"""
attention modules in ['SimAM', 'CBAM', 'SE', 'GAM']  were applied in the ablation study

ver： Dec 24th 15：00


ref:
https://github.com/xmu-xiaoma666/External-Attention-pytorch
"""

import torch
import torch.nn as nn
import math
import torch.nn.functional as F
from torch.nn import init


# help func
class BasicConv(nn.Module):
    def __init__(self, in_planes, out_planes, kernel_size, stride=1, padding=0, dilation=1, groups=1, relu=True,
                 bn=True, bias=False):
        super(BasicConv, self).__init__()
        self.out_channels = out_planes
        self.conv = nn.Conv2d(in_planes, out_planes, kernel_size=kernel_size, stride=stride, padding=padding,
                              dilation=dilation, groups=groups, bias=bias)
        self.bn = nn.BatchNorm2d(out_planes, eps=1e-5, momentum=0.01, affine=True) if bn else None
        self.relu = nn.ReLU() if relu else None

    def forward(self, x):
        x = self.conv(x)
        if self.bn is not None:
            x = self.bn(x)
        if self.relu is not None:
            x = self.relu(x)
        return x


class Flatten(nn.Module):
    def forward(self, x):
        return x.view(x.size(0), -1)


class ChannelGate(nn.Module):
    def __init__(self, gate_channels, reduction_ratio=16, pool_types=['avg', 'max']):
        super(ChannelGate, self).__init__()
        self.gate_channels = gate_channels
        self.mlp = nn.Sequential(
            Flatten(),
            nn.Linear(gate_channels, int(gate_channels // reduction_ratio)),
            nn.ReLU(),
            nn.Linear(int(gate_channels // reduction_ratio), gate_channels)
        )
        self.pool_types = pool_types

    def forward(self, x):
        channel_att_sum = None
        for pool_type in self.pool_types:
            if pool_type == 'avg':
                avg_pool = F.avg_pool2d(x, (x.size(2), x.size(3)), stride=(x.size(2), x.size(3)))
                channel_att_raw = self.mlp(avg_pool)
            elif pool_type == 'max':
                max_pool = F.max_pool2d(x, (x.size(2), x.size(3)), stride=(x.size(2), x.size(3)))
                channel_att_raw = self.mlp(max_pool)
            elif pool_type == 'lp':
                lp_pool = F.lp_pool2d(x, 2, (x.size(2), x.size(3)), stride=(x.size(2), x.size(3)))
                channel_att_raw = self.mlp(lp_pool)
            elif pool_type == 'lse':
                # LSE pool only
                lse_pool = logsumexp_2d(x)
                channel_att_raw = self.mlp(lse_pool)

            if channel_att_sum is None:
                channel_att_sum = channel_att_raw
            else:
                channel_att_sum = channel_att_sum + channel_att_raw

        scale = F.sigmoid(channel_att_sum).unsqueeze(2).unsqueeze(3).expand_as(x)
        return x * scale


def logsumexp_2d(tensor):
    tensor_flatten = tensor.view(tensor.size(0), tensor.size(1), -1)
    s, _ = torch.max(tensor_flatten, dim=2, keepdim=True)
    outputs = s + (tensor_flatten - s).exp().sum(dim=2, keepdim=True).log()
    return outputs


class ChannelPool(nn.Module):
    def forward(self, x):
        return torch.cat((torch.max(x, 1)[0].unsqueeze(1), torch.mean(x, 1).unsqueeze(1)), dim=1)


class SpatialGate(nn.Module):
    def __init__(self):
        super(SpatialGate, self).__init__()
        kernel_size = 7
        self.compress = ChannelPool()
        self.spatial = BasicConv(2, 1, kernel_size, stride=1, padding=int((kernel_size - 1) // 2), relu=False)

    def forward(self, x):
        x_compress = self.compress(x)
        x_out = self.spatial(x_compress)
        scale = F.sigmoid(x_out)  # broadcasting
        return x * scale


# attention modules：
class cbam_module(nn.Module):
    """
    module：CBAM

    input、output= b, c, h, w

    paper：
    https://arxiv.org/abs/1807.06521
    code：
    https://github.com/ZjjConan/SimAM/blob/master/networks/attentions
    """

    def __init__(self, gate_channels, reduction=16, pool_types=['avg', 'max'], no_spatial=False):
        super(cbam_module, self).__init__()
        self.ChannelGate = ChannelGate(gate_channels, reduction, pool_types)
        self.no_spatial = no_spatial
        if not no_spatial:
            self.SpatialGate = SpatialGate()

    @staticmethod
    def get_module_name():
        return "cbam"

    def forward(self, x):
        x_out = self.ChannelGate(x)
        if not self.no_spatial:
            x_out = self.SpatialGate(x_out)
        return x_out


class se_module(nn.Module):
    """
    module: SE

    input、output= b, c, h, w

    from paper Squeeze-and-Excitation Networks
    SE-Net  https://arxiv.org/abs/1709.01507
    code：
    https://github.com/ZjjConan/SimAM/blob/master/networks/attentions
    """

    def __init__(self, channel, reduction=16):
        super(se_module, self).__init__()
        self.avg_pool = nn.AdaptiveAvgPool2d(1)
        self.fc = nn.Sequential(
            nn.Linear(channel, int(channel // reduction), bias=False),
            nn.ReLU(inplace=True),
            nn.Linear(int(channel // reduction), channel, bias=False),
            nn.Sigmoid()
        )

