
        from vllm.model_executor.layers.quantization.mxfp4 import (
            Mxfp4Backend,
            get_mxfp4_backend,
        )

        current_mxfp4_backend = get_mxfp4_backend(is_lora_enabled)

        if (
            current_mxfp4_backend == Mxfp4Backend.SM90_FI_MXFP4_BF16
            or current_mxfp4_backend == Mxfp4Backend.SM100_FI_MXFP4_MXFP8_CUTLASS
        ):
            hidden_size = round_up(hidden_size, 128)
        elif (
            current_platform.is_rocm()
            or current_mxfp4_backend == Mxfp4Backend.SM100_FI_MXFP4_MXFP8_TRTLLM
            or current_mxfp4_backend == Mxfp4Backend.SM100_FI_MXFP4_BF16
            or current_mxfp4_backend == Mxfp4Backend.MARLIN
        ):
            hidden_size = round_up(hidden_size, 256)

    return hidden_size


# --8<-- [start:fused_moe]
@CustomOp.register("fused_moe")
class FusedMoE(CustomOp):
    """FusedMoE layer for MoE models.

    This layer contains both MergedColumnParallel weights (gate_up_proj /
    w13) and RowParallelLinear weights (down_proj/ w2).

    Note: Mixtral uses w1, w2, and w3 for gate, up, and down_proj. We
    copy that naming convention here and handle any remapping in the
    load_weights function in each model implementation.

    Args:
        num_experts: Number of experts in the model
        top_k: Number of experts selected for each token
        hidden_size: Input hidden state size of the transformer
        intermediate_size: Intermediate size of the experts
        params_dtype: Data type for the parameters.
        reduce_results: Whether to all_reduce on the output of the layer
        renormalize: Whether to renormalize the logits in the fused_moe kernel
        quant_config: Quantization configure.
        enable_eplb: Whether to enable expert parallelism load balancer.
        router_logits_dtype: Data type for router logits buffers.
    """

    # --8<-- [end:fused_moe]

    def __init__(
        self,
        num_experts: int,  # Global number of experts
        top_k: int,
        hidden_size: int,
        intermediate_size: int,
        params_dtype: torch.dtype | None = None,
        reduce_results: bool = False,
        renormalize: bool = True,
        use_grouped_topk: bool = False,
        num_expert_group: int | None = None,
        topk_group: int | None = None,
        quant_config: QuantizationConfig | None = None,
        tp_size: int | None = None,
        ep_size: int | None = None,
        dp_size: int | None = None,
        pcp_size: int | None = None,
        prefix: str = "",
        custom_routing_function: Callable | None = None,
        scoring_func: str = "softmax",
        routed_scaling_factor: float = 1.0,
        e_score_correction_bias: torch.Tensor | None = None,
        apply_router_weight_on_input: bool = False,
        activation: str = "silu",
        is_act_and_mul: bool = True,
        enable_eplb: bool = False,
        num_redundant_experts: int = 0,
        has_bias: bool = False,
        is_sequence_parallel=False,
        expert_mapping: list[tuple[str, str, int, str]] | None = None,
        n_shared_experts: int | None = None,
        router_logits_dtype: torch.dtype | None = None,
        gate: torch.nn.Module | None = None,
        shared_experts: torch.nn.Module | None = None,
        routed_input_transform: torch.nn.Module | None = None,
    ):
        super().__init__()

        self._gate = gate
        self._shared_experts = shared_experts
        self._routed_input_transform = routed_input_transform

        if params_dtype is None:
            params_dtype = torch.get_default_dtype()
        self.params_dtype = params_dtype

        vllm_config = get_current_vllm_config()
        self.vllm_config = vllm_config

        # FIXME (varun): We should have a better way of inferring the activation
        # datatype. This works for now as the tensor datatype entering the MoE
        # operation is typically unquantized (i.e. float16/bfloat16).
        if vllm_config.model_config is not None:
            moe_in_dtype = vllm_config.model_config.dtype
        else:
            # TODO (bnell): This is a hack to get test_mixtral_moe to work
            # since model_config is not set in the pytest test.
            moe_in_dtype = params_dtype

        tp_size_ = (
            tp_size if tp_size is not None else get_tensor_model_parallel_world_size()
        )
        dp_size_ = dp_size if dp_size is not None else get_dp_group().world_size
        pcp_size_ = pcp_size if pcp_size is not None else get_pcp_group().world_size

        self.is_sequence_parallel = is_sequence_parallel
        self.sp_size = tp_size_ if is_sequence_parallel else 1

        self.moe_parallel_config: FusedMoEParallelConfig = FusedMoEParallelConfig.make(
            tp_size_=tp_size_,
            pcp_size_=pcp_size_,
            dp_size_=dp_size_,
            sp_size_=self.sp_size,
            vllm_parallel_config=vllm_config.parallel_config,
        )

        assert self.moe_parallel_config.is_sequence_parallel == is_sequence_parallel

        self.global_num_experts = num_experts + num_redundant_experts
        self.logical_num_experts = num_experts

        # Expert mapping used in self.load_weights
        self.expert_mapping = expert_mapping

        # For smuggling this layer into the fused moe custom op
        compilation_config = vllm_config.compilation_config
        if prefix in compilation_config.static_forward_context:
            raise ValueError("Duplicate layer name: {}".format(prefix))
        compilation_config.static_forward_context[prefix] = self
        compilation_config.static_all_moe_layers.append(prefix)
        self.layer_name = prefix

        self.enable_eplb = enable_eplb
        # TODO(bnell): should this be owned by router?
        self.eplb_state = EplbLayerState()
        self.expert_placement_strategy: ExpertPlacementStrategy = (
            vllm_config.parallel_config.expert_placement_strategy
        )

