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

from abc import abstractmethod
from collections.abc import Iterable
from enum import Enum
from typing import Callable, Literal, Optional, overload

import torch
import torch.nn.functional as F
from torch.nn.parameter import UninitializedParameter

import vllm.envs as envs
from vllm.config import get_current_vllm_config
from vllm.distributed import (get_dp_group, get_ep_group,
                              get_tensor_model_parallel_world_size,
                              tensor_model_parallel_all_reduce)
from vllm.distributed.eplb.eplb_state import EplbState
from vllm.forward_context import ForwardContext, get_forward_context
from vllm.logger import init_logger
from vllm.model_executor.custom_op import CustomOp
# yapf: disable
from vllm.model_executor.layers.fused_moe.config import (
    FusedMoEConfig, FusedMoEParallelConfig)
# yapf: enable
from vllm.model_executor.layers.fused_moe.modular_kernel import (
    FusedMoEActivationFormat, FusedMoEModularKernel,
    FusedMoEPermuteExpertsUnpermute, FusedMoEPrepareAndFinalize)
from vllm.model_executor.layers.fused_moe.rocm_aiter_fused_moe import (
    is_rocm_aiter_moe_enabled)
from vllm.model_executor.layers.quantization.base_config import (
    QuantizationConfig, QuantizeMethodBase)
from vllm.model_executor.utils import set_weight_attrs
from vllm.platforms import current_platform
from vllm.platforms.interface import CpuArchEnum
from vllm.utils import direct_register_custom_op, has_deep_ep, has_pplx
from vllm.utils.flashinfer import has_flashinfer

if current_platform.is_cuda_alike():
    from .fused_batched_moe import BatchedTritonExperts
    from .fused_moe import TritonExperts, fused_experts
    if has_pplx():
        from .pplx_prepare_finalize import (PplxPrepareAndFinalize,
                                            pplx_hidden_dim_scale_bytes)
    if has_deep_ep():
        from .deepep_ht_prepare_finalize import DeepEPHTPrepareAndFinalize
        from .deepep_ll_prepare_finalize import (DEEPEP_QUANT_BLOCK_SHAPE,
                                                 DeepEPLLPrepareAndFinalize)
    if has_flashinfer():
        from .flashinfer_cutlass_prepare_finalize import (
            FlashInferCutlassMoEPrepareAndFinalize)
else:
    fused_experts = None  # type: ignore
    FusedMoEPermuteExpertsUnpermute = None  # type: ignore
    FusedMoEPrepareAndFinalize = None  # type: ignore
if is_rocm_aiter_moe_enabled():
    from vllm.model_executor.layers.fused_moe.rocm_aiter_fused_moe import (  # noqa: E501
        rocm_aiter_grouped_topk as grouped_topk)
elif current_platform.is_cpu():
    pass
else:
    from vllm.model_executor.layers.fused_moe.fused_moe import grouped_topk
if current_platform.is_tpu():
    from .moe_pallas import fused_moe as fused_moe_pallas
else:
    fused_moe_pallas = None  # type: ignore

logger = init_logger(__name__)


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


class FusedMoEMethodBase(QuantizeMethodBase):

    moe: FusedMoEConfig

    @abstractmethod
    def create_weights(self, layer: torch.nn.Module, num_experts: int,
                       hidden_size: int, intermediate_size_per_partition: int,
                       params_dtype: torch.dtype, **extra_weight_attrs):
        raise NotImplementedError

    def uses_weight_scale_2_pattern(self) -> bool:
        """
        Returns True if this quantization method uses 'weight_scale_2' pattern
        for per-tensor weight scales (e.g., FP4 variants), False otherwise.

        This method should be overridden by subclasses that use the
        'weight_scale_2' pattern instead of the standard 'weight_scale' pattern.
        """
        return False

    @staticmethod
    def maybe_make_prepare_finalize(
            moe: FusedMoEConfig) -> Optional[FusedMoEPrepareAndFinalize]:
        all2all_manager = get_ep_group().device_communicator.all2all_manager
        assert all2all_manager is not None

        prepare_finalize: Optional[FusedMoEPrepareAndFinalize] = None

        if moe.use_flashinfer_cutlass_kernels:
            prepare_finalize = FlashInferCutlassMoEPrepareAndFinalize(
                quant_dtype=moe.quant_dtype, )
        if moe.use_pplx_kernels:
            hidden_dim_bytes, hidden_scale_bytes = pplx_hidden_dim_scale_bytes(
                moe.max_num_tokens,
                moe.hidden_dim,
                moe.in_dtype,
                moe.quant_dtype,
                per_act_token_quant=moe.per_act_token_quant,
                block_shape=moe.block_shape,
            )

            all_to_all_args = dict(
                max_num_tokens=moe.max_num_tokens,
                num_experts=moe.num_experts,
                experts_per_token=moe.experts_per_token,  # topk
                rank=all2all_manager.rank,
                world_size=all2all_manager.world_size,
                # dp_size actually means tp_size, bug in pplx kernels
                dp_size=all2all_manager.tp_group.world_size,
                hidden_dim=moe.hidden_dim,
                hidden_dim_bytes=hidden_dim_bytes,
                hidden_dim_scale_bytes=hidden_scale_bytes,
            )

            num_dispatchers = (all2all_manager.world_size //
                               all2all_manager.tp_group.world_size)

