# Copyright (c) 2022-2026, NVIDIA CORPORATION & AFFILIATES. All rights reserved.
#
# See LICENSE for license information.

"""Internal function used by multiple modules."""

import dataclasses
import queue
from typing import Any, Callable, List, Optional, Tuple, Union

import torch

from .. import cpp_extensions as tex
from ..constants import TE_DType
from ..export import is_in_onnx_export_mode
from ..utils import get_default_init_method

import warnings
import os
enable_lightop = os.getenv("NVTE_USE_LIGHTOP", "false").strip().lower() in ["true", "1"]
if enable_lightop:
    try:
        from lightop import rmsnorm_forward,rmsnorm_backward
        enable_lightop = True
    except ImportError:
        enable_lightop = False
        warnings.warn("Failed to import lightop module. Falling back to alternative implementation.", UserWarning)

def _get_normalization_func(normalization: str, forward: bool):
    fwd_normalization_funcs = {
        "LayerNorm": tex.layernorm_fwd,
        "RMSNorm": tex.rmsnorm_fwd,
    }
    bwd_normalization_funcs = {
        "LayerNorm": tex.layernorm_bwd,
        "RMSNorm": tex.rmsnorm_bwd,
    }

    if forward:
        return fwd_normalization_funcs[normalization]
    return bwd_normalization_funcs[normalization]


def apply_normalization(
    inputmat: torch.Tensor,
    ln_out: torch.Tensor,
    ln_weight: torch.Tensor,
    ln_bias: Union[torch.Tensor, None],
    eps: float,
    output_quantizer,
    output_dtype,
    normalization: str,
    fwd_ln_sm_margin: int,
    zero_centered_gamma: bool,
):
    """Apply normalization to input."""
    normalization_func = _get_normalization_func(normalization, True)

    inputs = (inputmat, ln_weight) if ln_bias is None else (inputmat, ln_weight, ln_bias)
    if enable_lightop and (ln_bias is None) and normalization == "RMSNorm" and output_quantizer is None and (output_dtype is torch.bfloat16 or output_dtype is torch.float16 or output_dtype is torch.float32) and not zero_centered_gamma:
        out, rsigma = rmsnorm_forward(inputmat, ln_weight,ln_out,eps,True)
        return out, None, rsigma
    else:
        return normalization_func(
            *inputs,
            eps,
            ln_out,
            output_quantizer,
            TE_DType[output_dtype] if output_dtype in TE_DType else output_dtype,
            fwd_ln_sm_margin,
            zero_centered_gamma,
        )


class _NoopCatFunc(torch.autograd.Function):
    """Concatenate tensors, doing a no-op if possible

    See _noop_cat.

    """

    @staticmethod
    def forward(
        ctx: Any,
        dim: int,
        *tensors: Tuple[torch.Tensor, ...],
    ) -> torch.Tensor:
        # pylint: disable=missing-function-docstring

        # Check first tensor
        if not tensors:
            raise ValueError("Attempted to concatenate 0 tensors")
        num_dims = tensors[0].dim()
        if not -num_dims <= dim < num_dims:
            raise ValueError(
                "Attempted to concatenate tensor "
                f"with shape {list(tensors[0].size())} along dim {dim}"
            )
        dim %= num_dims

        # Check remaining tensors
        out_shape = list(tensors[0].size())
        split_ranges = [(0, tensors[0].size(dim))]
        for tensor in tensors[1:]:
            in_shape = list(tensor.size())
            if (
                len(in_shape) != num_dims
                or in_shape[:dim] != out_shape[:dim]
                or in_shape[dim + 1 :] != out_shape[dim + 1 :]
            ):
                raise ValueError(
                    "Attempted to concatenate tensors with shapes "
                    f"{[list(tensor.size()) for tensor in tensors]} "
                    f"along dim {dim}"
                )
            split_start = out_shape[dim]
            split_end = split_start + in_shape[dim]
            out_shape[dim] = split_end
            split_ranges.append((split_start, split_end))

        # Save state for backward
        ctx.dim = dim
        ctx.split_ranges = split_ranges

        # Out-of-place concatenation if needed
        dtype = tensors[0].dtype
        device = tensors[0].device
        strides = tensors[0].stride()
        data_ptr_stride = strides[dim] * tensors[0].element_size()
        data_ptr = tensors[0].data_ptr() + tensors[0].size(dim) * data_ptr_stride
        for tensor in tensors[1:]:
            if (
                tensor.dtype != dtype
                or tensor.device != device
                or tensor.stride() != strides
                or tensor.data_ptr() != data_ptr
            ):
                return torch.cat(tensors, dim=dim)
            data_ptr += tensor.size(dim) * data_ptr_stride