        # ROCm aiter shared experts fusion
        # AITER only supports gated activations (silu/gelu), so disable it
        # for non-gated MoE (is_act_and_mul=False)
        self.rocm_aiter_fmoe_enabled = (
            rocm_aiter_ops.is_fused_moe_enabled() and is_act_and_mul
        )
        self.aiter_fmoe_shared_expert_enabled = (
            rocm_aiter_ops.is_fusion_moe_shared_experts_enabled() and is_act_and_mul
        )

        self.num_fused_shared_experts = (
            n_shared_experts
            if n_shared_experts is not None and self.aiter_fmoe_shared_expert_enabled
            else 0
        )
        if (
            not self.aiter_fmoe_shared_expert_enabled
            and self.num_fused_shared_experts != 0
        ):
            raise ValueError(
                "n_shared_experts is only supported on ROCm aiter when "
                "VLLM_ROCM_USE_AITER_FUSION_SHARED_EXPERTS is enabled"
            )

        # Determine expert maps
        if self.use_ep:
            if self.enable_eplb:
                assert self.global_num_experts % self.ep_size == 0, (
                    "EPLB currently only supports even distribution of "
                    "experts across ranks."
                )
            else:
                assert num_redundant_experts == 0, (
                    "Redundant experts are only supported with EPLB."
                )

            self.expert_placement_strategy = determine_expert_placement_strategy(
                expert_placement_strategy=self.expert_placement_strategy,
                moe_parallel_config=self.moe_parallel_config,
                num_expert_group=num_expert_group,
                num_redundant_experts=num_redundant_experts,
                enable_eplb=self.enable_eplb,
            )

            self._expert_map: torch.Tensor | None
            local_num_experts, expert_map, expert_mask = determine_expert_map(
                ep_size=self.ep_size,
                ep_rank=self.ep_rank,
                global_num_experts=self.global_num_experts,
                expert_placement_strategy=self.expert_placement_strategy,
                num_fused_shared_experts=self.num_fused_shared_experts,
                return_expert_mask=self.rocm_aiter_fmoe_enabled,
            )
            self.local_num_experts = local_num_experts
            self.register_buffer("_expert_map", expert_map)
            self.register_buffer("expert_mask", expert_mask)
            self._maybe_init_expert_routing_tables()
            logger.info_once(
                "[EP Rank %s/%s] Expert parallelism is enabled. Expert "
                "placement strategy: %s. Local/global"
                " number of experts: %s/%s. Experts local to global index map:"
                " %s.",
                self.ep_rank,
                self.ep_size,
                self.expert_placement_strategy,
                self.local_num_experts,
                self.global_num_experts,
                get_compressed_expert_map(self._expert_map),
            )
        else:
            self.local_num_experts, self._expert_map, self.expert_mask = (
                self.global_num_experts,
                None,
                None,
            )

        self.top_k = top_k

        self._init_aiter_shared_experts_topK_buffer(
            vllm_config=vllm_config, dp_size=dp_size_
        )
        if self.use_ep and self.rocm_aiter_fmoe_enabled:
            assert self.expert_mask is None or torch.all(
                (expert_mask == 0) | (expert_mask == 1)
            ), "Aiter Fused MoE kernel only supports expert_map with 0 and 1s."

        assert intermediate_size % self.tp_size == 0
        self.intermediate_size_per_partition = intermediate_size // self.tp_size
        self.reduce_results = reduce_results
        self.renormalize = renormalize

        # TODO(bnell): these attributes are only used by monolithic kernels.
        # Put them in a MoERouterConfig dataclass?
        self.use_grouped_topk = use_grouped_topk
        if self.use_grouped_topk:
            assert num_expert_group is not None and topk_group is not None
        self.num_expert_group = num_expert_group
        self.topk_group = topk_group
        self.custom_routing_function = custom_routing_function
        self.scoring_func = scoring_func
        self.routed_scaling_factor = routed_scaling_factor
        self.e_score_correction_bias = e_score_correction_bias
        # TODO(bnell): end attributes

        self.apply_router_weight_on_input = apply_router_weight_on_input
        self.activation = MoEActivation.from_str(activation)

        self.router = create_fused_moe_router(
            top_k=top_k,
            global_num_experts=self.global_num_experts,
            eplb_state=self.eplb_state,
            renormalize=renormalize,
            use_grouped_topk=use_grouped_topk,
            num_expert_group=num_expert_group,
            topk_group=topk_group,
            custom_routing_function=custom_routing_function,
            scoring_func=scoring_func,
            routed_scaling_factor=routed_scaling_factor,
            e_score_correction_bias=e_score_correction_bias,
            num_fused_shared_experts=self.num_fused_shared_experts,
            enable_eplb=enable_eplb,
            # TODO(bnell): once we can construct the MK at init time, we
            # can make this a value.
            indices_type_getter=lambda: self.quant_method.topk_indices_dtype,
        )
        self.routing_method_type: RoutingMethodType = self.router.routing_method_type

        # Round up hidden size before creating moe_config.
        # This way moe_config is created with the correct hidden_size from the start.
        unpadded_hidden_size = hidden_size
        self.model_type = (
            self.vllm_config.model_config.hf_config.model_type
            if self.vllm_config.model_config is not None
            else None
        )
        hidden_size = maybe_roundup_hidden_size(
            hidden_size=hidden_size,
            act_dtype=moe_in_dtype,
            moe_parallel_config=self.moe_parallel_config,
            is_lora_enabled=vllm_config.lora_config is not None,
            model_type=self.model_type,
            is_mxfp4_quant=(
                quant_config is not None and quant_config.is_mxfp4_quant(prefix, self)
            ),
        )
        self.hidden_size = hidden_size

        self.moe_config: FusedMoEConfig = FusedMoEConfig(
            num_experts=self.global_num_experts,
            experts_per_token=top_k,
            hidden_dim=hidden_size,
            intermediate_size_per_partition=self.intermediate_size_per_partition,
            num_local_experts=self.local_num_experts,
            num_logical_experts=self.logical_num_experts,
            moe_parallel_config=self.moe_parallel_config,
            in_dtype=moe_in_dtype,
            moe_backend=vllm_config.kernel_config.moe_backend,
            router_logits_dtype=router_logits_dtype,
            max_num_tokens=envs.VLLM_MOE_DP_CHUNK_SIZE,
            has_bias=has_bias,
            is_act_and_mul=is_act_and_mul,
            is_lora_enabled=vllm_config.lora_config is not None,
            activation=self.activation,
            device=vllm_config.device_config.device,
            routing_method=self.routing_method_type,
            # TODO: in_dtype == out_dtype?
            disable_inplace=disable_inplace() or self._shared_experts is not None,
        )
        if self.moe_config.use_mori_kernels:
            assert self.rocm_aiter_fmoe_enabled, (
                "Mori needs to be used with aiter fused_moe for now."
            )
            assert not self.aiter_fmoe_shared_expert_enabled, (
                "Mori does not support fusion shared expert now. "
                "Turn it off by setting VLLM_ROCM_USE_AITER_FUSION_SHARED_EXPERTS=0"
            )

