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


##########
# Basic layers
##########
class ConvLayer(nn.Module):
    """Convolution layer (conv + bn + relu)."""

    def __init__(
        self,
        in_channels,
        out_channels,
        kernel_size,
        stride=1,
        padding=0,
        groups=1,
        IN=False
    ):
        super(ConvLayer, self).__init__()
        self.conv = nn.Conv2d(
            in_channels,
            out_channels,
            kernel_size,
            stride=stride,
            padding=padding,
            bias=False,
            groups=groups
        )
        if IN:
            self.bn = nn.InstanceNorm2d(out_channels, affine=True)
        else:
            self.bn = nn.BatchNorm2d(out_channels)
        self.relu = nn.ReLU(inplace=True)

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


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

    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)
        return self.relu(x)


class Conv1x1Linear(nn.Module):
    """1x1 convolution + bn (w/o non-linearity)."""

    def __init__(self, in_channels, out_channels, stride=1, bn=True):
        super(Conv1x1Linear, self).__init__()
        self.conv = nn.Conv2d(
            in_channels, out_channels, 1, stride=stride, padding=0, bias=False
        )
        self.bn = None
        if bn:
            self.bn = nn.BatchNorm2d(out_channels)

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


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

    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)
        return self.relu(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)
        return self.relu(x)


class LightConvStream(nn.Module):
    """Lightweight convolution stream."""

    def __init__(self, in_channels, out_channels, depth):
        super(LightConvStream, self).__init__()
        assert depth >= 1, 'depth must be equal to or larger than 1, but got {}'.format(
            depth
        )
        layers = []
        layers += [LightConv3x3(in_channels, out_channels)]
        for i in range(depth - 1):
            layers += [LightConv3x3(out_channels, out_channels)]
        self.layers = nn.Sequential(*layers)

    def forward(self, x):
        return self.layers(x)


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

    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, reduction=4, T=4, **kwargs):
        super(OSBlock, self).__init__()
        assert T >= 1
        assert out_channels >= reduction and out_channels % reduction == 0
        mid_channels = out_channels // reduction

        self.conv1 = Conv1x1(in_channels, mid_channels)
        self.conv2 = nn.ModuleList()
        for t in range(1, T + 1):
            self.conv2 += [LightConvStream(mid_channels, mid_channels, t)]
        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):
        identity = x
        x1 = self.conv1(x)
        x2 = 0
        for conv2_t in self.conv2:
            x2_t = conv2_t(x1)
            x2 = x2 + self.gate(x2_t)
        x3 = self.conv3(x2)
        if self.downsample is not None:
            identity = self.downsample(identity)
        out = x3 + identity
        return F.relu(out)


class OSBlockINv1(nn.Module):
    """Omni-scale feature learning block with instance normalization."""

    def __init__(self, in_channels, out_channels, reduction=4, T=4, **kwargs):
        super(OSBlockINv1, self).__init__()
        assert T >= 1
        assert out_channels >= reduction and out_channels % reduction == 0
        mid_channels = out_channels // reduction

        self.conv1 = Conv1x1(in_channels, mid_channels)
        self.conv2 = nn.ModuleList()
        for t in range(1, T + 1):
            self.conv2 += [LightConvStream(mid_channels, mid_channels, t)]
        self.gate = ChannelGate(mid_channels)
        self.conv3 = Conv1x1Linear(mid_channels, out_channels, bn=False)
        self.downsample = None
        if in_channels != out_channels:
            self.downsample = Conv1x1Linear(in_channels, out_channels)
        self.IN = nn.InstanceNorm2d(out_channels, affine=True)

    def forward(self, x):
        identity = x
        x1 = self.conv1(x)
        x2 = 0
        for conv2_t in self.conv2:
            x2_t = conv2_t(x1)
            x2 = x2 + self.gate(x2_t)
        x3 = self.conv3(x2)
        x3 = self.IN(x3) # IN inside residual
        if self.downsample is not None:
            identity = self.downsample(identity)
        out = x3 + identity
        return F.relu(out)


class OSBlockINv2(nn.Module):
    """Omni-scale feature learning block with instance normalization."""

    def __init__(self, in_channels, out_channels, reduction=4, T=4, **kwargs):
        super(OSBlockINv2, self).__init__()
        assert T >= 1
        assert out_channels >= reduction and out_channels % reduction == 0
        mid_channels = out_channels // reduction

        self.conv1 = Conv1x1(in_channels, mid_channels)
        self.conv2 = nn.ModuleList()
        for t in range(1, T + 1):
            self.conv2 += [LightConvStream(mid_channels, mid_channels, t)]
        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)
        self.IN = nn.InstanceNorm2d(out_channels, affine=True)

    def forward(self, x):
        identity = x
        x1 = self.conv1(x)
        x2 = 0
        for conv2_t in self.conv2:
            x2_t = conv2_t(x1)
            x2 = x2 + self.gate(x2_t)
        x3 = self.conv3(x2)
        if self.downsample is not None:
            identity = self.downsample(identity)
        out = x3 + identity
        out = self.IN(out) # IN outside residual
        return F.relu(out)


class OSBlockINv3(nn.Module):
    """Omni-scale feature learning block with instance normalization."""

