from typing import Callable, List, Optional, Tuple, Union

import torch
import torch.nn as nn

from sglang.srt.configs.model_config import ModelConfig
from sglang.srt.custom_op import CustomOp
from sglang.srt.distributed import (
    get_tensor_model_parallel_rank,
    get_tensor_model_parallel_world_size,
    tensor_model_parallel_all_gather,
    tensor_model_parallel_all_reduce,
)
from sglang.srt.distributed.utils import divide
from sglang.srt.layers.attention.fla.layernorm_gated import layernorm_fn
from sglang.srt.layers.attention.mamba.causal_conv1d import (
    causal_conv1d_fn,
    causal_conv1d_update,
)
from sglang.srt.layers.attention.mamba.mamba_utils import MambaStateShapeCalculator
from sglang.srt.layers.attention.mamba.ops import (
    mamba_chunk_scan_combined,
    selective_state_update,
)
from sglang.srt.layers.linear import (
    ColumnParallelLinear,
    MergedColumnParallelLinear,
    RowParallelLinear,
)
from sglang.srt.layers.quantization.base_config import QuantizationConfig
from sglang.srt.model_executor.forward_batch_info import ForwardBatch
from sglang.srt.model_loader.weight_utils import (
    composed_weight_loader,
    sharded_weight_loader,
)
from sglang.srt.utils import set_weight_attrs

LoaderFunction = Callable[[torch.Tensor, torch.Tensor], None]


def mamba_v2_sharded_weight_loader(
    shard_spec: List[Tuple[int, int, float]],
    tp_size: int,
    tp_rank: int,
) -> LoaderFunction:
    """Create a weight loader for mamba v2. This ensures that the projections
    are correctly sharded so that they can be split into x, B, C. It also
    ensures the the all the groups corresponding to a head shard is placed
    together with it.
    """

    def loader(param: torch.Tensor, loaded_weight: torch.Tensor) -> None:

        # - track boundary of (sharded) param, and loaded_weight, respectively
        boundary, loaded_boundary = 0, 0

        # - iterate over the shard specs
        for full_dim, extra, duplicate_groups in shard_spec:
            # - full dim is the model dim (before TP).
            # - extra > 0, means there is expected overall increase
            #   of dimensions. This is so because of replication.
            # - ratio is used map the tp_rank to the actual shard
            #   rank. This is useful when there is replication of
            #   groups to accompany head shards.

            # - size of the loaded shard
            shard_size = full_dim // tp_size

            # - compute the rank into the loaded shard.
            # - if there is replication, different TP shards will
            #   take from the same rank.
            # NOTE: currently we only support duplication
            # in the case where num_groups == 1
            rank = 0 if duplicate_groups else tp_rank

            # - leftmost boundary index into loaded weight.
            loaded_skip = rank * shard_size
            loaded_start_idx = loaded_boundary + loaded_skip

            # - take these many dims from the loaded weight.
            take = min(shard_size, full_dim - extra - loaded_skip)

            # - always shard on dim 0
            # - the ignore is for a mundane mypy error as it does not
            #   seem to handle slices well.
            # https://github.com/python/mypy/issues/2410
            param.data[
                boundary : (boundary + take), ...  # type: ignore[misc]
            ] = loaded_weight[
                loaded_start_idx : (loaded_start_idx + take)  # type: ignore[misc]
            ]  # type: ignore[misc]

            # move indexing boundaries
            boundary += shard_size
            loaded_boundary += full_dim - extra

    return loader


class Mixer2RMSNormGated(CustomOp):

    def __init__(
        self,
        full_hidden_size: int,
        full_n_groups: int,
        use_rms_norm: bool = True,
        eps: float = 1e-6,
    ):
        super().__init__()
        self.tp_size = get_tensor_model_parallel_world_size()
        self.tp_rank = get_tensor_model_parallel_rank()
        self.full_hidden_size = full_hidden_size
        self.group_size = full_hidden_size // full_n_groups
        self.per_rank_hidden_size = full_hidden_size // self.tp_size
        self.n_groups = full_hidden_size // self.group_size

        self.variance_epsilon = eps
        self.use_rms_norm = use_rms_norm
        if self.use_rms_norm:
            # Register norm weight only if we're actually applying RMSNorm
            self.weight = nn.Parameter(torch.ones(self.per_rank_hidden_size))
            set_weight_attrs(self.weight, {"weight_loader": sharded_weight_loader(0)})
        else:
            # Avoid checkpoint mismatch by skipping unused parameter
            self.register_parameter("weight", None)
        assert (
            self.full_hidden_size % self.tp_size == 0
        ), "Tensor parallel world size must divide hidden size."