        self.quant_config = quant_config

        def _get_quant_method() -> FusedMoEMethodBase:
            """
            Helper method to ensure self.quant_method is never None and
            of the proper type.
            """
            quant_method = None
            if self.quant_config is not None:
                quant_method = self.quant_config.get_quant_method(self, prefix)
            if quant_method is None:
                quant_method = UnquantizedFusedMoEMethod(self.moe_config)
            assert isinstance(quant_method, FusedMoEMethodBase)
            return quant_method

        # Note: get_quant_method will look at the layer's local_num_experts
        # for heuristic purposes, so it must be initialized first.
        self.quant_method: FusedMoEMethodBase = _get_quant_method()

        if not self.moe_config.is_act_and_mul and not current_platform.is_cuda_alike():
            raise NotImplementedError(
                "is_act_and_mul=False is supported only for CUDA and ROCm for now"
            )

        if self.enable_eplb and not self.quant_method.supports_eplb:
            # TODO: Add support for additional quantization methods.
            # The implementation for other quantization methods does not
            # contain essential differences, but the current quant API
            # design causes duplicated work when extending to new
            # quantization methods, so I'm leaving it for now.
            # If you plan to add support for more quantization methods,
            # please refer to the implementation in `Fp8MoEMethod`.
            raise NotImplementedError(
                f"EPLB is not supported {self.quant_method.__class__.__name__}."
            )

        moe_quant_params = {
            "num_experts": self.local_num_experts,
            "hidden_size": hidden_size,
            "unpadded_hidden_size": unpadded_hidden_size,
            "intermediate_size_per_partition": self.intermediate_size_per_partition,
            "params_dtype": params_dtype,
            "weight_loader": self.weight_loader,
            "global_num_experts": self.global_num_experts,
        }
        # need full intermediate size pre-sharding for WNA16 act order
        if self.quant_method.__class__.__name__ in (
            "GPTQMarlinMoEMethod",
            "CompressedTensorsWNA16MarlinMoEMethod",
            "CompressedTensorsWNA16MoEMethod",
        ):
            moe_quant_params["intermediate_size_full"] = intermediate_size

        self.quant_method.create_weights(layer=self, **moe_quant_params)
        self.base_quant_method = self.quant_method

        # Disable shared expert overlap if:
        #   - we are using eplb with non-default backend, because of correctness issues
        #   - we are using flashinfer with DP, since there nothing to gain
        #   - we are using marlin kernels
        backend = self.moe_parallel_config.all2all_backend
        self.use_overlapped = (
            not (
                (self.enable_eplb and backend != "allgather_reducescatter")
                or self.moe_parallel_config.use_fi_all2allv_kernels
            )
            and self._shared_experts is not None
        )

        self.runner = self._init_runner()

    def _init_runner(self):
        # Storing the runner in the FusedMoE is an intermediate state, eventually
        # the runner will own the FusedMoE layer and provide the execution interface
        # for MoE ops.
        return DefaultMoERunner(
            layer=self,
            moe_config=self.moe_config,
            router=self.router,
            routed_input_transform=self._routed_input_transform,
            gate=self.gate,
            shared_experts=self.shared_experts,
            quant_method=self.quant_method,
            reduce_results=self.reduce_results,
            enable_dbo=self.vllm_config.parallel_config.enable_dbo,
        )

    # TODO(bnell): This method is provided as a hook so vllm/lora/layers/fused_moe.py
    # can safely swap out the quant_method. We should figure out a less
    # intrusive way to do this.
    def _replace_quant_method(self, mk: FusedMoEMethodBase):
        self.quant_method = mk
        # We need to force reconstruction of runner because we're swapping out
        # the quant_method with a FusedMoEModularMethod. This logic can go
        # away once the FusedMoEModularMethod is eliminated.
        self.runner = self._init_runner()

    # Note: maybe_init_modular_kernel should only be called by
    # prepare_communication_buffer_for_model.
    # This is called after all weight loading and post-processing, so it
    # should be safe to swap out the quant_method.
    def maybe_init_modular_kernel(self) -> None:
        # NOTE(rob): WIP refactor. For quant methods that own the MK
        # we create the MK during process_weights_after_loading.
        if self.quant_method.supports_internal_mk or self.quant_method.is_monolithic:
            return None

        self.ensure_moe_quant_config_init()
        # routing_tables only needed for round-robin expert placement with
        # DeepEP all2all backend.
        routing_tables = self._maybe_init_expert_routing_tables()
        prepare_finalize = self.base_quant_method.maybe_make_prepare_finalize(
            routing_tables=routing_tables
        )
        if prepare_finalize is not None:
            logger.debug(
                "%s for %s(%s)", prepare_finalize.__class__.__name__, self, id(self)
            )
            self._replace_quant_method(
                FusedMoEModularMethod.make(
                    self,
                    self.base_quant_method,
                    prepare_finalize,
                    self.shared_experts,
                    inplace=not self.moe_config.disable_inplace,
                )
            )

    @property
    def shared_experts(self) -> torch.nn.Module | None:
        return self._shared_experts if self.use_overlapped else None

    @property
    def layer_id(self):
        # Delayed import to avoid circular dependency
        from vllm.model_executor.models.utils import extract_layer_index

        return extract_layer_index(self.layer_name)

    @property
    def gate(self) -> torch.nn.Module | None:
        return self._gate if self.use_overlapped else None