            # Intranode pplx a2a takes a group name while internode does not.
            if not all2all_manager.internode:
                all_to_all_args[
                    "group_name"] = all2all_manager.cpu_group.group_name

            handle = all2all_manager.get_handle(all_to_all_args)

            prepare_finalize = PplxPrepareAndFinalize(
                handle,
                max_num_tokens=moe.max_num_tokens,
                num_local_experts=moe.num_local_experts,
                num_dispatchers=num_dispatchers,
            )
        elif moe.use_deepep_ht_kernels:
            assert moe.dp_size == all2all_manager.dp_world_size

            all_to_all_args = dict()
            handle = all2all_manager.get_handle(all_to_all_args)
            prepare_finalize = DeepEPHTPrepareAndFinalize(
                handle,
                num_dispatchers=all2all_manager.world_size,
                dp_size=all2all_manager.dp_world_size,
                rank_expert_offset=all2all_manager.rank *
                moe.num_local_experts,
            )

        elif moe.use_deepep_ll_kernels:
            all_to_all_args = dict(
                max_num_tokens_per_dp_rank=moe.max_num_tokens,
                token_hidden_size=moe.hidden_dim,
                num_ep_ranks=all2all_manager.world_size,
                num_global_experts=moe.num_experts,
                num_local_experts=moe.num_experts //
                all2all_manager.world_size)
            handle = all2all_manager.get_handle(all_to_all_args)

            # Note : We may want to use FP8 dispatch even otherwise just to
            # reduce datamovement
            use_fp8_dispatch = (moe.quant_config is not None
                                and moe.quant_config.quant_dtype
                                == current_platform.fp8_dtype()
                                and moe.quant_config.block_shape
                                == DEEPEP_QUANT_BLOCK_SHAPE)

            prepare_finalize = DeepEPLLPrepareAndFinalize(
                handle,
                max_tokens_per_rank=moe.max_num_tokens,
                num_dispatchers=all2all_manager.world_size,
                use_fp8_dispatch=use_fp8_dispatch,
            )

        return prepare_finalize

    def init_prepare_finalize(self, moe: FusedMoEConfig):
        self.moe = moe
        prepare_finalize = FusedMoEMethodBase.maybe_make_prepare_finalize(
            self.moe)

        self.topk_indices_dtype = None
        if prepare_finalize is not None:
            logger.debug("%s", prepare_finalize.__class__.__name__)
            self.topk_indices_dtype = prepare_finalize.topk_indices_dtype()
            experts = self.select_gemm_impl(prepare_finalize, self.moe)
            self.fused_experts = FusedMoEModularKernel(
                prepare_finalize,
                experts,
            )

    def select_gemm_impl(
        self,
        prepare_finalize: FusedMoEPrepareAndFinalize,
        moe: FusedMoEConfig,
    ) -> FusedMoEPermuteExpertsUnpermute:
        # based on the all2all implementation, select the appropriate
        # gemm implementation
        raise NotImplementedError(
            f"{self.__class__.__name__} must select appropriate gemm "
            "implementation based on the prepare_finalize")

    def maybe_swap_experts_impl(
        self,
        moe_parallel_config: FusedMoEParallelConfig,
    ):
        pass

    @abstractmethod
    def apply(
        self,
        layer: torch.nn.Module,
        x: torch.Tensor,
        router_logits: torch.Tensor,
        top_k: int,
        renormalize: bool,
        use_grouped_topk: bool = False,
        topk_group: Optional[int] = None,
        num_expert_group: Optional[int] = None,
        global_num_experts: int = -1,
        expert_map: Optional[torch.Tensor] = None,
        custom_routing_function: Optional[Callable] = None,
        scoring_func: str = "softmax",
        e_score_correction_bias: Optional[torch.Tensor] = None,
        apply_router_weight_on_input: bool = False,
        activation: str = "silu",
        enable_eplb: bool = False,
        expert_load_view: Optional[torch.Tensor] = None,
        logical_to_physical_map: Optional[torch.Tensor] = None,
        logical_replica_count: Optional[torch.Tensor] = None,
    ) -> torch.Tensor:
        raise NotImplementedError


@CustomOp.register("unquantized_fused_moe")
class UnquantizedFusedMoEMethod(FusedMoEMethodBase, CustomOp):
    """MoE method without quantization."""

    def __init__(self, moe: FusedMoEConfig):
        super().__init__()
        self.fused_experts = fused_experts  # type: ignore
        self.topk_indices_dtype = None
        self.moe = moe

        self.rocm_aiter_moe_enabled = is_rocm_aiter_moe_enabled()
        if self.rocm_aiter_moe_enabled:
            from .rocm_aiter_fused_moe import rocm_aiter_fused_experts
            self.rocm_aiter_fused_experts = rocm_aiter_fused_experts
        else:
            self.rocm_aiter_fused_experts = None  # type: ignore

    def select_gemm_impl(
        self,
        prepare_finalize: FusedMoEPrepareAndFinalize,
        moe: FusedMoEConfig,
    ) -> FusedMoEPermuteExpertsUnpermute:
        if (prepare_finalize.activation_format ==
                FusedMoEActivationFormat.BatchedExperts):
            logger.debug("BatchedTritonExperts %s", self.moe)
            return BatchedTritonExperts(
                max_num_tokens=self.moe.max_num_tokens,
                num_dispatchers=prepare_finalize.num_dispatchers(),
            )
        else:
            logger.debug("TritonExperts %s", self.moe)
            return TritonExperts()

    def create_weights(self, layer: torch.nn.Module, num_experts: int,
                       hidden_size: int, intermediate_size_per_partition: int,
                       params_dtype: torch.dtype, **extra_weight_attrs):
        # Fused gate_up_proj (column parallel)
        w13_weight = torch.nn.Parameter(torch.empty(
            num_experts,
            2 * intermediate_size_per_partition,
            hidden_size,
            dtype=params_dtype),
                                        requires_grad=False)
        layer.register_parameter("w13_weight", w13_weight)
        set_weight_attrs(w13_weight, extra_weight_attrs)

