# coding=utf-8
# Copyright 2024 Zyphra Technologies and the HuggingFace Inc. team. All rights reserved.
#
# This code is based on EleutherAI's GPT-NeoX library and the GPT-NeoX
# and OPT implementations in this library. It has been modified from its
# original forms to accommodate minor architectural differences compared
# to GPT-NeoX and OPT used by the Meta AI team that trained the model.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""PyTorch Zamba model."""

import math
from collections.abc import Callable
from typing import Any, Optional, Union

import torch
from torch import nn
from torch.nn import BCEWithLogitsLoss, CrossEntropyLoss, MSELoss

from ...activations import ACT2FN
from ...cache_utils import Cache
from ...generation import GenerationMixin
from ...modeling_attn_mask_utils import AttentionMaskConverter
from ...modeling_flash_attention_utils import FlashAttentionKwargs
from ...modeling_outputs import BaseModelOutputWithPast, CausalLMOutputWithPast, SequenceClassifierOutputWithPast
from ...modeling_utils import ALL_ATTENTION_FUNCTIONS, PreTrainedModel
from ...processing_utils import Unpack
from ...utils import auto_docstring, logging
from ...utils.import_utils import is_causal_conv1d_available, is_mamba_ssm_available
from .configuration_zamba import ZambaConfig


if is_mamba_ssm_available():
    from mamba_ssm.ops.selective_scan_interface import mamba_inner_fn, selective_scan_fn
    from mamba_ssm.ops.triton.selective_state_update import selective_state_update
else:
    selective_state_update, selective_scan_fn, mamba_inner_fn = None, None, None

if is_causal_conv1d_available():
    from causal_conv1d import causal_conv1d_fn, causal_conv1d_update
else:
    causal_conv1d_update, causal_conv1d_fn = None, None

is_fast_path_available = all(
    (selective_state_update, selective_scan_fn, causal_conv1d_fn, causal_conv1d_update, mamba_inner_fn)
)


logger = logging.get_logger(__name__)


# Copied from transformers.models.llama.modeling_llama.LlamaRMSNorm with Llama->Zamba
class ZambaRMSNorm(nn.Module):
    def __init__(self, hidden_size, eps=1e-6):
        """
        ZambaRMSNorm is equivalent to T5LayerNorm
        """
        super().__init__()
        self.weight = nn.Parameter(torch.ones(hidden_size))
        self.variance_epsilon = eps

    def forward(self, hidden_states):
        input_dtype = hidden_states.dtype
        hidden_states = hidden_states.to(torch.float32)
        variance = hidden_states.pow(2).mean(-1, keepdim=True)
        hidden_states = hidden_states * torch.rsqrt(variance + self.variance_epsilon)
        return self.weight * hidden_states.to(input_dtype)

    def extra_repr(self):
        return f"{tuple(self.weight.shape)}, eps={self.variance_epsilon}"


# Copied from transformers.models.llama.modeling_llama.repeat_kv
def repeat_kv(hidden_states: torch.Tensor, n_rep: int) -> torch.Tensor:
    """
    This is the equivalent of torch.repeat_interleave(x, dim=1, repeats=n_rep). The hidden states go from (batch,
    num_key_value_heads, seqlen, head_dim) to (batch, num_attention_heads, seqlen, head_dim)
    """
    batch, num_key_value_heads, slen, head_dim = hidden_states.shape
    if n_rep == 1:
        return hidden_states
    hidden_states = hidden_states[:, :, None, :, :].expand(batch, num_key_value_heads, n_rep, slen, head_dim)
    return hidden_states.reshape(batch, num_key_value_heads * n_rep, slen, head_dim)


class ZambaHybridDynamicCache:
    """
    A dynamic cache that can handle both the attention cache (which has a seq_len dimension) and the mamba cache
    (which has a constant shape regardless of seq_len).

    This cache has two sets of lists of tensors: `key_cache` and `value_cache` for attention cache and `conv_states`
    and `ssm_states` for mamba cache. Each of these lists has `num_layers` tensors. The expected shape for each tensor
    For attention layers, `key_cache` and `value_cache` have a shape of `(batch_size, num_heads, seq_len, head_dim)`,
    while `conv_states` and `ssm_states` have a shape of `(batch_size, 0)` (empty tensors).
    For mamba layers, `key_cache` and `value_cache` have a shape of `(batch_size, 0)` (empty tensors),
    while `conv_states` represents the convolution state and has a shape of `(batch_size, d_inner, d_conv)`,
    and `ssm_states` represents the ssm state and has a shape of `(batch_size, d_inner, d_state)`.
    """

    is_compileable = False

    def __init__(self, config, batch_size, dtype=torch.float16, device=None):
        self.dtype = dtype
        self.is_compileable = False
        self.layers_block_type = config.layers_block_type
        self.has_previous_state = False  # only used by mamba
        self.intermediate_size = config.mamba_expand * config.hidden_size
        self.ssm_state_size = config.mamba_d_state
        self.conv_kernel_size = config.mamba_d_conv
        self.n_mamba_heads = config.n_mamba_heads
        self.conv_states = []
        self.ssm_states = []
        self.transformer_layers = []
        self._modules = {}
        self._parameters = {}
        self._buffers = {}
        for i in range(config.num_hidden_layers):
            self.conv_states += [
                torch.zeros(batch_size, self.intermediate_size, self.conv_kernel_size, device=device, dtype=dtype)
            ]
            cache_shape = (
                batch_size,
                self.n_mamba_heads,
                self.intermediate_size // self.n_mamba_heads,
                self.ssm_state_size,
            )
            self.ssm_states += [torch.zeros(cache_shape, device=device, dtype=dtype)]
            if self.layers_block_type[i] == "hybrid":
                self.transformer_layers.append(i)

        self.key_cache = [torch.tensor([[]] * batch_size, device=device) for _ in range(config.num_hidden_layers)]
        self.value_cache = [torch.tensor([[]] * batch_size, device=device) for _ in range(config.num_hidden_layers)]

    def __len__(self):
        return len(self.key_cache)

    # Copied from transformers.models.jamba.modeling_jamba.HybridMambaAttentionDynamicCache.update
    def update(
        self,
        key_states: torch.Tensor,
        value_states: torch.Tensor,
        layer_idx: int,
        cache_kwargs: Optional[dict[str, Any]] = None,
    ) -> tuple[torch.Tensor, torch.Tensor]:
        # Update the cache
        if self.key_cache[layer_idx].shape[-1] == 0:
            self.key_cache[layer_idx] = key_states
            self.value_cache[layer_idx] = value_states
        else:
            self.key_cache[layer_idx] = torch.cat([self.key_cache[layer_idx], key_states], dim=2)
            self.value_cache[layer_idx] = torch.cat([self.value_cache[layer_idx], value_states], dim=2)

        return self.key_cache[layer_idx], self.value_cache[layer_idx]