    @property
    def tp_size(self):
        return self.moe_parallel_config.tp_size

    @property
    def ep_size(self):
        return self.moe_parallel_config.ep_size

    @property
    def tp_rank(self):
        return self.moe_parallel_config.tp_rank

    @property
    def ep_rank(self):
        return self.moe_parallel_config.ep_rank

    @property
    def use_ep(self):
        return self.moe_parallel_config.use_ep

    @property
    def is_internal_router(self) -> bool:
        # By default, router/gate is called before FusedMoE forward pass
        return self.gate is not None

    def _maybe_init_expert_routing_tables(
        self,
    ) -> tuple[torch.Tensor, torch.Tensor, torch.Tensor] | None:
        # Currently routing_tables only needed for round-robin expert placement
        # with DeepEP-ll or NIXL EP all2all backends.
        if self.expert_placement_strategy != "round_robin" or (
            not self.moe_parallel_config.use_deepep_ll_kernels
            and not self.moe_parallel_config.use_nixl_ep_kernels
        ):
            return None

        if hasattr(self, "expert_global_to_physical"):
            return cast(
                tuple[torch.Tensor, torch.Tensor, torch.Tensor],
                (
                    self.expert_global_to_physical,
                    self.expert_physical_to_global,
                    self.expert_local_to_global,
                ),
            )

        if self._expert_map is None:
            return None

        routing_tables = self.ensure_round_robin_expert_routing_tables(
            global_num_experts=self.global_num_experts,
            ep_size=self.ep_size,
            ep_rank=self.ep_rank,
            local_num_experts=self.local_num_experts,
            device=self._expert_map.device,
        )

        global_to_physical, physical_to_global, local_global = routing_tables
        self.register_buffer("expert_global_to_physical", global_to_physical)
        self.register_buffer("expert_physical_to_global", physical_to_global)
        self.register_buffer("expert_local_to_global", local_global)

        return routing_tables

    @staticmethod
    def ensure_round_robin_expert_routing_tables(
        global_num_experts: int,
        ep_size: int,
        ep_rank: int,
        local_num_experts: int,
        device: torch.device | None = None,
    ) -> tuple[torch.Tensor, torch.Tensor, torch.Tensor]:
        device_kwargs = {"device": device} if device is not None else {}
        global_indices = torch.arange(
            global_num_experts, dtype=torch.long, **device_kwargs
        )
        owner = torch.remainder(global_indices, ep_size)
        local_index = torch.div(global_indices, ep_size, rounding_mode="floor")
        base = global_num_experts // ep_size
        remainder = global_num_experts % ep_size
        physical_offset = owner * base
        if remainder > 0:
            remainder_tensor = torch.tensor(
                remainder, dtype=torch.long, **device_kwargs
            )
            physical_offset = physical_offset + torch.minimum(owner, remainder_tensor)

        global_to_physical = physical_offset + local_index
        physical_to_global = torch.empty_like(global_to_physical)
        physical_to_global[global_to_physical] = global_indices

        local_global = torch.arange(
            ep_rank,
            global_num_experts,
            ep_size,
            dtype=torch.long,
            **device_kwargs,
        )
        if local_global.numel() != local_num_experts:
            local_global = local_global[:local_num_experts]

        return (global_to_physical, physical_to_global, local_global)

    def update_expert_map(self):
        # ep_size and ep_rank should already be updated
        assert self._expert_map is not None
        with self._expert_map.device:
            local_num_experts, expert_map, expert_mask = determine_expert_map(
                ep_size=self.ep_size,
                ep_rank=self.ep_rank,
                global_num_experts=self.global_num_experts,
                expert_placement_strategy=self.expert_placement_strategy,
                num_fused_shared_experts=self.num_fused_shared_experts,
                return_expert_mask=self.rocm_aiter_fmoe_enabled,
            )
            self.local_num_experts = local_num_experts
            self.register_buffer("_expert_map", expert_map)
            self.register_buffer("expert_mask", expert_mask)
            self._maybe_init_expert_routing_tables()
            if self.aiter_fmoe_shared_expert_enabled:
                self._init_aiter_shared_experts_topK_buffer(
                    vllm_config=get_current_vllm_config(),
                    dp_size=get_dp_group().world_size,
                )

    def _load_per_tensor_weight_scale(
        self,
        shard_id: str,
        param: torch.nn.Parameter,
        loaded_weight: torch.Tensor,
        expert_id: int,
    ):
        param_data = param.data
        # for per tensor weight quantization
        if shard_id in ("w1", "w3"):
            # We have to keep the weight scales of w1 and w3 because
            # we need to re-quantize w1/w3 weights after weight loading.
            idx = 0 if shard_id == "w1" else 1
            param_data[expert_id][idx] = loaded_weight
        # If we are in the row parallel case (down_proj)
        elif shard_id == "w2":
            param_data[expert_id] = loaded_weight

    def _load_combined_w13_weight_scale(
        self,
        shard_dim: int,
        loaded_weight: torch.Tensor,
        param: torch.Tensor,
        tp_rank: int,
    ):
        """
        Load w13 weight scales assuming that w1 weight scales and w3 weight
        scales are stored in the same loaded_weight tensor.
        """
        shard_size = param.shape[shard_dim]
        loaded_weight = loaded_weight.narrow(
            shard_dim, shard_size * tp_rank, shard_size
        )
        param.copy_(loaded_weight)

    def _load_model_weight_or_group_weight_scale(
        self,
        shard_dim: int,
        expert_data: torch.Tensor,
        shard_id: str,
        loaded_weight: torch.Tensor,
        tp_rank: int,
        load_full_w2: bool = False,
    ):
        """
        Load grouped weight scales for group quantization or model weights
            :param shard_dim: dimension to shard
            :param expert_data: parameter for a particular expert
            :param shard_id: either w1, w2, or w3
            :param loaded_weight: checkpoint weight to load into the param
            :param tp_rank: tensor parallel rank
            :param load_full_w2: whether or not the w2 loaded should be sharded.
        """
        if shard_id == "w2":
            # In the case where we have actorder/g_idx, we do not partition the
            # w2 scales, as indicated by `load_full` argument, for all tp cases
            self._load_w2(
                shard_dim=shard_dim,
                loaded_weight=loaded_weight,
                expert_data=expert_data,
                tp_rank=tp_rank,
                load_full=load_full_w2,
            )
        elif shard_id in ("w1", "w3"):
            self._load_w13(
                shard_id=shard_id,
                shard_dim=shard_dim,
                loaded_weight=loaded_weight,
                expert_data=expert_data,
                tp_rank=tp_rank,
            )

