# Copyright (c) Alibaba, Inc. and its affiliates.
# The AIRDet implementation is also open-sourced by the authors, and available at https://github.com/tinyvision/AIRDet.

import numpy as np
import torch
import torch.nn as nn
import torch.nn.functional as F
import torch.nn.init as init
from torch.nn.parameter import Parameter


def get_activation(name='silu', inplace=True):
    if name == 'silu':
        module = nn.SiLU(inplace=inplace)
    elif name == 'relu':
        module = nn.ReLU(inplace=inplace)
    elif name == 'lrelu':
        module = nn.LeakyReLU(0.1, inplace=inplace)
    elif name == 'identity':
        module = nn.Identity()
    else:
        raise AttributeError('Unsupported act type: {}'.format(name))
    return module


def conv_bn(in_channels, out_channels, kernel_size, stride, padding, groups=1):
    '''Basic cell for rep-style block, including conv and bn'''
    result = nn.Sequential()
    result.add_module(
        'conv',
        nn.Conv2d(
            in_channels=in_channels,
            out_channels=out_channels,
            kernel_size=kernel_size,
            stride=stride,
            padding=padding,
            groups=groups,
            bias=False))
    result.add_module('bn', nn.BatchNorm2d(num_features=out_channels))
    return result


class RepVggBlock(nn.Module):
    '''RepVggBlock is a basic rep-style block, including training and deploy status
    This code is based on https://github.com/DingXiaoH/RepVGG/blob/main/repvgg.py
    '''

    def __init__(self,
                 in_channels,
                 out_channels,
                 kernel_size=3,
                 stride=1,
                 padding=1,
                 dilation=1,
                 groups=1,
                 padding_mode='zeros',
                 deploy=False,
                 use_se=False,
                 act='relu',
                 norm=None):
        super(RepVggBlock, self).__init__()
        """ Initialization of the class.
        Args:
            in_channels (int): Number of channels in the input image
            out_channels (int): Number of channels produced by the convolution
            kernel_size (int or tuple): Size of the convolving kernel
            stride (int or tuple, optional): Stride of the convolution. Default: 1
            padding (int or tuple, optional): Zero-padding added to both sides of
                the input. Default: 1
            dilation (int or tuple, optional): Spacing between kernel elements. Default: 1
            groups (int, optional): Number of blocked connections from input
                channels to output channels. Default: 1
            padding_mode (string, optional): Default: 'zeros'
            deploy: Whether to be deploy status or training status. Default: False
            use_se: Whether to use se. Default: False
        """
        self.deploy = deploy
        self.groups = groups
        self.in_channels = in_channels
        self.out_channels = out_channels

        assert kernel_size == 3
        assert padding == 1

        padding_11 = padding - kernel_size // 2

        if isinstance(act, str):
            self.nonlinearity = get_activation(act)
        else:
            self.nonlinearity = act

        if use_se:
            raise NotImplementedError('se block not supported yet')
        else:
            self.se = nn.Identity()

        if deploy:
            self.rbr_reparam = nn.Conv2d(
                in_channels=in_channels,
                out_channels=out_channels,
                kernel_size=kernel_size,
                stride=stride,
                padding=padding,
                dilation=dilation,
                groups=groups,
                bias=True,
                padding_mode=padding_mode)

        else:
            self.rbr_identity = None
            self.rbr_dense = conv_bn(
                in_channels=in_channels,
                out_channels=out_channels,
                kernel_size=kernel_size,
                stride=stride,
                padding=padding,
                groups=groups)
            self.rbr_1x1 = conv_bn(
                in_channels=in_channels,
                out_channels=out_channels,
                kernel_size=1,
                stride=stride,
                padding=padding_11,
                groups=groups)

    def forward(self, inputs):
        '''Forward process'''
        if hasattr(self, 'rbr_reparam'):
            return self.nonlinearity(self.se(self.rbr_reparam(inputs)))

        if self.rbr_identity is None:
            id_out = 0
        else:
            id_out = self.rbr_identity(inputs)

        return self.nonlinearity(
            self.se(self.rbr_dense(inputs) + self.rbr_1x1(inputs) + id_out))

    def get_equivalent_kernel_bias(self):
        kernel3x3, bias3x3 = self._fuse_bn_tensor(self.rbr_dense)
        kernel1x1, bias1x1 = self._fuse_bn_tensor(self.rbr_1x1)
        kernelid, biasid = self._fuse_bn_tensor(self.rbr_identity)
        return kernel3x3 + self._pad_1x1_to_3x3_tensor(
            kernel1x1) + kernelid, bias3x3 + bias1x1 + biasid

    def _pad_1x1_to_3x3_tensor(self, kernel1x1):
        if kernel1x1 is None:
            return 0
        else:
            return torch.nn.functional.pad(kernel1x1, [1, 1, 1, 1])

    def _fuse_bn_tensor(self, branch):
        if branch is None:
            return 0, 0
        if isinstance(branch, nn.Sequential):
            kernel = branch.conv.weight
            running_mean = branch.bn.running_mean
            running_var = branch.bn.running_var
            gamma = branch.bn.weight
            beta = branch.bn.bias
            eps = branch.bn.eps
        else:
            assert isinstance(branch, nn.BatchNorm2d)
            if not hasattr(self, 'id_tensor'):
                input_dim = self.in_channels // self.groups
                kernel_value = np.zeros((self.in_channels, input_dim, 3, 3),
                                        dtype=np.float32)
                for i in range(self.in_channels):
                    kernel_value[i, i % input_dim, 1, 1] = 1
                self.id_tensor = torch.from_numpy(kernel_value).to(
                    branch.weight.device)
            kernel = self.id_tensor
            running_mean = branch.running_mean
            running_var = branch.running_var
            gamma = branch.weight
            beta = branch.bias
            eps = branch.eps
        std = (running_var + eps).sqrt()
        t = (gamma / std).reshape(-1, 1, 1, 1)
        return kernel * t, beta - running_mean * gamma / std

    def switch_to_deploy(self):
        if hasattr(self, 'rbr_reparam'):
            return
        kernel, bias = self.get_equivalent_kernel_bias()
        self.rbr_reparam = nn.Conv2d(
            in_channels=self.rbr_dense.conv.in_channels,
            out_channels=self.rbr_dense.conv.out_channels,
            kernel_size=self.rbr_dense.conv.kernel_size,
            stride=self.rbr_dense.conv.stride,
            padding=self.rbr_dense.conv.padding,
            dilation=self.rbr_dense.conv.dilation,
            groups=self.rbr_dense.conv.groups,
            bias=True)
        self.rbr_reparam.weight.data = kernel
        self.rbr_reparam.bias.data = bias
        for para in self.parameters():
            para.detach_()
        self.__delattr__('rbr_dense')
        self.__delattr__('rbr_1x1')
        if hasattr(self, 'rbr_identity'):
            self.__delattr__('rbr_identity')
        if hasattr(self, 'id_tensor'):
            self.__delattr__('id_tensor')
        self.deploy = True