    # Copied from transformers.models.jamba.modeling_jamba.HybridMambaAttentionDynamicCache.reorder_cache
    def reorder_cache(self, beam_idx: torch.LongTensor):
        """Reorders the cache for beam search, given the selected beam indices."""
        if self.get_seq_length() > 0:
            for layer_idx in range(len(self.key_cache)):
                device = self.key_cache[layer_idx].device
                self.key_cache[layer_idx] = self.key_cache[layer_idx].index_select(0, beam_idx.to(device))
                device = self.value_cache[layer_idx].device
                self.value_cache[layer_idx] = self.value_cache[layer_idx].index_select(0, beam_idx.to(device))

                device = self.conv_states[layer_idx].device
                self.conv_states[layer_idx] = self.conv_states[layer_idx].index_select(0, beam_idx.to(device))
                device = self.ssm_states[layer_idx].device
                self.ssm_states[layer_idx] = self.ssm_states[layer_idx].index_select(0, beam_idx.to(device))

    # Copied from transformers.models.jamba.modeling_jamba.HybridMambaAttentionDynamicCache.get_seq_length
    def get_seq_length(self, layer_idx: Optional[int] = 0) -> int:
        """Returns the sequence length of the cached states. A layer index can be optionally passed."""
        # take any layer that contains cache and not empty tensor
        layer_idx = self.transformer_layers[0] if layer_idx not in self.transformer_layers else layer_idx
        if len(self.key_cache) <= layer_idx or self.key_cache[layer_idx].shape[-1] == 0:
            return 0
        return self.key_cache[layer_idx].shape[-2]


def eager_attention_forward(
    module: nn.Module,
    query: torch.Tensor,
    key: torch.Tensor,
    value: torch.Tensor,
    attention_mask: Optional[torch.Tensor],
    scaling: float,
    dropout: float = 0.0,
    **kwargs,
):
    key_states = repeat_kv(key, module.num_key_value_groups)
    value_states = repeat_kv(value, module.num_key_value_groups)

    attn_weights = torch.matmul(query, key_states.transpose(2, 3)) * scaling
    if attention_mask is not None:
        causal_mask = attention_mask[:, :, :, : key_states.shape[-2]]
        attn_weights = attn_weights + causal_mask

    attn_weights = nn.functional.softmax(attn_weights, dim=-1, dtype=torch.float32).to(query.dtype)
    attn_weights = nn.functional.dropout(attn_weights, p=dropout, training=module.training)
    attn_output = torch.matmul(attn_weights, value_states)
    attn_output = attn_output.transpose(1, 2).contiguous()

    return attn_output, attn_weights


class ZambaAttention(nn.Module):
    """
    Multi-headed attention from 'Attention Is All You Need' paper. Modified to use sliding window attention: Longformer
    and "Generating Long Sequences with Sparse Transformers".

    Adapted from transformers.models.mistral.modeling_mistral.MistralAttention:
    The input dimension here is attention_hidden_size = 2 * hidden_size, and head_dim = attention_hidden_size // num_heads.
    The extra factor of 2 comes from the input being the concatenation of original_hidden_states with the output of the previous (mamba) layer
    (see fig. 2 in https://huggingface.co/papers/2405.16712).
    Additionally, replaced
    attn_weights = torch.matmul(query_states, key_states.transpose(2, 3)) / math.sqrt(self.head_dim) with
    attn_weights = torch.matmul(query_states, key_states.transpose(2, 3)) / math.sqrt(self.head_dim/2)
    """

    def __init__(self, config: ZambaConfig, layer_idx: int):
        super().__init__()
        self.config = config
        self.layer_idx = layer_idx

        self.attention_hidden_size = config.attention_hidden_size
        self.head_dim = config.attention_head_dim
        self.num_key_value_groups = config.num_attention_heads // config.num_key_value_heads
        self.max_position_embeddings = config.max_position_embeddings
        self.scaling = (self.head_dim / 2) ** -0.5
        self.is_causal = True
        self.attention_dropout = config.attention_dropout

        self.q_proj = nn.Linear(config.attention_hidden_size, config.num_attention_heads * self.head_dim, bias=False)
        self.k_proj = nn.Linear(config.attention_hidden_size, config.num_key_value_heads * self.head_dim, bias=False)
        self.v_proj = nn.Linear(config.attention_hidden_size, config.num_key_value_heads * self.head_dim, bias=False)
        self.o_proj = nn.Linear(config.num_attention_heads * self.head_dim, config.hidden_size, bias=False)

    def forward(
        self,
        hidden_states: torch.Tensor,
        layer_idx: int,
        attention_mask: Optional[torch.Tensor],
        past_key_values: Optional[ZambaHybridDynamicCache] = None,
        **kwargs: Unpack[FlashAttentionKwargs],
    ) -> tuple[torch.Tensor, Optional[torch.Tensor], Optional[tuple[torch.Tensor]]]:
        input_shape = hidden_states.shape[:-1]
        hidden_shape = (*input_shape, -1, self.head_dim)

        query_states = self.q_proj(hidden_states).view(hidden_shape).transpose(1, 2)
        key_states = self.k_proj(hidden_states).view(hidden_shape).transpose(1, 2)
        value_states = self.v_proj(hidden_states).view(hidden_shape).transpose(1, 2)

        if past_key_values is not None:
            key_states, value_states = past_key_values.update(key_states, value_states, layer_idx)

        attention_interface: Callable = eager_attention_forward
        if self.config._attn_implementation != "eager":
            attention_interface = ALL_ATTENTION_FUNCTIONS[self.config._attn_implementation]

        attn_output, attn_weights = attention_interface(
            self,
            query_states,
            key_states,
            value_states,
            attention_mask,
            dropout=0.0 if not self.training else self.attention_dropout,
            scaling=self.scaling,
            **kwargs,
        )

        attn_output = attn_output.reshape(*input_shape, -1).contiguous()
        attn_output = self.o_proj(attn_output)
        return attn_output, attn_weights


class ZambaMambaMixer(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)

    This module differs from `transformers.models.mamba.modeling_mamba.MambaMixer` in two ways:
    - Added multi-head: the output of `self.in_proj` is split into `self.n_mamba_heads` heads, and each head
    undergoes an independent forward pass, identical to the original `MambaMixer`, up until the pre-activations of
    `self.out_proj`. The pre-activations, coming from different mamba heads, are then concatenated and fed into `self.out_proj`.
    """

    def __init__(self, config: ZambaConfig, layer_idx):
        super().__init__()
        self.config = config
        self.layer_idx = layer_idx
        self.hidden_size = config.hidden_size
        self.ssm_state_size = config.mamba_d_state
        self.conv_kernel_size = config.mamba_d_conv
        self.intermediate_size = config.mamba_expand * config.hidden_size
        self.time_step_rank = config.mamba_dt_rank
        self.n_mamba_heads = config.n_mamba_heads
        self.mamba_head_dim = self.intermediate_size // self.n_mamba_heads
        self.use_conv_bias = config.mamba_conv_bias
        self.use_bias = config.mamba_proj_bias
        self.conv1d = nn.Conv1d(
            in_channels=self.intermediate_size,
            out_channels=self.intermediate_size,
            bias=self.use_conv_bias,
            kernel_size=self.conv_kernel_size,
            groups=self.intermediate_size,
            padding=self.conv_kernel_size - 1,
        )

        self.activation = config.hidden_mamba_act
        self.act = ACT2FN[config.hidden_mamba_act]

        self.use_fast_kernels = config.use_mamba_kernels

        # projection of the input hidden states
        self.in_proj = nn.Linear(self.hidden_size, self.intermediate_size * 2, bias=self.use_bias)
        # weight associated to the selective projection used to make dt, B and C input dependent
        # each mamba head is processed independently
        self.x_proj_weight = nn.Parameter(
            torch.zeros(
                self.n_mamba_heads,
                self.time_step_rank + self.ssm_state_size * 2,
                self.mamba_head_dim,
            )
        )
        # time step projection (discretization)
        self.dt_proj_weight = nn.Parameter(
            (torch.zeros(self.n_mamba_heads, self.mamba_head_dim, self.time_step_rank) - 0.5)
            * 2
            / self.time_step_rank**0.5
        )
        self.dt_proj_bias = nn.Parameter(torch.zeros(self.n_mamba_heads, self.mamba_head_dim))

