""" This file is adapted from https://github.com/thuyngch/Human-Segmentation-PyTorch"""

import math
import torch
from torch import nn

# ------------------------------------------------------------------------------
#  Useful functions
# ------------------------------------------------------------------------------


def _make_divisible(v, divisor, min_value=None):
    if min_value is None:
        min_value = divisor
    new_v = max(min_value, int(v + divisor / 2) // divisor * divisor)
    # Make sure that round down does not go down by more than 10%.
    if new_v < 0.9 * v:
        new_v += divisor
    return new_v


def conv_bn(inp, oup, stride):
    return nn.Sequential(nn.Conv2d(inp, oup, 3, stride, 1, bias=False), nn.BatchNorm2d(oup), nn.ReLU6(inplace=True))


def conv_1x1_bn(inp, oup):
    return nn.Sequential(nn.Conv2d(inp, oup, 1, 1, 0, bias=False), nn.BatchNorm2d(oup), nn.ReLU6(inplace=True))


# ------------------------------------------------------------------------------
#  Class of Inverted Residual block
# ------------------------------------------------------------------------------


class InvertedResidual(nn.Module):

    def __init__(self, inp, oup, stride, expansion, dilation=1):
        super(InvertedResidual, self).__init__()
        self.stride = stride
        assert stride in [1, 2]

        hidden_dim = round(inp * expansion)
        self.use_res_connect = self.stride == 1 and inp == oup

        if expansion == 1:
            self.conv = nn.Sequential(
                # dw
                nn.Conv2d(hidden_dim, hidden_dim, 3, stride, 1, groups=hidden_dim, dilation=dilation, bias=False),
                nn.BatchNorm2d(hidden_dim),
                nn.ReLU6(inplace=True),
                # pw-linear
                nn.Conv2d(hidden_dim, oup, 1, 1, 0, bias=False),
                nn.BatchNorm2d(oup),
            )
        else:
            self.conv = nn.Sequential(
                # pw
                nn.Conv2d(inp, hidden_dim, 1, 1, 0, bias=False),
                nn.BatchNorm2d(hidden_dim),
                nn.ReLU6(inplace=True),
                # dw
                nn.Conv2d(hidden_dim, hidden_dim, 3, stride, 1, groups=hidden_dim, dilation=dilation, bias=False),
                nn.BatchNorm2d(hidden_dim),
                nn.ReLU6(inplace=True),
                # pw-linear
                nn.Conv2d(hidden_dim, oup, 1, 1, 0, bias=False),
                nn.BatchNorm2d(oup),
            )

    def forward(self, x):
        if self.use_res_connect:
            return x + self.conv(x)
        else:
            return self.conv(x)


# ------------------------------------------------------------------------------
#  Class of MobileNetV2
# ------------------------------------------------------------------------------


class MobileNetV2(nn.Module):

    def __init__(self, in_channels, alpha=1.0, expansion=6, num_classes=1000):
        super(MobileNetV2, self).__init__()
        self.in_channels = in_channels
        self.num_classes = num_classes
        input_channel = 32
        last_channel = 1280
        interverted_residual_setting = [
            # t, c, n, s
            [1, 16, 1, 1],
            [expansion, 24, 2, 2],
            [expansion, 32, 3, 2],
            [expansion, 64, 4, 2],
            [expansion, 96, 3, 1],
            [expansion, 160, 3, 2],
            [expansion, 320, 1, 1],
        ]

        # building first layer
        input_channel = _make_divisible(input_channel * alpha, 8)
        self.last_channel = _make_divisible(last_channel * alpha, 8) if alpha > 1.0 else last_channel
        self.features = [conv_bn(self.in_channels, input_channel, 2)]

        # building inverted residual blocks
        for t, c, n, s in interverted_residual_setting:
            output_channel = _make_divisible(int(c * alpha), 8)
            for i in range(n):
                if i == 0:
                    self.features.append(InvertedResidual(input_channel, output_channel, s, expansion=t))
                else:
                    self.features.append(InvertedResidual(input_channel, output_channel, 1, expansion=t))
                input_channel = output_channel

        # building last several layers
        self.features.append(conv_1x1_bn(input_channel, self.last_channel))

        # make it nn.Sequential
        self.features = nn.Sequential(*self.features)

        # building classifier
        if self.num_classes is not None:
            self.classifier = nn.Sequential(
                nn.Dropout(0.2),
                nn.Linear(self.last_channel, num_classes),
            )

        # Initialize weights
        self._init_weights()

    def forward(self, x):
        # Stage1
        x = self.features[0](x)
        x = self.features[1](x)
        # Stage2
        x = self.features[2](x)
        x = self.features[3](x)
        # Stage3
        x = self.features[4](x)
        x = self.features[5](x)
        x = self.features[6](x)
        # Stage4
        x = self.features[7](x)
        x = self.features[8](x)
        x = self.features[9](x)
        x = self.features[10](x)
        x = self.features[11](x)
        x = self.features[12](x)
        x = self.features[13](x)
        # Stage5
        x = self.features[14](x)
        x = self.features[15](x)
        x = self.features[16](x)
        x = self.features[17](x)
        x = self.features[18](x)

        # Classification
        if self.num_classes is not None:
            x = x.mean(dim=(2, 3))
            x = self.classifier(x)

        # Output
        return x

    def _load_pretrained_model(self, pretrained_file):
        pretrain_dict = torch.load(pretrained_file, map_location='cpu')
        model_dict = {}
        state_dict = self.state_dict()
        print('[MobileNetV2] Loading pretrained model...')
        for k, v in pretrain_dict.items():
            if k in state_dict:
                model_dict[k] = v
            else:
                print(k, 'is ignored')
        state_dict.update(model_dict)
        self.load_state_dict(state_dict)

    def _init_weights(self):
        for m in self.modules():
            if isinstance(m, nn.Conv2d):
                n = m.kernel_size[0] * m.kernel_size[1] * m.out_channels
                m.weight.data.normal_(0, math.sqrt(2. / n))
                if m.bias is not None:
                    m.bias.data.zero_()
            elif isinstance(m, nn.BatchNorm2d):
                m.weight.data.fill_(1)
                m.bias.data.zero_()
            elif isinstance(m, nn.Linear):
                n = m.weight.size(1)
                m.weight.data.normal_(0, 0.01)
                m.bias.data.zero_()