    def forward_native(
        self,
        x: torch.Tensor,
        gate: torch.Tensor,
    ):
        # Three tensor-parallel cases:
        #   1. n_groups is 1
        #      In this case we parallelize along the reduction dim.
        #      Each rank computes a local sum of squares followed by AllReduce
        #   2. tp_size divides n_groups
        #      Each rank only reduces within its local group(s).
        #      No collective ops necessary.
        #   3. The general case can be pretty complicated so we AllGather
        #      the input and then redundantly compute the RMSNorm.
        input_dtype = x.dtype
        x = x * nn.functional.silu(gate.to(torch.float32))
        if not self.use_rms_norm:
            return x.to(input_dtype)

        if self.n_groups == 1:
            if self.tp_size > 1:
                # Compute local sum and then reduce to obtain global sum
                local_sums = x.pow(2).sum(dim=-1, keepdim=True)
                global_sums = tensor_model_parallel_all_reduce(local_sums)
                # Calculate the variance
                count = self.tp_size * x.shape[-1]
                variance = global_sums / count

            else:
                variance = x.pow(2).mean(-1, keepdim=True)
            x = x * torch.rsqrt(variance + self.variance_epsilon)
        else:
            redundant_tp: bool = self.n_groups % self.tp_size != 0
            if redundant_tp:
                # To handle the general case, redundantly apply the variance
                x = tensor_model_parallel_all_gather(x, -1)

            *prefix_dims, hidden_dim = x.shape
            group_count = hidden_dim // self.group_size
            x_grouped = x.view(*prefix_dims, group_count, self.group_size)
            variance = x_grouped.pow(2).mean(-1, keepdim=True)
            x_grouped = x_grouped * torch.rsqrt(variance + self.variance_epsilon)
            x = x_grouped.view(*prefix_dims, hidden_dim)

            if redundant_tp:
                start = self.per_rank_hidden_size * self.tp_rank
                end = start + self.per_rank_hidden_size
                x = x[..., start:end]

        return self.weight * x.to(input_dtype)

    def forward_cuda(
        self,
        x: torch.Tensor,
        gate: torch.Tensor,
    ) -> Union[torch.Tensor, tuple[torch.Tensor, torch.Tensor]]:
        input_dtype = x.dtype
        if not self.use_rms_norm:
            # Keep gate in float32 for numerical stability during silu
            return x * nn.functional.silu(gate.to(torch.float32)).to(input_dtype)

        if ((self.n_groups % self.tp_size) != 0) or self.n_groups != 1:
            return self.forward_native(x, gate)

        return layernorm_fn(
            x,
            self.weight.data,
            bias=None,
            z=gate,
            eps=self.variance_epsilon,
            norm_before_gate=False,
        )


class MambaMixer2(torch.nn.Module):
    """
    Compute ∆, A, B, C, and D the state space parameters and compute
    the `contextualized_states`. A, D are input independent
    (see Mamba paper [1] Section 3.5.2 "Interpretation of A"
    for why A isn't selective) ∆, B, C are input-dependent
    (this is a key difference between Mamba and the linear time
    invariant S4, and is why Mamba is called
    **selective** state spaces)
    """

    def __init__(
        self,
        hidden_size: int,
        ssm_state_size: int,
        conv_kernel_size: int,
        intermediate_size: int,
        use_conv_bias: bool,
        use_bias: bool,
        chunk_size: int,
        layer_id: int,
        n_groups: int = 1,
        num_heads: int = 128,
        head_dim: int = 64,
        rms_norm_eps: float = 1e-5,
        activation: str = "silu",
        use_rms_norm: bool = True,
        model_config: Optional[ModelConfig] = None,
        #  cache_config: Optional[CacheConfig] = None,
        quant_config: Optional[QuantizationConfig] = None,
        prefix: str = "",
    ):
        super().__init__()