        # S4D real initialization. These are not discretized!
        # The core is to load them, compute the discrete states, then write the updated state. Keeps the memory bounded
        A = torch.arange(1, self.ssm_state_size + 1, dtype=torch.float32)[None, :]
        A = A.expand(self.intermediate_size, -1).contiguous()
        self.A_log = nn.Parameter(torch.log(A).reshape(self.n_mamba_heads, self.mamba_head_dim, -1))
        self.D = nn.Parameter(torch.ones(self.n_mamba_heads, self.mamba_head_dim))
        self.out_proj = nn.Linear(self.intermediate_size, self.hidden_size, bias=self.use_bias)

        if not is_fast_path_available:
            logger.warning_once(
                "The fast path is not available because one of `(selective_state_update, selective_scan_fn, causal_conv1d_fn, causal_conv1d_update, mamba_inner_fn)`"
                " is None. To install follow https://github.com/state-spaces/mamba/#installation and"
                " https://github.com/Dao-AILab/causal-conv1d. If you want to use the naive implementation, set `use_mamba_kernels=False` in the model config"
            )

    def cuda_kernels_forward(
        self, hidden_states: torch.Tensor, cache_params: ZambaHybridDynamicCache = None, attention_mask=None
    ):
        batch_size, seq_len, _ = hidden_states.shape
        use_precomputed_states = cache_params is not None and cache_params.has_previous_state and seq_len == 1

        # 1. Gated linear projection
        projected_states = self.in_proj(hidden_states).transpose(1, 2)

        hidden_states, gate = projected_states.view(batch_size, -1, 2, seq_len).chunk(2, dim=2)
        hidden_states = hidden_states.squeeze(2).contiguous()
        gate = gate.squeeze(2)
        gate = gate.reshape(batch_size, self.n_mamba_heads, -1, seq_len).transpose(0, 1)

        # 2. Convolution sequence transformation
        conv_weights = self.conv1d.weight.view(self.conv1d.weight.size(0), self.conv1d.weight.size(2))
        if use_precomputed_states:
            hidden_states = causal_conv1d_update(
                hidden_states.squeeze(-1),
                cache_params.conv_states[self.layer_idx],
                conv_weights,
                self.conv1d.bias,
                self.activation,
            )
            hidden_states = hidden_states.unsqueeze(-1)
        else:
            if attention_mask is not None and not torch.all(attention_mask == 1):
                hidden_states = hidden_states * attention_mask.unsqueeze(1)
            if cache_params is not None:
                conv_states = nn.functional.pad(hidden_states, (self.conv_kernel_size - hidden_states.shape[-1], 0))
                cache_params.conv_states[self.layer_idx].copy_(conv_states)
            hidden_states = causal_conv1d_fn(hidden_states, conv_weights, self.conv1d.bias, activation=self.activation)
            if attention_mask is not None and not torch.all(attention_mask == 1):
                hidden_states = hidden_states * attention_mask.unsqueeze(1)

        # 3. SSM sequence transformation
        # 3.a. input varying initialization of time_step, B and C

        hidden_states = hidden_states.reshape(-1, self.n_mamba_heads, self.mamba_head_dim, seq_len).transpose(0, 1)
        ssm_parameters = (self.x_proj_weight[:, None, :, :] @ hidden_states).transpose(-1, -2)

        time_step, B, C = torch.split(
            ssm_parameters, [self.time_step_rank, self.ssm_state_size, self.ssm_state_size], dim=-1
        )

        discrete_time_step = self.dt_proj_weight[:, None] @ time_step.transpose(-1, -2)

        A = -torch.exp(self.A_log.float())

        # 3.c perform the recurrence y ← SSM(A, B, C)(x)
        time_proj_bias = self.dt_proj_bias.float() if self.dt_proj_bias is not None else None
        scan_outputs = torch.empty((batch_size, 0, seq_len), device=hidden_states.device, dtype=hidden_states.dtype)

        if use_precomputed_states:
            for n in range(self.n_mamba_heads):
                scan_outputs_ = selective_state_update(
                    cache_params.ssm_states[self.layer_idx][:, n],
                    hidden_states[n, ..., 0],
                    discrete_time_step[n, ..., 0],
                    A[n],
                    B[n, :, 0],
                    C[n, :, 0],
                    self.D[n],
                    gate[n, ..., 0],
                    time_proj_bias[n],
                    dt_softplus=True,
                ).unsqueeze(-1)
                scan_outputs = torch.cat((scan_outputs, scan_outputs_), dim=1)

        else:
            ssm_state = torch.empty(
                (batch_size, 0, self.mamba_head_dim, self.ssm_state_size),
                device=hidden_states.device,
                dtype=hidden_states.dtype,
            )
            for n in range(self.n_mamba_heads):
                scan_outputs_, ssm_state_ = selective_scan_fn(
                    hidden_states[n],
                    discrete_time_step[n],
                    A[n],
                    B[n].transpose(1, 2),
                    C[n].transpose(1, 2),
                    self.D[n].float(),
                    gate[n],
                    time_proj_bias[n],
                    delta_softplus=True,
                    return_last_state=True,
                )
                scan_outputs = torch.cat((scan_outputs, scan_outputs_), dim=1).contiguous()
                ssm_state = torch.cat((ssm_state, ssm_state_.unsqueeze(1)), dim=1)
            if ssm_state is not None and cache_params is not None:
                cache_params.ssm_states[self.layer_idx].copy_(ssm_state)

        # 4. Final linear projection
        contextualized_states = self.out_proj(scan_outputs.transpose(1, 2))
        return contextualized_states

    def slow_forward(self, input_states, cache_params: ZambaHybridDynamicCache = None, attention_mask=None):
        batch_size, seq_len, _ = input_states.shape
        dtype = input_states.dtype
        # 1. Gated linear projection
        projected_states = self.in_proj(input_states).transpose(1, 2)

        hidden_states, gate = projected_states.view(batch_size, -1, 2, seq_len).chunk(2, dim=2)
        hidden_states = hidden_states.squeeze(2).contiguous()
        gate = gate.squeeze(2)
        gate = gate.reshape(batch_size, self.n_mamba_heads, -1, seq_len).transpose(0, 1)

        use_cache = isinstance(cache_params, ZambaHybridDynamicCache)
        # 2. Convolution sequence transformation
        if use_cache and cache_params.ssm_states[self.layer_idx].shape[0] == batch_size:
            if self.training:
                # In training mode, we don't want to perform in-place operations on ssm_state so we can compute the backwards pass
                ssm_state = cache_params.ssm_states[self.layer_idx].clone()
            else:
                ssm_state = cache_params.ssm_states[self.layer_idx]

            ssm_state = ssm_state.to(hidden_states.device)

