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

from abc import abstractmethod

import torch

import vllm.model_executor.layers.fused_moe.modular_kernel as mk
from vllm.model_executor.layers.fused_moe import FusedMoEMethodBase
from vllm.model_executor.layers.fused_moe.config import FusedMoEQuantConfig
from vllm.model_executor.model_loader.reload.layerwise import (
    initialize_online_processing,
)
from vllm.model_executor.utils import set_weight_attrs


class OnlineMoEMethodBase(FusedMoEMethodBase):
    """Base for MoE methods that load full-precision weights on meta device
    and quantize them after loading via the QeRL layerwise processing system.
    """

    uses_meta_device: bool = True

    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,
    ):
        layer.num_experts = num_experts
        layer.orig_dtype = params_dtype
        layer.weight_block_size = None

        # Fused gate_up_proj (column parallel) — full precision on meta device
        w13_weight = torch.nn.Parameter(
            torch.empty(
                num_experts,
                2 * intermediate_size_per_partition,
                hidden_size,
                device="meta",
                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) — full precision on meta device
        w2_weight = torch.nn.Parameter(
            torch.empty(
                num_experts,
                hidden_size,
                intermediate_size_per_partition,
                device="meta",
                dtype=params_dtype,
            ),
            requires_grad=False,
        )
        layer.register_parameter("w2_weight", w2_weight)
        set_weight_attrs(w2_weight, extra_weight_attrs)

        # BIASES (for models like GPT-OSS that have biased MoE)
        if self.moe.has_bias:
            w13_bias = torch.nn.Parameter(
                torch.zeros(
                    num_experts,
                    2 * intermediate_size_per_partition,
                    device="meta",
                    dtype=layer.orig_dtype,
                ),
                requires_grad=False,
            )
            layer.register_parameter("w13_bias", w13_bias)
            set_weight_attrs(w13_bias, extra_weight_attrs)

            w2_bias = torch.nn.Parameter(
                torch.zeros(
                    num_experts,
                    hidden_size,
                    device="meta",
                    dtype=layer.orig_dtype,
                ),
                requires_grad=False,
            )
            layer.register_parameter("w2_bias", w2_bias)
            set_weight_attrs(w2_bias, extra_weight_attrs)

        layer.w13_input_scale = None
        layer.w2_input_scale = None

        initialize_online_processing(layer)

    @abstractmethod
    def process_weights_after_loading(self, layer: torch.nn.Module) -> None:
        pass

    def _maybe_inject_biases(
        self,
        quant_config: FusedMoEQuantConfig,
        layer: torch.nn.Module,
    ) -> None:
        """Inject biases into the quant config if the model has them
        (e.g. GPT-OSS biased MoE)."""
        if self.moe.has_bias:
            w13_bias = getattr(layer, "w13_bias", None)
            w2_bias = getattr(layer, "w2_bias", None)
            if w13_bias is not None:
                quant_config._w1.bias = w13_bias
            if w2_bias is not None:
                quant_config._w2.bias = w2_bias

    def maybe_make_prepare_finalize(
        self,
        routing_tables: tuple[torch.Tensor, torch.Tensor, torch.Tensor] | None = None,
    ) -> mk.FusedMoEPrepareAndFinalizeModular | None:
        raise ValueError(
            f"{self.__class__.__name__} uses the new modular kernel "
            "initialization logic. This function should not be called."
        )

    @property
    def supports_eplb(self) -> bool:
        return True

    def apply_monolithic(
        self,
        layer: "FusedMoE",  # type: ignore[name-defined] # noqa: F821
        x: torch.Tensor,
        router_logits: torch.Tensor,
    ) -> torch.Tensor | tuple[torch.Tensor, torch.Tensor]:
        assert self.is_monolithic
        assert self.moe_kernel is not None
        return self.moe_kernel.apply_monolithic(
            x,
            layer.w13_weight,
            layer.w2_weight,
            router_logits,
            activation=layer.activation,
            global_num_experts=layer.global_num_experts,
            expert_map=layer.expert_map,
            apply_router_weight_on_input=layer.apply_router_weight_on_input,
            num_expert_group=layer.num_expert_group,
            topk_group=layer.topk_group,
            e_score_correction_bias=layer.e_score_correction_bias,
            routed_scaling_factor=layer.routed_scaling_factor,
        )

    def apply(
        self,
        layer: "FusedMoE",  # type: ignore[name-defined] # noqa: F821
        x: torch.Tensor,
        topk_weights: torch.Tensor,
        topk_ids: torch.Tensor,
        shared_experts_input: torch.Tensor | None,
    ) -> torch.Tensor | tuple[torch.Tensor, torch.Tensor]:
        assert not self.is_monolithic
        assert self.moe_kernel is not None
        return self.moe_kernel.apply(
            x,
            layer.w13_weight,
            layer.w2_weight,
            topk_weights,
            topk_ids,
            activation=layer.activation,
            global_num_experts=layer.global_num_experts,
            expert_map=layer.expert_map,
            apply_router_weight_on_input=layer.apply_router_weight_on_input,
            shared_experts_input=shared_experts_input,
        )
