# Source code for dtw_loss_functions.soft_dtw_implementations.soft_dtw_cuda_ron.module

    from __future__ import annotations

    import math
    import torch
    from torch import nn

    from .distances import pairwise_distance
    from .autograd import SoftDTWAutograd
    from .autograd_xy import SoftDTWXYAutograd  # <-- new fused autograd

    class SoftDTW(nn.Module):
        """
        User-facing module.

        - dist: currently supports "sqeuclidean"
        - normalize: SoftDTW(x,y) - 0.5*(SoftDTW(x,x)+SoftDTW(y,y))
        - fused:
            None  -> auto (use fused only when possible)
            True  -> require fused (error if not possible)
            False -> never fused (always materialize D and use D-based autograd)
        """

        def __init__(
            self,
            *,
            gamma: float = 1.0,
            bandwidth: float | None = None,
            normalize: bool = False,
            dist: str = "sqeuclidean",
            fused: bool | None = None,
        ):
            super().__init__()
            self.gamma = float(gamma)
            if self.gamma <= 0:
                raise ValueError(f"gamma must be > 0, got {self.gamma}")
            if not math.isfinite(self.gamma):
                raise ValueError(f"gamma must be finite, got {self.gamma}")

            # treat None or <=0 as disabled
            if bandwidth is None:
                self.bandwidth = None
            else:
                bw = float(bandwidth)
                self.bandwidth = None if bw <= 0 else bw

            self.normalize = bool(normalize)
            self.dist = str(dist)
            self.fused = fused

        def _use_fused(self, x: torch.Tensor, y: torch.Tensor) -> bool:
            # Only supported for sqeuclidean on CUDA (for now)
            fused_ok = (
                self.dist.lower() in ("sqeuclidean", "sq_euclidean", "squared_euclidean")
                and x.is_cuda
                and y.is_cuda
                and x.device == y.device
            )
            if self.fused is True and not fused_ok:
                raise ValueError("fused=True requires CUDA tensors and dist='sqeuclidean'.")
            if self.fused is False:
                return False
            # auto or forced True
            return fused_ok

        def forward(self, x: torch.Tensor, y: torch.Tensor) -> torch.Tensor:
            # Accept (N,D) and (M,D)
            if x.dim() == 2:
                x = x.unsqueeze(0)
            if y.dim() == 2:
                y = y.unsqueeze(0)

            if x.dim() != 3 or y.dim() != 3:
                raise ValueError(
                    f"Expected x,y to have shape (B,N,D) and (B,M,D) (or unbatched (N,D)). "
                    f"Got x={tuple(x.shape)}, y={tuple(y.shape)}"
                )

            if self.normalize and x.shape[1] != y.shape[1]:
                raise ValueError(
                    f"normalize=True currently requires equal sequence lengths (N==M) because it uses the "
                    f"concatenation trick. Got N={x.shape[1]}, M={y.shape[1]}."
                )

            bx, _, dx = x.shape
            by, _, dy = y.shape
            if dx != dy:
                raise ValueError(f"Feature dims must match. Got x.shape[-1]={dx}, y.shape[-1]={dy}")
            if bx != by:
                raise ValueError(f"Batch sizes must match. Got x.shape[0]={bx}, y.shape[0]={by}")
            if x.shape[1] == 0 or y.shape[1] == 0:
                raise ValueError(
                    f"Sequence lengths must be > 0. Got N={x.shape[1]}, M={y.shape[1]}."
                )

            use_fused = self._use_fused(x, y)

            # ---- Normalization mode ----
            if self.normalize:
                # Stack everything up as in canonical normalization trick
                x_cat = torch.cat([x, x, y], dim=0)
                y_cat = torch.cat([y, x, y], dim=0)

                if use_fused:
                    out = SoftDTWXYAutograd.apply(x_cat, y_cat, self.gamma, self.bandwidth)
                else:
                    D = pairwise_distance(x_cat, y_cat, dist=self.dist)
                    out = SoftDTWAutograd.apply(D, self.gamma, self.bandwidth)

                out_xy, out_xx, out_yy = out.split(bx, dim=0)
                return out_xy - 0.5 * (out_xx + out_yy)

            # ---- Non-normalized ----
            if use_fused:
                return SoftDTWXYAutograd.apply(x, y, self.gamma, self.bandwidth)

            D_xy = pairwise_distance(x, y, dist=self.dist)
            return SoftDTWAutograd.apply(D_xy, self.gamma, self.bandwidth)