            if (
                cache_params.has_previous_state
                and seq_len == 1
                and cache_params.conv_states[self.layer_idx].shape[0] == batch_size
            ):
                conv_state = cache_params.conv_states[self.layer_idx]
                conv_state = torch.roll(conv_state, shifts=-1, dims=-1)
                conv_state[:, :, -1] = hidden_states[:, :, 0]
                cache_params.conv_states[self.layer_idx] = conv_state
                hidden_states = torch.sum(conv_state * self.conv1d.weight[:, 0, :], dim=-1)
                if self.use_conv_bias:
                    hidden_states += self.conv1d.bias
                hidden_states = self.act(hidden_states).to(dtype).unsqueeze(-1)
            else:
                if attention_mask is not None and not torch.all(attention_mask == 1):
                    hidden_states = hidden_states * attention_mask[:, -hidden_states.shape[-1] :].unsqueeze(1)
                conv_state = nn.functional.pad(hidden_states, (self.conv_kernel_size - hidden_states.shape[-1], 0))
                cache_params.conv_states[self.layer_idx] = conv_state
                hidden_states = self.act(self.conv1d(hidden_states)[..., :seq_len])
                if attention_mask is not None and not torch.all(attention_mask == 1):
                    hidden_states = hidden_states * attention_mask[:, -hidden_states.shape[-1] :].unsqueeze(1)
        else:
            ssm_state = torch.zeros(
                (batch_size, self.n_mamba_heads, self.mamba_head_dim, self.ssm_state_size),
                device=hidden_states.device,
                dtype=dtype,
            )
            if attention_mask is not None and not torch.all(attention_mask == 1):
                hidden_states = hidden_states * attention_mask.unsqueeze(1)
            hidden_states = self.act(self.conv1d(hidden_states)[..., :seq_len])
            if attention_mask is not None and not torch.all(attention_mask == 1):
                hidden_states = hidden_states * attention_mask.unsqueeze(1)

        # 3. State Space Model sequence transformation
        # 3.a. Selection:  [batch, seq_len, self.time_step_rank + self.ssm_state_size * 2]
        hidden_states = hidden_states.reshape(-1, self.n_mamba_heads, self.mamba_head_dim, seq_len).transpose(0, 1)
        ssm_parameters = (self.x_proj_weight[:, None, :, :] @ hidden_states).transpose(-1, -2)

        time_step, B, C = torch.split(
            ssm_parameters, [self.time_step_rank, self.ssm_state_size, self.ssm_state_size], dim=-1
        )
        discrete_time_step = (self.dt_proj_weight[:, None] @ time_step.transpose(-1, -2)) + self.dt_proj_bias[
            :, None, :, None
        ]

        discrete_time_step = nn.functional.softplus(discrete_time_step)

        # 3.b. Discretization: B and C to [batch, seq_len, intermediate_size, ssm_state_size] (SRAM)
        A = -torch.exp(self.A_log.float())
        discrete_A = torch.exp(A[:, None, :, None, :] * discrete_time_step[:, :, :, :, None])
        discrete_B = discrete_time_step[:, :, :, :, None] * B[:, :, None, :, :].float()
        deltaB_u = discrete_B * hidden_states[:, :, :, :, None].float()
        # 3.c perform the recurrence y ← SSM(A, B, C)(x)
        scan_outputs = []
        for i in range(seq_len):
            ssm_state = discrete_A[:, :, :, i, :].transpose(0, 1) * ssm_state + deltaB_u[:, :, :, i, :].transpose(0, 1)
            scan_output = torch.matmul(ssm_state.transpose(0, 1).to(dtype), C[:, :, i, :].unsqueeze(-1))
            scan_outputs.append(scan_output[:, :, :, 0])
        scan_output = torch.stack(scan_outputs, dim=-1)
        scan_output = scan_output + (hidden_states * self.D[:, None, :, None])
        scan_output = scan_output * self.act(gate)

        if use_cache:
            cache_params.ssm_states[self.layer_idx] = ssm_state

        # 4. Final linear projection
        contextualized_states = self.out_proj(
            scan_output.transpose(0, 1).reshape(batch_size, -1, seq_len).transpose(1, 2)
        )
        return contextualized_states

    def forward(self, hidden_states, cache_params: ZambaHybridDynamicCache = None, attention_mask=None):
        if self.use_fast_kernels:
            if not is_fast_path_available or "cuda" not in self.x_proj_weight.device.type:
                raise ValueError(
                    "Fast Mamba kernels are not available. Make sure to they are installed and that "
                    "the mamba module is on a CUDA device. lease run 'pip install causal-conv1d>=1.2.0' "
                    "and 'pip install mamba-ssm', or set use_mamba_kernels=False in the model's config."
                )
            return self.cuda_kernels_forward(hidden_states, cache_params, attention_mask=attention_mask)
        return self.slow_forward(hidden_states, cache_params, attention_mask=attention_mask)


# Copied from transformers.models.mistral.modeling_mistral.MistralMLP with Mistral->Zamba
class ZambaMLP(nn.Module):
    def __init__(self, config):
        super().__init__()
        self.config = config
        self.hidden_size = config.hidden_size
        self.intermediate_size = config.intermediate_size
        self.gate_proj = nn.Linear(self.hidden_size, self.intermediate_size, bias=False)
        self.up_proj = nn.Linear(self.hidden_size, self.intermediate_size, bias=False)
        self.down_proj = nn.Linear(self.intermediate_size, self.hidden_size, bias=False)
        self.act_fn = ACT2FN[config.hidden_act]

    def forward(self, x):
        down_proj = self.down_proj(self.act_fn(self.gate_proj(x)) * self.up_proj(x))
        return down_proj


class ZambaAttentionDecoderLayer(nn.Module):
    def __init__(self, config: ZambaConfig, layer_idx: Optional[int] = None):
        super().__init__()
        self.self_attn = ZambaAttention(config, layer_idx)

        self.feed_forward = ZambaMLP(config)
        self.input_layernorm = ZambaRMSNorm(config.attention_hidden_size, eps=config.rms_norm_eps)
        self.pre_ff_layernorm = ZambaRMSNorm(config.hidden_size, eps=config.rms_norm_eps)

    def forward(
        self,
        hidden_states: torch.Tensor,
        original_hidden_states: torch.Tensor,
        layer_idx: int,
        attention_mask: Optional[torch.Tensor] = None,
        past_key_values: Optional[ZambaHybridDynamicCache] = None,
        output_attentions: Optional[bool] = False,
        use_cache: Optional[bool] = False,
        **kwargs: Unpack[FlashAttentionKwargs],
    ) -> tuple[torch.FloatTensor, Optional[tuple[torch.FloatTensor, torch.FloatTensor]]]:
        """
        Args:
            hidden_states (`torch.FloatTensor`): output of previous Mamba layer of shape `(batch, seq_len, embed_dim)`
            original_hidden_states (`torch.FloatTensor`): word embedding output of shape `(batch, seq_len, embed_dim)`.
                This is concatenated with `hidden_states` (which is the output of the previous (mamba) layer). The
                concatenated tensor is then used as input of the pre-attention RMSNorm
                (see fig. 2 in https://huggingface.co/papers/2405.16712).
            layer_idx (`int`): layer_idx in the forward pass. Used to distinguish Zamba's tied transformer layers.
            attention_mask (`torch.FloatTensor`, *optional*): attention mask of size
                `(batch, sequence_length)` where padding elements are indicated by 0.
            past_key_values (`ZambaHybridDynamicCache`, *optional*): cached past key and value projection states
            output_attentions (`bool`, *optional*):
                Whether or not to return the attentions tensors of all attention layers. See `attentions` under
                returned tensors for more detail.
            use_cache (`bool`, *optional*):
                If set to `True`, `past_key_values` key value states are returned and can be used to speed up decoding
                (see `past_key_values`).
            cache_position (`torch.LongTensor` of shape `(sequence_length)`, *optional*):
                Indices depicting the position of the input sequence tokens in the sequence.
        """
        hidden_states = torch.concatenate([hidden_states, original_hidden_states], dim=-1)
        hidden_states = self.input_layernorm(hidden_states)
        hidden_states, self_attn_weights = self.self_attn(
            hidden_states=hidden_states,
            layer_idx=layer_idx,
            attention_mask=attention_mask,
            past_key_values=past_key_values,
            output_attentions=output_attentions,
            use_cache=use_cache,
            **kwargs,
        )
        # feed-forward (MLP)
        hidden_states = self.pre_ff_layernorm(hidden_states)
        hidden_states = self.feed_forward(hidden_states)

