from __future__ import division, absolute_import
import torch
from torch import nn
from torch.nn import functional as F

__all__ = ['osnet_avgpool', 'osnet_maxpool']


##########
# Basic layers
##########
class ConvLayer(nn.Module):
    """Convolution layer."""

    def __init__(
        self,
        in_channels,
        out_channels,
        kernel_size,
        stride=1,
        padding=0,
        groups=1
    ):
        super(ConvLayer, self).__init__()
        self.conv = nn.Conv2d(
            in_channels,
            out_channels,
            kernel_size,
            stride=stride,
            padding=padding,
            bias=False,
            groups=groups
        )
        self.bn = nn.BatchNorm2d(out_channels)
        self.relu = nn.ReLU(inplace=True)

    def forward(self, x):
        x = self.conv(x)
        x = self.bn(x)
        x = self.relu(x)
        return x


class Conv1x1(nn.Module):
    """1x1 convolution."""

    def __init__(self, in_channels, out_channels, stride=1, groups=1):
        super(Conv1x1, self).__init__()
        self.conv = nn.Conv2d(
            in_channels,
            out_channels,
            1,
            stride=stride,
            padding=0,
            bias=False,
            groups=groups
        )
        self.bn = nn.BatchNorm2d(out_channels)
        self.relu = nn.ReLU(inplace=True)

    def forward(self, x):
        x = self.conv(x)
        x = self.bn(x)
        x = self.relu(x)
        return x


class Conv1x1Linear(nn.Module):
    """1x1 convolution without non-linearity."""

    def __init__(self, in_channels, out_channels, stride=1):
        super(Conv1x1Linear, self).__init__()
        self.conv = nn.Conv2d(
            in_channels, out_channels, 1, stride=stride, padding=0, bias=False
        )
        self.bn = nn.BatchNorm2d(out_channels)

    def forward(self, x):
        x = self.conv(x)
        x = self.bn(x)
        return x


class Conv3x3(nn.Module):
    """3x3 convolution."""

    def __init__(self, in_channels, out_channels, stride=1, groups=1):
        super(Conv3x3, self).__init__()
        self.conv = nn.Conv2d(
            in_channels,
            out_channels,
            3,
            stride=stride,
            padding=1,
            bias=False,
            groups=groups
        )
        self.bn = nn.BatchNorm2d(out_channels)
        self.relu = nn.ReLU(inplace=True)

    def forward(self, x):
        x = self.conv(x)
        x = self.bn(x)
        x = self.relu(x)
        return x


class LightConv3x3(nn.Module):
    """Lightweight 3x3 convolution.

    1x1 (linear) + dw 3x3 (nonlinear).
    """

    def __init__(self, in_channels, out_channels):
        super(LightConv3x3, self).__init__()
        self.conv1 = nn.Conv2d(
            in_channels, out_channels, 1, stride=1, padding=0, bias=False
        )
        self.conv2 = nn.Conv2d(
            out_channels,
            out_channels,
            3,
            stride=1,
            padding=1,
            bias=False,
            groups=out_channels
        )
        self.bn = nn.BatchNorm2d(out_channels)
        self.relu = nn.ReLU(inplace=True)

    def forward(self, x):
        x = self.conv1(x)
        x = self.conv2(x)
        x = self.bn(x)
        x = self.relu(x)
        return x


##########
# Building blocks for omni-scale feature learning
##########
class ChannelGate(nn.Module):
    """A mini-network that generates channel-wise gates conditioned on input."""

    def __init__(
        self,
        in_channels,
        num_gates=None,
        return_gates=False,
        gate_activation='sigmoid',
        reduction=16,
        layer_norm=False
    ):
        super(ChannelGate, self).__init__()
        if num_gates is None:
            num_gates = in_channels
        self.return_gates = return_gates
        self.global_avgpool = nn.AdaptiveAvgPool2d(1)
        self.fc1 = nn.Conv2d(
            in_channels,
            in_channels // reduction,
            kernel_size=1,
            bias=True,
            padding=0
        )
        self.norm1 = None
        if layer_norm:
            self.norm1 = nn.LayerNorm((in_channels // reduction, 1, 1))
        self.relu = nn.ReLU(inplace=True)
        self.fc2 = nn.Conv2d(
            in_channels // reduction,
            num_gates,
            kernel_size=1,
            bias=True,
            padding=0
        )
        if gate_activation == 'sigmoid':
            self.gate_activation = nn.Sigmoid()
        elif gate_activation == 'relu':
            self.gate_activation = nn.ReLU(inplace=True)
        elif gate_activation == 'linear':
            self.gate_activation = None
        else:
            raise RuntimeError(
                "Unknown gate activation: {}".format(gate_activation)
            )

    def forward(self, x):
        input = x
        x = self.global_avgpool(x)
        x = self.fc1(x)
        if self.norm1 is not None:
            x = self.norm1(x)
        x = self.relu(x)
        x = self.fc2(x)
        if self.gate_activation is not None:
            x = self.gate_activation(x)
        if self.return_gates:
            return x
        return input * x


class OSBlock(nn.Module):
    """Omni-scale feature learning block."""