        # down_proj (row parallel)
        w2_weight = torch.nn.Parameter(torch.empty(
            num_experts,
            hidden_size,
            intermediate_size_per_partition,
            dtype=params_dtype),
                                       requires_grad=False)
        layer.register_parameter("w2_weight", w2_weight)
        set_weight_attrs(w2_weight, extra_weight_attrs)

    def _maybe_pad_weight(self, weight: torch.Tensor) -> torch.Tensor:
        # Pad the weight tensor. This is an optimization on ROCm platform, which
        # can benefit from tensors located far enough from one another in memory
        if (envs.VLLM_ROCM_MOE_PADDING and current_platform.is_rocm()
                and weight.stride(-1) == 1
                and (weight.stride(-2) * weight.element_size()) % 512 == 0):
            num_pad = 256 // weight.element_size()
            weight = F.pad(weight, (0, num_pad), "constant", 0)[..., :-num_pad]
            torch.cuda.empty_cache()
        return weight

    def process_weights_after_loading(self, layer: torch.nn.Module) -> None:
        super().process_weights_after_loading(layer)

        # Padding the weight for better performance on ROCm
        layer.w13_weight.data = self._maybe_pad_weight(layer.w13_weight.data)
        layer.w2_weight.data = self._maybe_pad_weight(layer.w2_weight.data)
        # Lazy import to avoid importing triton.
        from vllm.model_executor.layers.fused_moe.rocm_aiter_fused_moe import (
            shuffle_weights)

        if self.rocm_aiter_moe_enabled:
            shuffled_w13, shuffled_w2 = shuffle_weights(
                layer.w13_weight.data, layer.w2_weight.data)

            layer.w13_weight.data = shuffled_w13
            layer.w2_weight.data = shuffled_w2

        if current_platform.is_cpu():
            if current_platform.get_cpu_architecture() == CpuArchEnum.X86:
                from vllm.model_executor.layers.fused_moe import cpu_fused_moe
                dtype = layer.w13_weight.dtype
                if (envs.VLLM_CPU_SGL_KERNEL
                        and torch._C._cpu._is_amx_tile_supported()
                        and dtype == torch.bfloat16):
                    packed_w13_weight = torch.ops._C.convert_weight_packed(
                        layer.w13_weight)
                    assert packed_w13_weight.size() == layer.w13_weight.size()
                    layer.w13_weight.copy_(packed_w13_weight)
                    del packed_w13_weight
                    packed_w2_weight = torch.ops._C.convert_weight_packed(
                        layer.w2_weight)
                    assert packed_w2_weight.size() == layer.w2_weight.size()
                    layer.w2_weight.copy_(packed_w2_weight)
                    layer.cpu_fused_moe = cpu_fused_moe.SGLFusedMOE(layer)
                else:
                    layer.cpu_fused_moe = cpu_fused_moe.IPEXFusedMOE(layer)
            else:
                raise NotImplementedError("CPU MOE only supports x86 arch.")

    def apply(
        self,
        layer: torch.nn.Module,
        x: torch.Tensor,
        router_logits: torch.Tensor,
        top_k: int,
        renormalize: bool,
        use_grouped_topk: bool = False,
        topk_group: Optional[int] = None,
        num_expert_group: Optional[int] = None,
        global_num_experts: int = -1,
        expert_map: Optional[torch.Tensor] = None,
        custom_routing_function: Optional[Callable] = None,
        scoring_func: str = "softmax",
        e_score_correction_bias: Optional[torch.Tensor] = None,
        apply_router_weight_on_input: bool = False,
        activation: str = "silu",
        enable_eplb: bool = False,
        expert_load_view: Optional[torch.Tensor] = None,
        logical_to_physical_map: Optional[torch.Tensor] = None,
        logical_replica_count: Optional[torch.Tensor] = None,
    ) -> torch.Tensor:
        if enable_eplb:
            assert expert_load_view is not None
            assert logical_to_physical_map is not None
            assert logical_replica_count is not None
            assert isinstance(layer, FusedMoE)

        return self.forward(
            x=x,
            layer=layer,
            router_logits=router_logits,
            top_k=top_k,
            renormalize=renormalize,
            use_grouped_topk=use_grouped_topk,
            topk_group=topk_group,
            num_expert_group=num_expert_group,
            global_num_experts=global_num_experts,
            expert_map=expert_map,
            custom_routing_function=custom_routing_function,
            scoring_func=scoring_func,
            e_score_correction_bias=e_score_correction_bias,
            activation=activation,
            apply_router_weight_on_input=apply_router_weight_on_input,
            enable_eplb=enable_eplb,
            expert_load_view=expert_load_view,
            logical_to_physical_map=logical_to_physical_map,
            logical_replica_count=logical_replica_count,
        )

