"""3D CNN baseline: whole-brain volume classification via MONAI ResNet.

Input volumes are (B, 1, D, H, W). MONAI's resnet18 with spatial_dims=3 is a clean,
reproducible baseline for the value-of-volume question.
"""
from __future__ import annotations

import torch
import torch.nn as nn
from monai.networks.nets import resnet18


class ResNet3D(nn.Module):
    def __init__(self, n_classes: int = 3, in_channels: int = 1):
        super().__init__()
        self.net = resnet18(
            spatial_dims=3, n_input_channels=in_channels, num_classes=n_classes,
        )

    def forward(self, vol: torch.Tensor, tab: torch.Tensor | None = None) -> torch.Tensor:
        return self.net(vol)