        # For TP, the sharding plan is as follows:
        # - for the conv modules, since
        #   conv_dim = intermediate_size * 2 * n_groups * ssm_state_size,
        #   we shard intermediate_size and n_groups
        # - since intermediate_size = n_heads * head_dim, sharding on
        #   intermediate_size is achieved by sharding on n_heads.
        # - IF, world_size divides groups, then sharding
        #   (n_groups / world_size, n_heads / world_size)
        #   also maintains the invariant n_heads % n_groups == 0
        # - HOWEVER IF, world_size DOES NOT divide groups, then we need
        #   to allocate extra space in the shard, such that groups
        #   may be replicated to follow the head shard.
        # - NOTE: currently for the world size DOES NOT divide groups
        #   case, we only support the case when n_groups == 1
        self.tp_size = get_tensor_model_parallel_world_size()
        self.tp_rank = get_tensor_model_parallel_rank()

        assert (
            num_heads % self.tp_size == 0
        ), "Tensor parallel world size must divide num heads."

        assert (n_groups % self.tp_size) == 0 or n_groups == 1, (
            "If tensor parallel world size does not divide num_groups, "
            "then num_groups must equal 1."
        )

        self.ssm_state_size = ssm_state_size
        self.conv_kernel_size = conv_kernel_size
        self.activation = activation
        self.layer_id = layer_id

        self.intermediate_size = intermediate_size
        self.head_dim = head_dim
        self.num_heads = num_heads
        self.chunk_size = chunk_size

        self.n_groups = n_groups
        if n_groups % self.tp_size != 0:
            # - for TP we shard conv_dim by sharding on n_groups,
            # - but if n_groups cannot divide tp_size, we need to
            #   extend some extra groups
            groups = MambaStateShapeCalculator.extra_groups_for_head_shards(
                n_groups, self.tp_size
            )
            self.n_groups = n_groups + groups

        self.groups_ssm_state_size = self.n_groups * self.ssm_state_size
        self.conv_dim = intermediate_size + 2 * self.groups_ssm_state_size

        self.conv1d = MergedColumnParallelLinear(
            input_size=conv_kernel_size,
            output_sizes=[
                intermediate_size,
                self.groups_ssm_state_size,
                self.groups_ssm_state_size,
            ],
            bias=use_conv_bias,
            quant_config=None,
            prefix=f"{prefix}.conv1d",
        )

        self.in_proj = MergedColumnParallelLinear(
            input_size=hidden_size,
            output_sizes=[
                intermediate_size,
                intermediate_size,
                self.groups_ssm_state_size,
                self.groups_ssm_state_size,
                self.num_heads,
            ],
            bias=use_bias,
            prefix=f"{prefix}.in_proj",
        )
        if n_groups % self.tp_size != 0:
            # This is the n_groups == 1 case,
            # where we need to duplicate groups if TP>1.

            # - because in_proj is a concatenation of 3 weights, we
            #   need to interleave them before sharding
            # - use the custom weight loader mamba_v2_sharded_weight_loader
            #   for conv1d.bias, covn1d.weight and in_proj.weight
            # - need to set these settings, to assign the groups
            #   to the head shards
            group_shard_settings = (
                self.groups_ssm_state_size,  # expected model size
                (self.n_groups - n_groups) * self.ssm_state_size,  # extra dims assigned
                n_groups == 1,  # if there was only one group
            )
            intermediate_settings = (intermediate_size, 0, False)
            head_settings = (self.num_heads, 0, False)

            # - the weight already has a "weight_loader" attribute
            #   which set_weight_attrs will raise if we do not
            #   delete before trying to override it
            # - ditto for the other two weights below
            delattr(self.conv1d.bias, "weight_loader")
            set_weight_attrs(
                self.conv1d.bias,
                {
                    "weight_loader": mamba_v2_sharded_weight_loader(
                        [
                            intermediate_settings,
                            group_shard_settings,
                            group_shard_settings,
                        ],
                        self.tp_size,
                        self.tp_rank,
                    )
                },
            )

            delattr(self.conv1d.weight, "weight_loader")
            set_weight_attrs(
                self.conv1d.weight,
                {
                    "weight_loader": mamba_v2_sharded_weight_loader(
                        [
                            intermediate_settings,
                            group_shard_settings,
                            group_shard_settings,
                        ],
                        self.tp_size,
                        self.tp_rank,
                    )
                },
            )

            if quant_config is None:
                # - quant layers do not have a weight loader
                delattr(self.in_proj.weight, "weight_loader")
                set_weight_attrs(
                    self.in_proj.weight,
                    {
                        "weight_loader": mamba_v2_sharded_weight_loader(
                            [
                                intermediate_settings,  # for gate
                                intermediate_settings,
                                group_shard_settings,
                                group_shard_settings,
                                head_settings,  # for dt
                            ],
                            self.tp_size,
                            self.tp_rank,
                        )
                    },
                )