    def forward_cuda(
        self,
        layer: torch.nn.Module,
        x: torch.Tensor,
        use_grouped_topk: bool,
        top_k: int,
        router_logits: torch.Tensor,
        renormalize: bool,
        topk_group: Optional[int] = None,
        num_expert_group: Optional[int] = None,
        global_num_experts: int = -1,
        expert_map: Optional[torch.Tensor] = None,
        custom_routing_function: Optional[Callable] = None,
        scoring_func: str = "softmax",
        e_score_correction_bias: Optional[torch.Tensor] = None,
        apply_router_weight_on_input: bool = False,
        activation: str = "silu",
        enable_eplb: bool = False,
        expert_load_view: Optional[torch.Tensor] = None,
        logical_to_physical_map: Optional[torch.Tensor] = None,
        logical_replica_count: Optional[torch.Tensor] = None,
    ) -> torch.Tensor:

        topk_weights, topk_ids = FusedMoE.select_experts(
            hidden_states=x,
            router_logits=router_logits,
            use_grouped_topk=use_grouped_topk,
            top_k=top_k,
            renormalize=renormalize,
            topk_group=topk_group,
            num_expert_group=num_expert_group,
            custom_routing_function=custom_routing_function,
            scoring_func=scoring_func,
            e_score_correction_bias=e_score_correction_bias,
            indices_type=self.topk_indices_dtype,
            enable_eplb=enable_eplb,
            expert_map=expert_map,
            expert_load_view=expert_load_view,
            logical_to_physical_map=logical_to_physical_map,
            logical_replica_count=logical_replica_count)

        if self.rocm_aiter_moe_enabled:
            return self.rocm_aiter_fused_experts(
                hidden_states=x,
                w1=layer.w13_weight,
                w2=layer.w2_weight,
                topk_weights=topk_weights,
                topk_ids=topk_ids,
                expert_map=expert_map,
                activation=activation,
                apply_router_weight_on_input=apply_router_weight_on_input)
        else:
            return self.fused_experts(
                hidden_states=x,
                w1=layer.w13_weight,
                w2=layer.w2_weight,
                topk_weights=topk_weights,
                topk_ids=topk_ids,
                inplace=True,
                activation=activation,
                apply_router_weight_on_input=apply_router_weight_on_input,
                global_num_experts=global_num_experts,
                expert_map=expert_map,
            )

    def forward_cpu(
        self,
        layer: torch.nn.Module,
        x: torch.Tensor,
        use_grouped_topk: bool,
        top_k: int,
        router_logits: torch.Tensor,
        renormalize: bool,
        topk_group: Optional[int] = None,
        num_expert_group: Optional[int] = None,
        global_num_experts: int = -1,
        expert_map: Optional[torch.Tensor] = None,
        custom_routing_function: Optional[Callable] = None,
        scoring_func: str = "softmax",
        e_score_correction_bias: Optional[torch.Tensor] = None,
        apply_router_weight_on_input: bool = False,
        activation: str = "silu",
        enable_eplb: bool = False,
        expert_load_view: Optional[torch.Tensor] = None,
        logical_to_physical_map: Optional[torch.Tensor] = None,
        logical_replica_count: Optional[torch.Tensor] = None,
    ):
        if enable_eplb is not False or expert_load_view is not None or \
                logical_to_physical_map is not None or \
                logical_replica_count is not None:
            raise NotImplementedError("Expert load balancing is not supported "
                                      "for CPU.")
        return layer.cpu_fused_moe(
            layer,
            x,
            use_grouped_topk,
            top_k,
            router_logits,
            renormalize,
            topk_group,
            num_expert_group,
            global_num_experts,
            expert_map,
            custom_routing_function,
            scoring_func,
            e_score_correction_bias,
            apply_router_weight_on_input,
            activation,
        )

    def forward_tpu(
        self,
        layer: torch.nn.Module,
        x: torch.Tensor,
        use_grouped_topk: bool,
        top_k: int,
        router_logits: torch.Tensor,
        renormalize: bool,
        topk_group: Optional[int] = None,
        num_expert_group: Optional[int] = None,
        global_num_experts: int = -1,
        expert_map: Optional[torch.Tensor] = None,
        custom_routing_function: Optional[Callable] = None,
        scoring_func: str = "softmax",
        e_score_correction_bias: Optional[torch.Tensor] = None,
        apply_router_weight_on_input: bool = False,
        activation: str = "silu",
        enable_eplb: bool = False,
        expert_load_view: Optional[torch.Tensor] = None,
        logical_to_physical_map: Optional[torch.Tensor] = None,
        logical_replica_count: Optional[torch.Tensor] = None,
    ) -> torch.Tensor:
        assert not use_grouped_topk
        assert num_expert_group is None
        assert topk_group is None
        assert custom_routing_function is None
        assert apply_router_weight_on_input is False
        if scoring_func != "softmax":
            raise NotImplementedError(
                "Only softmax scoring function is supported for TPU.")
        if e_score_correction_bias is not None:
            raise NotImplementedError(
                "Expert score correction bias is not supported for TPU.")
        assert activation == "silu", f"{activation} is not supported for TPU."
        if enable_eplb is not False or expert_load_view is not None or \
                logical_to_physical_map is not None or \
                logical_replica_count is not None:
            raise NotImplementedError("Expert load balancing is not supported "
                                      "for TPU.")
        return fused_moe_pallas(hidden_states=x,
                                w1=layer.w13_weight,
                                w2=layer.w2_weight,
                                topk=top_k,
                                gating_output=router_logits,
                                global_num_experts=global_num_experts,
                                expert_map=expert_map,
                                renormalize=renormalize)

    if current_platform.is_tpu():
        forward_native = forward_tpu
    elif current_platform.is_cpu():
        forward_native = forward_cpu
    else:
        forward_native = forward_cuda


def determine_expert_map(
        ep_size: int, ep_rank: int,
        global_num_experts: int) -> tuple[int, Optional[torch.Tensor]]:
    """
        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 (int): The size of the expert parallel group
            global_num_experts (int): The total number of experts in the model.