    def _load_per_channel_weight_scale(
        self,
        expert_data: torch.Tensor,
        shard_dim: int,
        shard_id: str,
        loaded_weight: torch.Tensor,
        tp_rank: int,
    ):
        # for per channel weight quantization
        if shard_id == "w2":
            expert_data.copy_(loaded_weight)
        elif shard_id in ("w1", "w3"):
            self._load_w13(
                shard_id=shard_id,
                shard_dim=shard_dim,
                loaded_weight=loaded_weight,
                expert_data=expert_data,
                tp_rank=tp_rank,
            )

    def _load_w13(
        self,
        expert_data: torch.Tensor,
        shard_dim: int,
        shard_id: str,
        loaded_weight: torch.Tensor,
        tp_rank: int,
        load_full: bool = False,
    ):
        # Index the loaded weight for tp sharding.
        # gate_up_proj: "MergedColumnParallel", so tp sharding on output_dim
        if self.moe_config.is_act_and_mul:
            shard_size = expert_data.shape[shard_dim] // 2
        else:
            shard_size = expert_data.shape[shard_dim]
        # Only narrow if the loaded_weight is not a scalar (0-dim tensor)
        # and we're not loading the full weight
        if not load_full and loaded_weight.ndim > 0:
            loaded_weight = loaded_weight.narrow(
                shard_dim, shard_size * tp_rank, shard_size
            )
        # Narrow parameter and load.
        # w1, gate_proj: Load into first logical weight of w13.
        if shard_id == "w1":
            expert_data = expert_data.narrow(shard_dim, 0, shard_size)
        # w3, up_proj: Load into second logical weight of w13.
        else:
            assert shard_id == "w3"
            expert_data = expert_data.narrow(shard_dim, shard_size, shard_size)
        expert_data.copy_(loaded_weight)

    def _load_w2(
        self,
        expert_data: torch.Tensor,
        shard_dim: int,
        loaded_weight: torch.Tensor,
        tp_rank: int,
        load_full: bool = False,
    ):
        # Index the loaded weight for tp sharding.
        # down_proj: "RowParallel" so tp sharding on input_dim
        # Narrow parameter and load.
        shard_size = expert_data.shape[shard_dim]
        # Only narrow if the loaded_weight is not a scalar (0-dim tensor)
        # and we're not loading the full weight
        if not load_full and loaded_weight.ndim > 0:
            loaded_weight = loaded_weight.narrow(
                shard_dim, shard_size * tp_rank, shard_size
            )
        # w2, down_proj: Load into only logical weight of w2.
        expert_data.copy_(loaded_weight)

    def _load_single_value(
        self, param: torch.nn.Parameter, loaded_weight: torch.Tensor, expert_id: int
    ):
        param_data = param.data

        # Input scales can be loaded directly and should be equal.
        param_data[expert_id] = loaded_weight

    def _load_g_idx(
        self,
        shard_id: str,
        expert_data: torch.Tensor,
        shard_dim: int,
        loaded_weight: torch.Tensor,
        tp_rank: int,
    ):
        if shard_id == "w2":
            self._load_w2(
                shard_dim=shard_dim,
                loaded_weight=loaded_weight,
                expert_data=expert_data,
                tp_rank=tp_rank,
            )
        else:
            assert shard_id in ("w1", "w3")
            expert_data.copy_(loaded_weight)

    def _map_global_expert_id_to_local_expert_id(self, expert_id: int) -> int:
        if self._expert_map is None:
            return expert_id
        return self._expert_map[expert_id].item()

    def _init_aiter_shared_experts_topK_buffer(
        self, vllm_config: VllmConfig, dp_size: int
    ):
        if self.num_fused_shared_experts > 0:
            init_aiter_topK_meta_data(
                n_routed_experts=self.global_num_experts,
                n_shared_experts=self.num_fused_shared_experts,
                top_k=self.top_k,
                tp_rank=self.ep_rank if self.use_ep else self.tp_rank,
                tp_size=self.ep_size if self.use_ep else self.tp_size,
                shared_experts_score=1.0,
                max_num_tokens=vllm_config.scheduler_config.max_num_batched_tokens
                * dp_size,
                is_EP=self.use_ep,
            )
        self.local_num_experts += self.num_fused_shared_experts

    @overload
    def weight_loader(
        self,
        param: torch.nn.Parameter,
        loaded_weight: torch.Tensor,
        weight_name: str,
        shard_id: str,
        expert_id: int,
        return_success: Literal[False],
    ) -> None: ...

    @overload
    def weight_loader(
        self,
        param: torch.nn.Parameter,
        loaded_weight: torch.Tensor,
        weight_name: str,
        shard_id: str,
        expert_id: int,
        return_success: Literal[True],
    ) -> bool: ...

    def weight_loader(
        self,
        param: torch.nn.Parameter,
        loaded_weight: torch.Tensor,
        weight_name: str,
        shard_id: str,
        expert_id: int,
        return_success: bool = False,
    ) -> bool | None:
        if self.quant_config and self.quant_config.get_name() == "mxfp4":
            # (FIXME) for gpt-oss all experts are combined
            if "bias" in weight_name:
                dim1 = loaded_weight.shape[1]
                param.data[:, :dim1].copy_(loaded_weight)
            else:
                dim1 = loaded_weight.shape[1]
                dim2 = loaded_weight.shape[2]
                param.data[:, :dim1, :dim2].copy_(loaded_weight)
            return True if return_success else None

        quant_method_name = self.quant_method.__class__.__name__
        global_expert_id = expert_id
        expert_id = self._map_global_expert_id_to_local_expert_id(global_expert_id)

        use_global_sf = (
            getattr(self.quant_method, "use_global_sf", False)
            and "input_scale" in weight_name
        )

        if expert_id == -1 and not use_global_sf:
            # Failed to load this param since it's not local to this rank
            return False if return_success else None
        # Hereafter, `expert_id` is local physical id