        # No-op concatenation
        out = tensors[0].new()
        out.set_(
            tensors[0].untyped_storage(),
            tensors[0].storage_offset(),
            out_shape,
            strides,
        )
        out.requires_grad = any(tensor.requires_grad for tensor in tensors)
        return out

    @staticmethod
    def backward(
        ctx,
        grad_output: torch.Tensor,
    ) -> Tuple[Optional[torch.Tensor], ...]:
        # pylint: disable=missing-function-docstring
        grad_inputs = []
        for split_start, split_end in ctx.split_ranges:
            slices = [slice(None)] * grad_output.dim()
            slices[ctx.dim] = slice(split_start, split_end)
            grad_inputs.append(grad_output[tuple(slices)])
        return None, *grad_inputs


def noop_cat(
    tensors: List[torch.Tensor],
    dim: int = 0,
) -> torch.Tensor:
    """Concatenate tensors, doing a no-op if possible

    If tensors are already concatenated in memory, a tensor view of
    that memory region will be returned. Otherwise the tensors will be
    concatenated out-of-place, as usual.

    """
    if not tensors:
        raise ValueError("Attempted to concatenate 0 tensors")
    if len(tensors) == 1:
        return tensors[0]
    if is_in_onnx_export_mode():
        return torch.cat(tensors, dim=dim)
    return _NoopCatFunc.apply(dim, *tensors)


@dataclasses.dataclass
class _ParameterInitMeta:
    """
    Stores essential metadata needed to support deferred parameter initialization.
    """

    init_fn: Optional[Callable] = get_default_init_method()
    get_rng_state_tracker: Optional[Callable] = None
    fp8_meta_index: Optional[int] = None

    def __post_init__(self):
        """Safeguard reference to the parameter's parent module and initialization function."""
        if self.init_fn is None:
            self.init_fn = get_default_init_method()


class WeightGradStore:
    """
    A class to manage weight gradient storage and computation in Transformer modules.
    This class enables split backward propagation for better memory efficiency.
    """

    def __init__(self, delay_wgrad_compute=False, ub_bulk_wgrad=False):
        """
        Initialize the WeightGradStore.

        Args:
            delay_wgrad_compute (bool): Whether to delay weight gradient computation
            ub_bulk_wgrad (bool): Whether to enable bulk weight gradient computation
        """
        if delay_wgrad_compute:
            self.context = queue.Queue()
            assert (
                ub_bulk_wgrad is False
            ), "ub_bulk_wgrad is not supported when enabling delay_wgrad_compute"
            self.enabled = delay_wgrad_compute
        else:
            self.context = None
            self.enabled = False

    def delay_wgrad_compute(self):
        """
        Get the current split backward propagation status.

        Returns:
            bool: True if split backward is enabled, False otherwise
        """
        return self.enabled

    def enable_delay_wgrad_compute(self):
        """Enable split backward propagation."""
        self.enabled = True

    def disable_delay_wgrad_compute(self):
        """Disable split backward propagation."""
        self.enabled = False

    def put(self, tensor_list, func):
        """
        Store tensors and computation function for later execution.

        Args:
            tensor_list (list): List of tensors needed for computation
            func (callable): Function to be executed with the tensors
        """
        assert self.enabled is True, "delay_wgrad_compute is not enabled"
        self.context.put([tensor_list, func])

    def pop(self):
        """
        Execute the stored computation with the stored tensors.
        Raises an exception if the queue is empty.
        """
        assert self.enabled is True, "delay_wgrad_compute is not enabled"
        if self.context.qsize() > 0:
            tensor_list, func = self.context.get()
            return func(*tensor_list), tensor_list
        if torch.distributed.is_initialized():
            rank = torch.distributed.get_rank()
            raise RuntimeError(f"Pop empty queue. rank {rank}")
        raise RuntimeError("Pop empty queue. No distributed environment detected.")

    def assert_empty(self):
        """
        Assert that the queue is empty.
        Used for debugging and ensuring proper cleanup.
        """
        assert self.enabled is True, "delay_wgrad_compute is not enabled"
        rank = torch.distributed.get_rank()
        assert self.context.empty(), f"Queue is not empty. rank {rank}"