        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.
        """
    assert ep_size > 0
    if ep_size == 1:
        return (global_num_experts, None)

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

    # Create a tensor of size num_experts filled with -1
    expert_map = torch.full((global_num_experts, ), -1, dtype=torch.int32)
    # Create a expert map for the local experts
    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)
    return (local_num_experts, expert_map)


class FusedMoE(torch.nn.Module):
    """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 all_reduce on the output of the layer
        renomalize: Whether to renormalize the logits in the fused_moe kernel
        quant_config: Quantization configure.
        enable_eplb: Whether to enable expert parallelism load balancer.
    """

    def __init__(
        self,
        num_experts: int,  # Global number of experts
        top_k: int,
        hidden_size: int,
        intermediate_size: int,
        params_dtype: Optional[torch.dtype] = None,
        reduce_results: bool = False,
        renormalize: bool = True,
        use_grouped_topk: bool = False,
        num_expert_group: Optional[int] = None,
        topk_group: Optional[int] = None,
        quant_config: Optional[QuantizationConfig] = None,
        tp_size: Optional[int] = None,
        ep_size: Optional[int] = None,
        dp_size: Optional[int] = None,
        prefix: str = "",
        custom_routing_function: Optional[Callable] = None,
        scoring_func: str = "softmax",
        e_score_correction_bias: Optional[torch.Tensor] = None,
        apply_router_weight_on_input: bool = False,
        activation: str = "silu",
        enable_eplb: bool = False,
        num_redundant_experts: int = 0,
    ):
        super().__init__()
        if params_dtype is None:
            params_dtype = torch.get_default_dtype()
        self.params_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)

        vllm_config = get_current_vllm_config()
        self.moe_parallel_config: FusedMoEParallelConfig = (
            FusedMoEParallelConfig.make(
                tp_size_=tp_size_,
                dp_size_=dp_size_,
                vllm_parallel_config=vllm_config.parallel_config))

        self.global_num_experts = num_experts + num_redundant_experts

        # 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
        self.layer_name = prefix

        self.enable_eplb = enable_eplb
        self.expert_load_view: Optional[torch.Tensor] = None
        self.logical_to_physical_map: Optional[torch.Tensor] = None
        self.logical_replica_count: Optional[torch.Tensor] = None

        # 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.local_num_experts, self.expert_map = determine_expert_map(
                ep_size=self.ep_size,
                ep_rank=self.ep_rank,
                global_num_experts=self.global_num_experts)
        else:
            self.local_num_experts, self.expert_map = (self.global_num_experts,
                                                       None)

        self.top_k = top_k

        assert intermediate_size % self.tp_size == 0
        self.hidden_size = hidden_size
        self.intermediate_size_per_partition = intermediate_size // self.tp_size
        self.reduce_results = reduce_results
        self.renormalize = renormalize
        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.e_score_correction_bias = e_score_correction_bias
        self.apply_router_weight_on_input = apply_router_weight_on_input
        self.activation = activation

        if self.scoring_func != "softmax" and not self.use_grouped_topk:
            raise ValueError("Only softmax scoring function is supported for "
                             "non-grouped topk.")

        if vllm_config.model_config is not None:
            model_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.
            model_dtype = params_dtype

        moe = FusedMoEConfig.make(
            num_experts=self.global_num_experts,
            experts_per_token=top_k,
            hidden_dim=hidden_size,
            num_local_experts=self.local_num_experts,
            moe_parallel_config=self.moe_parallel_config,
            in_dtype=model_dtype,
            max_num_tokens=envs.VLLM_MOE_DP_CHUNK_SIZE,
            quant_config=quant_config,
        )
        self.moe_config = moe
        self.quant_config = quant_config

        # Note: get_quant_method will look at the layer's local_num_experts
        # for heuristic purposes, so it must be initialized first.
        quant_method: Optional[QuantizeMethodBase] = None
        quant_method = (UnquantizedFusedMoEMethod(moe) if quant_config is None
                        else quant_config.get_quant_method(self, prefix))

        assert quant_method is not None
        assert isinstance(quant_method, FusedMoEMethodBase)
        self.quant_method = quant_method

        if self.enable_eplb:
            from vllm.model_executor.layers.quantization.fp8 import (
                Fp8MoEMethod)
            if not isinstance(quant_method,
                              (Fp8MoEMethod, UnquantizedFusedMoEMethod)):
                # 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("EPLB is only supported for FP8 "
                                          "quantization for now.")

        moe_quant_params = {
            "num_experts": self.local_num_experts,
            "hidden_size": hidden_size,
            "intermediate_size_per_partition":
            self.intermediate_size_per_partition,
            "params_dtype": params_dtype,
            "weight_loader": self.weight_loader,
        }
        # 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)
        if isinstance(self.quant_method, FusedMoEMethodBase):
            self.quant_method.maybe_swap_experts_impl(self.moe_parallel_config)