    def __init__(self, in_channels, out_channels, **kwargs):
        super(OSBlock, self).__init__()
        mid_channels = out_channels // 4
        self.conv1 = Conv1x1(in_channels, mid_channels)
        self.conv2a = LightConv3x3(mid_channels, mid_channels)
        self.conv2b = nn.Sequential(
            LightConv3x3(mid_channels, mid_channels),
            LightConv3x3(mid_channels, mid_channels),
        )
        self.conv2c = nn.Sequential(
            LightConv3x3(mid_channels, mid_channels),
            LightConv3x3(mid_channels, mid_channels),
            LightConv3x3(mid_channels, mid_channels),
        )
        self.conv2d = nn.Sequential(
            LightConv3x3(mid_channels, mid_channels),
            LightConv3x3(mid_channels, mid_channels),
            LightConv3x3(mid_channels, mid_channels),
            LightConv3x3(mid_channels, mid_channels),
        )
        self.gate = ChannelGate(mid_channels)
        self.conv3 = Conv1x1Linear(mid_channels, out_channels)
        self.downsample = None
        if in_channels != out_channels:
            self.downsample = Conv1x1Linear(in_channels, out_channels)

    def forward(self, x):
        residual = x
        x1 = self.conv1(x)
        x2a = self.conv2a(x1)
        x2b = self.conv2b(x1)
        x2c = self.conv2c(x1)
        x2d = self.conv2d(x1)
        x2 = self.gate(x2a) + self.gate(x2b) + self.gate(x2c) + self.gate(x2d)
        x3 = self.conv3(x2)
        if self.downsample is not None:
            residual = self.downsample(residual)
        out = x3 + residual
        return F.relu(out)


##########
# Network architecture
##########
class BaseNet(nn.Module):

    def _make_layer(
        self, block, layer, in_channels, out_channels, reduce_spatial_size
    ):
        layers = []

        layers.append(block(in_channels, out_channels))
        for i in range(1, layer):
            layers.append(block(out_channels, out_channels))

        if reduce_spatial_size:
            layers.append(
                nn.Sequential(
                    Conv1x1(out_channels, out_channels),
                    nn.AvgPool2d(2, stride=2)
                )
            )

        return nn.Sequential(*layers)

    def _construct_fc_layer(self, fc_dims, input_dim, dropout_p=None):
        if fc_dims is None or fc_dims < 0:
            self.feature_dim = input_dim
            return None

        if isinstance(fc_dims, int):
            fc_dims = [fc_dims]

        layers = []
        for dim in fc_dims:
            layers.append(nn.Linear(input_dim, dim))
            layers.append(nn.BatchNorm1d(dim))
            layers.append(nn.ReLU(inplace=True))
            if dropout_p is not None:
                layers.append(nn.Dropout(p=dropout_p))
            input_dim = dim

        self.feature_dim = fc_dims[-1]

        return nn.Sequential(*layers)

    def init_params(self):
        for m in self.modules():
            if isinstance(m, nn.Conv2d):
                nn.init.kaiming_normal_(
                    m.weight, mode='fan_out', nonlinearity='relu'
                )
                if m.bias is not None:
                    nn.init.constant_(m.bias, 0)

            elif isinstance(m, nn.BatchNorm2d):
                nn.init.constant_(m.weight, 1)
                nn.init.constant_(m.bias, 0)

            elif isinstance(m, nn.BatchNorm1d):
                nn.init.constant_(m.weight, 1)
                nn.init.constant_(m.bias, 0)

            elif isinstance(m, nn.Linear):
                nn.init.normal_(m.weight, 0, 0.01)
                if m.bias is not None:
                    nn.init.constant_(m.bias, 0)


class OSNet(BaseNet):

    def __init__(
        self,
        num_classes,
        blocks,
        layers,
        channels,
        feature_dim=512,
        loss='softmax',
        pool='avg',
        **kwargs
    ):
        super(OSNet, self).__init__()
        num_blocks = len(blocks)
        assert num_blocks == len(layers)
        assert num_blocks == len(channels) - 1
        self.loss = loss

        # convolutional backbone
        self.conv1 = ConvLayer(3, channels[0], 7, stride=2, padding=3)
        self.maxpool = nn.MaxPool2d(3, stride=2, padding=1)
        self.conv2 = self._make_layer(
            blocks[0],
            layers[0],
            channels[0],
            channels[1],
            reduce_spatial_size=True
        )
        self.conv3 = self._make_layer(
            blocks[1],
            layers[1],
            channels[1],
            channels[2],
            reduce_spatial_size=True
        )
        self.conv4 = self._make_layer(
            blocks[2],
            layers[2],
            channels[2],
            channels[3],
            reduce_spatial_size=False
        )
        self.conv5 = Conv1x1(channels[3], channels[3])
        if pool == 'avg':
            self.global_pool = nn.AdaptiveAvgPool2d(1)
        else:
            self.global_pool = nn.AdaptiveMaxPool2d(1)
        # fully connected layer
        self.fc = self._construct_fc_layer(
            feature_dim, channels[3], dropout_p=None
        )
        # classification layer
        self.classifier = nn.Linear(self.feature_dim, num_classes)

        self.init_params()

    def featuremaps(self, x):
        x = self.conv1(x)
        x = self.maxpool(x)
        x = self.conv2(x)
        x = self.conv3(x)
        x = self.conv4(x)
        x = self.conv5(x)
        return x

    def forward(self, x):
        x = self.featuremaps(x)
        v = self.global_pool(x)
        v = v.view(v.size(0), -1)
        if self.fc is not None:
            v = self.fc(v)
        y = self.classifier(v)
        if not self.training:
            y = torch.sigmoid(y)
        return y


def osnet_avgpool(num_classes=1000, loss='softmax', **kwargs):
    return OSNet(
        num_classes,
        blocks=[OSBlock, OSBlock, OSBlock],
        layers=[2, 2, 2],
        channels=[64, 256, 384, 512],
        loss=loss,
        pool='avg',
        **kwargs
    )


def osnet_maxpool(num_classes=1000, loss='softmax', **kwargs):
    return OSNet(
        num_classes,
        blocks=[OSBlock, OSBlock, OSBlock],
        layers=[2, 2, 2],
        channels=[64, 256, 384, 512],
        loss=loss,
        pool='max',
        **kwargs
    )