        outputs = (hidden_states,)

        if output_attentions:
            outputs += (self_attn_weights,)

        return outputs


class ZambaMambaDecoderLayer(nn.Module):
    def __init__(self, config: ZambaConfig, layer_idx: int):
        super().__init__()
        self.mamba = ZambaMambaMixer(config=config, layer_idx=layer_idx)
        self.input_layernorm = ZambaRMSNorm(config.hidden_size, eps=config.rms_norm_eps)
        self.layer_idx = layer_idx

    def forward(
        self,
        hidden_states: torch.Tensor,
        original_hidden_states: Optional[torch.Tensor] = None,
        layer_idx: Optional[int] = None,
        attention_mask: Optional[torch.Tensor] = None,
        causal_mask: Optional[torch.Tensor] = None,
        past_key_values: Optional[ZambaHybridDynamicCache] = None,
        output_attentions: Optional[bool] = False,
        use_cache: Optional[bool] = False,
        cache_position: Optional[torch.LongTensor] = None,
        position_ids: Optional[torch.LongTensor] = None,
        transformer_hidden_states: Optional[torch.Tensor] = None,
        **kwargs,
    ) -> tuple[torch.FloatTensor, Optional[tuple[torch.FloatTensor, torch.FloatTensor]]]:
        """
        Args:
            hidden_states (`torch.FloatTensor`): input to the layer of shape `(batch, seq_len, embed_dim)`
            attention_mask (`torch.FloatTensor`, *optional*): attention mask of size
                `(batch, sequence_length)` where padding elements are indicated by 0.
            past_key_values (`ZambaHybridDynamicCache`, *optional*): cached past key and value projection states
            output_attentions (`bool`, *optional*):
                Whether or not to return the attentions tensors of all attention layers. See `attentions` under
                returned tensors for more detail.
            use_cache (`bool`, *optional*):
                If set to `True`, `past_key_values` key value states are returned and can be used to speed up decoding
                (see `past_key_values`).
            cache_position (`torch.LongTensor` of shape `(sequence_length)`, *optional*):
                Indices depicting the position of the input sequence tokens in the sequence.
        """

        residual = hidden_states

        # `transformer_hidden_states` is the output from shared transformer + linear layer (see fig. 2 in https://huggingface.co/papers/2405.16712).
        # `transformer_hidden_states` is then added to the input to the mamba layer below (as described in eq. (6) of https://huggingface.co/papers/2405.16712).
        hidden_states = (
            hidden_states + transformer_hidden_states if transformer_hidden_states is not None else hidden_states
        )
        hidden_states = self.input_layernorm(hidden_states)

        hidden_states = self.mamba(
            hidden_states=hidden_states,
            cache_params=past_key_values,
            attention_mask=attention_mask,
        )

        self_attn_weights = None

        # residual connection after mamba
        hidden_states = residual + hidden_states

        outputs = (hidden_states,)

        if output_attentions:
            outputs += (self_attn_weights,)

        if use_cache:
            outputs += (past_key_values,)

        return outputs


class ZambaHybridLayer(nn.Module):
    def __init__(self, shared_transf: ZambaAttentionDecoderLayer, linear: nn.Linear, mamba: ZambaMambaDecoderLayer):
        super().__init__()
        self.shared_transf = shared_transf
        self.linear = linear
        self.mamba_decoder = mamba

    def forward(
        self,
        hidden_states: torch.Tensor,
        original_hidden_states: Optional[torch.Tensor] = None,
        layer_idx: Optional[int] = None,
        attention_mask: Optional[torch.Tensor] = None,
        causal_mask: Optional[torch.Tensor] = None,
        past_key_values: Optional[ZambaHybridDynamicCache] = None,
        output_attentions: Optional[bool] = False,
        use_cache: Optional[bool] = False,
        cache_position: Optional[torch.LongTensor] = None,
    ) -> tuple[torch.FloatTensor, Optional[tuple[torch.FloatTensor, torch.FloatTensor]]]:
        """
        Args:
            hidden_states (`torch.FloatTensor`): input to the layer of shape `(batch, seq_len, embed_dim)`
            original_hidden_states (`torch.FloatTensor`): word embedding output that will be concatenated with
            hidden activations to form the input of the shared transformer layer.
            layer_idx (`int`): layer number.
            attention_mask (`torch.FloatTensor`, *optional*): attention mask of size
                `(batch, sequence_length)` where padding elements are indicated by 0.
            past_key_values (`ZambaHybridDynamicCache`, *optional*): cached past key and value projection states
            output_attentions (`bool`, *optional*):
                Whether or not to return the attentions tensors of all attention layers. See `attentions` under
                returned tensors for more detail.
            use_cache (`bool`, *optional*):
                If set to `True`, `past_key_values` key value states are returned and can be used to speed up decoding
                (see `past_key_values`).
            cache_position (`torch.LongTensor` of shape `(sequence_length)`, *optional*):
                Indices depicting the position of the input sequence tokens in the sequence.
        """

        layer_outputs = self.shared_transf(
            hidden_states,
            original_hidden_states=original_hidden_states,
            layer_idx=layer_idx,
            attention_mask=causal_mask,
            past_key_values=past_key_values,
            output_attentions=output_attentions,
            use_cache=use_cache,
            cache_position=cache_position,
        )

        transformer_hidden_states = layer_outputs[0]

        if output_attentions:
            self_attn_weights = layer_outputs[1]

        transformer_hidden_states = self.linear(transformer_hidden_states)

        layer_outputs = self.mamba_decoder(
            hidden_states,
            transformer_hidden_states=transformer_hidden_states,
            attention_mask=attention_mask,
            past_key_values=past_key_values,
            output_attentions=output_attentions,
            use_cache=use_cache,
            cache_position=cache_position,
        )

        if output_attentions:
            layer_outputs = (layer_outputs[0], self_attn_weights) + layer_outputs[2:]

        return layer_outputs


@auto_docstring
class ZambaPreTrainedModel(PreTrainedModel):
    config: ZambaConfig
    base_model_prefix = "model"
    supports_gradient_checkpointing = True
    _no_split_modules = ["ZambaAttentionDecoderLayer", "ZambaMambaDecoderLayer"]
    _skip_keys_device_placement = "past_key_values"
    _supports_flash_attn = False
    _supports_sdpa = False
    # Note: only supports ZambaHybridDynamicCache
    _is_stateful = True