        # Chunked all2all staging tensor
        self.batched_hidden_states: Optional[torch.Tensor] = None
        self.batched_router_logits: Optional[torch.Tensor] = None
        if (self.moe_parallel_config.use_pplx_kernels
                or self.moe_parallel_config.use_deepep_ll_kernels
                or self.moe_parallel_config.use_flashinfer_cutlass_kernels):
            self.batched_hidden_states = torch.zeros(
                (moe.max_num_tokens, self.hidden_size),
                dtype=moe.in_dtype,
                device=torch.cuda.current_device())

            # Note here we use `num_experts` which is logical expert count
            self.batched_router_logits = torch.zeros(
                (moe.max_num_tokens, num_experts),
                dtype=moe.in_dtype,
                device=torch.cuda.current_device())

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

    @property
    def dp_size(self):
        return self.moe_parallel_config.dp_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 dp_rank(self):
        return self.moe_parallel_config.dp_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 use_pplx_kernels(self):
        return self.moe_parallel_config.use_pplx_kernels

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

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

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

    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:
            self.local_num_experts, self.expert_map = determine_expert_map(
                ep_size=self.ep_size,
                ep_rank=self.ep_rank,
                global_num_experts=self.global_num_experts)

    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_w13_weight_scale(self, shard_dim: int,
                               loaded_weight: torch.Tensor,
                               param: torch.Tensor, tp_rank: int):
        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
        shard_size = expert_data.shape[shard_dim] // 2
        if not load_full:
            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]
        if not load_full:
            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()

    @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) -> Optional[bool]:
        expert_id = self._map_global_expert_id_to_local_expert_id(expert_id)
        if expert_id == -1:
            # 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

        quant_method_name = self.quant_method.__class__.__name__
        # 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 self.quant_method.__class__.__name__ in (
                "CompressedTensorsWNA16MarlinMoEMethod",
                "CompressedTensorsWNA16MoEMethod"):
            loaded_weight = loaded_weight.t().contiguous()

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

        WEIGHT_SCALE_SUPPORTED = [
            e.value for e in FusedMoeWeightScaleSupported
        ]
        # 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

        # 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)
        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
        if is_gguf_weight and isinstance(param, UninitializedParameter):
            final_shape = list(loaded_weight.shape)
            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=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(
            )

            # For per-tensor, FP4 uses "weight_scale_2", FP8 uses "weight_scale"
            per_tensor_conditions = (
                "weight_scale_2" in weight_name if uses_weight_scale_2 else
                "weight_scale" in weight_name) or "input_scale" in weight_name

            if "w13_weight_scale" in weight_name:
                self._load_w13_weight_scale(shard_dim=shard_dim,
                                            loaded_weight=loaded_weight,
                                            param=param,
                                            tp_rank=self.tp_rank)
            elif per_tensor_conditions:
                self._load_per_tensor_weight_scale(
                    shard_id=shard_id,
                    param=param,
                    loaded_weight=loaded_weight,
                    expert_id=expert_id,
                )
            elif "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:
                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 get_expert_weights(self) -> Iterable[torch.Tensor]:
        weights = list(self.named_parameters())
        assert all(weight.is_contiguous() for _, weight in weights)

        # 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
        ]

    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.expert_load_view = expert_load_view[moe_layer_idx]
        self.logical_to_physical_map = logical_to_physical_map[moe_layer_idx]
        self.logical_replica_count = logical_replica_count[moe_layer_idx]

    @staticmethod
    def select_experts(
        hidden_states: torch.Tensor,
        router_logits: torch.Tensor,
        top_k: int,
        use_grouped_topk: bool,
        renormalize: bool,
        topk_group: Optional[int] = None,
        num_expert_group: Optional[int] = None,
        custom_routing_function: Optional[Callable] = None,
        scoring_func: str = "softmax",
        e_score_correction_bias: Optional[torch.Tensor] = None,
        indices_type: Optional[torch.dtype] = None,
        enable_eplb: bool = False,
        expert_map: Optional[torch.Tensor] = None,
        expert_load_view: Optional[torch.Tensor] = None,
        logical_to_physical_map: Optional[torch.Tensor] = None,
        logical_replica_count: Optional[torch.Tensor] = None,
    ) -> tuple[torch.Tensor, torch.Tensor]:
        """
        Route the input hidden states to the top-k experts based on the
        router logits.

        Returns:
            (topk_weights, topk_ids) (tuple[torch.Tensor, torch.Tensor]):
            The weights and *global physical* expert ids of the top-k experts.

            **Compatibility**: When EPLB is not enabled, the returned ids are
            equivalent to global logical ids, so should be compatible with
            plain MoE implementations without redundant experts.
        """
        from vllm.model_executor.layers.fused_moe.fused_moe import fused_topk

        # DeepSeekv2 uses grouped_top_k
        if use_grouped_topk:
            assert topk_group is not None
            assert num_expert_group is not None
            topk_weights, topk_ids = grouped_topk(
                hidden_states=hidden_states,
                gating_output=router_logits,
                topk=top_k,
                renormalize=renormalize,
                num_expert_group=num_expert_group,
                topk_group=topk_group,
                scoring_func=scoring_func,
                e_score_correction_bias=e_score_correction_bias)
            if indices_type is not None:
                topk_ids = topk_ids.to(dtype=indices_type)
        elif custom_routing_function is None:
            topk_weights, topk_ids, token_expert_indices = fused_topk(
                hidden_states=hidden_states,
                gating_output=router_logits,
                topk=top_k,
                renormalize=renormalize,
                indices_type=indices_type,
            )
        else:
            topk_weights, topk_ids = custom_routing_function(
                hidden_states=hidden_states,
                gating_output=router_logits,
                topk=top_k,
                renormalize=renormalize)
            if indices_type is not None:
                topk_ids = topk_ids.to(dtype=indices_type)

        if enable_eplb:
            assert expert_load_view is not None
            assert logical_to_physical_map is not None
            assert logical_replica_count is not None