        # unsqueeze to fit conv1d weights shape into the linear weights shape.
        # Can't do this in `weight_loader` since it already exists in
        # `ColumnParallelLinear` and `MergedColumnParallelLinear`,
        # and `set_weight_attrs` doesn't allow to override it
        self.conv1d.weight.data = self.conv1d.weight.data.unsqueeze(1)

        # - these are TPed by heads to reduce the size of the
        #   temporal shape
        self.A = nn.Parameter(
            torch.empty(
                divide(num_heads, self.tp_size),
                dtype=torch.float32,
            )
        )
        self.D = nn.Parameter(torch.ones(num_heads // self.tp_size))
        self.dt_bias = nn.Parameter(torch.ones(num_heads // self.tp_size))
        self.use_rms_norm = use_rms_norm

        set_weight_attrs(self.D, {"weight_loader": sharded_weight_loader(0)})
        a_weight_loader = composed_weight_loader(
            sharded_weight_loader(0), lambda x: -torch.exp(x.float())
        )
        set_weight_attrs(self.A, {"weight_loader": a_weight_loader})
        set_weight_attrs(self.dt_bias, {"weight_loader": sharded_weight_loader(0)})

        self.out_proj = RowParallelLinear(
            intermediate_size,
            hidden_size,
            bias=use_bias,
            input_is_parallel=True,
            quant_config=quant_config,
            prefix=f"{prefix}.out_proj",
            reduce_results=False,
        )

        self.norm = Mixer2RMSNormGated(
            intermediate_size, n_groups, self.use_rms_norm, eps=rms_norm_eps
        )

        # The tuple is (conv_state, ssm_state)
        self.kv_cache = (torch.tensor([]), torch.tensor([]))

        self.model_config = model_config
        self.prefix = prefix

    def forward_native(
        self,
        hidden_states: torch.Tensor,
        output: torch.Tensor,
        mup_vector: Optional[torch.Tensor] = None,
    ):
        pass

    def forward(
        self,
        hidden_states: torch.Tensor,
        output: torch.Tensor,
        forward_batch: ForwardBatch,
        mup_vector: Optional[torch.Tensor] = None,
    ):
        # attn_backend_list[-1] gives access to MambaAttnBackend
        mamba_backend = forward_batch.attn_backend.attn_backend_list[-1]
        attn_metadata = mamba_backend.forward_metadata
        state_indices_tensor = attn_metadata.mamba_cache_indices
        chunk_size = self.chunk_size

        conv_state, ssm_state, *rest = mamba_backend.req_to_token_pool.get_mamba_params(
            self.layer_id
        )

        assert (
            ssm_state.size(1) == self.ssm_state_size
        ), f"dstate must be {self.ssm_state_size}, got {ssm_state.size(1)}"

        query_start_loc = attn_metadata.query_start_loc

        chunk_size = self.chunk_size

        # TODO: properly support this
        prep_initial_states = False

        # 1. Gated MLP's linear projection
        projected_states, _ = self.in_proj(hidden_states)

        if mup_vector is not None:
            projected_states = projected_states * mup_vector

        gate, hidden_states_B_C, dt = torch.split(
            projected_states,
            [
                self.intermediate_size // self.tp_size,
                self.conv_dim // self.tp_size,
                self.num_heads // self.tp_size,
            ],
            dim=-1,
        )
        conv_weights = self.conv1d.weight.view(
            self.conv1d.weight.size(0), self.conv1d.weight.size(2)
        )

        # - get hidden_states, B and C after depthwise convolution.
        split_hidden_states_B_C_fn = lambda hidden_states_B_C: torch.split(
            hidden_states_B_C,
            [
                self.intermediate_size // self.tp_size,
                self.groups_ssm_state_size // self.tp_size,
                self.groups_ssm_state_size // self.tp_size,
            ],
            dim=-1,
        )

        preallocated_ssm_out = torch.empty(
            [
                projected_states.shape[0],
                (self.num_heads * self.head_dim) // self.tp_size,
            ],
            dtype=hidden_states.dtype,
            device=hidden_states.device,
        )

