# SAFM
class SAFM(nn.Module):
    def __init__(self, dim, n_levels=4):
        super().__init__()
        self.n_levels = n_levels
        chunk_dim = dim // n_levels

        # Spatial Weighting
        self.mfr = nn.ModuleList([nn.Conv2d(chunk_dim, chunk_dim, 3, 1, 1, groups=chunk_dim) for i in range(self.n_levels)])

        # # Feature Aggregation
        self.aggr = nn.Conv2d(dim, dim, 1, 1, 0)

        # Activation
        self.act = nn.GELU() 

    def forward(self, x):
        h, w = x.size()[-2:]

        xc = x.chunk(self.n_levels, dim=1)
        out = []
        for i in range(self.n_levels):
            if i > 0:
                p_size = (h//2**i, w//2**i)
                s = F.adaptive_max_pool2d(xc[i], p_size)
                s = self.mfr[i](s)
                s = F.interpolate(s, size=(h, w), mode='nearest')
            else:
                s = self.mfr[i](xc[i])
            out.append(s)

        out = self.aggr(torch.cat(out, dim=1))
        out = self.act(out) * x
        return out