    def _init_weights(self, module):
        std = self.config.initializer_range
        if isinstance(module, (nn.Linear, nn.Conv1d)):
            module.weight.data.normal_(mean=0.0, std=std)
            if module.bias is not None:
                module.bias.data.zero_()
        elif isinstance(module, nn.Embedding):
            module.weight.data.normal_(mean=0.0, std=std)
            if module.padding_idx is not None:
                module.weight.data[module.padding_idx].zero_()
        elif isinstance(module, ZambaRMSNorm):
            module.weight.data.fill_(1.0)
        elif isinstance(module, ZambaMambaMixer):
            module.x_proj_weight.data.normal_(mean=0.0, std=std)
            dt_init_std = self.config.mamba_dt_rank**-0.5
            nn.init.uniform_(module.dt_proj_weight, -dt_init_std, dt_init_std)

            mamba_head_dim = self.config.mamba_expand * self.config.hidden_size // self.config.n_mamba_heads
            dt = torch.exp(
                torch.rand(self.config.n_mamba_heads, mamba_head_dim)
                * (math.log(self.config.time_step_max) - math.log(self.config.time_step_min))
                + math.log(self.config.time_step_min)
            ).clamp(min=self.config.time_step_floor)
            # # Inverse of softplus: https://github.com/pytorch/pytorch/issues/72759
            inv_dt = dt + torch.log(-torch.expm1(-dt))
            module.dt_proj_bias.data.copy_(inv_dt)

            A = torch.arange(1, module.ssm_state_size + 1, dtype=torch.float32)[None, :]
            A = A.expand(module.intermediate_size, -1).contiguous()
            module.A_log.data.copy_(torch.log(A).reshape(module.n_mamba_heads, module.mamba_head_dim, -1))
            module.D.data.fill_(1.0)


@auto_docstring
class ZambaModel(ZambaPreTrainedModel):
    """
    Transformer decoder consisting of *config.num_hidden_layers* layers. Each layer is a [`ZambaDecoderLayer`]

    Args:
        config: ZambaConfig
    """

    def __init__(self, config: ZambaConfig):
        super().__init__(config)
        self.padding_idx = config.pad_token_id
        self.vocab_size = config.vocab_size

        self.embed_tokens = nn.Embedding(config.vocab_size, config.hidden_size, self.padding_idx)
        block = ZambaAttentionDecoderLayer(config)
        mamba_layers = []
        linear_layers = []
        self.layers_block_type = config.layers_block_type
        for i in range(config.num_hidden_layers):
            if config.layers_block_type[i] == "mamba":
                mamba_layers.append(ZambaMambaDecoderLayer(config, layer_idx=i))
            elif config.layers_block_type[i] == "hybrid":
                linear_layers.append(nn.Linear(self.config.hidden_size, self.config.hidden_size, bias=False))
                mamba_layers.append(ZambaMambaDecoderLayer(config, layer_idx=i))
        mamba_layers = iter(mamba_layers)
        linear_layers = iter(linear_layers)
        layers = []
        self._tied_weights_keys = []
        for layer_id, layer_type in enumerate(self.layers_block_type):
            if layer_type == "hybrid":
                prefix_name = f"layers.{layer_id}."
                tied_keys = [
                    "shared_transf.self_attn.q_proj.weight",
                    "shared_transf.self_attn.k_proj.weight",
                    "shared_transf.self_attn.v_proj.weight",
                    "shared_transf.self_attn.o_proj.weight",
                    "shared_transf.feed_forward.gate_proj.weight",
                    "shared_transf.feed_forward.up_proj.weight",
                    "shared_transf.feed_forward.down_proj.weight",
                    "shared_transf.input_layernorm.weight",
                    "shared_transf.pre_ff_layernorm.weight",
                ]
                self._tied_weights_keys = [*self._tied_weights_keys, *[prefix_name + key for key in tied_keys]]
                layers.append(ZambaHybridLayer(block, next(linear_layers), next(mamba_layers)))
            else:
                layers.append(next(mamba_layers))
        self.layers = nn.ModuleList(layers)

        self._attn_implementation = config._attn_implementation
        self.final_layernorm = ZambaRMSNorm(config.hidden_size, eps=config.rms_norm_eps)

        self.gradient_checkpointing = False
        # Initialize weights and apply final processing
        self.post_init()

    @auto_docstring
    def forward(
        self,
        input_ids: Optional[torch.LongTensor] = None,
        attention_mask: Optional[torch.Tensor] = None,
        position_ids: Optional[torch.LongTensor] = None,
        past_key_values: Optional[ZambaHybridDynamicCache] = None,
        inputs_embeds: Optional[torch.FloatTensor] = None,
        use_cache: Optional[bool] = None,
        output_attentions: Optional[bool] = None,
        output_hidden_states: Optional[bool] = None,
        return_dict: Optional[bool] = None,
        cache_position: Optional[torch.LongTensor] = None,
    ) -> Union[tuple, BaseModelOutputWithPast]:
        output_attentions = output_attentions if output_attentions is not None else self.config.output_attentions
        output_hidden_states = (
            output_hidden_states if output_hidden_states is not None else self.config.output_hidden_states
        )
        use_cache = use_cache if use_cache is not None else self.config.use_cache

        return_dict = return_dict if return_dict is not None else self.config.use_return_dict

        if (input_ids is None) ^ (inputs_embeds is not None):
            raise ValueError(
                "You cannot specify both input_ids and inputs_embeds at the same time, and must specify either one"
            )

        if self.gradient_checkpointing and self.training and use_cache:
            logger.warning_once(
                "`use_cache=True` is incompatible with gradient checkpointing. Setting `use_cache=False`."
            )
            use_cache = False

        if inputs_embeds is None:
            inputs_embeds = self.embed_tokens(input_ids)

        hidden_states = inputs_embeds

        original_hidden_states = torch.clone(inputs_embeds)
        # original_hidden_states: word embedding output that will be concatenated with hidden activations to form the input of the shared transformer layer

        if use_cache and past_key_values is None:
            logger.warning_once(
                "Zamba requires an initialized `ZambaHybridDynamicCache` to return a cache. None was "
                "provided, so no cache will be returned."
            )

        if cache_position is None:
            cache_position = torch.arange(hidden_states.shape[1], device=hidden_states.device)
        if position_ids is None:
            position_ids = cache_position.unsqueeze(0)

        causal_mask = self._update_causal_mask(attention_mask, inputs_embeds, cache_position)

        all_hidden_states = () if output_hidden_states else None
        all_self_attns = () if output_attentions else None

        for layer_idx, layer in enumerate(self.layers):
            if output_hidden_states:
                all_hidden_states += (hidden_states,)

            if self.gradient_checkpointing and self.training:
                layer_outputs = self._gradient_checkpointing_func(
                    layer.__call__,
                    hidden_states,
                    original_hidden_states,
                    layer_idx,
                    attention_mask,
                    causal_mask,
                    past_key_values,
                    output_attentions,
                    use_cache,
                    cache_position,
                )
            else:
                layer_outputs = layer(
                    hidden_states,
                    original_hidden_states=original_hidden_states,
                    layer_idx=layer_idx,
                    attention_mask=attention_mask,
                    causal_mask=causal_mask,
                    past_key_values=past_key_values,
                    output_attentions=output_attentions,
                    use_cache=use_cache,
                    cache_position=cache_position,
                )
            hidden_states = layer_outputs[0]

            if output_attentions:
                if layer_outputs[1] is not None:
                    # append attentions only of attention layers. Mamba layers return `None` as the attention weights
                    all_self_attns += (layer_outputs[1],)

        hidden_states = self.final_layernorm(hidden_states)