        # is_transposed: if the dim to shard the weight
        # should be flipped. Required by GPTQ, compressed-tensors
        # should be whatever dimension intermediate_size_per_partition is
        is_transposed = getattr(param, "is_transposed", False)

        # compressed-tensors checkpoints with packed weights are stored flipped
        # TODO (mgoin): check self.quant_method.quant_config.quant_format
        # against known CompressionFormat enum values that have this quality
        if quant_method_name in (
            "CompressedTensorsWNA16MarlinMoEMethod",
            "CompressedTensorsWNA16MoEMethod",
        ):
            if is_transposed:
                loaded_weight = loaded_weight.t().contiguous()
            else:
                loaded_weight = loaded_weight

        if shard_id not in ("w1", "w2", "w3"):
            raise ValueError(f"shard_id must be ['w1','w2','w3'] but got {shard_id}.")

        # Fetch the dim to shard the parameter/loaded weight
        # based on the shard id. This will be whatever
        # dimension intermediate_size_per_partition is used.
        SHARD_ID_TO_SHARDED_DIM = {"w1": 0, "w2": 1, "w3": 0}

        is_gguf_weight = getattr(param, "is_gguf_weight", False)
        is_gguf_weight_type = getattr(param, "is_gguf_weight_type", False)
        if is_gguf_weight_type:
            param.weight_type = loaded_weight.item()
            param.data.copy_(loaded_weight)
            return True if return_success else None

        # Case for BitsAndBytes
        use_bitsandbytes_4bit = getattr(param, "use_bitsandbytes_4bit", False)
        if use_bitsandbytes_4bit:
            shard_dim = 0

            expert_data = param.data[expert_id]
            if shard_id == "w2":
                expert_data.copy_(loaded_weight)
            elif shard_id in ("w1", "w3"):
                # BNB inflight quantization has already sharded the weights
                full_load = True
                self._load_w13(
                    shard_id=shard_id,
                    shard_dim=shard_dim,
                    loaded_weight=loaded_weight,
                    expert_data=expert_data,
                    tp_rank=self.tp_rank,
                    load_full=full_load,
                )
            return True if return_success else None

        shard_dim = SHARD_ID_TO_SHARDED_DIM[shard_id]
        if is_transposed:
            shard_dim = int(not shard_dim)

        full_load = len(loaded_weight.shape) == 3
        if full_load:
            shard_dim += 1

        # Materialize GGUF UninitializedParameter accounting merged weights
        if is_gguf_weight and isinstance(param, UninitializedParameter):
            # To materialize a tensor, we must have full shape including
            # number of experts, making this portion to require `full_load`.
            assert full_load
            final_shape = list(loaded_weight.shape)
            # w1 and w3 are merged per expert.
            if shard_id in {"w1", "w3"}:
                final_shape[1] *= 2
            final_shape[shard_dim] = final_shape[shard_dim] // self.tp_size
            param.materialize(final_shape, dtype=loaded_weight.dtype)

        expert_data = param.data if full_load else param.data[expert_id]

        # Case input scale: input_scale loading is only supported for fp8
        if "input_scale" in weight_name:
            # this is needed for compressed-tensors only
            loaded_weight = loaded_weight.to(param.data.device)

            if (
                "compressed" in quant_method_name.lower()
                and param.data[expert_id] != 1
                and (param.data[expert_id] - loaded_weight).abs() > 1e-5
            ):
                raise ValueError(
                    "input_scales of w1 and w3 of a layer "
                    f"must be equal. But got {param.data[expert_id]} "
                    f"vs. {loaded_weight}"
                )

            self._load_single_value(
                param=param,
                loaded_weight=loaded_weight,
                expert_id=global_expert_id if use_global_sf else expert_id,
            )
            return True if return_success else None

        # Case g_idx
        if "g_idx" in weight_name:
            self._load_g_idx(
                shard_dim=0,
                shard_id=shard_id,
                loaded_weight=loaded_weight,
                expert_data=expert_data,
                tp_rank=self.tp_rank,
            )
            return True if return_success else None

        # TODO @dsikka: ModelOpt should follow the proper MoE loading pattern
        if "ModelOpt" in quant_method_name:
            # Determine per-tensor weight scale patterns based on variant
            # Use the dedicated method instead of brittle string matching
            uses_weight_scale_2 = self.quant_method.uses_weight_scale_2_pattern()
            quant_method = getattr(param, "quant_method", None)

            # Call _load_per_tensor_weight_scale() to load per-tensor (scalar)
            # weights scales.
            # Input scales are always per-tensor.
            # Weight scales: FP4 uses "weight_scale_2" and FP8 uses
            # "weight_scale" for per-tensor scales.
            # NOTE: ModelOpt MXFP8 MoE uses block scales in weight_scale
            # tensors (quant_method=BLOCK), so those must not be treated
            # as per-tensor scalars here.
            is_block_weight_scale = (
                "weight_scale" in weight_name
                and quant_method == FusedMoeWeightScaleSupported.BLOCK.value
            )
            is_per_tensor = (
                "weight_scale_2" in weight_name
                if uses_weight_scale_2
                else "weight_scale" in weight_name
            ) or "input_scale" in weight_name
            is_per_tensor = is_per_tensor and not is_block_weight_scale
            if is_per_tensor:
                self._load_per_tensor_weight_scale(
                    shard_id=shard_id,
                    param=param,
                    loaded_weight=loaded_weight,
                    expert_id=expert_id,
                )
                return True if return_success else None

            # If the weight is w13_weight_scale and w13_weight_scales are
            # combined into single loaded_weight, call
            # _load_combined_w13_weight_scale() to load it.
            # This is checked by comparing the hidden_out dims of the
            # loaded_weight and the param.
            if "w13_weight_scale" in weight_name:
                loaded_weight_hidden_out = loaded_weight.shape[-2]
                param_hidden_out = param.data.shape[-2] * self.tp_size
                if loaded_weight_hidden_out == param_hidden_out:
                    self._load_combined_w13_weight_scale(
                        shard_dim=shard_dim,
                        loaded_weight=loaded_weight,
                        param=expert_data,
                        tp_rank=self.tp_rank,
                    )
                    return True if return_success else None