        # Process prefill requests
        if forward_batch.forward_mode.is_extend():
            # 2. Convolution sequence transformation
            # - "cache_indices" updates the conv_state cache in positions
            #   pointed to by "state_indices_tensor"
            num_prefill_tokens = forward_batch.extend_num_tokens or 0
            has_initial_states = forward_batch.extend_prefix_lens > 0
            cache_indices = attn_metadata.mamba_cache_indices

            x = hidden_states_B_C.transpose(
                0, 1
            )  # this is the form that causal-conv see
            hidden_states_B_C = causal_conv1d_fn(
                x,
                conv_weights,
                self.conv1d.bias,
                activation=self.activation,
                conv_states=conv_state,
                has_initial_state=has_initial_states,
                cache_indices=cache_indices,
                query_start_loc=query_start_loc,
                seq_lens_cpu=forward_batch.extend_seq_lens_cpu,
            ).transpose(0, 1)

            hidden_states, B, C = split_hidden_states_B_C_fn(hidden_states_B_C)

            # 3. State Space Model sequence transformation
            initial_states = None

            if has_initial_states is not None and prep_initial_states:
                initial_states = torch.where(
                    has_initial_states[:, None, None, None],
                    ssm_state[state_indices_tensor],
                    0,
                )

            # NOTE: final output is an in-place update of out tensor
            varlen_state = mamba_chunk_scan_combined(
                hidden_states.view(
                    1, num_prefill_tokens, self.num_heads // self.tp_size, self.head_dim
                ),
                dt.unsqueeze(0),
                self.A,
                B.view(1, num_prefill_tokens, self.n_groups // self.tp_size, -1),
                C.view(1, num_prefill_tokens, self.n_groups // self.tp_size, -1),
                chunk_size=chunk_size,
                D=self.D,
                z=None,
                dt_bias=self.dt_bias,
                cu_seqlens=query_start_loc,
                initial_states=initial_states,
                return_varlen_states=True,
                return_final_states=False,
                dt_softplus=True,
                dt_limit=(0.0, float("inf")),
                out=preallocated_ssm_out.view(1, num_prefill_tokens, -1, self.head_dim),
                state_dtype=ssm_state.dtype,
            )

            # update ssm states
            # - varlen state is a (num_prefills, nheads, headdim, dstate) tensor
            ssm_state[state_indices_tensor] = varlen_state.permute(0, 3, 2, 1)
        elif forward_batch.forward_mode.is_decode():
            num_decodes = len(query_start_loc) - 1
            # 2. Convolution sequence transformation
            hidden_states_B_C = causal_conv1d_update(
                hidden_states_B_C,
                conv_state,
                conv_weights,
                self.conv1d.bias,
                self.activation,
                conv_state_indices=state_indices_tensor,
            )

            hidden_states, B, C = split_hidden_states_B_C_fn(hidden_states_B_C)

            # 3. State Space Model sequence transformation
            n_groups = self.n_groups // self.tp_size
            A = (
                self.A[:, None, ...][:, :, None]
                .expand(-1, self.head_dim, self.ssm_state_size)
                .to(dtype=torch.float32)
            )
            dt = dt[:, :, None].expand(-1, -1, self.head_dim)
            dt_bias = self.dt_bias[:, None, ...].expand(-1, self.head_dim)
            D = self.D[:, None, ...].expand(-1, self.head_dim)
            B = B.view(-1, n_groups, B.shape[1] // n_groups)
            C = C.view(-1, n_groups, C.shape[1] // n_groups)
            hidden_states = hidden_states.view(
                -1, self.num_heads // self.tp_size, self.head_dim
            )

            # - the hidden is reshaped into (bs, num_heads, head_dim)
            # - mamba_cache_params.ssm_state's slots will be selected
            #   using state_indices_tensor_d
            # NOTE: final output is an in-place update of out tensor
            selective_state_update(
                ssm_state.permute(0, 3, 2, 1),
                hidden_states,
                dt,
                A,
                B,
                C,
                D,
                z=None,
                dt_bias=dt_bias,
                dt_softplus=True,
                state_batch_indices=state_indices_tensor,
                out=preallocated_ssm_out.view(num_decodes, -1, self.head_dim),
            )
        elif forward_batch.forward_mode.is_idle():
            preallocated_ssm_out = preallocated_ssm_out

        # 4. gated MLP
        # GatedRMSNorm internally applying SiLU to the gate
        # SiLU is applied internally before normalization, unlike standard
        # norm usage
        hidden_states = self.norm(preallocated_ssm_out, gate)

        # 5. Final linear projection
        output[:], _ = self.out_proj(hidden_states)

    @property
    def mamba_type(self) -> str:
        return "mamba2"
