import numpy as np
import torch
from torch import nn
from torch.nn import init
from collections import OrderedDict


class SKAttention(nn.Module):

    def __init__(self, channel=512, kernels=[1,3,5,7], reduction=16, group=1, L=32):
        super().__init__()
        self.d = max(L, channel // reduction)
        self.convs = nn.ModuleList([])
        for k in kernels:
            self.convs.append(
                nn.Sequential(OrderedDict([
                    ('conv', nn.Conv2d(channel, channel, kernel_size=k, padding=k // 2, groups=group)),
                    ('bn', nn.BatchNorm2d(channel)),
                    ('relu', nn.ReLU())
                ]))
            )
        self.fc = nn.Linear(channel, self.d)
        self.fcs = nn.ModuleList([])
        for i in range(len(kernels)):
            self.fcs.append(nn.Linear(self.d, channel))
        self.softmax = nn.Softmax(dim=0)

    def forward(self, x):
        bs, c, _, _ = x.size()
        conv_outs = []
        ### split
        for conv in self.convs:
            conv_outs.append(conv(x))
        feats = torch.stack(conv_outs, 0)  # k,bs,channel,h,w

        ### fuse
        U = sum(conv_outs)  # bs,c,h,w

        ### reduction channel
        S = U.mean(-1).mean(-1)  # bs,c
        Z = self.fc(S)  # bs,d

        ### calculate attention weight
        weights = []
        for fc in self.fcs:
            weight = fc(Z)
            weights.append(weight.view(bs, c, 1, 1))  # bs,channel
        attention_weughts = torch.stack(weights, 0)  # k,bs,channel,1,1
        attention_weughts = self.softmax(attention_weughts)  # k,bs,channel,1,1

        ### fuse
        V = (attention_weughts * feats).sum(0)
        return V