            # For other weights, call _load_model_weight_or_group_weight_scale()
            # to load it.
            if "weight" in weight_name:
                self._load_model_weight_or_group_weight_scale(
                    shard_id=shard_id,
                    shard_dim=shard_dim,
                    loaded_weight=loaded_weight,
                    expert_data=expert_data,
                    tp_rank=self.tp_rank,
                )
            return True if return_success else None

        # Case weight scales, zero_points and offset, weight/input global scales
        if "scale" in weight_name or "zero" in weight_name or "offset" in weight_name:
            # load the weight scales and zp based on the quantization scheme
            # supported weight scales/zp can be found in
            # FusedMoeWeightScaleSupported
            # TODO @dsikka: once hardened, refactor to use vLLM Parameters
            # specific to each case
            quant_method = getattr(param, "quant_method", None)
            if quant_method == FusedMoeWeightScaleSupported.CHANNEL.value:
                self._load_per_channel_weight_scale(
                    shard_id=shard_id,
                    shard_dim=shard_dim,
                    loaded_weight=loaded_weight,
                    expert_data=expert_data,
                    tp_rank=self.tp_rank,
                )
            elif quant_method in [
                FusedMoeWeightScaleSupported.GROUP.value,
                FusedMoeWeightScaleSupported.BLOCK.value,
            ]:
                self._load_model_weight_or_group_weight_scale(
                    shard_id=shard_id,
                    shard_dim=shard_dim,
                    loaded_weight=loaded_weight,
                    expert_data=expert_data,
                    tp_rank=self.tp_rank,
                    load_full_w2=getattr(param, "load_full_w2", False),
                )
            elif quant_method == FusedMoeWeightScaleSupported.TENSOR.value:
                self._load_per_tensor_weight_scale(
                    shard_id=shard_id,
                    param=param,
                    loaded_weight=loaded_weight,
                    expert_id=expert_id,
                )
            else:
                WEIGHT_SCALE_SUPPORTED = [e.value for e in FusedMoeWeightScaleSupported]
                raise ValueError(
                    f"quant method must be one of {WEIGHT_SCALE_SUPPORTED}"
                )
            return True if return_success else None

        # Case weight_shape
        if "weight_shape" in weight_name:
            # only required by compressed-tensors
            self._load_single_value(
                param=param, loaded_weight=loaded_weight, expert_id=expert_id
            )
            return True if return_success else None

        # Case model weights
        if "weight" in weight_name:
            self._load_model_weight_or_group_weight_scale(
                shard_id=shard_id,
                shard_dim=shard_dim,
                loaded_weight=loaded_weight,
                expert_data=expert_data,
                tp_rank=self.tp_rank,
            )
            return True if return_success else None

        return False if return_success else None

    def load_weights(
        self, weights: Iterable[tuple[str, torch.Tensor]]
    ) -> Iterable[str]:
        if (expert_mapping := self.expert_mapping) is None:
            raise ValueError(
                "`self.expert_mapping` must be provided to "
                "load weights using `self.load_weights`."
            )
        for expert_name, loaded_weight in weights:
            qual_name = f"{self.layer_name}.{expert_name}"
            for param_name, weight_name, expert_id, shard_id in expert_mapping:
                if weight_name not in qual_name:
                    continue
                weight_name = qual_name.replace(weight_name, param_name)
                param_name = weight_name.removeprefix(f"{self.layer_name}.")
                param = getattr(self, param_name)
                # Fused expert weights can be identified by their 3D tensors
                if loaded_weight.dim() == 3:
                    # Repurpose expert_id as shard_idx for deconcatenating w1 and w3
                    if shard_id in {"w1", "w3"}:
                        shard_idx = expert_id
                        experts_shard = loaded_weight.chunk(2, dim=1)[shard_idx]
                    else:
                        experts_shard = loaded_weight
                    start = 0
                else:
                    # loaded_weight is a single expert weight, so we add a dummy expert
                    # dimension to unify the loading logic with the fused case
                    experts_shard = loaded_weight.unsqueeze(0)
                    start = expert_id

                # Unified loading logic for fused and non-fused experts
                loaded_experts = experts_shard.unbind()
                for expert_id, loaded_expert in enumerate(loaded_experts, start=start):
                    success = self.weight_loader(
                        param=param,
                        loaded_weight=loaded_expert,
                        weight_name=weight_name,
                        shard_id=shard_id,
                        expert_id=expert_id,
                        return_success=True,
                    )
                    if success:
                        logger.debug(
                            "Loaded expert %d of shard %s into %s for layer %s",
                            expert_id,
                            shard_id,
                            param_name,
                            self.layer_name,
                        )
                        yield param_name

    def get_expert_weights(self) -> Iterable[torch.Tensor]:
        def _maybe_make_contiguous(
            name: str, p: torch.nn.Parameter
        ) -> torch.nn.Parameter:
            """
            In some cases, the last 2 dimensions (the non-expert dimensions)
            of the weight scale tensor are transposed. This function
            transforms the tensor (view update) so the tensor is contiguous().
            Example: A non-contiguous scale tensor,
              `x` of shape (E, 32, 16) and stride (512, 1, 32) is transformed to
              `x_` of shape (E, 16, 32) and stride (512, 32, 1).
              Note that we specifically use torch.transpose() so `x_` refers
              to the same underlying memory. The tensors `x` and `x_`, pointing
              to the same underlying memory make this transformation safe in the
              context of EPLB. i.e. It is the same memory and just the view
              is different.
            Note: This function handles the "weight_scale" tensors specifically.
            This could however be generalized to handle similar tensors.
            """
            if p.ndim != 3:
                return p
            if p.is_contiguous():
                # Already contiguous. do nothing.
                return p
            # p is non-contiguous. We only handle the case where the last 2
            # dimensions of the scales tensor is transposed. We can handle
            # other cases when they become relevant.
            is_transposed_12 = p.stride(1) == 1 and p.stride(2) != 1
            if "weight_scale" not in name or not is_transposed_12:
                # do nothing.
                return p

