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"""
S. Fang, K. Li, J. Shao, and Z. Li, 
“SNUNet-CD: A Densely Connected Siamese Network for Change Detection of VHR Images,” 
IEEE Geosci. Remote Sensing Lett., pp. 1-5, 2021, doi: 10.1109/LGRS.2021.3056416.
"""

import torch
import torch.nn as nn

from opencd.registry import MODELS


class conv_block_nested(nn.Module):
    def __init__(self, in_ch, mid_ch, out_ch):
        super(conv_block_nested, self).__init__()
        self.activation = nn.ReLU(inplace=True)
        self.conv1 = nn.Conv2d(in_ch, mid_ch, kernel_size=3, padding=1, bias=True)
        self.bn1 = nn.BatchNorm2d(mid_ch)
        self.conv2 = nn.Conv2d(mid_ch, out_ch, kernel_size=3, padding=1, bias=True)
        self.bn2 = nn.BatchNorm2d(out_ch)

    def forward(self, x):
        x = self.conv1(x)
        identity = x
        x = self.bn1(x)
        x = self.activation(x)

        x = self.conv2(x)
        x = self.bn2(x)
        output = self.activation(x + identity)
        return output


class up(nn.Module):
    def __init__(self, in_ch, bilinear=False):
        super(up, self).__init__()

        if bilinear:
            self.up = nn.Upsample(scale_factor=2,
                                  mode='bilinear',
                                  align_corners=True)
        else:
            self.up = nn.ConvTranspose2d(in_ch, in_ch, 2, stride=2)

    def forward(self, x):

        x = self.up(x)
        return x


class ChannelAttention(nn.Module):
    def __init__(self, in_channels, ratio = 16):
        super(ChannelAttention, self).__init__()
        self.avg_pool = nn.AdaptiveAvgPool2d(1)
        self.max_pool = nn.AdaptiveMaxPool2d(1)
        self.fc1 = nn.Conv2d(in_channels,in_channels//ratio,1,bias=False)
        self.relu1 = nn.ReLU()
        self.fc2 = nn.Conv2d(in_channels//ratio, in_channels,1,bias=False)
        self.sigmod = nn.Sigmoid()
    def forward(self,x):
        avg_out = self.fc2(self.relu1(self.fc1(self.avg_pool(x))))
        max_out = self.fc2(self.relu1(self.fc1(self.max_pool(x))))
        out = avg_out + max_out
        return self.sigmod(out)


@MODELS.register_module()
class SNUNet_ECAM(nn.Module):
    # SNUNet-CD with ECAM
    def __init__(self, in_channels, base_channel=32):
        super(SNUNet_ECAM, self).__init__()
        torch.nn.Module.dump_patches = True
        n1 = base_channel     # the initial number of channels of feature map
        filters = [n1, n1 * 2, n1 * 4, n1 * 8, n1 * 16]

        self.pool = nn.MaxPool2d(kernel_size=2, stride=2)

        self.conv0_0 = conv_block_nested(in_channels, filters[0], filters[0])
        self.conv1_0 = conv_block_nested(filters[0], filters[1], filters[1])
        self.Up1_0 = up(filters[1])
        self.conv2_0 = conv_block_nested(filters[1], filters[2], filters[2])
        self.Up2_0 = up(filters[2])
        self.conv3_0 = conv_block_nested(filters[2], filters[3], filters[3])
        self.Up3_0 = up(filters[3])
        self.conv4_0 = conv_block_nested(filters[3], filters[4], filters[4])
        self.Up4_0 = up(filters[4])

        self.conv0_1 = conv_block_nested(filters[0] * 2 + filters[1], filters[0], filters[0])
        self.conv1_1 = conv_block_nested(filters[1] * 2 + filters[2], filters[1], filters[1])
        self.Up1_1 = up(filters[1])
        self.conv2_1 = conv_block_nested(filters[2] * 2 + filters[3], filters[2], filters[2])
        self.Up2_1 = up(filters[2])
        self.conv3_1 = conv_block_nested(filters[3] * 2 + filters[4], filters[3], filters[3])
        self.Up3_1 = up(filters[3])