    @staticmethod
    def get_module_name():
        return "se"

    def forward(self, x):
        b, c, _, _ = x.size()
        y = self.avg_pool(x).view(b, c)
        y = self.fc(y).view(b, c, 1, 1)
        return x * y


class simam_module(torch.nn.Module):
    """
    module:SimAM

    input、output= b, c, h, w

    paper:(ICML)
    SimAM: A Simple, Parameter-Free Attention Module for Convolutional Neural Networks
    code:
    https://github.com/ZjjConan/SimAM/blob/master/networks/attentions/simam_module.py
    """

    def __init__(self, channels=None, e_lambda=1e-4):
        super(simam_module, self).__init__()

        self.activaton = nn.Sigmoid()
        self.e_lambda = e_lambda

    def __repr__(self):
        s = self.__class__.__name__ + '('
        s += ('lambda=%f)' % self.e_lambda)
        return s

    @staticmethod
    def get_module_name():
        return "simam"

    def forward(self, x):
        b, c, h, w = x.size()

        n = w * h - 1

        x_minus_mu_square = (x - x.mean(dim=[2, 3], keepdim=True)).pow(2)
        y = x_minus_mu_square / (4 * (x_minus_mu_square.sum(dim=[2, 3], keepdim=True) / n + self.e_lambda)) + 0.5

        return x * self.activaton(y)


class ResidualAttention(nn.Module):
    """
    module: ResidualAttention

    input、output= b, c, h, w

    Paper：ICCV 2021 Residual Attention: A Simple but Effective Method for Multi-Label Recognition
    code：https://github.com/xmu-xiaoma666/External-Attention-pytorch/blob/master/attention/ResidualAttention.py
    """

    def __init__(self, channel=512, num_class=1000, la=0.2):
        super().__init__()
        self.la = la
        self.fc = nn.Conv2d(in_channels=channel, out_channels=num_class, kernel_size=1, stride=1, bias=False)

    def forward(self, x):
        b, c, h, w = x.shape
        y_raw = self.fc(x).flatten(2)  # b,num_class,hxw
        y_avg = torch.mean(y_raw, dim=2)  # b,num_class
        y_max = torch.max(y_raw, dim=2)[0]  # b,num_class
        score = y_avg + self.la * y_max
        return score


class eca_module(nn.Module):
    """Constructs a ECA module.

    Args:
        channel: Number of channels of the input feature map
        k_size: Adaptive selection of kernel size
    """
    def __init__(self, channel, k_size=3):
        super(eca_module, self).__init__()
        self.avg_pool = nn.AdaptiveAvgPool2d(1)
        self.conv = nn.Conv1d(1, 1, kernel_size=k_size, padding=(k_size - 1) // 2, bias=False)
        self.sigmoid = nn.Sigmoid()

    def forward(self, x):
        # x: input features with shape [b, c, h, w]
        b, c, h, w = x.size()

        # feature descriptor on the global spatial information
        y = self.avg_pool(x)

        # Two different branches of ECA module
        y = self.conv(y.squeeze(-1).transpose(-1, -2)).transpose(-1, -2).unsqueeze(-1)

        # Multi-scale information fusion
        y = self.sigmoid(y)

        return x * y.expand_as(x)


class GAM_Attention(nn.Module):
    """
    module：GAM

    input= b, in_channels, h, w
    output= b, out_channels, h, w

    paper：
    Global Attention Mechanism: Retain Information to Enhance Channel-Spatial Interactions
    https://arxiv.org/abs/2112.05561
    code：
    https://mp.weixin.qq.com/s/VL6rXjyUDmHToYTqM32hUg
    """
    def __init__(self, in_channels, out_channels, rate=4):
        super(GAM_Attention, self).__init__()

        self.channel_attention = nn.Sequential(
            nn.Linear(in_channels, int(in_channels / rate)),
            nn.ReLU(inplace=True),
            nn.Linear(int(in_channels / rate), in_channels)
        )

        self.spatial_attention = nn.Sequential(
            nn.Conv2d(in_channels, int(in_channels / rate), kernel_size=7, padding=3),
            nn.BatchNorm2d(int(in_channels / rate)),
            nn.ReLU(inplace=True),
            nn.Conv2d(int(in_channels / rate), out_channels, kernel_size=7, padding=3),
            nn.BatchNorm2d(out_channels)
        )

    def forward(self, x):
        b, c, h, w = x.shape
        x_permute = x.permute(0, 2, 3, 1).view(b, -1, c)
        x_att_permute = self.channel_attention(x_permute).view(b, h, w, c)
        x_channel_att = x_att_permute.permute(0, 3, 1, 2)

        x = x * x_channel_att

        x_spatial_att = self.spatial_attention(x).sigmoid()
        out = x * x_spatial_att

        return out