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# Copyright (c) Xuanyi Dong [GitHub D-X-Y], 2019 #
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import math, torch
import torch.nn as nn
import torch.nn.functional as F
from .initialization import initialize_resnet


class Bottleneck(nn.Module):
    def __init__(self, nChannels, growthRate):
        super(Bottleneck, self).__init__()
        interChannels = 4 * growthRate
        self.bn1 = nn.BatchNorm2d(nChannels)
        self.conv1 = nn.Conv2d(nChannels, interChannels, kernel_size=1, bias=False)
        self.bn2 = nn.BatchNorm2d(interChannels)
        self.conv2 = nn.Conv2d(interChannels, growthRate, kernel_size=3, padding=1, bias=False)

    def forward(self, x):
        out = self.conv1(F.relu(self.bn1(x)))
        out = self.conv2(F.relu(self.bn2(out)))
        out = torch.cat((x, out), 1)
        return out


class SingleLayer(nn.Module):
    def __init__(self, nChannels, growthRate):
        super(SingleLayer, self).__init__()
        self.bn1 = nn.BatchNorm2d(nChannels)
        self.conv1 = nn.Conv2d(nChannels, growthRate, kernel_size=3, padding=1, bias=False)

    def forward(self, x):
        out = self.conv1(F.relu(self.bn1(x)))
        out = torch.cat((x, out), 1)
        return out


class Transition(nn.Module):
    def __init__(self, nChannels, nOutChannels):
        super(Transition, self).__init__()
        self.bn1 = nn.BatchNorm2d(nChannels)
        self.conv1 = nn.Conv2d(nChannels, nOutChannels, kernel_size=1, bias=False)

    def forward(self, x):
        out = self.conv1(F.relu(self.bn1(x)))
        out = F.avg_pool2d(out, 2)
        return out


class DenseNet(nn.Module):
    def __init__(self, growthRate, depth, reduction, nClasses, bottleneck):
        super(DenseNet, self).__init__()

        if bottleneck:
            nDenseBlocks = int((depth - 4) / 6)
        else:
            nDenseBlocks = int((depth - 4) / 3)

        self.message = 'CifarDenseNet : block : {:}, depth : {:}, reduction : {:}, growth-rate = {:}, class = {:}'.format(
            'bottleneck' if bottleneck else 'basic', depth, reduction, growthRate, nClasses)

        nChannels = 2 * growthRate
        self.conv1 = nn.Conv2d(3, nChannels, kernel_size=3, padding=1, bias=False)

        self.dense1 = self._make_dense(nChannels, growthRate, nDenseBlocks, bottleneck)
        nChannels += nDenseBlocks * growthRate
        nOutChannels = int(math.floor(nChannels * reduction))
        self.trans1 = Transition(nChannels, nOutChannels)

        nChannels = nOutChannels
        self.dense2 = self._make_dense(nChannels, growthRate, nDenseBlocks, bottleneck)
        nChannels += nDenseBlocks * growthRate
        nOutChannels = int(math.floor(nChannels * reduction))
        self.trans2 = Transition(nChannels, nOutChannels)

        nChannels = nOutChannels
        self.dense3 = self._make_dense(nChannels, growthRate, nDenseBlocks, bottleneck)
        nChannels += nDenseBlocks * growthRate

        self.act = nn.Sequential(
            nn.BatchNorm2d(nChannels), nn.ReLU(inplace=True),
            nn.AvgPool2d(8))
        self.fc = nn.Linear(nChannels, nClasses)

        self.apply(initialize_resnet)

    def get_message(self):
        return self.message

    def _make_dense(self, nChannels, growthRate, nDenseBlocks, bottleneck):
        layers = []
        for i in range(int(nDenseBlocks)):
            if bottleneck:
                layers.append(Bottleneck(nChannels, growthRate))
            else:
                layers.append(SingleLayer(nChannels, growthRate))
            nChannels += growthRate
        return nn.Sequential(*layers)

    def forward(self, inputs):
        out = self.conv1(inputs)
        out = self.trans1(self.dense1(out))
        out = self.trans2(self.dense2(out))
        out = self.dense3(out)
        features = self.act(out)
        features = features.view(features.size(0), -1)
        out = self.fc(features)
        return features, out
