import torch
import torch.nn as nn
import torch.nn.functional as F
from torch.utils.checkpoint import checkpoint_sequential

from models.archs.arch_util import make_layer, default_init_weights


class ResidualDenseBlock(nn.Module):
    """Residual Dense Block.

    Used in RRDB block in ESRGAN.

    Args:
        mid_channels (int): Channel number of intermediate features.
        growth_channels (int): Channels for each growth.
    """

    def __init__(self, mid_channels=64, growth_channels=32):
        super(ResidualDenseBlock, self).__init__()
        for i in range(5):
            out_channels = mid_channels if i == 4 else growth_channels
            self.add_module(
                f'conv{i+1}',
                nn.Conv2d(mid_channels + i * growth_channels, out_channels, 3,
                          1, 1))
        self.lrelu = nn.LeakyReLU(negative_slope=0.2, inplace=True)
        for i in range(5):
            default_init_weights(getattr(self, f'conv{i+1}'), 0.1)


    def forward(self, x):
        """Forward function.

        Args:
            x (Tensor): Input tensor with shape (n, c, h, w).

        Returns:
            Tensor: Forward results.
        """
        x1 = self.lrelu(self.conv1(x))
        x2 = self.lrelu(self.conv2(torch.cat((x, x1), 1)))
        x3 = self.lrelu(self.conv3(torch.cat((x, x1, x2), 1)))
        x4 = self.lrelu(self.conv4(torch.cat((x, x1, x2, x3), 1)))
        x5 = self.conv5(torch.cat((x, x1, x2, x3, x4), 1))
        # Emperically, we use 0.2 to scale the residual for better performance
        return x5 * 0.2 + x


class RRDB(nn.Module):
    """Residual in Residual Dense Block.

    Used in RRDB-Net in ESRGAN.

    Args:
        mid_channels (int): Channel number of intermediate features.
        growth_channels (int): Channels for each growth.
    """

    def __init__(self, mid_channels, growth_channels=32):
        super(RRDB, self).__init__()
        self.rdb1 = ResidualDenseBlock(mid_channels, growth_channels)
        self.rdb2 = ResidualDenseBlock(mid_channels, growth_channels)
        self.rdb3 = ResidualDenseBlock(mid_channels, growth_channels)

    def forward(self, x):
        """Forward function.

        Args:
            x (Tensor): Input tensor with shape (n, c, h, w).

        Returns:
            Tensor: Forward results.
        """
        out = self.rdb1(x)
        out = self.rdb2(out)
        out = self.rdb3(out)
        # Emperically, we use 0.2 to scale the residual for better performance
        return out * 0.2 + x


class RRDBNet(nn.Module):
    """Networks consisting of Residual in Residual Dense Block, which is used
    in ESRGAN.

    ESRGAN: Enhanced Super-Resolution Generative Adversarial Networks.
    Currently, it supports x4 upsampling scale factor.

    Args:
        in_channels (int): Channel number of inputs.
        out_channels (int): Channel number of outputs.
        mid_channels (int): Channel number of intermediate features.
            Default: 64
        num_blocks (int): Block number in the trunk network. Defaults: 23
        growth_channels (int): Channels for each growth. Default: 32.
    """

    def __init__(self,
                 in_channels,
                 out_channels,
                 mid_channels=64,
                 num_blocks=23,
                 growth_channels=32):
        super(RRDBNet, self).__init__()
        self.conv_first = nn.Conv2d(in_channels, mid_channels, 3, 1, 1)
        self.body = make_layer(
            RRDB,
            num_blocks,
            mid_channels=mid_channels,
            growth_channels=growth_channels)
        self.conv_body = nn.Conv2d(mid_channels, mid_channels, 3, 1, 1)
        # upsample
        self.conv_up1 = nn.Conv2d(mid_channels, mid_channels, 3, 1, 1)
        self.conv_up2 = nn.Conv2d(mid_channels, mid_channels, 3, 1, 1)
        self.conv_hr = nn.Conv2d(mid_channels, mid_channels, 3, 1, 1)
        self.conv_last = nn.Conv2d(mid_channels, out_channels, 3, 1, 1)

        self.lrelu = nn.LeakyReLU(negative_slope=0.2, inplace=True)

        for m in [
            self.conv_first, self.conv_body, self.conv_up1,
            self.conv_up2, self.conv_hr, self.conv_last
        ]:
            default_init_weights(m, 0.1)

    def forward(self, x):
        """Forward function.

        Args:
            x (Tensor): Input tensor with shape (n, c, h, w).

        Returns:
            Tensor: Forward results.
        """

        feat = self.conv_first(x)
        body_feat = self.conv_body(checkpoint_sequential(self.body, 5, feat))
        feat = feat + body_feat
        # upsample
        feat = self.lrelu(
            self.conv_up1(F.interpolate(feat, scale_factor=2, mode='nearest')))
        feat = self.lrelu(
            self.conv_up2(F.interpolate(feat, scale_factor=2, mode='nearest')))
        out = self.conv_last(self.lrelu(self.conv_hr(feat)))
        return out