        # add hidden states from the last decoder layer
        if output_hidden_states:
            all_hidden_states += (hidden_states,)

        if past_key_values and not past_key_values.has_previous_state:
            past_key_values.has_previous_state = True

        output = BaseModelOutputWithPast(
            last_hidden_state=hidden_states,
            past_key_values=past_key_values if use_cache else None,
            hidden_states=all_hidden_states,
            attentions=all_self_attns,
        )
        return output if return_dict else output.to_tuple()

    def _update_causal_mask(self, attention_mask, input_tensor, cache_position):
        if self.config._attn_implementation == "flash_attention_2":
            if attention_mask is not None and 0.0 in attention_mask:
                return attention_mask
            return None

        dtype, device = input_tensor.dtype, input_tensor.device
        min_dtype = torch.finfo(dtype).min
        sequence_length = input_tensor.shape[1]
        if cache_position is None:
            target_length = sequence_length
        else:
            target_length = cache_position[-1] + 1

        causal_mask = torch.full((sequence_length, target_length), fill_value=min_dtype, dtype=dtype, device=device)
        if sequence_length != 1:
            causal_mask = torch.triu(causal_mask, diagonal=1)
        if cache_position is not None:
            causal_mask *= (torch.arange(target_length, device=device) > cache_position.reshape(-1, 1)).to(torch.bool)
        causal_mask = causal_mask[None, None, :, :].expand(input_tensor.shape[0], 1, -1, -1)
        if attention_mask is not None:
            causal_mask = causal_mask.clone()  # copy to contiguous memory for in-place edit
            if attention_mask.dim() == 2:
                mask_length = attention_mask.shape[-1]
                padding_mask = causal_mask[..., :mask_length].eq(0.0) * attention_mask[:, None, None, :].eq(0.0)
                causal_mask[..., :mask_length] = causal_mask[..., :mask_length].masked_fill(padding_mask, min_dtype)

        if (
            self.config._attn_implementation == "sdpa"
            and attention_mask is not None
            and attention_mask.device.type in ["cuda", "xpu", "npu"]
        ):
            # Attend to all tokens in fully masked rows in the causal_mask, for example the relevant first rows when
            # using left padding. This is required by F.scaled_dot_product_attention memory-efficient attention path.
            # Details: https://github.com/pytorch/pytorch/issues/110213
            causal_mask = AttentionMaskConverter._unmask_unattended(causal_mask, min_dtype)

        return causal_mask


# Adapted from transformers.models.jamba.modeling_jamba.JambaForCausalLM with Jamba->Zamba, JAMBA->ZAMBA
class ZambaForCausalLM(ZambaPreTrainedModel, GenerationMixin):
    def __init__(self, config: ZambaConfig):
        super().__init__(config)
        self.model = ZambaModel(config)
        self._tied_weights_keys = ["lm_head.weight", *self.model._tied_weights_keys]
        self.vocab_size = config.vocab_size
        self.lm_head = nn.Linear(config.hidden_size, config.vocab_size, bias=False)

        # Initialize weights and apply final processing
        self.post_init()

    @auto_docstring
    def forward(
        self,
        input_ids: Optional[torch.LongTensor] = None,
        attention_mask: Optional[torch.Tensor] = None,
        position_ids: Optional[torch.LongTensor] = None,
        past_key_values: Optional[ZambaHybridDynamicCache] = None,
        inputs_embeds: Optional[torch.FloatTensor] = None,
        labels: Optional[torch.LongTensor] = None,
        use_cache: Optional[bool] = None,
        output_attentions: Optional[bool] = None,
        output_hidden_states: Optional[bool] = None,
        return_dict: Optional[bool] = None,
        cache_position: Optional[torch.LongTensor] = None,
        logits_to_keep: Union[int, torch.Tensor] = 0,
        **kwargs,
    ) -> Union[tuple, CausalLMOutputWithPast]:
        r"""
        labels (`torch.LongTensor` of shape `(batch_size, sequence_length)`, *optional*):
            Labels for computing the masked language modeling loss. Indices should either be in `[0, ...,
            config.vocab_size]` or -100 (see `input_ids` docstring). Tokens with indices set to `-100` are ignored
            (masked), the loss is only computed for the tokens with labels in `[0, ..., config.vocab_size]`.

        Example:

        ```python
        >>> from transformers import AutoTokenizer, ZambaForCausalLM

        >>> model = ZambaForCausalLM.from_pretrained("Zyphra/Zamba-7B-v1")
        >>> tokenizer = AutoTokenizer.from_pretrained("Zyphra/Zamba-7B-v1")

        >>> prompt = "Hey, are you conscious? Can you talk to me?"
        >>> inputs = tokenizer(prompt, return_tensors="pt")

        >>> # Generate
        >>> generate_ids = model.generate(inputs.input_ids, max_length=30)
        >>> tokenizer.batch_decode(generate_ids, skip_special_tokens=True, clean_up_tokenization_spaces=False)[0]
        "Hey, are you conscious? Can you talk to me?\nI'm not conscious, but I can talk to you."
        ```"""

        output_attentions = output_attentions if output_attentions is not None else self.config.output_attentions

        output_hidden_states = (
            output_hidden_states if output_hidden_states is not None else self.config.output_hidden_states
        )
        return_dict = return_dict if return_dict is not None else self.config.use_return_dict

        # decoder outputs consists of (dec_features, layer_state, dec_hidden, dec_attn)
        outputs = self.model(
            input_ids=input_ids,
            attention_mask=attention_mask,
            position_ids=position_ids,
            past_key_values=past_key_values,
            inputs_embeds=inputs_embeds,
            use_cache=use_cache,
            output_attentions=output_attentions,
            output_hidden_states=output_hidden_states,
            cache_position=cache_position,
            return_dict=return_dict,
        )

        hidden_states = outputs[0]
        # Only compute necessary logits, and do not upcast them to float if we are not computing the loss
        slice_indices = slice(-logits_to_keep, None) if isinstance(logits_to_keep, int) else logits_to_keep
        logits = self.lm_head(hidden_states[:, slice_indices, :])

        loss = None
        if labels is not None:
            loss = self.loss_function(logits, labels, self.vocab_size, **kwargs)

        if not return_dict:
            output = (logits,) + outputs[1:]
            return (loss,) + output if loss is not None else output

        return CausalLMOutputWithPast(
            loss=loss,
            logits=logits,
            past_key_values=outputs.past_key_values,
            hidden_states=outputs.hidden_states,
            attentions=outputs.attentions,
        )

    def prepare_inputs_for_generation(
        self,
        input_ids,
        past_key_values=None,
        attention_mask=None,
        inputs_embeds=None,
        cache_position=None,
        position_ids=None,
        use_cache=True,
        **kwargs,
    ):
        # Overwritten -- has a unique cache type, `ZambaHybridDynamicCache`