    def __init__(self, in_channels, out_channels, reduction=4, T=4, **kwargs):
        super(OSBlockINv3, self).__init__()
        assert T >= 1
        assert out_channels >= reduction and out_channels % reduction == 0
        mid_channels = out_channels // reduction

        self.conv1 = Conv1x1(in_channels, mid_channels)
        self.conv2 = nn.ModuleList()
        for t in range(1, T + 1):
            self.conv2 += [LightConvStream(mid_channels, mid_channels, t)]
        self.gate = ChannelGate(mid_channels)
        self.conv3 = Conv1x1Linear(mid_channels, out_channels, bn=False)
        self.downsample = None
        if in_channels != out_channels:
            self.downsample = Conv1x1Linear(in_channels, out_channels)
        self.IN_in = nn.InstanceNorm2d(out_channels, affine=True)
        self.IN_out = nn.InstanceNorm2d(out_channels, affine=True)

    def forward(self, x):
        identity = x
        x1 = self.conv1(x)
        x2 = 0
        for conv2_t in self.conv2:
            x2_t = conv2_t(x1)
            x2 = x2 + self.gate(x2_t)
        x3 = self.conv3(x2)
        x3 = self.IN_in(x3) # IN inside residual
        if self.downsample is not None:
            identity = self.downsample(identity)
        out = x3 + identity
        out = self.IN_out(out) # IN outside residual
        return F.relu(out)


##########
# Network architecture
##########
class OSNet(nn.Module):
    """Omni-Scale Network.
    
    Reference:
        - Zhou et al. Omni-Scale Feature Learning for Person Re-Identification. ICCV, 2019.
        - Zhou et al. Learning Generalisable Omni-Scale Representations
          for Person Re-Identification. TPAMI, 2021.
    """

    def __init__(
        self,
        num_classes,
        blocks,
        layers,
        channels,
        feature_dim=512,
        loss='softmax',
        conv1_IN=True,
        **kwargs
    ):
        super(OSNet, self).__init__()
        num_blocks = len(blocks)
        assert num_blocks == len(layers)
        assert num_blocks == len(channels) - 1
        self.loss = loss
        self.feature_dim = feature_dim

        # convolutional backbone
        self.conv1 = ConvLayer(
            3, channels[0], 7, stride=2, padding=3, IN=conv1_IN
        )
        self.maxpool = nn.MaxPool2d(3, stride=2, padding=1)
        self.conv2 = self._make_layer(
            blocks[0], layers[0], channels[0], channels[1]
        )
        self.pool2 = nn.Sequential(
            Conv1x1(channels[1], channels[1]), nn.AvgPool2d(2, stride=2)
        )
        self.conv3 = self._make_layer(
            blocks[1], layers[1], channels[1], channels[2]
        )
        self.pool3 = nn.Sequential(
            Conv1x1(channels[2], channels[2]), nn.AvgPool2d(2, stride=2)
        )
        self.conv4 = self._make_layer(
            blocks[2], layers[2], channels[2], channels[3]
        )
        self.conv5 = Conv1x1(channels[3], channels[3])
        self.global_avgpool = nn.AdaptiveAvgPool2d(1)
        # fully connected layer
        self.fc = self._construct_fc_layer(
            self.feature_dim, channels[3], dropout_p=None
        )
        # identity classification layer
        self.classifier = nn.Linear(self.feature_dim, num_classes)

        self._init_params()

    def _make_layer(self, blocks, layer, in_channels, out_channels):
        layers = []
        layers += [blocks[0](in_channels, out_channels)]
        for i in range(1, len(blocks)):
            layers += [blocks[i](out_channels, out_channels)]
        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.InstanceNorm2d):
                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)

    def featuremaps(self, x):
        x = self.conv1(x)
        x = self.maxpool(x)
        x = self.conv2(x)
        x = self.pool2(x)
        x = self.conv3(x)
        x = self.pool3(x)
        x = self.conv4(x)
        return self.conv5(x)

    def forward(self, x, return_featuremaps=False, **kwargs):
        x = self.featuremaps(x)
        if return_featuremaps:
            return x
        v = self.global_avgpool(x)
        v = v.view(v.size(0), -1)
        if self.fc is not None:
            v = self.fc(v)
        if not self.training:
            return v
        y = self.classifier(v)
        if self.loss == 'softmax':
            return y
        elif self.loss == 'triplet':
            return y, v
        else:
            raise KeyError("Unsupported loss: {}".format(self.loss))


##########
# Instantiation
##########
def osnet_ain_x1_0(
    num_classes=1000, pretrained=True, loss='softmax', **kwargs
):
    model = OSNet(
        num_classes,
        blocks=[
            [OSBlockINv1, OSBlockINv1], [OSBlock, OSBlockINv1],
            [OSBlockINv1, OSBlock]
        ],
        layers=[2, 2, 2],
        channels=[64, 256, 384, 512],
        loss=loss,
        conv1_IN=True,
        **kwargs
    )
    return model


__models = {'osnet_ain_x1_0': osnet_ain_x1_0}


def build_model(name, num_classes=100):
    avai_models = list(__models.keys())
    if name not in avai_models:
        raise KeyError(
            'Unknown model: {}. Must be one of {}'.format(name, avai_models)
        )
    return __models[name](num_classes=num_classes)