            # 1. Convert the logical expert ids to physical expert ids
            # Directly select a random replica for each logical expert

            # TODO: maybe optimize this by using specified kernels,
            # or compute pseudo-random indices by modulo

            # In case `indices_type` is not `torch.long` or `torch.int`,
            # e.g. `torch.uint32` as required by dispatch/combine kernels
            topk_ids_long = topk_ids.long()
            replica_indices = (
                torch.rand_like(topk_ids, dtype=torch.float) *
                logical_replica_count[topk_ids_long]).long().unsqueeze(-1)
            physical_ids = logical_to_physical_map[topk_ids_long].gather(
                -1, replica_indices).squeeze(-1)

            topk_ids = physical_ids

            # 2. Record expert load metrics.

            # TODO(bowen): When using `FusedMoEModularKernel`, this
            # can be done in a more unified way, since
            # `FusedMoEPrepareAndFinalize` will return the expert
            # token count, in some cases directly from the kernel.
            # However, now there are many code paths not using
            # the modular kernel, e.g. calling `fused_experts`,
            # so we decide to keep the logic here.
            #
            # If later refactor moved all the MoE kernel calls
            # to the modular kernel, we can move this logic there
            # to achieve better efficiency.

            # `expert_load_view`: (num_logical_experts,)

            # Mask out non-local experts
            if expert_map is not None:
                topk_ids_local = expert_map[topk_ids]
                topk_ids_flatten = topk_ids_local.flatten()
            else:
                topk_ids_flatten = topk_ids.flatten()

            # Should be equivalent to:
            # ```
            # topk_ids_masked = topk_ids_local[topk_ids_local >= 0]
            # expert_load_view += topk_ids_masked.bincount(
            #     minlength=expert_load_view.shape[0])
            # ```
            # We use `scatter_add_` since `bincount` cannot be compiled

            # Performance optimization:
            # `masked_fill` is significantly faster than `masked_select`
            invalid_mask = topk_ids_flatten < 0
            # Replace invalid expert ids with 0 (just a dummy position)
            # to avoid out-of-bounds errors in scatter_add_
            index = topk_ids_flatten.masked_fill_(invalid_mask, 0)
            # `src` is the valid mask, which is 1 for valid and 0 for invalid
            src = ~invalid_mask

            expert_load_view.scatter_add_(dim=0,
                                          index=index.long(),
                                          src=src.to(expert_load_view))

            topk_ids = topk_ids.to(dtype=indices_type)

        assert topk_ids.dtype == indices_type or indices_type is None

        return topk_weights, topk_ids

    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.use_pplx_kernels or self.use_deepep_ht_kernels
                or self.use_deepep_ll_kernels)

    def maybe_all_reduce_tensor_model_parallel(
            self, final_hidden_states: torch.Tensor):
        """
        The pplx combine kernel reduces across GPU ranks by default.
        """
        if (self.use_pplx_kernels or self.use_deepep_ht_kernels
                or self.use_deepep_ll_kernels):
            return final_hidden_states
        else:
            return tensor_model_parallel_all_reduce(final_hidden_states)

    def forward(self, hidden_states: torch.Tensor,
                router_logits: torch.Tensor):
        # TODO: Once the OOM issue for the TPU backend is resolved, we will
        # switch to using the moe_forward custom op.
        if current_platform.is_tpu():
            return self.forward_impl(hidden_states, router_logits)
        else:
            return torch.ops.vllm.moe_forward(hidden_states, router_logits,
                                              self.layer_name)

    def forward_impl_chunked(self, full_hidden_states: torch.Tensor,
                             full_router_logits: torch.Tensor):
        assert self.batched_hidden_states is not None
        assert self.batched_router_logits is not None
        assert self.batched_hidden_states.dtype == full_hidden_states.dtype
        assert self.batched_router_logits.dtype == full_router_logits.dtype
        # Check size compatibility.
        assert (
            self.batched_hidden_states.size(-1) == full_hidden_states.size(-1))
        assert (
            self.batched_router_logits.size(-1) == full_router_logits.size(-1))

        full_final_hidden_states = torch.empty_like(full_hidden_states)

        def process_chunk(chunk_start, chunk_end, skip_result_store=False):
            chunk_size = chunk_end - chunk_start
            hidden_states = full_hidden_states[chunk_start:chunk_end, :]
            router_logits = full_router_logits[chunk_start:chunk_end, :]

            assert (self.batched_hidden_states.size(0)  # type: ignore
                    >= chunk_size)
            assert (self.batched_router_logits.size(0)  # type: ignore
                    >= chunk_size)
            staged_hidden_states = self.batched_hidden_states[:
                                                              chunk_size, :]  # type: ignore
            staged_router_logits = self.batched_router_logits[:
                                                              chunk_size, :]  # type: ignore
            staged_hidden_states.copy_(hidden_states, non_blocking=True)
            staged_router_logits.copy_(router_logits, non_blocking=True)