        empty_past_kv = past_key_values is None

        # Omit tokens covered by past_key_values
        if not empty_past_kv:
            # If we have cache: let's slice `input_ids` through `cache_position`, to keep only the unprocessed tokens
            # Exception 1: when passing input_embeds, input_ids may be missing entries
            # Exception 2: some generation methods do special slicing of input_ids, so we don't need to do it here
            # Exception 3: with synced GPUs cache_position may go out of bounds, but we only want dummy token in that case.
            #              (we can't check exception 3 while compiling)
            if (
                inputs_embeds is not None  # Exception 1
                or cache_position[-1] >= input_ids.shape[1]  # Exception 3
            ):
                input_ids = input_ids[:, -cache_position.shape[0] :]
            elif input_ids.shape[1] != cache_position.shape[0]:  # Default case (the "else", a no op, is Exception 2)
                input_ids = input_ids[:, cache_position]
        else:
            past_key_values = ZambaHybridDynamicCache(
                self.config, input_ids.shape[0], dtype=self.dtype, device=self.device
            )

        if attention_mask is not None and position_ids is None:
            # create position_ids on the fly for batch generation
            position_ids = attention_mask.long().cumsum(-1) - 1
            position_ids.masked_fill_(attention_mask == 0, 1)
            if not empty_past_kv:
                position_ids = position_ids[:, -input_ids.shape[1] :]

        # if `inputs_embeds` are passed, we only want to use them in the 1st generation step
        if inputs_embeds is not None and empty_past_kv:
            model_inputs = {"inputs_embeds": inputs_embeds}
        else:
            model_inputs = {"input_ids": input_ids.contiguous()}  # `contiguous()` needed for compilation use cases

        model_inputs.update(
            {
                "position_ids": position_ids,
                "past_key_values": past_key_values,
                "use_cache": use_cache,
                "attention_mask": attention_mask,
                "logits_to_keep": self.config.num_logits_to_keep,
                "cache_position": cache_position,
            }
        )

        # Forward ALL kwargs that are uninitialized (e.g. `use_cache`).
        for key, value in kwargs.items():
            if key not in model_inputs:
                model_inputs[key] = value

        return model_inputs


@auto_docstring(
    custom_intro="""
    The Zamba Model with a sequence classification head on top (linear layer).

    [`ZambaForSequenceClassification`] uses the last token in order to do the classification, as other causal models
    (e.g. GPT-2) do.

    Since it does classification on the last token, it requires to know the position of the last token. If a
    `pad_token_id` is defined in the configuration, it finds the last token that is not a padding token in each row. If
    no `pad_token_id` is defined, it simply takes the last value in each row of the batch. Since it cannot guess the
    padding tokens when `inputs_embeds` are passed instead of `input_ids`, it does the same (take the last value in
    each row of the batch).
    """
)
class ZambaForSequenceClassification(ZambaPreTrainedModel):
    def __init__(self, config):
        super().__init__(config)
        self.num_labels = config.num_labels
        self.model = ZambaModel(config)
        self._tied_weights_keys = self.model._tied_weights_keys
        self.score = nn.Linear(config.hidden_size, self.num_labels, bias=False)

        # Initialize weights and apply final processing
        self.post_init()

    @auto_docstring
    def forward(
        self,
        input_ids: Optional[torch.LongTensor] = None,
        attention_mask: Optional[torch.Tensor] = None,
        position_ids: Optional[torch.LongTensor] = None,
        past_key_values: Optional[Cache] = None,
        inputs_embeds: Optional[torch.FloatTensor] = None,
        labels: Optional[torch.LongTensor] = None,
        use_cache: Optional[bool] = None,
        output_attentions: Optional[bool] = None,
        output_hidden_states: Optional[bool] = None,
        return_dict: Optional[bool] = None,
    ) -> Union[tuple, SequenceClassifierOutputWithPast]:
        r"""
        labels (`torch.LongTensor` of shape `(batch_size,)`, *optional*):
            Labels for computing the sequence classification/regression loss. Indices should be in `[0, ...,
            config.num_labels - 1]`. If `config.num_labels == 1` a regression loss is computed (Mean-Square loss), If
            `config.num_labels > 1` a classification loss is computed (Cross-Entropy).
        """
        return_dict = return_dict if return_dict is not None else self.config.use_return_dict

        transformer_outputs = self.model(
            input_ids,
            attention_mask=attention_mask,
            position_ids=position_ids,
            past_key_values=past_key_values,
            inputs_embeds=inputs_embeds,
            use_cache=use_cache,
            output_attentions=output_attentions,
            output_hidden_states=output_hidden_states,
            return_dict=return_dict,
        )
        hidden_states = transformer_outputs[0]
        logits = self.score(hidden_states)

        if input_ids is not None:
            batch_size = input_ids.shape[0]
        else:
            batch_size = inputs_embeds.shape[0]

        if self.config.pad_token_id is None and batch_size != 1:
            raise ValueError("Cannot handle batch sizes > 1 if no padding token is defined.")
        if self.config.pad_token_id is None:
            last_non_pad_token = -1
        elif input_ids is not None:
            # To handle both left- and right- padding, we take the rightmost token that is not equal to pad_token_id
            non_pad_mask = (input_ids != self.config.pad_token_id).to(logits.device, torch.int32)
            token_indices = torch.arange(input_ids.shape[-1], device=logits.device, dtype=torch.int32)
            last_non_pad_token = (token_indices * non_pad_mask).argmax(-1)
        else:
            last_non_pad_token = -1
            logger.warning_once(
                f"{self.__class__.__name__} will not detect padding tokens in `inputs_embeds`. Results may be "
                "unexpected if using padding tokens in conjunction with `inputs_embeds.`"
            )

        pooled_logits = logits[torch.arange(batch_size, device=logits.device), last_non_pad_token]

        loss = None
        if labels is not None:
            labels = labels.to(logits.device)
            if self.config.problem_type is None:
                if self.num_labels == 1:
                    self.config.problem_type = "regression"
                elif self.num_labels > 1 and (labels.dtype == torch.long or labels.dtype == torch.int):
                    self.config.problem_type = "single_label_classification"
                else:
                    self.config.problem_type = "multi_label_classification"

            if self.config.problem_type == "regression":
                loss_fct = MSELoss()
                if self.num_labels == 1:
                    loss = loss_fct(pooled_logits.squeeze(), labels.squeeze())
                else:
                    loss = loss_fct(pooled_logits, labels)
            elif self.config.problem_type == "single_label_classification":
                loss_fct = CrossEntropyLoss()
                loss = loss_fct(pooled_logits.view(-1, self.num_labels), labels.view(-1))
            elif self.config.problem_type == "multi_label_classification":
                loss_fct = BCEWithLogitsLoss()
                loss = loss_fct(pooled_logits, labels)
        if not return_dict:
            output = (pooled_logits,) + transformer_outputs[1:]
            return ((loss,) + output) if loss is not None else output

        return SequenceClassifierOutputWithPast(
            loss=loss,
            logits=pooled_logits,
            past_key_values=transformer_outputs.past_key_values,
            hidden_states=transformer_outputs.hidden_states,
            attentions=transformer_outputs.attentions,
        )


__all__ = ["ZambaForCausalLM", "ZambaForSequenceClassification", "ZambaModel", "ZambaPreTrainedModel"]