        self.conv0_2 = conv_block_nested(filters[0] * 3 + filters[1], filters[0], filters[0])
        self.conv1_2 = conv_block_nested(filters[1] * 3 + filters[2], filters[1], filters[1])
        self.Up1_2 = up(filters[1])
        self.conv2_2 = conv_block_nested(filters[2] * 3 + filters[3], filters[2], filters[2])
        self.Up2_2 = up(filters[2])

        self.conv0_3 = conv_block_nested(filters[0] * 4 + filters[1], filters[0], filters[0])
        self.conv1_3 = conv_block_nested(filters[1] * 4 + filters[2], filters[1], filters[1])
        self.Up1_3 = up(filters[1])

        self.conv0_4 = conv_block_nested(filters[0] * 5 + filters[1], filters[0], filters[0])

        self.ca = ChannelAttention(filters[0] * 4, ratio=16)
        self.ca1 = ChannelAttention(filters[0], ratio=16 // 4)

        # self.conv_final = nn.Conv2d(filters[0] * 4, out_ch, kernel_size=1)

        for m in self.modules():
            if isinstance(m, nn.Conv2d):
                nn.init.kaiming_normal_(m.weight, mode='fan_out', nonlinearity='relu')
            elif isinstance(m, (nn.BatchNorm2d, nn.GroupNorm)):
                nn.init.constant_(m.weight, 1)
                nn.init.constant_(m.bias, 0)


    def forward(self, xA, xB):
        '''xA'''
        x0_0A = self.conv0_0(xA)
        x1_0A = self.conv1_0(self.pool(x0_0A))
        x2_0A = self.conv2_0(self.pool(x1_0A))
        x3_0A = self.conv3_0(self.pool(x2_0A))
        # x4_0A = self.conv4_0(self.pool(x3_0A))
        '''xB'''
        x0_0B = self.conv0_0(xB)
        x1_0B = self.conv1_0(self.pool(x0_0B))
        x2_0B = self.conv2_0(self.pool(x1_0B))
        x3_0B = self.conv3_0(self.pool(x2_0B))
        x4_0B = self.conv4_0(self.pool(x3_0B))

        x0_1 = self.conv0_1(torch.cat([x0_0A, x0_0B, self.Up1_0(x1_0B)], 1))
        x1_1 = self.conv1_1(torch.cat([x1_0A, x1_0B, self.Up2_0(x2_0B)], 1))
        x0_2 = self.conv0_2(torch.cat([x0_0A, x0_0B, x0_1, self.Up1_1(x1_1)], 1))


        x2_1 = self.conv2_1(torch.cat([x2_0A, x2_0B, self.Up3_0(x3_0B)], 1))
        x1_2 = self.conv1_2(torch.cat([x1_0A, x1_0B, x1_1, self.Up2_1(x2_1)], 1))
        x0_3 = self.conv0_3(torch.cat([x0_0A, x0_0B, x0_1, x0_2, self.Up1_2(x1_2)], 1))

        x3_1 = self.conv3_1(torch.cat([x3_0A, x3_0B, self.Up4_0(x4_0B)], 1))
        x2_2 = self.conv2_2(torch.cat([x2_0A, x2_0B, x2_1, self.Up3_1(x3_1)], 1))
        x1_3 = self.conv1_3(torch.cat([x1_0A, x1_0B, x1_1, x1_2, self.Up2_2(x2_2)], 1))
        x0_4 = self.conv0_4(torch.cat([x0_0A, x0_0B, x0_1, x0_2, x0_3, self.Up1_3(x1_3)], 1))

        out = torch.cat([x0_1, x0_2, x0_3, x0_4], 1)

        intra = torch.sum(torch.stack((x0_1, x0_2, x0_3, x0_4)), dim=0)
        ca1 = self.ca1(intra)
        out = self.ca(out) * (out + ca1.repeat(1, 4, 1, 1))
        # out = self.conv_final(out)

        return (out, )