            # Matrix multiply.
            final_hidden_states = self.quant_method.apply(
                layer=self,
                x=staged_hidden_states,
                router_logits=staged_router_logits,
                top_k=self.top_k,
                renormalize=self.renormalize,
                use_grouped_topk=self.use_grouped_topk,
                global_num_experts=self.global_num_experts,
                expert_map=self.expert_map,
                topk_group=self.topk_group,
                num_expert_group=self.num_expert_group,
                custom_routing_function=self.custom_routing_function,
                scoring_func=self.scoring_func,
                e_score_correction_bias=self.e_score_correction_bias,
                activation=self.activation,
                enable_eplb=self.enable_eplb,
                expert_load_view=self.expert_load_view,
                logical_to_physical_map=self.logical_to_physical_map,
                logical_replica_count=self.logical_replica_count,
            )

            if not skip_result_store:
                full_final_hidden_states[chunk_start:chunk_end, :].copy_(
                    final_hidden_states, non_blocking=True)

        ctx = get_forward_context()
        # flashinfer_cutlass_kernels can handle: optional DP + TP/EP
        max_tokens_across_dp = ctx.dp_metadata.max_tokens_across_dp_cpu
        moe_dp_chunk_size_per_rank = self.moe_config.max_num_tokens
        num_tokens = full_hidden_states.size(0)
        for chunk_start_ in range(0, max_tokens_across_dp,
                                  moe_dp_chunk_size_per_rank):
            chunk_start = chunk_start_
            chunk_end = min(chunk_start + moe_dp_chunk_size_per_rank,
                            max_tokens_across_dp)
            # clamp start and end
            chunk_start = min(chunk_start, num_tokens - 1)
            chunk_end = min(chunk_end, num_tokens)

            process_chunk(chunk_start,
                          chunk_end,
                          skip_result_store=chunk_start_ >= num_tokens)

        return full_final_hidden_states

    def forward_impl(self, hidden_states: torch.Tensor,
                     router_logits: torch.Tensor):
        assert self.quant_method is not None
        # Route to the chunked forward path using the FlashInfer Cutlass kernel
        # only when data parallelism (DP) is enabled.
        use_flashinfer_cutlass_kernels = (
            self.dp_size > 1
            and self.moe_parallel_config.use_flashinfer_cutlass_kernels)
        if (self.moe_parallel_config.use_pplx_kernels
                or self.moe_parallel_config.use_deepep_ll_kernels
                or use_flashinfer_cutlass_kernels):
            return self.forward_impl_chunked(hidden_states, router_logits)

        do_naive_dispatch_combine: bool = (
            self.dp_size > 1
            and not self.moe_parallel_config.use_deepep_ht_kernels
            and not self.moe_parallel_config.use_flashinfer_cutlass_kernels)
        if do_naive_dispatch_combine:
            hidden_states, router_logits = get_ep_group().dispatch(
                hidden_states, router_logits)

        # Matrix multiply.
        final_hidden_states = self.quant_method.apply(
            layer=self,
            x=hidden_states,
            router_logits=router_logits,
            top_k=self.top_k,
            renormalize=self.renormalize,
            use_grouped_topk=self.use_grouped_topk,
            global_num_experts=self.global_num_experts,
            expert_map=self.expert_map,
            topk_group=self.topk_group,
            num_expert_group=self.num_expert_group,
            custom_routing_function=self.custom_routing_function,
            scoring_func=self.scoring_func,
            e_score_correction_bias=self.e_score_correction_bias,
            activation=self.activation,
            apply_router_weight_on_input=self.apply_router_weight_on_input,
            enable_eplb=self.enable_eplb,
            expert_load_view=self.expert_load_view,
            logical_to_physical_map=self.logical_to_physical_map,
            logical_replica_count=self.logical_replica_count,
        )

        if do_naive_dispatch_combine:
            final_hidden_states = get_ep_group().combine(final_hidden_states)
        if self.reduce_results and (self.tp_size > 1 or self.ep_size > 1):
            # Default set to False. (May have to add shared expert outputs.
            final_hidden_states = self.maybe_all_reduce_tensor_model_parallel(
                final_hidden_states)

        return final_hidden_states

    @classmethod
    def make_expert_params_mapping(
            cls,
            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)

        return [
            # (param_name, weight_name, expert_id, shard_id)
            ("experts.w13_" if weight_name
             in [ckpt_gate_proj_name, ckpt_up_proj_name] else "experts.w2_",
             f"experts.{physical_to_logical_map[expert_id]}.{weight_name}.",
             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}, "
            f"renormalize={self.renormalize}, "
            f"use_grouped_topk={self.use_grouped_topk}")

        if self.use_grouped_topk:
            s += f", num_expert_group={self.num_expert_group}, topk_group={self.topk_group}"  # noqa: E501

        s += f", scoring_func='{self.scoring_func}', activation='{self.activation}'"  # noqa: E501

        return s


def moe_forward(hidden_states: torch.Tensor, router_logits: torch.Tensor,
                layer_name: str) -> torch.Tensor:
    forward_context: ForwardContext = get_forward_context()
    self = forward_context.no_compile_layers[layer_name]
    assert self.quant_method is not None

    return self.forward_impl(hidden_states, router_logits)


def moe_forward_fake(hidden_states: torch.Tensor, router_logits: torch.Tensor,
                     layer_name: str) -> torch.Tensor:
    return torch.empty_like(hidden_states)


direct_register_custom_op(
    op_name="moe_forward",
    op_func=moe_forward,
    mutates_args=["hidden_states"],
    fake_impl=moe_forward_fake,
    dispatch_key=current_platform.dispatch_key,
    tags=(torch.Tag.needs_fixed_stride_order, ),
)

# 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]