            # Do not update the layer parameter as the layer's MoE operations would
            # expect the parameter's tensor to the same shape / stride. Instead,
            # make a new torch.nn.Parameter that is used just in the context of
            # EPLB.
            return torch.nn.Parameter(
                torch.transpose(p.data, 1, 2), requires_grad=False
            )

        weights = list(self.named_parameters())
        weights = [(name, _maybe_make_contiguous(name, p)) for name, p in weights]

        assert all(
            weight.is_contiguous()
            for name, weight in weights
            if not (name.startswith("_shared_experts.") or name.startswith("_gate."))
        )

        # Filter out the non-expert weights.
        # `e_score_correction_bias` is a bias for each logical expert,
        # with shape (num_logical_experts,), not an expert weight.
        NON_EXPERT_WEIGHTS = {
            "e_score_correction_bias",
        }

        return [
            weight.view(self.local_num_experts, -1)
            for name, weight in weights
            if name not in NON_EXPERT_WEIGHTS
            and weight.shape != torch.Size([])
            and not name.startswith("_shared_experts.")
            # exclude parameters from non-expert submodules (e.g. gate/shared)
            and not name.startswith("_gate.")
        ]

    def set_eplb_state(
        self,
        moe_layer_idx: int,
        expert_load_view: torch.Tensor,
        logical_to_physical_map: torch.Tensor,
        logical_replica_count: torch.Tensor,
    ) -> None:
        """
        Register the EPLB state in this layer.

        This is used later in forward pass, where we get the expert mapping
        and record the load metrics in `expert_load_view`.
        """
        self.eplb_state.expert_load_view = expert_load_view[moe_layer_idx]
        self.eplb_state.logical_to_physical_map = logical_to_physical_map[moe_layer_idx]
        self.eplb_state.logical_replica_count = logical_replica_count[moe_layer_idx]

    def ensure_moe_quant_config_init(self):
        if self.quant_method.moe_quant_config is None:
            # Note: the moe_quant_config can't be constructed until after
            # weight loading post processing.
            self.quant_method.moe_quant_config = (
                self.quant_method.get_fused_moe_quant_config(self)
            )

    @property
    def moe_quant_config(self) -> FusedMoEQuantConfig | None:
        self.ensure_moe_quant_config_init()
        return self.quant_method.moe_quant_config

    def must_reduce_shared_expert_outputs(self) -> bool:
        """
        The shared_experts are typically computed using the RowParallelLinear
        layer. The result of this function is typically used as
        the reduce_results argument to the module.
        When just tensor-parallel is used, it is not required to reduce
        the shared_experts results immediately. Instead we reduce at the
        once at the end of the MoE op. (Refer to DeepSeekV2MoE module)
        With EP and all2all kernels - this is no longer viable as all
        GPU ranks in DP, produce the complete set of hidden_states.
        Therefore it is required that we reduce the shared_experts output
        early.
        """
        return self.runner.must_reduce_shared_expert_outputs()

    def maybe_all_reduce_tensor_model_parallel(self, final_hidden_states: torch.Tensor):
        """
        Some combine kernels reduce across GPU ranks by default.
        """
        return self.runner.maybe_all_reduce_tensor_model_parallel(final_hidden_states)

    def forward_native(
        self,
        hidden_states: torch.Tensor,
        router_logits: torch.Tensor,
    ) -> torch.Tensor | tuple[torch.Tensor, torch.Tensor]:
        return self.runner.forward(
            hidden_states,
            router_logits,
        )

    @property
    def expert_map(self) -> torch.Tensor | None:
        return (
            self._expert_map if not self.rocm_aiter_fmoe_enabled else self.expert_mask
        )

    def forward_cuda(
        self,
        hidden_states: torch.Tensor,
        router_logits: torch.Tensor,
    ) -> torch.Tensor | tuple[torch.Tensor, torch.Tensor]:
        return self.forward_native(hidden_states, router_logits)

    @classmethod
    def make_expert_params_mapping(
        cls,
        model: torch.nn.Module,
        ckpt_gate_proj_name: str,
        ckpt_down_proj_name: str,
        ckpt_up_proj_name: str,
        num_experts: int,
        num_redundant_experts: int = 0,
    ) -> list[tuple[str, str, int, str]]:
        num_physical_experts = num_experts + num_redundant_experts

        # In the returned mapping:
        # - `expert_id` is the physical expert id
        # - `weight_name` contains the weight name of the logical expert
        # So that we should map the expert id to logical in `weight_name`
        physical_to_logical_map = (
            EplbState.build_initial_global_physical_to_logical_map(
                num_experts, num_redundant_experts
            )
        )

        base_layer = (
            "base_layer."
            if any(".base_layer." in name for name, _ in model.named_parameters())
            else ""
        )

        return [
            # (param_name, weight_name, expert_id, shard_id)
            (
                f"experts.{base_layer}w13_"
                if weight_name in [ckpt_gate_proj_name, ckpt_up_proj_name]
                else f"experts.{base_layer}w2_",
                f"experts.{physical_to_logical_map[expert_id]}.{weight_name}.{base_layer}",
                expert_id,
                shard_id,
            )
            for expert_id in range(num_physical_experts)
            for shard_id, weight_name in [
                ("w1", ckpt_gate_proj_name),
                ("w2", ckpt_down_proj_name),
                ("w3", ckpt_up_proj_name),
            ]
        ]

    def extra_repr(self) -> str:
        s = (
            f"global_num_experts={self.global_num_experts}, "
            f"local_num_experts={self.local_num_experts}, "
            f"top_k={self.top_k}, "
            f"intermediate_size_per_partition={self.intermediate_size_per_partition}, "  # noqa: E501
            f"tp_size={self.tp_size},\n"
            f"ep_size={self.ep_size}, "
            f"reduce_results={self.reduce_results}, "
        )

        return s


# Mark the FusedMoE weight_loader as supporting MoE-specific parameters
# to avoid expensive runtime reflection in model loading code
FusedMoE.weight_loader.supports_moe_loading = True  # type: ignore[attr-defined]
